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Proceedings of the Zoological Institute RAS
Vol. 319, No. 2, 2015, рр. 141–181
УДК 599.3
TAXONOMIC REVISION OF TRIBOSPHENIC MAMMALS FROM THE LOWER
CRETACEOUS ANTLERS FORMATION OF TEXAS AND OKLAHOMA, USA
A.O. Averianov
1, 2
1
Zoological Institute of the Russian Academy of Sciences, Universitetskaya Emb. 1, 199034 Saint Petersburg,
Russia; e-mail: dzharakuduk@mail.ru
2
Department of Sedimentary Geology, Geological Faculty, Saint Petersburg State University, 16 Liniya VO 29,
199178 Saint Petersburg, Russia
ABSTRACT
There are five taxa of tribosphenic mammals in the Early Cretaceous Antlers Formation of Texas and Oklahoma, USA:
a basal stem therian (Kermackia texana), stem therians near the eutherian-metatherian dichotomy (Holoclemensia
texana and Pappotherium pattersoni), and stem marsupials (Atokatheridium boreni and Oklatheridium szalayi). K.
texana has a primitive therian postcanine formula with three molars, replacement of p5, M3 with low protocone
and no conules, lower molars with a large trigonid angle, oblique protocristid, paraconid smaller than metaconid
(except m3), strong distal metacristid, narrow talonid, small talonid basin, and small entoconid (absent on m3). H.
texana also has replacement in the fifth premolar locus and three molars. It is more derived in having a larger proto-
conal region with higher protocone and conules present, lack of distal metacristid, smaller trigonid angle, transverse
protocristid, and wide talonid with larger talonid basin. It is similar to Eutheria by having M1 with reduced ecto-
flexus, semimolariform p5, and low trigonid angle with transverse protocristid. Holoclemensia cannot be referred
to Eutheria because of the lack of the second rank postvallum/prevallid shear and unwinged conules. P. pattersoni
(=Slaughteria eruptens) has replacement in the fifth premolar position, premolariform p5, and three molars (symple-
siomorphies for Theria). It is more derived than Holoclemensia in having a wider and shorter talonid. Pappotherium
is similar to Eutheria in having a low trigonid angle, transverse protocristid, and the cristid obliqua labial to the
protocristid notch. It cannot be attributed to the Eutheria because of the narrow protoconal region, low protocone,
small conules lacking internal cristae, postprotocrista not extending labially past the metacone base, and a small
talonid basin. Atokatheridium boreni and Oklatheridium szalayi (=O. minax, syn. nov.) have four molars and emphasis
on the postvallum/prevallid shear (large metacone on M2, strong postmetacrista, paraconid higher than metaco-
nid). These taxa cannot be attributed to the Deltatheroida because of large protoconal region with winged conules.
Oklatheridium is further different from the Deltatheroida in having a wider talonid and better developed entoconid.
Key words: Antlers Formation, Early Cretaceous, evolution, Mammalia, North America, Theria
ТАКСОНОМИЧЕСКАЯ РЕВИЗИЯ ТРИБОСФЕНИЧЕСКИХ МЛЕКОПИТАЮЩИХ
ИЗ НИЖНЕМЕЛОВОЙ ФОРМАЦИИ АНТЛЕРС ТЕХАСА И ОКЛАХОМЫ, США
А.О. Аверьянов
1, 2
1
Зоологический институт Российской академии наук, Университетская наб. 1, 199034 Санкт-Петербург, Россия;
e-mail: dzharakuduk@mail.ru
2
Кафедра осадочной геологии, Геологический факультет, Санкт-Петербургский университет, 16 линия ВО 29,
199178 Санкт-Петербург, Россия
РЕЗЮМЕ
Установлено присутствие 5 таксонов трибосфенических млекопитающих в раннемеловой формации
Антлерс в Техасе и Оклахоме, США: базальное стволовое териевое млекопитающее (Kermackia texana), ство-
ловые таксоны териевых млекопитающих вблизи дивергенции сумчатых и плацентарных (Holoclemensia
A.O. Averianov
142
INTRODUCTION
Isolated teeth and jaw fragments of tribosphenic
mammals from the Lower Cretaceous (Aptian-
Albian) Antlers Formation in northern Texas, USA,
collectively called “Trinity therians”, are among the
most hard-won paleontological finds. An “acciden-
tal” discovery of two triconodontan jaw fragments
and an indeterminate mammalian humerus in 1949
by R.H. Denison in the “Trinity Sand” (now Antlers
Formation of Trinity Group) at Greenwood Canyon
near Forestburg (Zangerl and Denison 1950; Pat-
terson 1951), followed by extensive prospecting and
processing of fossiliferous matrix in the Forestburg
area. This work resulted in discovery of two new
mammal localities, while the original Greenwood
Canyon was the most productive. During four field
seasons about 46 tons of matrix were screen-washed,
which produced approximately 300 mammalian
specimens (Patterson 1955, 1956). Among these only
34 specimens were referable to therian mammals
(Patterson 1956). This is 11% of the whole mamma-
lian sample, dominated by multituberculates and tri-
conodontans, and about 1.35 tons of matrix per each
therian specimen. Discovery of Early Cretaceous
mammals in Texas was spectacular because Early
Cretaceous mammals were not known previously in
North America and only one mammal locality of that
age was known elsewhere (the rich Purbeck fauna
from the Berriasian of England was considered Late
Jurassic in age by that time). Moreover, the Early
Cretaceous is the time when divergence and early
evolution of two major groups of modern mammals,
Eutheria and Metatheria, occurred. The “Forestburg
therians” allowed for the first study of this problem
utilizing fossils (Patterson 1956). The Trinity mam-
mal localities were destroyed because of subsequent
urbanization of the Forestburg area. However, a new
productive microvertebrate locality with tribos-
phenic mammals was discovered within the Antlers
Formation in neighboring Oklahoma (Cifelli 1997;
Kielan-Jaworowska and Cifelli 2001; Davis et al.
2008; Davis and Cifelli 2011).
The Trinity therians are most interesting because
they are close phylogenetically to the metatherian-
eutherian dichotomy. But because of this the mor-
phology of their dentition is mostly plesiomorphic.
This, coupled with the scarcity and fragmentary
nature of the specimens, caused a great controversy
in interpretation of the Trinity therians in the past
(see “review of the previous work” below). Davis
and Cifelli (2011) provided the last comprehensive
taxonomic revision of these mammals. However, my
study of all available specimens in US museums led
texana и Pappotherium pattersoni), и стволовые таксоны сумчатых млекопитающих (Atokatheridium boreni и
Oklatheridium szalayi). K. texana характеризуется примитивной для териев формулой щечных зубов с тремя
молярами, сменой зубов в пятом премолярном локусе, M3 с низким протоконом без конулей, нижние моля-
ры с большим углом тригонида, косым протокристидом, параконид меньше метаконида (кроме m3), сильно
выраженным дистальным метакристидом, узким талонидом, маленьким бассейном талонида, маленьким эн-
токонидом (отсутствует на m3). У H. texana также была смена в пятом премолярном локусе и три моляра.
Этот таксон более продвинут по наличию более крупного протокона с конулями, отсутствием дистального
метакристида, меньшим углом тригонида, поперечным протокристидом, и широким талонидом с большим
бассейном. Близок к Eutheria по строению M1 с редуцированным эктофлексусом, полумоляриформным p5,
и небольшим углом тригонида с поперечным протокристидом. Однако Holoclemensia не может быть отнесе-
на к Eutheria из-за отсутствия дополнительных режущих кромок на коренных зубах и внутренних гребней
конулей. Для P. pattersoni (=Slaughteria eruptens) была характерна смена пятого премоляра, премоляриформ-
ный p5 и три моляра (симплезиоморфии для Theria). Этот таксон более продвинут, чем Holoclemensia по на-
личию более широкого и короткого талонида. Pappotherium близок к Eutheria по небольшому углу тригони-
да, поперечному протокристиду, и положении бокового кристида лабиальнее бороздки протокристида. Этот
таксон не относится к Eutheria из-за узкого и низкого протокона, маленьких конулей без внутренних крист,
короткой постпротокристы, и небольшого бассейна талонида. Atokatheridium boreni и Oklatheridium szalayi
(=O. minax, syn. nov.) характеризуются четырмя молярами и усиленными режущими кромками метаконида
и параконида. Эти таксоны не относятся к Deltatheroida из-за крупного протокона и наличием внутренних
гребней конулей. Oklatheridium также отличается от Deltatheroida более широким талонидом и лучше раз-
витым энтоконидом.
Ключевые слова: формация Антлерс, ранний мел, эволюция, Mammalia, Северная Америка, Theria
Tribosphenic mammals from the Lower Cretaceous of USA
143
to considerable different results, which are discussed
in this article. The discussion about attribution of the
specimens is present in the “comments” section of the
respective taxa under “systematic paleontology.”
Institutional abbreviations. CNHM, Chicago
Natural History Museum (Field Museum), Chicago,
USA; OMNH, Oklahoma Museum of Natural History,
Norman, USA; SMP–SMU, Shuler Museum of Pale-
ontology, Sothern Methodist University, Dallas, USA.
REVIEW OF THE PREVIOUS WORKS
The first scientific treatment of Forestburg
therians was published by Patterson (1956). He in-
tentionally did not apply taxonomic names because
of the fragmentary nature of the material. Patterson
provided detailed descriptions and illustrations of 14
molars or molar fragments and one edentulous den-
tary fragment in the CNHM collection (Greenwood
Canyon locality). He recognized two morphological
types of upper molars and three types of lower mo-
lars. Patterson (1956: 13) classified these specimens
as “therian mammals of uncertain infraclass affinities
but of metatherian-eutherian grade.” This concept of
therians of “metatherian-eutherian grade” persisted
for a long time in the literature (Kielan-Jaworowska
et al. 1979). Based on new materials, Patterson
(1956) provided a thorough discussion of the evo-
lution of mammalian molar teeth. In particular, he
introduced the term stylocone for the large stylar
cusp of the upper molars and proposed that the
lingual cusp of the upper molars of “pantotherians,”
identified previously as a protocone, is homologous
with the paracone of tribosphenic molars. According
to Patterson (1956), some of the Forestburg therians
may represent the group from which Eutheria and
Metatheria arose.
Mills (1964: fig.6D) published a diagram showing
occlusal relationships of upper and lower molars of a
Forestburg therian, based on CNHM PM 884 (up-
per) and CNHM PM 1005 (lower) from Greenwood
Canyon locality. In CNHM PM 884 the protocone
is missing and Mills mistook the small preserved
paraconule for the protocone. Hence this Forestburg
therian, in Mill’s interpretation, is only slightly more
derived compared with Peramus in having paracone
and metacone of equal size and somewhat larger pro-
tocone (lacking altogether in Peramus).
The first named taxon of Trinity therians was
Pappotherium pattersoni Slaughter, 1965, referred
to the new family Pappotheriidae Slaughter, 1965
within Theria incertae sedis, based on a maxillary
fragment with the two last molars (SMP–SMU
61725) from Butler Farm locality (Slaughter 1965).
Slaughter identified in the material from Butler Farm
three types of lower molars, types 4–6, additional to
the types 1–3 described by Patterson (1956) from
Greenwood Canyon. Slaughter assumed that one
of the upper molar types, recognized by Patterson
(1956), corresponds to the molars of Pappotherium.
Slaughter described also two premolars, a lower
(SMP–SMU 61730) and an upper (SMP–SMU
61731). These premolars were later referred to a
triconodontan (Butler 1978: 14). According to
Slaughter (1965: 18) “Pappotherium and Patterson’s
forms from Greenwood Canyon […] apparently are
very near the point of divergence of placentals and
marsupials from a common ancestor – either just
before, just after, or during this event.” Thus the first
interpretation of Trinity therians (Patterson 1956;
Slaughter 1965; Clemens 1966, 1968, 1970; Hopson
and Crompton 1969; Lillegraven 1969; Butler 1977,
1990, 1992) was, in modern usage, placement of them
within the stem group of Theria, but not attributable
to the crown groups Marsupialia or Placentalia.
The next described taxon was Holoclemensia
texana Slaughter, 1968 based on an upper molar
missing the protocone (SMP–SMU 61997, holo-
type), ultimate upper molar (SMP–SMU 62009),
and lower molar (SMP–SMU 62131) from Butler
Farm (Slaughter 1968b, c). The new taxon was re-
ferred to the marsupial family Didelphidae and was
considered the earliest known marsupial. The refer-
ral to Metatheria was based on “large stylar cusp C,
increased size of metacone, and accompanying in-
cipient twinning of the hypoconulid and entoconid”
(Slaughter 1968b: 255). The attribution to Didel-
phidae was explained by the similarity to Alphadon,
a Late Cretaceous stem marsupial referred at that
time to Didelphidae (Clemens 1979). According to
the modern phylogenetic nomenclature, this classifi-
cation implies that H. texana belongs to the crown
group Marsupialia.
The same year Slaughter (1968a) published two
premolars from Butler Farm, SMP–SMU 61948, an
upper penultimate premolar with a purported proto-
cone, and SMP–SMU 61947, a lower ultimate pre-
molar with a small metaconid. Slaughter interpreted
the morphology of these premolars as submolariform.
Because submolariform premolars are not known in
A.O. Averianov
144
marsupials, he considered these specimens as evi-
dence of eutherians in the Butler Farm locality.
In a review on origin and early differentiation of
therian mammals McKenna (1969) placed Pappoth-
erium and Holoclemensia at the roots of Eutheria and
Metatheria, respectively. In modern usage this means
that Pappotherium is a stem placental and Holoclem-
ensia is a stem marsupial.
The first revision of all tribosphenic mammals
from Butler Farm locality was published by Slaugh-
ter (1971). The previously identified type 6 of Trin-
ity lower molars, represented by a single specimen
(SMP–SMU 61728), was considered as belonging
to a taxon morphologically intermediate between
“pantotherians” and therians. It has a complete
distal metacristid and incipient entoconid, but the
entocristid is lacking. Another lower molar (SMP–
SMU 62398) with a complete distal metacristid and
entocristid was referred to a new taxon, Kermackia
texana Slaughter, 1971. K. texana was viewed as a
taxon intermediate between the previous one (molar
type 6) and Holoclemensia and Pappotherium. The
metatherians were represented by H. texana with
three specimens originally referred to that taxon
(Slaughter 1968b). The eutherians were represented
by more numerous specimens. Among these there are
three submolariform premolars, two of which were
reported previously (Slaughter 1968a) and one new
tooth, SMP–SMU 62399, a lower ultimate premolar
with a metaconid and a single-cusped talonid with
an incipient talonid basin. P. pattersoni was also re-
ferred to Eutheria, as well as a smaller pappotheriid
represented by an upper molar (SMP–SMU 62402).
A dentary specimen with four cheek teeth, first of
which is an erupting premolar (SMP–SMU 61992),
was tentatively referred to Pappotherium based on
size and occlusal relationships. The dentition of this
specimen was interpreted as two simple premolars, a
molariform ultimate premolar, and first molar, as in
eutherians. X-rays of this specimen show no erupting
teeth other than the first premolar. A back-to-front
replacement sequence has been reconstructed for this
specimen (see also Slaughter et al. 1974). The previ-
ously recognized Trinity molar type 4 (SMP–SMU
61726), a dentary fragment with canine (SMP–SMU
62400), and an upper incisor (SMP–SMU 62401)
were also referred to Eutheria.
Turnbull (1971) reviewed the Trinity therians
from Greenwood Canyon with special emphasis
on their bearing to marsupial evolution. He identi-
fied four taxa in this material: Holoclemensia cf.
texana (uppers: CNHM PM 1000, 1004, 1238; low-
ers: CNHM PM 1005), Holoclemensia sp. (uppers:
CNHM PM 886, 1015; lowers: CNHM PM 660,
887, 930, 948, 965, 966, 1119, 1249), Pappotherium
cf. pattersoni (uppers: CNHM PM 884, 999, 1075;
lowers: CNHM PM 922, 1046, 1120, 1245), and Pap-
potherium sp. (upper: CNHM PM 1287). Turnbull
considered both Pappotherium and Holoclemensia as
stem therians (order Tribosphena nov. and cohort
Tribosphenata nov. within Theria).
Crompton (1971: fig.3) reconstructed occlusal
relationships and wear facet for Pappotherium based
on the penultimate upper molar of the holotype
and referred lower molar from Butler Farm locality
(SMP–SMU 61726). He noted absence of internal
conular cristae (second rank shearing surfaces 3b and
4b) and weak development of shearing surfaces 5 and
6 on a small protocone in this taxon. The external
conular cristae duplicated the shearing surfaces of
the preparacrista and postmetacrista, thus providing
a second rank of cutting edges. A new reconstruction
of wear facets on P. pattersoni upper molar, without
wear on protocone, has been published by Kielan-
Jaworowska (1975: fig. 8) and Crompton and Kielan-
Jaworowska (1978: fig. 4).
The molar structure of Trinity therians was revised
by Fox (1975). Pappotherium and Holoclemensia are
more derived than primitive therians (exemplified by
Aegialodon, Kermackia, and Potamotelses) in having
double-rank prevallum-postvallid shear and loss of
contact between the paracone and distal metacristid.
Fox argued that Pappotherium has three molars and
Holoclemensia – four molars. The main argument was
that in Holoclemensia both ultimate upper molars
have a similar morphology, with a reduced metastylar
lobe, while in Pappotherium only ultimate molar have
this morphology. In Deltatheroides with four molars
the metastylar lobe is reduced on both ultimate and
penultimate molars. Butler (1977: 243) considered
that this argument is “based on a misinterpretation
of the evidence,” but did not provide further explana-
tion in that paper. Later he noted that the case with
Deltatheroides is not typical because the last molar is
in the state of reduction in this taxon and a variety of
Late Cretaceous metatherians have the penultimate
molar with a well-developed metastylar lobe (Butler
1978: 21). Because of the supposed dental formula
and other dental characters, F
ox followed Slaughter
(1971) in referring Pappotherium and Holoclemensia
Tribosphenic mammals from the Lower Cretaceous of USA
145
to stem Placentalia and Marsupialia, respectively.
Fox also noted a the presence of new taxa among
undescribed specimens of Trinity therians.
A new interpretation of Trinity therians based
on revision of the whole sample from Greenwood
Canyon and Butler Farm localities was presented by
Butler (1978). According to this revision, there are
at least five or six taxa of Trinity therians: Pappoth-
erium pattersoni, Holoclemensia texana, Kermackia
texana, Trinititherium slaughteri Butler 1978, and
Slaughteria eruptens Butler, 1978. Pappotherium
and Holoclemensia are the most common taxa; both
have four molars, as in marsupials, and complex
premolars, as in placentals. Both are referred to the
Pappotheriidae, which cannot be attributed to either
Marsupialia or Placentalia but represents a separate
evolutionary lineage (new order Pappotherida). The
two smaller forms, Kermackia and Trinititherium, have
lower molars more primitive than in Pappotheriidae
and were placed in a new family Kermackiidae (new
order Aegialodontia). Trinititherium slaughteri is
based on a single lower molar (SMP–SMU 61728),
the molar type 6 of Slaughter (1965). A small upper
molar (SMP–SMU 62402) could belong to either
Kermackia or Trinititherium. Slaughteria eruptens is
based on a dentary fragment with four cheek teeth
(SMP–SMU 61992), which was referred previously
to P. pattersoni by Slaughter (1971). Butler consid-
ered it unlikely that this specimen has a molariform
premolar because of its Early Cretaceous age and
interpreted its dentition as the last two premolars
and the first two molars. It was placed provisionally
in Kermackiidae. Orders Aegialodontia (Aegialo-
dontidae, Kermackiidae, Deltatheriidae, and Pota-
motelses) and Pappotheriidae constitute the new
subclass Tribotheria. Tribotherians are mammals
with tribosphenic molars that are not classifiable as
marsupials or placentals.
Fox (1980) placed Kermackiidae (Kermackia and
?Trinititherium) in Tribotheria, incertae sedis. Ho-
loclemensia was referred to the recent order Marsu-
picarnivora, incertae sedis, and Pappotheriidae (Pap-
potherium and Slaughteria) to the extinct suborder
Proteutheria of recent Insectivora.
Slaughter (1981) criticized Butler’s reconstruc-
tion of cheek dentitions for Pappotherium and Ho-
loclemensia. He thought that Holoclemensia has not
a molariform premolar and that Pappotherium has
three molars and a molariform ultimate premolar.
This interpretation allows referral of Holoclemensia
to the stem Marsupialia and Pappotherium to the
stem Placentalia.
Hershkovitz (1982) restudied CNHM PM 583,
and the edentulous dentary fragment from Green-
wood Canyon described by Patterson (1956). After
immersion of the specimen in oil of anise, he found
that the alveolus of the third incisor is “staggered”
between the i2 and i4 alveoli, as in modern didelphid
marsupials. Butler (1978) thought that this specimen
possible belongs to either Holoclemensia or Pappoth-
erium. Later Hershkovitz (1995) erected a new taxon,
Adinodon pattersoni Hershkovitz, 1995, referred to a
new subfamily Adinodontinae within the modern di-
delphimorphian family Marmosidae (=Didelphidae),
for CNHM PM 583. Thus, according to Hershkovitz
at least one of Trinity therians belongs to the crown
group Marsupialia.
Archer (1984) proposed the supercohort Proto-
delphia to contain Holoclemensia. Later Aplin and
Archer (1987) erected the monotypic family Holo-
clemensiidae for the latter genus. Holoclemensia was
viewed by these authors a stem marsupial.
Jacobs et al. (1989) described Comanchea hilli Ja-
cobs et al., 1989 based on a fragmented upper molar
(SMP–SMU 71848) from the Pecan Valley Estates
locality within the P
aluxy Formation in Central
Texas, a lateral equivalent of the upper section of
the Antlers Formation in North-Central Texas, USA
(Winkler et al. 1990). The new taxon was referred to
Aegialodontia. SMP–SMU 71848 is similar to the
hypothetically reconstructed upper molar of Aegialo-
don (Crompton 1971) in having a small protocone
but has an unexpectedly derived stylar region, with
the stylar shelf reduced mesially and well-developed
stylar cusps. Later this specimen was considered a
molar, premolar, or deciduous tooth (Winkler et al.
1990). Jacobs et al. (1989) concluded that Holoclem-
ensia is not a marsupial because a stylar cusp C could
be developed independently, as in Comanchea, and
the degree of twinning of entoconid and hypoconulid
is not the same as in Late Cretaceous metatherians.
According to these authors, the Trinity therians
represent two evolutionary grades, aegialodontids
(Comanchea, Kermackia, and Trinititherium) and
pappotheriids (Pappotherium, Holoclemensia, and
Slaughteria). Jacobs et al. (1989) and Winkler et al.
(1990) also published an edentulous dentary frag-
ment with alveoli for five double-rooted premolars
(SMP–SMU 62006) from the Paluxy Church local-
ity within the Twin Mountains Formation, a lateral
A.O. Averianov
146
equivalent of the lower section of the Antlers Forma-
tion. This specimen may belong to either Pappoth-
erium or Holoclemensia.
Marshall and Kielan-Jaworowska (1992) consid-
ered only Slaughteria among Trinity therians refer-
able to Eutheria, because of a supposedly molariform
ultimate premolar.
Cifelli (1993a) published the first phylogenetic
analysis that included Trinity therians. This analysis
resulted in an unresolved position of Kermackia, Trin-
ititherium, and Slaughteria at the root of the tree before
the split of Metatheria and Eutheria, while Kielanthe-
rium with more plesiomorphic tribosphenic molars
was included in Metatheria. Comanchea was grouped
together with “Picopsidae” in a sister taxon to Theria.
This is not surprising because all these taxa, as was
found later, are based on deciduous teeth (Averianov
et al. 2010; Davis and Cifelli 2011). Pappotherium and
Holoclemensia were included in Eutheria.
Turnbull (1995) presented in a poster form an at-
tempt to attribute edentulous dentary fragments from
the Antlers Formation to the described taxa. In par-
ticular, he was inclined to refer the holotype of Adin-
odon pattersoni (CNHM PM 583) to Holoclemensia.
Cifelli and Muizon (1997) did not confirm the
presence of a “staggered” lower incisor in CNHM
PM 583 or in any Late Cretaceous metatherian. Ac-
cording to these authors, this character first appeared
only in the Paleocene South American marsupials.
Consequently, Adinodon pattersoni was considered a
nomen dubium.
Cifelli (1997) announced discovery of Early
Cretaceous mammals in a new microvertebrate
locality McLeod 2 within the Antlers Formation in
Oklahoma, USA. This locality is gone now (Davis et
al. 2008). Among two first mammal specimens from
this locality, one was an upper tribosphenic molar
(OMNH 33455). This specimen is more derived
than Pappotherium and Holoclemensia in having
a taller protocone, and more developed and more
labially placed conules, with internal crista at least
on the paraconule. It was considered as representing
a possible new taxon, which was not named. Cifelli
proposed that the first molariform tooth in the holo-
type of Slaughteria eruptens is a deciduous premolar.
Based on this, he questioned validity of this taxon,
which may be synonymous with P. pattersoni. He also
questioned reference of Slaughteria to Kermackiidae,
which was based on possible presence of a distal meta-
cristid in S. eruptens, but otherwise the latter taxon,
having a larger talonid basin and strong entoconid,
is similar with Pappotheriidae. Cifelli concurred with
Slaughter (1971) that presence of molariform premo-
lars in the Antlers Formation of Texas strongly sug-
gests that eutherians were present in North America
during the Early Cretaceous.
Analyses of the metatherian relationships follow-
ing discovery of new specimens of deltatheroidans
from the Late Cretaceous of Mongolia (Rougier et
al. 1998, 2004), identified Holoclemensia as a basal
metatherian, at a trichotomy with Deltatheroida and
a clade of all other metatherians. The same result was
repeated by Wible et al. (2001). However, adding of
Atokatheridium and Nanocuris to the same data ma-
trix resulted in the position of Deltatheroida as the
sister taxon for the clade Holoclemensia + all other
metatherians (Wilson and Riedel 2010).
In a phylogenetic analysis presented by Averianov
and Skutschas (1999) Pappotherium is a stem placen-
tal, Holoclemensia is a stem therian, and Kermackia
and Slaughteria are unresolved sister taxa to the
group Holoclemensia + Theria. Comanchea was clus-
tered with Picopsis, as in Cifelli (1993b).
Novacek (1999: fig. 7) presented a cladogram of
major clades of therians showing Holoclemensia as a
stem marsupial.
F
our additional specimens of tribosphenic mam-
mals from the McLeod 2 locality have been described
by Kielan-Jaworowska and Cifelli (2001). The upper
molar (OMNH 61623) with a small protocone and
unwinged conules is the holotype of Atokatheridium
boreni Kielan-Jaworowska and Cifelli, 2001. This tax-
on was tentatively referred to Deltatheroida because
of extreme development of stylar shelf, considered as
a derived character. A lower molar (OMNH 61624)
with obtuse trigonid angle, distal metacristid, and
only two talonid cusps, was questionably referred to
A. boreni. Two lower molar trigonids (OMNH 61642
and 61643) have been identified as ?Deltatheroida
indet. Placement of Atokatheridium within Deltathe-
roida has been confirmed in the phylogenetic analysis
by Rougier, Wible et al. (2004).
Kobayashi et al. (2002) used X-ray CT scanning
of SMP–SMU 61992, the holotype of Slaughteria
eruptens. They found a germ of a replacement tooth
under the first molariform tooth, showing that this
tooth is a deciduous premolar, as was suggested pre-
viously by Cifelli (1997). The erupted teeth in this
specimen have been identified as p2, p3, dp4, and m1,
assuming that this animal had four premolars. The
Tribosphenic mammals from the Lower Cretaceous of USA
147
reconstructed eruption sequence is (dp3?) → dp4 →
m1/p3 → p2 → p4. Different interpretations of the
eruption sequence in this specimen were presented by
Luo et al. (2004), Archibald and Averianov (2012),
and Davis (2011b). Kobayashi et al. (2002) noted
that it is possible that Slaughteria is a juvenile of
Pappotherium, as was originally suggested by Slaugh-
ter (1971). Kobayashi et al. (2002) also suggested
that SMP–SMU 62398, the holotype of Kermackia
texana, could be a deciduous premolar.
In the analysis by Luo et al. (2003) Holoclemensia
is a basal metatherian forming a trichotomy with
Sinodelphys and a clade of remaining metatherians.
Atokatheridium clustered with Deltatheridium. In
the analysis of a modified version of this dataset
presented by Luo and Wible (2005) Holoclemensia
is clustered with Sinodelphys in a taxon sister to the
remaining metatherians. Deltatheroida is not mono-
phyletic and Atokatheridium forms a trichotomy with
Deltatheridium and the clade containing remaining
metatherians. In a subsequent analysis of the same
matrix Luo et al. 2011 the phylogenetic position of
discussed taxa is the same as in Luo et al. (2003).
In a now classical book on Mesozoic mammals
(Kielan-Jaworowska et al. 2004) classified Trinity
therians as “tribotherians,” or stem “boreospheni-
dans.” The term Boreosphenida is redundant (Rou-
gier et al. 2007; Davis 2011b) and here I use the
traditional concept of Tribosphenida (McKenna
1975). Three families, not referred to any order, have
been recognized: Kermackiidae (Kermackia and
Trinititherium), Pappotheriidae (Pappotherium), and
Holoclemensiidae (Holoclemensia). The difference
between the holotypes of K. texana and T. slaughteri
are slight and may represent positional variation in
teeth. Slaughteria was not referred to any family and
its potential synonymy with Pappotherium has been
noted. Atokatheridium was referred to Deltatheroida,
family incertae sedis. Adinodon pattersoni was omit-
ted from classification because it is indeterminate.
Davis et al. (2008) decribed a considerably im-
proved sample of tribosphenic molars from McLeod
2 locality (Tomato Hill local fauna). The deltatheroi-
dan Oklatheridium szalayi Davis et al., 2008 is based
on the holotype upper molar (OMNH 62410) and
eight referred upper and lower molars. The latter in-
cluded OMNH 61643 was referred to ?Deltatheroida
indet. by Kielan-Jaworowska and Cifelli (2001). The
upper molars represent three molar loci (M1–4) but
authors did not exclude the possibility of a fourth
molar. All lower molars are represented by the trigo-
nid only and do not help to establish a dental formula
for this taxon. O. szalayi is larger than A. boreni but
considerably smaller than Late Cretaceous Asiatic
deltatheroidans. O. szalayi differs from other deltath-
eroidans by well-developed conular cristae. OMNH
33455, the upper molar described previously by Cife-
lli (1997), has been identified as ?Oklatheridium sp.
Davis et al. (2008) also added five new molars to A.
boreni, two uppers and three lowers. Their hypoth-
esized dental formula was four molars for this taxon,
although the referred specimens documented only
M1–3 loci. Attribution of the lower molar (OMNH
61624) to A. boreni (Kielan-Jaworowska and Cifelli
2001) was more confidently confirmed. The authors
followed W.A. Clemens, cited in Butler (1978: 11),
in considering SMP–SMU 61728, the holotype of
Trinititherium pattersoni, as a positional variant of
Kermackia texana. They also agreed with Slaughter
(1971) and Kobayashi et al. (2002) in considering
the holotype of Slaughteria eruptens as possiblly
belonging to P
appotherium pattersoni but did not
synonymize these taxa formally.
In a phylogenetic analysis performed by Vullo et
al. (2009), Holoclemensia appeared as a stem therian.
Describing new specimens of the Late Cretaceous
Asiatic deltatheroidan Sulestes, Averianov et al.
(2010) commented on several taxa of Trinity theri-
ans. OMNH 63725, identified as M3 of A. boreni by
Davis et al. (2008) is considerably larger than other
upper molars of this species and differs in having a
distinctly wider stylar shelf. This specimen was
referred to Oklatheridium. This referral resulted in
placement of Atokatheridium among stem therians
rather than deltatheroidans in the phylogenetic
analysis. In this analysis Pappotherium is a stem the-
rian and Holoclemensia a stem placental. On the their
cladogram (Averianov et al. 2010: fig. 8) and in the
list of synapomorphies, clade 10 was erroneously des-
ignated as Eutheria, while it should have been clade
9, including Holoclemensia. Averianov et al. (2010:
fig. 9) published a reconstruction of the upper cheek
teeth of Holoclemensia with three molars.
During the reanalysis of the CT scans of SMP–
SMU 61992 made by Kobayashi et al. (2002), Davis
(2011b) found a small partially calcified tooth germ
under the last preserved molariform tooth in this
specimen, implying that it had two molariform decid-
uous teeth, dp4 and dp5, a pattern not known in any
extinct or extant therian. Winkler et al. (2011), used
A.O. Averianov
148
higher resolution CT scans of SMP–SMU 61992 and
concluded that the conjectural structure below the
last preserved molariform tooth is posteriorly open
and resembles neither the cap nor bell stage of a de-
veloping tooth. Here we accept the replacement pat-
tern for SMP–SMU 61992 suggested by Kobayashi
et al. (2002) and Winkler et al. (2011). Winkler et al.
(2011) also used the size comparison for attribution
of lower molars to the taxa based on upper molars,
Holoclemensia and Pappotherium. They formally
synonymized Slaughteria eruptens and Pappotherium
pattersoni.
Davis and Cifelli (2011) presented a thorough
revision of all Trinity therians. In this paper the
McLeod 2 locality was considered in the context of
the Tomato Hill local fauna. Atokatheridium boreni
(Deltatheriidae) is represented by eleven molars
from Tomato Hill locality – three uppers and eight
lowers. M4 is still unknown but hypothesized. The
interpretation of Oklatheridium was changed, with
two species now recognized, O. szalayi and O. minax
Davis and Cifelli, 2011. Only upper molars were at-
tributed to the named species, while lower molars
were identified as Oklatheridium sp. The sample of
O. szalayi includes five molars, three M1, one M2,
and one M3. All but one of these molars comes from
Tomato Hill locality, the exception being CNHM
PM 1238, which is from the Greenwood Canyon
locality. The holotype of O. minax (OMNH 33455)
is a tooth (M2) from Tomato Hill locality described
by Cifelli (1997) and identified as ?Oklatheridium sp.
in Davis et al. (2008). Two other upper molars have
been referred to this species: CNHM PM 884 (M1)
from Greenwood Canyon locality and OMNH 63727
(RM3) from Tomato Hill locality. Pappotherium pat-
tersoni was provisionally referred to the Metatheria
based on presumed presence of four molars. Except
the holotype, five upper molars and five lower molar
trigonids from Greenwood Canyon and Tomato Hill
localities have been referred to this species. Holocle-
mensia texana, placed in Eutheria incertae sedis, is
known from five upper and eleven lower molars from
the Butler Farm, Greenwood Canyon, and Tomato
Hill localities. Also one upper premolar (P4, SMP–
SMU 61948), one lower premolar (p5, SMP–SMU
62399), and a deciduous upper premolar (DP5,
SMP–SMU 71848, holotype of Comanchea hilli from
Pecan Valley Estates locality) have been tentatively
referred to H. texana. In spite of this referral being
only tentative, C. hilli was unquestionably synony-
mized with H. texana. One lower molar (SMP–SMU
61726) from Butler Farm locality has been identified
as Holoclemensia sp. One lower premolar (p5, OMNH
67134), and seven lower molars, including SMP–
SMU 61728, the holotype of Trinititherium slaughteri,
have been referred to Kermackia texana (Kermacki-
idae, Tribosphenida incertae sedis). One upper molar
(SMP–SMU 62402) was referred to K. texana tenta-
tively. These specimens come from the Butler Farm,
Greenwood Canyon, and Tomato Hill localities.
Slaughteria eruptens (Tribosphenida, family incertae
sedis) includes, except the holotype, a lower premolar
(p5, CNHM PM 1098), and two fragmented lower
molars (OMNH 63726 and 63721). Thus this taxon
is also known from the three localities mentioned
above. Two specimens from the Greenwood Canyon
locality, an upper ultimate molar (CNHM PM 1075)
and lower molar (CNHM PM948), were identified as
Tribosphenida incertae sedis.
As the above review shows, considerable contro-
versy surrounds interpretations of the Trinity theri-
ans. This is undoubtedly caused by the fragmentary
nature of most specimens and their largely plesio-
morphic morphology. The postulated phylogenetic
position of these taxa is heavily influenced by their
taxonomic interpretation, association of upper and
lower dentitions, identification of the molar posi-
tions, and hence the dental formula. In the next sec-
tion I present a view on the classification of Trinity
therians. All numerical indices mentioned in the text
are based on the measurements provided by Davis
and Cifelli (2011).
SYSTEMATIC PALEONTOLOGY
Mammalia Linnaeus, 1758
Tribosphenida McKenna, 1975
Stem group of Theria Parker and Haswell, 1897
Kermackia texana Slaughter, 1971
(Fig. 1)
Theria indet.: Patterson (1956: fig. 4A).
Trinity lower molar type 3: Patterson (1956: fig. 9B);
Winkler et al. (2011: fig. 10).
Trinity lower molar type 6: Slaughter (1965: fig. 4);
Slaughter (1971: pl. 1); Fox (1975: fig. 7A).
Kermackia texana: Slaughter (1971: 133, pl. 2); Fox
(1975: fig. 7B); Butler (1978: fig. 3K); Kielan-Jaworowska
et al. (2004: fig. 11.4D); Davis and Cifelli (2011: fig. 8C–G).
Tribosphenic mammals from the Lower Cretaceous of USA
149
Pappotherium cf. pattersoni: Turnbull (1971: figs. 3C,
6D–F).
Trinititherium slaughteri: Butler (1978: 10, fig. 3T);
Kielan-Jaworowska et al. (2004: 419, fig. 11.4E).
Kermackia or Trinititherium: Butler (1978: fig. 2c).
Tribosphenida indet.: Davis and Cifelli (2011: fig. 10A).
Holotype. SMP–SMU 62398, right dp5.
Type locality and horizon. Butler Farm locality,
Wise County, Texas, USA; Antlers Formation, Lower
Cretaceous (Aptian-Albian).
Referred specimens. Type locality: SMP–SMU
61728, left dentary fragment with m3 and alveoli
for m2 (holotype of Trinititherium slaughteri Butler,
1978).
Fig. 1. The stem therian Kermackia texana from the Early Cretaceous Antlers Formation of Texas and Oklahoma, USA. Upper teeth are
in labial and occlusal views, lower teeth – in occlusal and lingual views. Worn cusps and crests are reconstructed. Mesial end is to the left.
Asterisk denotes reversed image at the collection number. Scale bar = 1 mm.
A.O. Averianov
150
Greenwood Canyon locality: CNHM PM 1075,
left M3. CNHM PM 1245, right m1. CNHM PM
922, right m2. CNHM PM 1046, left mx trigonid.
Possible also the lost mx trigonid (CNHM PM 1065)
mentioned by Butler (1978: 10).
Tomato Hill locality: OMNH 61178, right mx
trigonid. OMNH 63893, left mx trigonid. OMNH
63731, left mx talonid.
Differential diagnosis. A stem therian different
from Metatheria by replacement in fifth premolar
locus, three molars, and paraconid smaller than meta-
conid (except on m3). Differs from Metatheria and
Eutheria by small and low protocone, lack of conules,
strong distal metacristid, narrow talonid, and small
entoconid, lacking on m3. Additionally differs from
Eutheria by keel-like vertical crest on paraconid.
Differs from the Trinity stem therians Holoclemensia
and Pappotherium by lack of conules, greater trigonid
angle, paraconid and metaconid separated by lingual
groove, oblique protocristid, distal metacristid pres-
ent, narrow talonid, and keel-like vertical crest of
paraconid. Among other stem therians differs from
Aegialodon, Kielantherium, and Hypomylos by larger
talonid with entoconid, from Juramaia by lack of
conules, and from Tribactonodon by having keel-like
vertical crest of paraconid instead of mesiolingual
cuspule e. Differs also from Aegialodon and Kielan-
therium by paraconid smaller than metaconid. Differs
from a premetatherian stem therian Montanalestes
by distal metacristid present, paraconid smaller than
metaconid, and paraconid and metaconid separated
by lingual groove.
Description. CNHM PM 1075 is an ultimate up-
per molar, M3 based on the dental formula inferred
from the lower molars (see below). The crown is
dominated by a large paracone, which occupies a
central position, with the parastylar lobe and proto-
conal region almost equal in width. The metacone is
strongly reduced and the metastylar lobe is lacking.
The preprotocrista is long and strong. It connects the
relatively large stylocone. The parastyle is somewhat
smaller than the stylocone. There is a prominent
ectocingulum on the parastylar lobe, with a minute
stylar cusp. The protocone is very low and narrow
mesiodistally. There are no conules. The preprot-
ocrista connects the parastyle. The postmetacrista
terminates at the base of the metacone.
There are four complete lower molars and sev-
eral fragments. Among complete molars, SMP–SMU
62398 is the smallest and CNHM PM 922 is the
largest. The ultimate molar in a dentary fragment
(SMP–SMU 61728) is somewhat smaller than the
latter tooth. These size differences between the speci-
mens may reflect a size trend within the molar series:
gradual increase towards the penultimate molar and
decrease on the ultimate molar. Two alternative in-
terpretations of this trend are possible: these teeth
are m1–4 or an ultimate deciduous premolar and
m1–3. The second alternative is preferred here be-
cause SMP–SMU 62398 is 7% shorter than CNHM
PM 1245, while in stem therians with four molars m1
and m2 have a similar length (Dashzeveg and Kielan-
Jaworowska 1984). Moreover, on SMP–SMU 62398
the precingulid is very faint and the mesiolingual
cuspule e is lacking. These features are common for
the deciduous ultimate premolar abutting the simple
deciduous penultimate premolar. The m1 contacts
with the ultimate permanent premolar, which has
a developed talonid heel, and thus it possesses an
elaborated precingulid and mesiolingual cuspule e for
the interlocking with p5. Thus Kermackia likely had
three molars (see also Davis and Cifelli 2011).
SMP–SMU 61728 is a posterior dentary frag-
ment with m3 and alveoli for m2. The broken base of
the coronoid process can be seen just posterior to the
m3 (Davis and Cifelli 2011: fig. 8G3). The specimen
is likely not mature because the coronoid process
closely approximates the unworn last molar and the
retromolar space is not developed. The difference
between the mesial and distal alveoli in m2 is less
pronounced compared with m3. This suggests that
m2 had a larger talonid. The lingual alveolar border is
sharp and higher than the labial alveolar border. This
is correlated with the unequal height of the molar
crown, which is deeper on the labial side.
All molariform teeth (dp5 and m1–3) are similar
in having a low and labially deflected talonid, long
talonid isthmus, and prominent distal metacristid.
The protoconid is heavily worn on dp5 but appar-
ently was lower compared with the molars. The
trigonid angle is ~52° (dp5), ~54° (m1), ~46° (m2),
and ~48° (m3). The protoconid is the highest on m3.
The protocristid is oblique on dp5 and m1 but more
transverse on m2–3. The protocristid usually lacks
the protocristid notch (present on trigonid frag-
ments from the Tomato Hill locality). The metaconid
is robust, about half the height of the protoconid. On
m3 the metaconid is greatly reduced and similar in
height with the paraconid. The paraconid is small,
spike-like, and placed somewhat labial to the metaco-
Tribosphenic mammals from the Lower Cretaceous of USA
151
nid. It is pointed vertically, parallel to the metaconid.
These cusps are separated by a small gap allowing
the trigonid basin to open lingually. All molars have
a well-developed precingulid (mesiolabial cuspule f).
On dp5 the precingulid is very faint. On m1–2 there
is a slight vertical keel on the mesiolingual slope of
the paraconid representing the mesiolingual cuspule
e. There is a strong distal metacristid extending from
the metaconid tip towards the base of the hypoconid
where it is separated from the cristid obliqua by a
distinct notch. Slaughter (1971) and Butler (1978)
noted an additional cusp on the distal metacristid on
m3. This is a preservation artifact caused by chipping
of this crest in SMP–SMU 61728.
The talonid is narrower than the trigonid. The tal-
onid width to trigonid width ratio is 0.77 (dp5), 0.74
(m1), 0.81 (m2), and 0.68 (m3). The talonid isthmus
opposite the hypoflexid is very long, compatible in
length with the remaining part of the talonid. The
hypoconid is the highest cusp, about twice higher
than the hypoconulid. The small entoconid is present
on dp5 and m1–2 and lacking on m3 (Butler’s (1978)
identification of the rudimentary entoconid on this
tooth cannot be confirmed). The talonid basin is
small and sloping lingually. The entocristid is hardly
discernable on m1–2, and lacking on dp5 and m3.
Thus the talonid basin is open lingually.
Comments. Davis and Cifelli (2011) refereed
SMP–SMU 62402, an isolated upper molar from
Butler Farm, to K. texana. This specimen is identified
here as dP5 of Pappotherium pattersoni (see below).
These authors also referred to K. texana a lower ul-
timate premolar, OMNH 67134 (Davis and Cifelli
2011: fig. 8B) because of characteristic notch on the
crest between the trigonid and the talonid cusp. This
notch has been considered as serially homologous
with the notch between the distal metacristid and
the cristid obliqua of the lower molars in Kermackia.
This notch cannot be homologous because on the pre-
molar it is on the crest between the protoconid and
hypoconid (talonid cusp), while on molars it is on the
crest between the metaconid and hypoconid. More-
over, it is highly improbable that such a primitive
tribosphenic taxon had a semimolariform premolar. A
similar notch is present on p5 referred to Holoclemen-
sia texana (SMP–SMU 61947). Otherwise OMNH
67134 is very similar with p5s of Holoclemensia and it
is referred here to that taxon. It differs by somewhat
smaller size, but the lower molars of Holoclemensia
from the Tomato Hill locality are also distinctly
smaller than those from the Butler Farm locality (see
comments to Holoclemensia).
Holoclemensia texana Slaughter, 1968
(Fig. 2)
Theria indet.: Patterson (1956: figs. 3B, 5, 6); Clemens
(1966: fig. 13b).
Trinity lower molar type 2: Patterson (1956: fig. 8B).
Forestburg molar: Mills (1964: fig. 6D).
Trinity lower molar type 4: Slaughter (1965: fig. 2);
Slaughter (1971: pl.10C, D).
Trinity lower molar type 5: Slaughter (1965: fig. 3).
Eutheria indet.: Slaughter (1968a: fig. 1); Slaughter
(1971: pls. 5, 6, 7D–G).
Clemensia texana [preoccupied generic name]: Slaugh-
ter (1968b: 254, fig. 1).
Holoclemensia texana: Slaughter (1968c: 1306); Slaugh-
ter (1971: pls. 3, 4); Fox (1975: fig. 2B); Butler (1978: figs.
1H, 2k-o, 3H, 4g, h, 5H); Kielan-Jaworowska et al. (1979:
fig. 10–4C–F); Kielan-Jaworowska et al. (2004: fig. 11.5E);
Averianov et al. (2010: fig. 9); Davis and Cifelli (2011: figs.
6A–G, 7A–E).
Unidentified lower molar: Crompton (1971: fig. 3).
Holoclemensia cf. texana: Turnbull (1971: figs. 2A, C,
5C).
Holoclemensia sp.: Turnbull (1971: figs. 2D, 5A, B);
Davis and Cifelli (2011: fig. 7F).
Pappotherium pattersoni: Butler (1978: fig. 4f).
Comanchea hilli: Jacobs et al. (1989: 4992, figs. 1, 2);
Winkler et al. (1990: fig. 10); Kielan-Jaworowska et al.
(2004: fig. 11.6B).
Kermackia texana: Davis and Cifelli (2011: fig. 8B).
Holotype. SMP–SMU 61197, right M2 missing
protocone.
Type locality and horizon. Butler Farm locality,
Wise County, Texas, USA; Antlers Formation, Lower
Cretaceous (Aptian-Albian).
Referred specimens. Type locality: SMP–SMU
61948, left P4. SMP–SMU 62009, right M3. SMP–
SMU 61947, left p5 (the specimen is now heavily
damaged). SMP–SMU 62399, left p5. SMP–SMU
62722, right m1 (Davis and Cifelli (2011) indicated
that this specimen has only talonid preserved, possible
because of broken cast at their disposal). SMP–SMU
61726, left m1. SMP–SMU 62131, left m1. SMP–
SMU 61727, left m2. SMP–SMU 62721, right m3.
Greenwood Canyon locality: CNHM PM 1000,
left M1 missing protocone. CNHM PM 1004, right
M1 missing protocone and parastylar and metastylar
lobes. CNHM PM 886, right M2 missing protocone
and parastylar lobe. CNHM PM 1005, right m1.
A.O. Averianov
152
CNHM PM 887, right mx trigonid. CNHM PM
3877, right mx trigonid.
Tomato Hill locality: OMNH 67134, right p5.
OMNH 62412, heavily worn right mx. OMNH 62414,
left mx talonid. OMNH 63894, right mx talonid.
Pecan Valley Estates locality: SMP–SMU 71848,
left dP5 (holotype of Comanchea hilli).
Differential diagnosis. A stem therian different
from Metatheria by replacement in fifth premolar
locus, three molars, and paraconid smaller than
Fig. 2. The stem therian Holoclemensia texana from the Early Cretaceous Antlers Formation of Texas, USA. Upper teeth are in labial and
occlusal views, lower teeth – in occlusal and lingual views. Worn cusps and crests are reconstructed. Mesial end is to the left. Asterisk
denotes reversed image at the collection number. Scale bar = 1 mm.
Tribosphenic mammals from the Lower Cretaceous of USA
153
metaconid. Similar with Eutheria and different from
other stem therians by M1 with reduced ectoflexus,
semimolariform p5, and low trigonid angle with
transverse protocristid. Differs from Eutheria by
postprotocrista not extending labially past metacone
base and conules lacking internal cristae. Differs from
Kermackia by conules present, smaller trigonid angle,
transverse protocristid, paraconid and metaconid
bases not separate, distal metacristid lacking, wider
talonid, and larger entoconid. Differs from Pappoth-
erium by large stylar cusp C, larger protocone and
conules, and cristid obliqua lingual to protocristid
notch. Differs from a premetatherian stem therian
Montanalestes by paraconid smaller than metaconid.
Description. The SMP–SMU 61948 is the pen-
ultimate upper premolar (P4) referable to H. texana
(Butler 1978; Averianov et al. 2010; Davis and Cifelli
2011). The main cusp is tall and trenchant. Its tip is
somewhat deflected distally. The mesial side of the
main cusp is rounded, while along the distal side
there is a sharp ridge connecting the distal cingulum.
On the labial side of the crown, closer to the mesial
end, there is a shallow ectoflexus. There is a distinct
mesial cingulum with small mesial cusp at the base
of the crown. The distal end of the crown is more
transversely expanded, and bears three cusps. The
distolabial cusp is the largest. It is placed on the dis-
tolabial cingulum which is disrupted from the distal
cingulum. Slaughter (1981) identified the distolabial
cusp in this specimen as a stylar cusp C, but it is more
corresponding to the position of the stylar cusp E
on molars. A somewhat smaller distal cusp is on the
distal cingulum which continues into the lingual
cingulum. A third minute cusp is just an eminence on
the meeting of the distal cingulum and the crest from
the main cusp. The lingual cingulum was apparently
present on the broken area between the mesial and
distal cingula. Possible a small protoconal bulge was
present there, but not a true protocone, as was sug-
gested previously by Slaughter (1968a) and Butler
(1978). Certainly there is no root supporting the
protocone mentioned by Slaughter (1981: 682). The
premolar has two roots.
The dP5 (SMP–SMU 71848) is a triangular
tooth with a mesiodistally wide and transversely
short protoconal region. The paracone is the largest
cusp. The metacone is distinctly smaller and sepa-
rated from the latter. The labial margin of the tooth
is skewed mesially, with the stylar shelf mesially
reduced, as typical for the dP5. I cannot discern the
preparacrista described by Davis and Cifelli (2011).
The parastyle and stylocone are poorly differentiated
and almost non-existent. The large stylar cusp C is
similar in size to the metacone. It is connected to a
smaller stylar cusp D by a strong ridge. The metastyle
is not differentiated. The postmetacrista is relatively
long and straight. The protocone is low, more than
twice smaller than the paracone. There is a relatively
large paraconule without internal crista. The prepro-
tocrista terminates at the base of the paracone. The
metaconule region is damaged.
All upper molars except M3 (SMP–SMU 62009)
have the protoconal region broken. The M1 is repre-
sented by two fragments, one heavily worn (CNHM
PM 1000) and another missing the parastylar and
metastylar lobes (CNHM PM 1004). In the latter
specimen the paracone is broken but it has a larger
base compared with the metacone and certainly was
a highest labial cusp. In CNHM PM 1000 the height
differential between the labial cusps is decreased by
substantial wear. Butler’s (1978: 5) observation that
on CNHM PM 1000 “the metacone is farther from
the buccal edge than the paracone” is not correct.
In all upper molars of Holoclemensia, as well as in
other stem therians, the metacone is slightly labial
to the paracone. The preprotocrista is incompletely
preserved (CNHM PM 1004) or eliminated by wear
(CNHM PM 1000). Evidently it was short and
extending to a small stylocone. The parastylar lobe
protrudes mesially and only little labially. The para-
style was likely larger than stylocone and separated
from the latter by the parastylar groove. The meta-
stylar lobe is very small, with short and weak post-
metacrista. It does not project labially beyond the
labial extent of the parastylar lobe. The stylar cusp C
(=mesostyle of Davis and Cifelli 2011) is very large
and occupies a position between the paracone and
metacone. In both specimens there is a minute stylar
cusp in D position distal to the cusp C. The labial ex-
tent of preprotocrista is not certain because of wear
in CNHM PM 1000. Fox (1975: 420) considered that
in this specimen the preprotocrista extended mesial
to the paracone. The postprotocrista terminates at
the base of the metacone (CNHM PM 1004).
The M2 is represented by two labial fragments,
the holotype and CNHM PM 886. On the holotype
the paracone and metacone are almost totally elimi-
nated by wear. In CNHM 886 these cusps are little
worn, with metacone lower and somewhat labially
placed. The preparacrista is long and low, extending
A.O. Averianov
154
labially towards a very small stylocone. At the labial
base of the paracone, just distal to the preparacrista,
there is a peculiar furrow. This furrow, although less
developed, can be seen in another M2 (CNHM PM
886) and on M1 (CNHM PM 1004). This character
might be diagnostic for Holoclemensia. The para-
stylar lobe is very narrow and projects mesiolabi-
ally to a great extent. The parastyle is about twice
larger and higher than the stylocone, not equal in
size to the stylocone, as was described by Davis and
Cifelli (2011: 452). The parastylar groove is almost
vertical. The metastylar lobe is small, but larger than
on M1. It projects labially as far as the stylar cusp
C. The latter is somewhat smaller than in M1 and
have a similar central position. It is not as high as
the metacone. On the holotype there are two cusps
on the metastylar lobe, the distal metastyle and the
mesial cusp which is likely corresponds to the cusp
D of M1. In CHNM PM 886 this cusp is represented
by a minute enamel swelling. The postmetacrista
is short and low, as in M1. The labial extent of the
preprotocrista is obscured by intensive wear facet
1b on the holotype. According to Slaughter (1968b:
254) the preprotocrista extends from the protoconal
region to the parastyle. According to Fox (1975: 420)
there is no preprotocrista (=anterior cingulum) me-
sial to the paracone. The latter observation might be
correct because the preprotocrista is interrupted at
the paracone on an unworn M3 (see below).
The single known M3 (SMP–SMU 62009) is
almost complete, except missing the lingual portion
of the protocone. The metacone is more than twice
smaller than the paracone and the metastylar lobe is
reduced, as typical for ultimate molars. The prepro-
tocrista extends labially, but terminates before the
parastyle. The parastylar lobe is large and projects
labially. The parastyle is large and more than twice
larger than the stylocone. The cusp C is distinctly
smaller than in M2. It is little higher than the sty-
locone and spire-like. The protocone is relatively
high, about two–thirds the height of the paracone.
The conules lack internal cristae and are close to the
protocone. The preprotocrista is interrupted mesial
to the paracone. The postprotocrista does not extend
labially beyond the base of the metacone.
There are three ultimate lower premolars (p5)
referred to H. texana (SMP–SMU 62399 lacks the
paraconid and OMNH 67134 has a broken labial
side). There are some minor differences between the
specimens caused by individual variation. The p5
has a fully developed trigonid with high protoconid,
small metaconid appressed to the latter, and low
cingular paraconid. The metaconid is variably devel-
oped. It is approximately one-third of the protoconid
height. The protocristid is a low ridge not elevated
above the cusps’ surface. The talonid is single-cusped
and not basined. The protoconid and talonid cusp
(hypoconid) are connected by two ridges, a straight
ridge in the middle of the crown and an arcuate ridge
along the labial crown side. There is a notch on the
median ridge at the base of the talonid cusp (this
ridge is heavily worn in OMNH 67134). A third, less
pronounced ridge, is also along the labial crown side
and connects the protoconid with the mesial cingulid.
The two roots are similar in size and widely spaced.
There are six more or less complete lower molars
and two trigonids referable to H. texana. According
to Davis and Cifelli (2011: 453) the m1 is character-
ized “by less inflation of the metaconid relative to
the other loci, and less height and transverse width
differential between the trigonid and talonid.” How-
ever, the single complete molar identified as m1 by
these authors (SMPU–SMU 61727) has the largest
value of talonid width to trigonid width ratio (0.85).
In the four molars identified here as m1 this ratio is
0.63–0.75, M=0.71±0.03. SMPU–SMU 61727 is
considered here as the single known m2. SMP–SMU
62721, with the talonid width to trigonid width ratio
of 0.80 and distinctly short talonid is considered here
as m3. The trigonid fragments cannot be identified as
to tooth locus.
In all lower molars the trigonid is more than
twice higher than the talonid, except the m2 which
has a high hypoconid. The metaconid is robust and
only slightly smaller than the protoconid; in one m1
(SMP–SMU 62131) and m3 both cusps are of nearly
equal height. The paraconid is a spike-like and pro-
cumbent cusp, which is about twice smaller than the
metaconid, and placed labial to the metaconid apex.
The paraconid is smallest in SMP–SMU 62722 (m1)
and largest on m3. The bases of paraconid and meta-
conid are confluent. The trigonid angle is 32–42° in
m1 and 30° in m3. The protocristid is transverse with
a deep carnassial notch. On the mesial side of the tri-
gonid there is a long oblique precingulid (mesiolabial
cuspule f). The mesiolingual cuspule e is present only
in SMP–SMU 62131. There is no distal metacristid,
but there is a faint ridge along the distolingual corner
of the metaconid connecting the tip of metaconid
with the entocristid.
Tribosphenic mammals from the Lower Cretaceous of USA
155
The talonid is distinctly narrower transversely
compared with the trigonid on m1. On m2–3 the
talonid is more transversely expanded but still nar-
rower than the trigonid. The deep hypoflexid widely
separates the trigonid and the talonid has a narrow
mesial end. This narrowed mesial part of the talonid
is longer on m2 compared the m1, except one m1
(SMP–SMU 61726), where it is as long as in m2.
Because of a deep hypoflexid, the cristid obliqua is
located lingual to the protocristid notch, not below
this notch, as was described by Davis and Cifelli
(2011). Only in SMP–SMU 62131 does the cristid
oblique extend along the metaconid wall above the
protocristid notch; in other molars it terminates low-
er. The talonid cusps are pointed and vertical. The
hypoconid is the biggest cusp, the entoconid is the
smallest. The bases of the entoconid and hypoconulid
are approximated or separated by a small gap. On the
m3 the hypoconulid is more projecting distally than
in other molars. The talonid basin is sloping lingually,
with the deepest point on the talonid isthmus. The
entocristid is distinctly lower compared with the
cristid obliqua.
Comments. The lost upper premolar CNHM PM
931 (Patterson 1956: fig. 2A; Butler 1978: fig. 4d)
was identified as P5 of H. texana by Averianov et al.
(2010: fig. 9). However, this tooth, with length 1.31
and width 0.73 (Patterson 1956: 28), appears to be
too small for this species. The size of CNHM PM 931
is suitable for Pappotherium or Atokatheridium. It is
considered here as Theria indet.
CNHM PM 583, a dentary fragment with alveoli
for i1–4, single-rooted, possibly not fully erupted ca-
nine, and double-rooted p1–4 (Patterson 1956: figs.
10, 11; Hershkovitz 1982: fig. 5; Hershkovitz 1995:
fig. 9), the holotype of Adinodon pattersoni Hershko-
vitz, 1995, may belong to H. texana based on suitable
size, as was previously suggested by Butler (1978)
and Turnbull (1995). This, however, should be con-
firmed by discovery of jaws with dentition.
OMNH 62412, the heavily worn lower molar
from the Tomato Hill locality, was identified as m3
of H. texana (Davis and Cifelli 2011: fig. 7E). In the
structure of the trigonid it agrees with the lower
molars of H. texana, but it is distinctly smaller. The
cristid obliqua extends to the level of the protocristid
notch approximately at the middle of the metaconid
transverse width. The talonid is almost eliminated
by wear. Two other specimens from the Tomato
Hill locality (OMNH 62414 and 63894) referred
to H. texana are talonid fragments. OMNH 67134,
a p5 from the Tomato Hill locality, is also definitely
smaller than p5s of Holoclemensia from the Butler
Farm locality. A distinct taxon, closely related to
Holoclemensia, may be present in the Tomato Hill
fauna. Similarly, a single specimen from the Pecan
Valley Estates locality (dP5, SMP–SMU 71848)
may belong not to H. texana (there are no dP5’s from
the type locality) but to a similar taxon. However, all
these taxonomic issues cannot be resolved without
additional specimens. In particular, new taxa similar
to Holoclemensia should be based on upper molars.
Pappotherium pattersoni Slaughter, 1965
(Fig. 3)
Pappotherium pattersoni: Slaughter (1965: 4, fig. 1);
Crompton (1971: fig. 3); Slaughter (1971: pls. 7A, B, 8D–F,
9); Fox (1975: fig. 1); Kielan-Jaworowska (1975: fig. 8);
Butler (1978: figs. 1P, 2a, d, 5P); Kielan-Jaworowska et
al. (1979: fig. 10–4A, B); Kielan-Jaworowska and Cifelli
(2001: fig. 4A); Kielan-Jaworowska et al. (2004: fig. 11.5D);
Davis and Cifelli (2011: fig. 5D).
Pappotheriidae indet.: Slaughter (1971: pl. 7C).
Slaughteria eruptens: Butler (1978: 12, fig. 3S); Ko-
bayashi et al. (2002: figs. 1, 2); Kielan-Jaworowska et al.
(2004: figs. 3.24C, 11.4F); Luo et al. (2004: fig. 4C); Davis
(2011b: figs. 1A, 2); Davis and Cifelli (2011: fig. 9D, E);
Winkler et al. (2011: figs. 1–4).
Kermackia or Trinititherium: Butler (1978: fig. 2j).
Cf. Kermackia or Trinititherium sp.: Kielan-Jaworowska
and Cifelli (2001: fig. 2A).
Kermackia texana: Davis and Cifelli (2011: fig. 8A).
Holotype. SMP–SMU 61725, right maxilla frag-
ment with M2–3.
Type locality and horizon. Butler Farm locality,
Wise County, Texas, USA; Antlers Formation, Lower
Cretaceous (Aptian-Albian).
Referred specimens. Type locality: SMP–SMU
62402, right dP5. SMP–SMU 61992, left dentary
fragment with p3, p4, p5 in crypt, dp5, and m1 (holo-
type of Slaughteria eruptens Butler, 1978).
Differential diagnosis. A stem therian differ-
ing from Metatheria in replacing the fifth premolar
locus, three molars, and paraconid smaller than meta-
conid. Similar to Eutheria and differing from other
stem therians in having a low trigonid angle with a
transverse protocristid. Differs from Eutheria by
postprotocrista not extending labially past metacone
base and conules lacking internal cristae. Differs from
Kermackia in possessing conules, a smaller trigonid
A.O. Averianov
156
angle, a transverse protocristid, paraconid and meta-
conid conjoined lingually, a distal metacristid lack-
ing, a wider talonid, and a larger entoconid. Differs
from Holoclemensia in lacking large stylar cusp C, in
having smaller protocone and conules, and cristid
obliqua labial to protocristid notch. Differs from the
premetatherian stem therian Montanalestes in having
paraconid smaller than metaconid.
Description. The DP5 is very similar in the
structure and proportions to the M2 of the holotype
Fig. 3. The stem therian Pappotherium pattersoni from the Early Cretaceous Antlers Formation of Texas, USA. Upper teeth are in labial
and occlusal views, lower teeth – in occlusal and lingual views. Worn cusps and crests are reconstructed. Mesial end is to the left. Asterisk
denotes reversed image at the collection number. The protoconal region of M3, now broken, is based on Slaughter (1965: fig. 1C) and
(Butler 1978: fig. 1P). Scale bar = 1 mm.
Tribosphenic mammals from the Lower Cretaceous of USA
157
but significantly smaller. The parastylar lobe is de-
stroyed (reconstructed on Fig. 3) and likely was less
expanded compared with M2. According to Davis
and Cifelli (2011: 454) “the stylocone appears to
have been very large and closely appressed to the
paracone.” This is likely a characteristic of dP5,
which usually has a short preparacrista and mesially
reduced stylar shelf. The protocone region is small
so the paracone and metacone are placed closer to
the lingual side of the crown. These cusps are high
and have deep vertical lingual walls. The metacone
is smaller and lower than the paracone and labially
placed compared with the latter. The tips of the labial
cusps, especially the paracone, are heavily worn. The
postmetacrista is relatively short and cusp-like. The
protocone is very low, only about half of the paracone
height, and narrow mesiodistally. The preprotocrista
and postprotocrista do not extend labially pass the
bases of the paracone and metacone, respectively. The
conules are very small. The metaconule likely had a
short premetaconule crista while the paraconule is
not winged. The paraconule is somewhat closer to the
protocone compared with the metaconule.
On M2 the parastylar lobe is larger and more labi-
ally projecting compared with the metastylar lobe.
The parastylar lobe is expanded distally, with a large
stylocone and parastyle, while the metastylar lobe is
pointed terminally. The stylocone and the parastyle
are of similar size but the latter cusp is placed lower
on the crown. The ectoflexus is deep and pointed. The
stylar shelf, a flat area between the labial margin and
the bases of labial cusps, is relatively wide. There is a
faint ectocingulum along the ectoflexus, interrupted
in the deepest point of the latter. The ectocingulum
bears two additional cingular cusps. One is very
small and placed on the distal slope of the stylocone.
The other is just mesial to the metastyle and likely
corresponds to the stylar cusp D. The paracone and
metacone are placed in the center of the crown and
have deep, vertical lingual walls. The paracone is a
massive cusp, highest on the crown. The metacone
is about twice lower than the paracone, significantly
compressed labio-lingually, and pointed distoven-
trally. The centrocrista is straight and extends down
the crown less the half of the paracone height, so
the paracone and the metacone are connate at their
bases. The preparacrista is a strong and relatively long
crest between the paracone and the stylocone. The
postmetacrista is slightly shorter, with a central post-
metacrista cusp. The protoconal region is less than
half of the crown width and narrow mesiodistally. The
protocone is very low, less than half of the paracone
height. The conules are small and lack internal cristae.
The larger paraconule is about midway between the
protocone and the base of paracone. There is a minute
additional cusp on the preprotocrista just labial to the
paraconule (Crompton 1971: fig. 3A). The metaconule
is almost undistinguishable and slightly more distant
from the protocone compared with the paraconule.
The preprotocrista extends labially towards the
parastyle according to the earlier illustrations (now
this region is heavily damaged). The postprotocrista
terminates at the base of the metacone.
On M3 the parastylar lobe extends labially to
the same extent as on M2, but less expanded termi-
nally. The stylocone and parastyle are similar in size
and somewhat smaller than on M2. The parastyle
is more labially placed compared to the M2 and ap-
pressed to the metastyle of M2. The metastylar lobe
is completely reduced. There is a short ectocingulum
labial of the centrocrista notch as well as a short
segment extending distally from the stylocone. The
paracone is lower than on M2 but has a mesiodistally
wider base on the expense of the metacone, which
is small but still a distinct cusp. The preparacrista
is longer than on M2 and also extends towards the
stylocone. The protoconal region is now missing on
this specimen. According to the earlier illustrations
it was similar to that of M2 except the conules, if
present, were even smaller. These illustrations show
the preprotocrista of M3 extending labially towards
the parastyle. This cannot be confirmed based on
the study of the specimen and cast. This is unlikely
because the preparacrista of M3 closely appressed the
postmetacrista of M2 leaving no space for an addi-
tional crest (preprotocrista) between them. The M3
had a labiolingual width similar to that of M2. There
is a terminal part of the postprotocrista preserved at
the lingual base of the metacone.
The single known dentary fragment (SMP–SMU
61992) is twice deeper at the posterior end compared
with the anterior end. The posterior mental foramen
is located between the dp5 and m1. I cannot confirm
presence of the Meckelian groove, suggested by Da-
vis (2011b: 677).
The lower dentition is known from a single speci-
men (SMP–SMU 61992) with p3, p4, p5 in crypt,
dp5, and m1 (for an alternative interpretation, not fol-
lowed here, see Davis 2011b; Davis and Cifelli 2011).
On p3 the main cusp is blade-like, convex anteriorly
A.O. Averianov
158
and straight posteriorly. The apex of the crown oc-
curs dorsally midway between the roots. There is a
small distal cusp on p3 revealed by CT scans. On p4
the apex of the main cusp is above the mesial root.
The mesial side of the main cusp is vertical; the distal
side is gradually sloping towards the distal cusp. The
p3 and p4 are similar in size. The unerupted p5 is dis-
tinctly larger than p4 and its main cusp is similar to
that in p3, except the tip is distally tilted. There is no
mesial cusp on either known premolar, although on
p5 it could be added later in ontogeny. On p4 there
is a very faint mesial cingulid. The size of distal cusp
increases from p3 to p5.
The dp5 is distinctly narrower than m1 and has a
wide trigonid angle (~74°) and the talonid which is
narrower than the trigonid (talonid width to trigo-
nid width ratio is 0.66). The protocristid is slightly
oblique. The tips of the protoconid and metaconid are
heavily worn. The metaconid is about twice smaller
than the protoconid. The paraconid is little worn and
smaller than the metaconid. It is widely separated from
the metaconid and placed mesially so the entire cusp
is completely mesiolingual to the protoconid. There is
a very faint precingulid below the paracristid notch.
There is no distal metacristid on dp5, as well as on m1.
The talonid is almost as long as the trigonid, with a
long talonid isthmus opposite to the hypoflexid. The
talonid cusps are relatively small. The hypoconid is
the largest and the entoconid is the smallest. The hy-
poconulid is equidistant from the other talonid cusps.
Almost all the talonid basin is filled by the bases of the
talonid cusp, with a small flat area near the talonid
isthmus. The cristid obliqua is short, does not extend
vertically on the metaconid wall, and terminates la-
bial to the protocristid notch. Some part of the cristid
obliqua might be eliminated by wear. The roots are
well separated. The distal root is about twice longer
mesiodistally than the mesial root.
The m1 agrees in morphology with dp5 except the
trigonid is mesiodistally compressed, with trigonid
angle of ~36°, and the talonid is shorter and wider
(talonid width to trigonid width ratio is 0.94). The
protoconid is broken and the tips of paraconid and
metaconid are worn. In occlusal view the protoconid
occupies almost half of the trigonid. The bases of
the paraconid and metaconid are conjoined, leaving
a very small trigonid basin. The paraconid is placed
entirely mesial to the protoconid, as in dp5. The pro-
tocristid is more transverse than on dp5. There are a
strong cusp-like precingulid (mesiolabial cuspule f)
and a very faint mesiolingual cuspule e separated by
a depression for the dp5’s hypoconulid. The talonid
is similar in most respects to that of dp5, except the
entoconid is higher than the hypoconulid. Because
of expanded hypoconid, the hypoconulid is closer to
the entoconid. The talonid basin is very small, as in
dp5. The cristid obliqua is similarly short and termi-
nates labial to the protocristid notch. The distal root
is slightly longer mesiodistally compared with the
mesial root.
Comments. Davis and Cifelli (2011) referred ten
isolated teeth or tooth fragments from Greenwood
Canyon and Tomato Hill localities to P. pattersoni.
CNHM PM 999 and 1749 have been identified
as M1 and M2 of P. pattersoni by Davis and Cifelli
(2011) Because these teeth are structurally different
from the ultimate and penultimate molars in the ho-
lotype of P. pattersoni, it was supposed that this taxon
had four upper molars. I refer CNHM PM 999 and
1749 to Atokatheridium and Oklatheridium, respec-
tively. Consequently, there is no basis for inference of
the four molars dental formula for P. pattersoni.
The protoconal region CNHM PM 1325 (Turn-
bull 1971: fig. 3E; Butler 1978: fig. 2g; Davis and
Cifelli 2011: fig. 5C) has been identified as M2 of P.
pattersoni. It is considerably larger than the proto-
cone of M2 of the P. pattersoni holotype.
The trigonids CNHM PM 930 (Patterson 1956:
fig. 8C; Turnbull 1971: fig. 6A; Davis and Cifelli 2011:
fig. 5G), CNHM PM 1119 (Turnbull 1971: fig. 5F),
CNHM PM 1249 (Turnbull 1971: fig. 5E; Davis
and Cifelli 2011: fig. 5I), OMNH 61219 (Davis and
Cifelli 2011: fig. 5J), and OMNH 63729 (Davis and
Cifelli 2011: fig. 5H) are not referable to P. pattersoni
because of their larger size, trigonid not compressed
mesiodistally, and paraconid not reduced.
An incomplete lower premolar with two talonid
cusps, CNHM PM 1098 (Butler 1978: fig. 4b; Davis
and Cifelli 2011: fig. 9A), referred to Slaughteria
eruptens (Davis and Cifelli 2011), is similar in size
with dp5 of Pappotherium pattersoni. It cannot be p5
of this taxon because its p5, as revealed by CT-scans,
is not molariform, with single large talonid cusp.
The lower molar OMNH 63726 with a damaged
talonid (Davis 2011b: fig. 1B; Davis and Cifelli 2011:
fig. 9B), referred to Slaughteria eruptens, is similar in
size with the m1 on the holotype of S. eruptens but
differs in having uncompressed trigonid and unre-
duced paraconid, which is somewhat higher than the
metaconid.
Tribosphenic mammals from the Lower Cretaceous of USA
159
The talonid OMNH 63721 (Davis 2011b: fig. 1C;
Davis and Cifelli 2011: fig. 9C), referred to Slaugh-
teria eruptens, is similar in size and proportions of the
talonid cusps with m1 of the S. eruptens holotype, but
has a distinctly shorter talonid isthmus lingual to the
hypoflexid.
Stem group of Marsupialia Illiger, 1811
Atokatheridium boreni Kielan-Jaworowska
and Cifelli, 2001
(Fig. 4)
Theria indet.: Patterson (1956: fig. 3A); Butler (1978:
fig. 2b).
Holoclemensia sp.: Turnbull (1971: fig. 2E).
Pappotherium cf. pattersoni: Turnbull (1971: fig. 3B).
Pappotherium pattersoni: Butler (1978: figs. 2h, 5P);
Davis and Cifelli (2011: fig. 5A, E, F).
Atokatheridium boreni: Kielan-Jaworowska and Cifelli
(2001: 379, figs. 2B, 4B); Kielan-Jaworowska et al. (2004:
fig. 12.7D); Rougier et al. (2004: fig. 6E); Davis et al. (2008:
figs. 1.5A, B, 1.6A, B, 1.9E); Davis and Cifelli (2011: fig. 2A,
B, D, E).
Atokatheridium boreni?: Kielan-Jaworowska and Cifelli
(2001: figs. 3A, 5B); Kielan-Jaworowska et al. (2004: fig.
12.7E).
Holotype. OMNH 61623, right M2.
Type locality and horizon. Tomato Hill locality,
Atoka County, Oklahoma, USA; Antlers Formation,
Lower Cretaceous (Aptian-Albian).
Referred specimens. Type locality: OMNH
61151, left dP3. OMNH 61185, right M3. OMNH
61624, left m4. OMNH 34905, right mx trigonid.
OMNH 61181, left mx trigonid. OMNH 63724, left
mx trigonid.
Greenwood Canyon locality: CNHM PM 999,
right M1 missing protocone. CNHM PM 1015, left
M3 missing protocone.
Differential diagnosis. A stem marsupial differ-
ent from stem therians and Eutheria in possessing
four molars and paraconid higher than metaconid.
Differs from premetatherian stem therian Monta-
nalestes in having four molars, and paraconid and
metaconid separated by lingual groove. Differs from
stem marsupial Oklatheridium by parastylar lobe re-
duced, small stylar cusp C present at least in some
specimens, paraconid with keel-like vertical crest,
and distal metacristid better developed. Differs from
Deltatheroida by larger protoconal region with bet-
ter developed winged conules. Differs from stem
marsupial Kokopellia in having conules with shorter
internal cristae, paraconid higher than metaconid,
and lack of labial postcingulid.
Description. The single known dP3 (OMNH
61151) is heavily worn and chemically eroded, with
most of the enamel gone. This tooth has been inter-
preted previously as M1 (Davis et al. 2008; Davis and
Cifelli 2011). However, it is distinctly smaller than
M2 and smaller than the expected size of M1 for this
taxon. Davis et al. (2008) explained the considerable
size differences between OMNH 61623 (M2) and
61151 (M1) by the enamel loss in the latter. How-
ever, both specimens are abraded in a similar extent.
This size differences are more appropriately found be-
tween an M2 and dP3, which is accepted here. More
importantly, it has the stylar shelf reduced mesially,
a distinct character of deciduous upper premolars
in stem marsupials and placentals (Averianov et al.
2010; Archibald and Averianov 2012; Gheerbrant and
Astibia 2012). The stylocone and parastyle cannot be
recognized. These cusps are likely removed by abra-
sion (the stylocone is reconstructed on Fig. 4). The
paracone and metacone are connate at their bases and
divergent. The paracone is somewhat higher than the
metacone. The preparacrista is short and low. The
postmetacrista is tall and almost labially directed.
The protocone is relatively tall, similar in height to
the metacone, and mesiodistally wide. There are no
conules but according to Davis et al. (2008) they
were likely present before abrasion because they are
present on the M2. More likely, only a paraconule was
present, or both conules were absent, as in deciduous
upper premolars of stem marsupials exemplified by
the “Picopsis” morphotype (Fox 1980; Cifelli 1990;
Averianov et al. 2010). The preprotocrista extends
to the parastylar region, while the postprotocrista
terminates at the base of the metacone.
The M1 is represented by a single incomplete
specimen, CNHM PM 999. This tooth has been re-
ferred previously to Pappotherium (Turnbull 1971;
Butler 1978; Davis and Cifelli 2011). Before this,
Slaughter (1965: 12, 14) mentioned a notable dif-
ference of this specimen from Pappotherium: “the
parastyle is small, low and poorly demarcated from
the stylocone, whereas the parastyle in Pappotherium
[M2] is almost as large as the stylocone and separated
by a deep V-shaped notch.” This difference cannot be
related to the position variation, as on M1 the para-
stylar lobe is expected to be larger than on M2. The
construction of the parastylar lobe in CNHM PM
A.O. Averianov
160
Fig. 4. The stem marsupial Atokatheridium boreni from the Early Cretaceous Antlers Formation of Texas and Oklahoma, USA. Upper
teeth are in labial and occlusal views, lower teeth – in occlusal and lingual views. Worn cusps and crests are reconstructed. Mesial end is to
the left. Asterisk denotes reversed image at the collection number. The dP3 and M2 are based on heavily abraded molars which may lose
some structural details. The damaged metastylar region of M3 is restored from CNHM PM 1015. Scale bar = 1 mm.
Tribosphenic mammals from the Lower Cretaceous of USA
161
999 agrees more with the holotype M2 of Atokath-
eridium boreni. The parastylar lobe is distinctly nar-
rower labiolingually than the metastylar lobe, which
is a positional character of M1. However, the paras-
tylar lobe does not expand mesially, as in Juramaia or
Prokennalestes (Kielan-Jaworowska and Dashzeveg
1989; Luo et al. 2011). The parastyle is a low small
cusp. The preparacrista is short and concave mesially
in occlusal view. It is a low ridge depressed between
the bases of the paracone and stylocone. The stylo-
cone has a wide base but the cusp is not as high as
in Oklatheridium. Both Patterson (1956) and Butler
(1978) noted a slight enamel elevation in the position
of the stylar cusp C. There is a slight ectocingulum
distal to this elevation. The postmetacrista is a strong
and long ridge, notched at the base of the metacone.
The protoconal region is missing. The preprotocrista
extends labially to the parastyle. The postprotocrista
terminates at the base of the metacone.
The holotype M2 (OMNH 61623) is modified
by chemical abrasion that led to loss of all enamel
and some dentine. In particular, large portions of the
surface of labial cusps has been removed by abrasion,
giving them a peculiar spire-like appearance. The
parastylar lobe is only slightly narrower compared
with the metastylar lobe. The ectoflexus is shallow
and symmetrical. The labial cingulum if were pres-
ent, is completely gone by abrasion. The paracone
and metacone are connate at the base and divergent.
The metacone is distinctly shorter than the paracone.
The preparacrista is short and terminates at the
stylocone, which is rather small, even if the abrasion
is considered. The protocone is similar in height to
the metacone, and mesiodistally wider than the para-
cone. There are winged conules, which are slightly
closer to the protocone than to the apices of the labial
cusps. The size and position of the conules are likely
affected by the abrasion.
The M3 is known from two specimens, OMNH
61185 and CNHM PM 1015, both worn and the lat-
ter missing the protocone. Both specimens are similar
in size and morphology, except the metacone, which
is more reduced in OMNH 61185. Davis and Cifelli
(2011) identified both these teeth as the penultimate
teeth (M3 in their interpretation) of Pappotherium.
The metastylar lobe was considered by these authors
as missing in both specimens. This region is damaged
in OMNH 61185, but intact in CNHM PM 1015
(pers. obs.; see also interpretation in Butler 1978: fig.
2b). The peculiar morphology of these teeth, having
a reduced metastylar lobe but relatively large meta-
cone and protoconal region suggests that these are
indeed penultimate molars, as was suggested by Da-
vis and Cifelli (2011). However, these teeth are not
referable to Pappotherium because the penultimate
molar in that taxon has unreduced metastylar lobe.
The paracone is distinctly larger than the metacone.
In CNHM PM 1015 the metacone has a short post-
metacrista, which is totally absent in ONHM 61185.
The parastylar lobe is prominent, with strong and
long preparacrista, which is almost labially directing.
The stylocone is small and separated from a somewhat
smaller parastyle by a distinct parastylar groove. Dis-
tal to the stylocone there is a small stylar cusp. Butler
(1978: 5) was uncertain if this cusp is equivalent to
the stylar cusp C. Certainly it is not homologous
with the large stylar cusp C in Holoclemensia. The
protocone, known only in OMNH 61185, is heavily
worn and its original height cannot be estimated. It is
relatively wide mesiodistally. In this specimen there
are winged conules, which are close to the paracone
than to the labial cusps.
OMNH 61624 is a single complete lower molar
referable to Atokatheridium boreni. This tooth was
first questionably (Kielan-Jaworowska and Cife-
lli 2001; Kielan-Jaworowska et al. 2004) and later
confidently referred to this taxon (Davis et al. 2008;
Davis and Cifelli 2011). The tooth is similar to del-
tatheroidans in having the paraconid much higher
than the metaconid and a small two-cusped talonid.
The protoconid is partially broken. The paracristid
is heavily worn. The paraconid is inclined mesially.
The protocristid is almost transverse. The trigonid
angle is ~50°. The bases of paraconid and metaconid
are separated by a vertical groove. At the base of
the paraconid there is a distinct vertical keel-like
ridge representing the mesiolingual cuspule e. It is
separated by an embayment for the hypoconulid
of the preceding molar from the short precingulid
(mesiolabial cuspule f). Both these structures have
been described as precingulid in Kielan-Jaworowska
and Cifelli (2001). The distal metacristid is almost
completely eliminated by wear against the mesial
side of the protocone (wear facet 5). In any case it
cannot be characterized as strong. The talonid is
about twice narrower and somewhat shorter than
the trigonid. The hypoconid is low. The hypoconulid
is about twice smaller. Both cusps are heavily worn.
There is no entoconid. The talonid basin is small and
slopes lingually.
A.O. Averianov
162
The position of OMNH 61624 within the molar
series has been considered uncertain in earlier publi-
cations (Kielan-Jaworowska and Cifelli 2001; Davis
et al. 2008; Davis and Cifelli 2011). Based on trigonid
angle, it was compared with m3 (penultimate molar)
of Deltatheridium (Davis et al. 2008). Later was
found that this tooth might represent the m4, but sig-
nificant differences with m4s of deltatheroidans have
been noted (Davis and Cifelli 2011). OMNH 61624
is considered here the ultimate molar (m4) because of
reduction of metaconid and talonid, and a relatively
great trigonid angle. The presence of four molars is
inferred from the morphology of the upper molars.
Two (Kielan-Jaworowska and Cifelli 2001; Da-
vis et al. 2008) and subsequently seven (Davis and
Cifelli 2011) isolated trigonids from the Tomato Hill
locality have been referred to Atokatheridium boreni
(OMNH 34095, 61181, 63724, 63889, 63890, 63891,
and 63892). These trigonids vary in size and mor-
phology. In all specimens, except OMNH 63892, the
paraconid is higher than the metaconid at a various
extent. In three specimens (OMNH 34905, 61181,
and 63724) there is a faint cristid obliqua, which
reachs the metaconid apex only in OMNH 34905.
These three specimens are similar with OMNH
61624 in the structure of the precingulid and a keel-
like vertical cuspule e. Only these three specimens
are here attributed to A. boreni. In OMNH 63889
and 63890 there is no distal metacristid but there
is a cristid obliqua extending on the distal trigonid
wall towards a point below the protocristid notch.
OMNH 63724 has been identified as m1 based on
larger trigonid angle (~70°) and relative cusp heights
after comparison with deltatheroidans (Davis and
Cifelli 2011).
Comments. The previous interpretation of Ato-
katheridium as a deltatheroidan was based on a mixed
sample of upper molars, including one specimen of
Oklatheridium (OMNH 63725), and on deltatheroid-
an-like morphology of a lower molar (OMNH 61624)
and referred trigonids. Attribution of OMNH 63725
to Atokatheridium has been disputed by Averianov,
Archibald et al. (2010). In response to this critique,
Davis and Cifelli (2011: 444) noted that referral
of Atokatheridium to the Deltatheroida is based
on “both upper and lower molar morphology at all
known loci.” However, the holotype upper molar
(OMNH 61623) has no specific similarities with del-
tatheroidans. It has narrower stylar shelf and a larger
protocone with winged conules. The postmetacrista
is less pronounced. Reference to the work of Rougier
et al. (2004) as supporting the deltatheroidan affini-
ties of Atokatheridium is misleading because this, as
well as other successive publications, used a chimeric
association of Atokatheridium and Oklatheridium in
the phylogenetic analysis. Atokatheridium is consid-
ered here as a stem marsupial (see the next section).
Oklatheridium szalayi Davis, Cifelli
et Kielan-Jaworowska, 2008
(Fig. 5)
Theria indet.: Patterson (1956: figs. 2B, 4B); Vande-
broek (1961: fig. 37); Mills (1964: fig. 6D); Butler (1978:
fig. 2p).
Trinity lower molar type 2: Patterson (1956: figs. 7, 8A,
9A); Winkler et al. (2011: figs. 8, 9).
Holoclemensia cf. texana: Turnbull (1971: fig. 2B).
Pappotherium cf. pattersoni: Turnbull (1971: fig. 3A).
Pappotherium sp.: Turnbull (1971: fig. 3D).
Holoclemensia sp.: Turnbull (1971: figs. 5D, 6B, C).
Pappotherium pattersoni: Butler (1978: figs. 2e, f, i, 3P,
5H); Davis and Cifelli (2011: fig. 5B).
Tribosphenida indet.: Cifelli (1997: fig. 3); Davis and
Cifelli (2011: fig. 10B).
Deltatheroida? indet.: Kielan-Jaworowska and Cifelli
(2001: fig. 3B, C).
Oklatheridium szalayi: Davis et al. (2008: figs. 1.3A–C,
1.4, 1.7F, 1.8B, 1.9F); Davis and Cifelli (2011: fig. 3A–E).
Oklatheridium? sp.: Davis et al. (2008: fig. 1.3E).
Atokatheridium boreni: Davis et al. (2008: fig. 1.5C);
Davis and Cifelli (2011: fig. 2C).
Oklatheridium minax: Davis and Cifelli (2011: 444, fig.
3F–G).
Oklatheridium sp.: Davis and Cifelli (2011: fig. 4).
Holotype. OMNH 62410, left M2 missing proto-
cone.
Type locality and horizon. Tomato Hill locality,
Atoka County, Oklahoma, USA; Antlers Formation,
Lower Cretaceous (Aptian-Albian).
Referred specimens. Type locality: OMNH
62411, left M1 with broken protocone. OMNH
61180, left M2 missing protocone. OMNH 63725, left
M2 with abraded crown and missing parastylar re-
gion. OMNH 33455, left M3 missing metastylar lobe
(holotype of Oklatheridium minax Davis and Cifelli,
2011). OMNH 63986, right M3 missing protocone.
OMNH 61642, right dp3 trigonid. OMNH 33945,
left m4 trigonid. OMNH 33940, right mx trigonid.
OMNH 61643, right mx trigonid. OMNH 63728,
right mx trigonid. OMNH 63730, left mx trigonid.
OMNH 66771, right mx trigonid.
Tribosphenic mammals from the Lower Cretaceous of USA
163
Fig. 5. The stem marsupial Oklatheridium szalayi from the Early Cretaceous Antlers Formation of Texas and Oklahoma, USA. Upper teeth
are in labial and occlusal views, lower teeth – in occlusal and lingual views. Worn cusps and crests are reconstructed. Mesial end is to the
left. The broken parts of M1 and M3 are shown in grey. Asterisk denotes reversed image at the collection number. Scale bar = 1 mm.
A.O. Averianov
164
Greenwood Canyon locality: CNHM PM 884,
left M1 missing protocone and metastylar lobe.
CNHM PM 1238, left M1 missing protocone and
parastylar lobe. CNHM PM 1749, left M2 missing
protocone and metastylar lobe. CNHM PM 1287,
left M4. CNHM PM 948, right m1. CNHM PM 965,
right mx. CNHM PM 660, right mx trigonid.
Differential diagnosis. A stem marsupial differ-
ent from stem therians and Eutheria in having four
molars and paraconid higher than metaconid. Differs
from premetatherian stem therian Montanalestes in
having four molars, paraconid and metaconid sepa-
rated by lingual groove, and longer cristid obliqua.
Differs from stem marsupial Atokatheridium in having
parastylar lobe larger, parastyle with keel-like verti-
cal crest, stylar cusp C absent, paraconid without
with keel-like vertical crest, and distal metacristid
lacking in most specimens. Differs from Deltath-
eroida in having larger protoconal region with better
developed winged conules and, wider talonid, and
well-developed entoconid. Differs from stem mar-
supial Kokopellia in having conules with shorter in-
ternal cristae, paraconid higher than metaconid, lack
of keel-like vertical crest of paraconid, longer cristid
obliqua, and lack of labial postcingulid.
Description. Four upper molar positions can be
identified (M1–4). The M1 is interpreted here as
unreplaced dP5. The M1 (OMNH 62411, CNHM
PM 1238) has distinctly smaller size compared with
M2–3, and reduced anteriorly stylar shelf, a charac-
ter also found in ultimate deciduous premolars. The
CNHM PM 884, identified as M1 because of short
preparacrista, is somewhat larger than other M1s,
which is interpreted as individual variation. The
OMNH 33455 has been identified as M2 (Davis et
al. 2008; Davis and Cifelli 2011). However, it has the
preparacrista distinctly longer than in the specimens
identified as M2 (OMNH 61180, 62410, CNHM PM
1749) but compatible in length with the preparac-
rista in M3 (OMNH 63986). Thus OMNH 33455
is identified here as M3. The M4 is represented by a
single specimen (CNHM PM 1287).
The M1 has reduced parastylar lobe and short
preparacrista, while the metastylar lobe is long, labi-
ally projecting, and with a long postmetacrista. On
M2 the parastylar and metastylar lobes are of similar
size. On M3 the parastylar lobe is longer and the
metastylar lobe is broken on both known specimens
(OMNH 33455, 63986). The nature of the breakage
suggests that the metastylar lobe was unreduced
on M3. The metastylar lobe is absent on M4. The
metacone is lower than the paracone but somewhat
broader at least on M2. According to Davis et al.
(2008) the height differential between the paracone
in metacone in Oklatheridium is smaller than in any
other Trinity therian. On M4 the metacone is much
smaller than the paracone. On M4 the parastylar lobe
constitutes the half of the tooth transverse width.
The preparacrista connects the stylocone on M1–3,
except OMNH 63986 (M3), where it terns abruptly
towards the parastyle. On the M4 the preparacrista
terminates before the reduced stylocone and paras-
tyle. The parastyle is a prominent cusp with a pecu-
liar sharp mesial keel extending towards the base of
the crown, except the M4, where it is considerably
reduced. The stylocone is distinctly higher than the
parastyle. There are no other stylar cusps, except a
small cuspule immediately distal to the stylocone
present in some specimens (CNHM PM 1749, M2,
and OMNH 63986, M3). Davis and Cifelli (2011:
446) described this cuspule also for OMNH 61180
(M2), but in this specimen it is an artifact of ec-
tocingulum breakage in a more distal position. The
ectocingulum is sharp and prominent, especially on
the metastylar lobe on M1–3. On M4 the ectocin-
gulum is prominent along the parastylar lobe but
absent opposite to the metacone. The stylar shelf,
a flat area between the ectocingulum and the bases
of paracone and metacone, is distinctly narrower
compared with deltatheroidans. The preprotocrista
extends labially towards the parastyle. The postpro-
tocrista terminates at the base of the metacone. The
protoconal region is present only in OMNH 33455
(M3) and CNHM PM 12867 (M4). On OMNH
33455 the protocone is broken and its height cannot
be estimated. The paraconule is heavily born. A small
metaconule is placed closer to the protocone. The
premetaconule crista is not present. Davis and Cifelli
(2011: 446) found no evidence of internal cristae in
OMNH 33455. However, the postparaconule crista
was likely present but obliterated by wear. On the
M4 there is a very small unwinged metaconule and
a small crenulation of the preprotocrista on the place
of the paraconule. The protocone is small, more than
twice lower and mesiodistally shorter compared with
the paracone.
The lower molars are represented by two com-
plete specimens (CNHM PM 948 and 985) and
several trigonid fragments. Both CNHM PM 948
and 985 has been identified as belonging to the same
Tribosphenic mammals from the Lower Cretaceous of USA
165
molar type 2 by Patterson (1956). Davis and Cifelli
(2011) referred the first specimen to Oklatheridium
sp. and the second to Tribosphenida indet. CNHM
PM 948 identified here as m1 of O. szalayi because
of paraconid higher than metaconid and short trigo-
nid. This specimen has a peculiar lingual cingulid at
the paraconid (Davis and Cifelli 2011), which is ac-
counted here as individual variation. A crest within
the talonid basin on this specimen described by Davis
and Cifelli (2011) is likely a preservation artifact.
One small trigonid (OMNH 61642), identified previ-
ously as m1 (Davis and Cifelli 2011), is likely dp3. In
transversely narrow crown and widely open trigonid
(75°) it is similar with dp3 in the Late Cretaceous
stem marsupials (Cifelli and Muizon 1998: fig. 3B).
Another small trigonid (OMNH 33945) with the
smallest metaconid may be m4. The other specimens
are either m2 or m3.
On all specimens the paraconid is higher than the
metaconid. The protoconid is the highest trigonid
cusp. The paracristid is strong, with a deep carnas-
sial notch. The protocristid is weaker and transverse.
The trigonid angle is 75° in dp3, 51° in m1, 45–51°
in m2–3, and 52° in m4. The bases of paraconid and
metaconid are separated and the trigonid basin is
open lingually via a small gap. The precingulid (me-
siolabial cuspule f) is long and oblique, separated by a
depression from the variable developed mesiolingual
cuspule e. In CNHM PM 948 the cuspule e continues
lingually as a cingulid at the base of the paraconid.
The cristid obliqua connects the protocristid notch
or somewhat lingual to it (CNHM PM 948, 965). In
two specimens (OMNH 61642 and 61643) it extends
to the metaconid apex or near so and formally can be
called the distal metacristid. Along the distolingual
edge of the metaconid there is a faint crest connect-
ing the entocristid.
The talonid is known only in CNHM PM 948 (m1)
and 965 (m2 or 3). It is narrower than the talonid. The
talonid width to trigonid width ratio is 0.91 (m1) or
0.80 (m2–3). The talonid is distinctly shorter on m1
compared with the middle molar. On CNHM PM 948
the talonid cusps are damaged. On CNHM PM 965
the hypoconid and hypoconulid are of similar size.
The entoconid is somewhat smaller. The hypoconulid
is equidistant from other talonid cusps and somewhat
projecting distally. The talonid basin is horizontal and
closed lingually by the entocristid.
Comments. The CNHM PM 884 has been con-
sidered as M2 of Pappotherium by Butler (1978). The
OMNH 63727, missing the protocone and metastylar
lobe, has been identified as M3 of O. szalayi (Davis
et al. 2008: fig. 1.3D) or O. minax (Davis and Cifelli
2011: fig. 3H). This tooth is remarkable in having a
completely reduced metastylar lobe combined with
relatively unreduced metacone, which is half the
height of the paracone. It is distinctly larger than any
other upper molar referred here to Oklatheridium and
it is considered here as Tribosphenida indet.
Originally Oklatheridium has been identified as a
deltatheroidan (Davis et al. 2008; Davis and Cifelli
2011). However, it differs from the Deltatheroida in a
number of important characters (Table 1, characters
5, and 9–12): the protoconal region is larger, with
better developed conules, the protocristid is more
transverse, there is no distal metacristid, and the
talonid is much wider, with unreduced entoconid.
Oklatheridium is considered here as a stem marsupial
(see the next section).
PHYLOGENETIC POSITION
OF TRINITY THERIANS
Historically the interpretation of the Trinity
therians underwent three phases (see review of the
previous work for details and references):
1) Both placentals and marsupials have been identi-
fied based on molar count, submolariform premo-
lars, and development of stylar cusps on upper
molars;
2) All taxa have been referred to the “Theria of
metatherian-eutherian grade,” i.e. stem therians
in modern usage;
3) Some taxa have been included in the numerical
phylogenetic analyses, which showed conflicting
results.
The inconsistent position of Trinity therians on
cladograms has been caused by incompleteness of the
materials and different interpretation of the content
of the taxa. With two exceptions, the Trinity therians
are represented by isolated teeth or tooth fragments.
Table 2 summarizes the dental synapomorphies for
the major therian clades proposed in the recent phy-
logenetic analyses focused on the interrelationships
of Mesozoic therians. The characters relevant to the
Trinity therians are discussed hereinafter.
Upper incisors. SMP–SMU 62401 from the
Butler farm locality has been identified as eutherian
upper incisor (Slaughter 1971: 138, fig. 1B, pl. 10A).
The crown is spatulate and bicuspate, with a strong
A.O. Averianov
166
distal cusp, and median ridge on the lingual side. The
root is rounded, while the upper incisors of therians
should have transversely compressed root (Table 2,
character 2). This tooth could be a lower incisor of
the alticonodontid triconodontan Astroconodon den-
isoni Patterson, 1951 known from the Butler Farm
locality (Patterson 1951; Slaughter 1969; Turnbull
and Cifelli 1999). A single spatulate lower incisor is
characteristic for the Alticonodontidae (Cifelli and
Madsen 1998).
CNHM PM 1100 from the Greenwood Canyon
locality is a small incisor with spatulate crown, which
is about twice wider than the transversely compressed
root. There is a distinct lingual cingulum. This tooth
could be an upper incisor of a therian (Table 2, char-
acter 2), but its attribution to any known taxon of
Trinity therians is problematic.
Lower incisors. The now lost specimen SMP–
SMU 62400 from the Butler Farm locality has
been attributed to Eutheria by Slaughter (1971:
138, fig. 1A, pl. 10B). It is a dentary fragment with
a simple peg-like procumbent tooth and alveoli for
a double-rooted tooth behind. The dentary is very
shallow, with a large mental foramen posterior to
the preserved tooth. Slaughter (1971) and Butler
(1978: 16) considered this tooth as a canine followed
by double-rooted p1. However, it is more likely that
these teeth are the last incisor and double-rooted
canine. The procumbent posterior lower incisor is
characteristic for the Cimolestidae and Zalambdal-
estidae among Mesozoic Eutheria (Wible et al. 2009:
character 21). By size this specimen is suitable for
Pappotherium pattersoni.
An edentulous dentary fragment CNHM PM 583
from the Greenwood Canyon locality, attributable to
Holoclemensia texana by size (see comments to that
taxon above), preserves alveoli for the four incisors.
Hershkovitz (1982, 1995) identified five incisors in
this specimen, third of which is “staggered’ between
the two adjacent incisors. However, the “staggered”
condition of the incisor in this specimen cannot be
verified (Cifelli and Muizon 1997). The absence of i4
(Table 2, character 6) is not a eutherian synapomor-
phy, because i4 is present in Prokennalestes and Zhe-
lestidae (Sigogneau-Russell et al. 1992; Archibald
and Averianov 2012). The two other purported
eutherians with four lower incisors, Eomaia and Jura-
maia (Ji et al. 2002; Luo et al. 2011), are likely stem
therians O’Leary et al. 2013. Thus, if CNHM PM
583 indeed belongs to H. texana, the presence of four
lower incisors will not preclude attribution of this
taxon to Eutheria.
Table 1. Proposed synapomorphies for Deltatheroida.
# Character References
1 Size of molars increases markedly posteriorly Rougier et al. 1998, 2004
2 Stylar cusp D absent Luo et al. 2003
3 Metacone and paracone bases adjoined Averianov et al. 2010
4
Strongly developed salient postmetacrista
with paraconid enlarged and metaconid reduced
Rougier et al. 1998, 2004
5 Protocone small with distinct trigon basin Rougier et al. 1998, 2004
6 Trigonid open, with anteromedial paraconid Rougier et al. 2004
7 Paraconid taller than metaconid Rougier et al. 1998, 2004
8 Paraconid and metaconid aligned Rougier et al. 1998, 2004
9 Protocristid oblique to jaw axis Rougier et al. 2004
10 Distal metacristid present Rougier et al. 2004
11
Talonid very narrow, subequal to base of metaconid,
developed lingually
Rougier et al. 1998; Averianov et al. 2010
12 Entoconid absent* Luo et al. 2003
*Present in Sulestes (Averianov et al. 2010).
Tribosphenic mammals from the Lower Cretaceous of USA
167
Table 2. Proposed dental synapomorphies for the major therian clades. Theria is a crown group including Metatheria and Eutheria.
Metatheria is the total clade for Marsupialia (crown group) plus stem marsupials. Eutheria is the total clade for Placentalia (crown group)
plus stem placentals.
# Character Clade References
Incisors
1 Five upper incisors Eutheria Luo et al. 2003, 2011
2 Upper incisors root transversely compressed Theria O’Leary et al. 2013
3 I1 orthodont Theria O’Leary et al. 2013
4 I4 rhomboidal Theria O’Leary et al. 2013
5 Staggered lower incisor present Metatheria
Wible et al. 2007, 2009;
Averianov et al. 2010
6 i4 absent Eutheria O’Leary et al. 2013
Canines
7 Deciduous canine absent Metatheria Rougier et al. 1998, 2004
8 Upper canine single rooted Metatheria
Rougier et al. 1998, 2004;
Averianov et al. 2010
9 Lower canines divergent Metatheria O’Leary et al. 2013
Cheek teeth general
10 Seven postcanine loci Metatheria
Rougier et al. 1998, 2004; Wible et al.
2007, 2009
Premolars general
11 Three premolars Metatheria
Cifelli 1993a, b; Rougier et al. 1998, 2004;
Averianov and Skutschas 1999;
Wible et al. 2007, 2009
12 Replacement of dP1/dp1 and dP2/dp2 absent Metatheria Rougier et al. 1998, 2004
13 Only ultimate premolar replaced Metatheria Averianov and Skutschas 1999
Upper premolars
14 Procumbent first upper premolar separated by diastema Metatheria Rougier et al. 1998, 2004
15 P2 crown with two or more clearly defined cusps Theria O’Leary et al. 2013
16 P2 position replacement absent Metatheria O’Leary et al. 2013
17 P2 somewhat smaller than M1 (=M2) Metatheria O’Leary et al. 2013
18a Tall trenchant premolar in penultimate position Eutheria
Rougier et al. 1998, 2004; Wible et al.
2007, 2009; Averianov et al. 2010
18b Tall trenchant premolar in penultimate position Marsupialia* Luo et al. 2003
18c P4 height greater than P5 height Theria O’Leary et al. 2013
19 Penultimate premolar parastylar lobe absent or small Placentalia Wible et al. 2007, 2009
A.O. Averianov
168
# Character Clade References
20 P4 metacone absent Metatheria O’Leary et al. 2013
21 P4 metastyle (stylar cusp E) distolabial to paracone or metacone Eutheria O’Leary et al. 2013
22a Penultimate premolar with protoconal bulge Eutheria
Rougier et al. 1998, 2004; Wible et al.
2007, 2009; Luo et al. 2011
22b P4 protocone present Eutheria O’Leary et al. 2013
23 P5 position replacement absent Metatheria O’Leary et al. 2013
24a Ultimate premolar with protocone or protoconal swelling Eutheria Luo et al. 2003, 2011
24b Ultimate premolar protocone smaller than paracone Eutheria Wible et al. 2007, 2009
25 Ultimate premolar molariform Eutheria Rougier et al. 1998, 2004
Lower premolars
26 Five lower premolars Eutheria Luo et al. 2011
27a First premolar oblique Metatheria Wible et al. 2007, 2009
27b p1 mesial root labial to distal root Metatheria O’Leary et al. 2013
28 p2 position replacement absent Metatheria O’Leary et al. 2013
29 p2 talonid present Theria O’Leary et al. 2013
30 p3 absent Theria* O’Leary et al. 2013
31 p5 position replacement absent Metatheria O’Leary et al. 2013
32 Ultimate premolar symmetrical Eutheria Luo et al. 2003, 2011
33 Ultimate premolar paraconid distinctive but low Eutheria Wible et al. 2007, 2009
34 Ultimate premolar with paraconid enlarged Eutheria Luo et al. 2003, 2011
35 Ultimate premolar complex, with a partial trigonid and/or talonid Eutheria Averianov et al. 2010
36 Ultimate premolar mesiolingual cingulid absent Placentalia Wible et al. 2007, 2009
Molars general
37a Three molars Eutheria Rougier et al. 1998, 2004
37b Three molars Metatheria* Vullo et al. 2009
38 Four molars Metatheria Cifelli 1993a; Averianov et al. 2010
39 Size of molars increases posteriorly Metatheria Rougier et al. 2004; Wible et al. 2007, 2009
40 Size of molars does not increase posteriorly Eutheria Rougier et al. 1998
Upper molars
41 Molars interlock absent Eutheria O’Leary et al. 2013
42 M1 has three roots Theria O’Leary et al. 2013
43 Parastylar groove well developed Theria Averianov and Skutschas 1999
44a Stylar shelf slightly reduced labial to paracone Marsupialia Rougier et al. 1998
Table 2. Continued
Tribosphenic mammals from the Lower Cretaceous of USA
169
# Character Clade References
44b
M1 stylar shelf labial to paracone narrower than stylar
shelf labial to metacone
Theria O’Leary et al. 2013
45 Preparastyle present Eutheria Luo et al. 2011
46 Stylar cusp A (parastyle) small to indistinct Marsupialia Rougier et al. 1998
47 M2 stylar cusp A (parastyle) subequal to larger than B (stylocone) Theria Wible et al. 2007, 2009
48 Stylar cusp C absent Theria Averianov and Skutschas 1999
49 Stylar cusp D present Metatheria Luo et al. 2003
50 Stylar cusp E poorly developed or absent Eutheria Luo et al. 2003
51 Deep ectoflexus on penultimate and preceding molar Metatheria Rougier et al. 1998, 2004
52 Metacone slightly smaller than paracone Metatheria Rougier et al. 1998, 2004; Luo et al. 2003
53a Metacone enlarged Metatheria Cifelli 1993b
53b M1 (=M2) metacone taller than paracone Metatheria O’Leary et al. 2013
53c M2 (=M3) metacone taller than paracone Metatheria O’Leary et al. 2013
54a M1 (=M2) metacone more lingual than paracone Metatheria O’Leary et al. 2013
54b M2 (=M3) metacone more lingual than paracone Metatheria O’Leary et al. 2013
55a Centrocrista V-shaped Marsupialia Luo et al. 2003
55b M2 (=M3) premetacrista mesiolabial Metatheria O’Leary et al. 2013
56 Postmetacrista cusp absent Eutheria Averianov and Skutschas 1999
57a
Postmetacrista strongly developed, with paraconid enlarged
and metaconid reduced on lower molars
Metatheria Averianov et al. 2010
57b M1 (=M2) postmetacrista long Metatheria O’Leary et al. 2013
58 M2 postparacrista and postmetacrista subequal Eutheria O’Leary et al. 2013
59 Preprotocrista extends labially past the base of paracone Theria Rougier et al. 1998, 2004
60a Postprotocrista extends labially past base of metacone Theria Cifelli 1993a, b
60b Postprotocrista extends labially past base of metacone Eutheria Rougier et al. 1998, 2004; Luo et al. 2011
60c Postprotocrista extends labially past base of metacone Metatheria Vullo et al. 2009
70a Protocone broadened Metatheria Cifelli 1993b
70b Protocone slightly expanded in its apical half Eutheria Luo et al. 2011
71a M1 (=M2) protocone larger than paracone Metatheria O’Leary et al. 2013
71b M2 (=M3) protocone larger than paracone Metatheria O’Leary et al. 2013
72 Conules absent Marsupialia Rougier et al. 1998; Luo et al. 2003
73
Metacingulum and metaconule present in addition to
postprotocrista
Theria Luo et al. 2011
Table 2. Continued
A.O. Averianov
170
# Character Clade References
74 Conules well developed, trenchant, and bearing cristae Theria Cifelli 1993b
75 M2 paraconule prominent, midway or closer to paracone Theria Wible et al. 2007, 2009
76 M2 metaconule prominent, midway or closer to protocone Theria Wible et al. 2007, 2009
77a Distance between conules 31–50% of total tooth length Eutheria Luo et al. 2003, 2011
77b M2 conular region moderate, 31–50% of total tooth length Theria Wible et al. 2007, 2009
78 M2 postcingulum present, extending to labial margin Placentalia Wible et al. 2007, 2009
Lower molars
79 Interlocking mechanism between adjacent molars absent Placentalia O’Leary et al. 2013
80 m1 smaller than succeeding molars Metatheria Cifelli 1993a
81a Height differential between trigonid and talonid reduced Metatheria Cifelli 1993a, b
81b Trigonid less than twice higher than talonid Eutheria Vullo et al. 2009
82a Trigonid angle acute Theria Rougier et al. 2004
82b Trigonid angle less than 35° Eutheria Luo et al. 2003
83
m2 trigonid mesiodistally compressed, less than 50%
of total tooth length
Eutheria Wible et al. 2007, 2009
84 Prevallid shearing facets strongly developed and transverse Theria Luo et al. 2003
85 Paracristid with deep carnassial notch Eutheria Vullo et al. 2009
86a m1 paracristid not notched Eutheria O’Leary et al. 2013
86b m2 paracristid not notched Eutheria O’Leary et al. 2013
87 Protocristid transverse Theria Rougier et al. 2004
88
m2 protocristid complete but depressed protoconid and
metaconid stands above depressed central section of protocristid
Eutheria O’Leary et al. 2013
89 m1 (=m2) protocristid discontinuous and deeply notched Metatheria O’Leary et al. 2013
90 m1 (=m2) postenocristid present Metatheria O’Leary et al. 2013
91 m2 metaconid subequal to protoconid, 80–100% of its height Eutheria O’Leary et al. 2013
92a dp5 (=m1) paraconid forming vertical keel Metatheria O’Leary et al. 2013
92b m1 (=m2) paraconid forming vertical keel Metatheria O’Leary et al. 2013
92c m2 (=m3) paraconid forming a vertical keel Metatheria O’Leary et al. 2013
93a Paraconid shorter than metaconid Theria Rougier et al. 1998, 2004
93b m2 paraconid lower than metaconid Theria O’Leary et al. 2013
93c Paraconid reduced Eutheria Averianov and Skutschas 1999
Table 2. Continued
Tribosphenic mammals from the Lower Cretaceous of USA
171
# Character Clade References
94
Paraconid and metaconid subequal in height, or paraconid
slightly smaller
Eutheria Vullo et al. 2009
95 Posterior molars with lingual crests in trigonid Eutheria Vullo et al. 2009
96 dp5 (=m1) trigonid distal wall weakly inclined Metatheria O’Leary et al. 2013
97 Talonid 40–70% of trigonid width Theria Luo et al. 2003
98 Talonid broadened Metatheria Cifelli 1993a, b
99 dp5 (=m1) wear present in bottom of talonid basin Metatheria O’Leary et al. 2013
100 dp5 (=m1) talonid notched lingually but not open Metatheria O’Leary et al. 2013
101 Distal metacristid absent Eutheria Luo et al. 2003
102a dp5 (=m1) cristid obliqua strong trenchant Metatheria O’Leary et al. 2013
102b m1 cristid obliqua very strong trenchant Theria O’Leary et al. 2013
103 Cristid obliqua contacts trigonid at protocristid notch Eutheria Luo et al. 2003
104
m2 (=m3) cristid obliqua contact to midpoint between
protoconid and metaconid in vicinity of protoconid
Metatheria O’Leary et al. 2013
105a dp5 (=m1) talonid distolabial side angular Metatheria O’Leary et al. 2013
105b m1 (=m2) hypoconid distolabial side angular Metatheria O’Leary et al. 2013
105c m2 (=m3) hypoconid distolabial side angular Metatheria O’Leary et al. 2013
106 Hypoconid/protoconid height ratio between 40–60% Eutheria Luo et al. 2003, 2011
107 m1 (=m2) hypoconid-hypoconulid crest weak Metatheria O’Leary et al. 2013
108 Entoconid present, with slight approximation to hypoconulid Metatheria Luo et al. 2003
109 m2 entoconid smaller than hypoconid and/or hypoconulid Theria Wible et al. 2007, 2009
110 Wear facet 5 and 6 differentiated on labial face of entoconid Eutheria Luo et al. 2003, 2011
111a Hypoconulid “twinned” with entoconid Metatheria Cifelli 1993b
111b m2 (=m3) hypoconulid twinned to entoconid Metatheria O’Leary et al. 2013
112 Strong labial postcingulid present Metatheria Cifelli 1993a, b
113 Penultimate molar longest Eutheria Luo et al. 2011
114 m3 shorter than m1 (50–90%) Theria O’Leary et al. 2013
115 Ultimate molars rotates during eruption Metatheria Rougier et al. 1998, 2004
116 Ultimate molar hypoconulid short and erect Marsupialia Rougier et al. 1998; Luo et al. 2003
117 Ultimate molar hypoconulid tall and sharply recurved Theria Wible et al. 2007, 2009
*Possible typographic error or miscoding artifact.
Table 2. Continued
A.O. Averianov
172
Canines. The likely upper double-rooted canine
CNHM PM 1124 (Butler 1978: fig. 4e) is too small
to be assigned to Holoclemensia or Oklatheridium, but
is of right size for Atokatheridium. If attributed to the
latter taxon, this would advocate against its metathe-
rian affinities (Table 2, character 8).
The large canine alveolus in CNHM PM 583 is
likely for the erupting permanent canine which could
be double rooted.
There are two isolated canines from the Green-
wood Canyon locality with small crown and subdi-
vided root, which are likely lower canines (CNHM
PM 982 and 1070). Attribution of these specimens to
the Theria is not certain.
Postcanine dental formula. A large suite of
synapomorphies is related to the postcanine dental
formula (Table 2, characters 10–13, 16, 18, 23, 26, 28,
30, 31, 37, 38, and 80). The current consensus is that
the primitive dental formula for the Theria includes
five premolars and three molars (Averianov et al.
2010; O’Leary et al. 2013). In eutherian lineage P3/
p3 has been reduced (Archibald and Averianov 2012)
and lost in Placentalia (O’Leary et al. 2013). O’Leary
et al. (2013) listed absence of p3 (Table 2, character
30) as a synapomorphy for the Theria, which is an ob-
vious mistake. The metatherians evolved four molars
via non replacement of the ultimate deciduous pre-
molar, dP5/dp5 (O’Leary et al. 2013). Metatherians
also lost one premolar position, P1/p1 (Averianov
et al. 2010) or P3/p3 (O’Leary et al. 2013), which,
together with transferal of the fifth premolar posi-
tion to the molars, resulted in three premolars in this
group. Only the last of these premolar positions, P3/
p3, homologues to P4/p4 of primitive therian form,
is replaced (Luckett 1993; Rougier et al. 1998; Luo
et al. 2004). Pappotherium (=Slaughteria) displays
replacement at least in two premolar positions, a
primitive therian condition, used previously to prove
attribution of this taxon to the Eutheria (Slaughter
1971, 1981). Among Trinity therians, Kermackia,
Holoclemensia, and Pappotherium are interpreted as
having three molars. Holoclemensia might also have
five premolars, if SMP–SMU 62006 (Jacobs et al.
1989: fig. 4; Winkler et al. 1990: fig. 11C, D) belongs
to that taxon. These characters exclude all the three
taxa from the Metatheria and Holoclemensia from the
Placentalia, but not from the Eutheria. The four mo-
lar positions can be reconstructed for Atokatheridium
and Oklatheridium, which suggests attribution of
these taxa to the Metatheria (table 1, character 38).
Tall trenchant upper premolar. It has long been
accepted that the tall trenchant upper premolar is in
the ultimate position in metatherians and in the pen-
ultimate position in eutherians (Table 2, character
18). Now it is clear that this character is correlated
with the change in the postcanine dental formula. In
stem therians, as exemplified by Peramus (Clemens
and Mills 1971; Averianov et al. 2010), and in euthe-
rians the tallest upper premolar is the penultimate
tooth (P4). In metatherians this tooth becomes the
ultimate premolar because of lack of replacement
in the fifth premolar locus. A tall trenchant upper
premolar attributed to Holoclemensia (SMP–SMU
61948) is identified as P4, following Davis and Cifelli
(2011), because a primitive therian – eutherian den-
tal formula is inferred for this taxon.
Penultimate upper premolar parastylar lobe. In
stem therians, such as Peramus and Juramaia (Clem-
ens and Mills 1971; Luo et al. 2011), as well as in basal
eutherians such as Prokennalestes and Zhelestidae
(Kielan-Jaworowska and Dashzeveg 1989; Archibald
and Averianov 2012), there is no parastylar lobe on
the penultimate upper premolar (P4). A small mesial
cusp and/or mesial cingulum can be present there.
This condition is also present in SMP–SMU 61948,
the P4 referred to Holoclemensia. Wible et al. (2007,
2009) listed the parastylar lobe of the penultimate
upper premolar absent or small as a synapomorphy
for the Placentalia (Table 2, character 19). This is
likely an artifact of taxon sampling and/or coding.
Penultimate upper premolar protoconal bulge.
Presence of a protocone or protoconal bulge has
been cited as a synapomorphy for the Eutheria
(Table 2, character 22). A small protoconal bulge,
but not a true protocone, might be present in P4 of
Holoclemensia (SMP–SMU 61948). This specimen
likely had a complete lingual cingulum. In Peramus
there is no lingual cingulum on P4 (Clemens and
Mills 1971). On P4 of Juramaia there is a complete
lingual cingulum but no a protocone swelling. The
protocone swelling is present on P4 in Prokennalestes
and Zhelestidae (Kielan-Jaworowska and Dashzeveg
1989; Archibald and Averianov 2012). This character
seems to be a good synapomorphy for the Eutheria.
If indeed present in Holoclemensia, it would suggest
attribution of this taxon to the Eutheria.
Ultimate lower premolar submolariform. There
are several proposed synapomorphies related to the
molarization of the ultimate lower premolar (Table
2, characters 32–35). The submolariform lower pre-
Tribosphenic mammals from the Lower Cretaceous of USA
173
molars from the Butler Farm locality (SMP–SMU
61947 and 62399) have been used to prove pres-
ence of Eutheria in the Trinity fauna (Slaughter
1968a, 1971, 1981). Later these premolars have
been referred to Pappotherium (SMP–SMU 62399)
and Holoclemensia (SMP–SMU 61947), classified
as stem therians (Butler 1978). Davis and Cifelli
(2011) referred SMP–SMU 62399 to Holoclemensia
and a similar tooth from the Tomato Hill locality
(OMNH 67134) to Kermackia. Holoclemensia is a
eutherian and Kermackia is a stem therian according
to these authors. Here all these three specimens re-
ferred to Holoclemensia. As described in the previous
systematic section, there is some size and structural
variation between these specimens. These premolars
have a trigonid with low cingular paraconid and vari-
able developed metaconid, which is from one third to
one half of the protoconid height. The protocristid
is a low ridge. The talonid is single cusped and not
basined. Among the stem therians the ultimate lower
premolar is known for Amphitherium, Nanolestes,
Arguimus, Mozomus, Peramus, Juramaia, and Eomaia
(Clemens and Mills 1971; Butler and Clemens 2001;
Ji et al. 2002; Martin 2002; Li et al. 2005; Lopatin
and Averianov 2006; Luo et al. 2011). In all these
taxa it is a simple premolariform tooth. Davis and
Cifelli (2011) maintain that m1 of Arguimus is a mo-
lariform ultimate premolar but gave no arguments in
support of their view. The p5 is premolariform in the
eutherians Prokennalestes, Paranyctoides, Maelestes,
and Asioryctitheria, in spite that P5 is submolari-
form, with fully developed protocone, in these taxa
(Kielan-Jaworowska and Dashzeveg 1989; Sigog-
neau-Russell et al. 1992; Archibald and Averianov
2006; Wible et al. 2009; Averianov and Archibald
2013). The p5 is premolariform also in the Early
Cretaceous eutherians Acristatherium and Sasaya-
mamylos, for which the structure of P5 is uncertain
or unknown (Hu et al. 2010; Kusuhashi et al. 2013).
Among zhelestids the p5 is premolariform in the
Cenomanian – early Turonian taxa and has a vari-
able developed small metaconid in the late Turonian
taxa (Averianov and Archibald 2005; Archibald
and Averianov 2012). The p5 is submolariform,
with a well-developed metaconid, in a Cenomanian
eutherian Bobolestes and the Turonian-Campanian
Zalambdalestidae (Archibald and Averianov 2003;
Wible et al. 2004; Averianov and Archibald 2005;
Zan et al. 2006). Apparently, molarization of p5
developed independently in different eutherian lin-
eages. This undermines significance of this character
as a eutherian synapomorphy and an argument for
attributing of Holoclemensia to that group.
Upper molars stylar cusps. A number of pur-
ported synapomorphies describe development of the
stylar cusps on the upper molars (Table 2, characters
45–50). Noteworthy, presence of a large stylar cusp
C in Holoclemensia have long been used as an argu-
ment for reference of this taxon to the Metatheria
(see review of the previous work). Among Trinity
therians, a much smaller stylar cusp C is variable
present in Atokatheridium. As was discussed by Davis
and Cifelli (2011), the early metatherians lack the
stylar cusp C and thus it was acquired by Holocle-
mensia independently from the Metatheria. Wible
et al. (2007, 2009) cited the parastyle subequal to
larger than the stylocone as a therian synapomorphy
(Table 2, character 47). Similarly, Davis and Cifelli
(2011) considered reduced stylocone of Holoclemen-
sia as a eutherian character. The significance of this
character is not certain. In some stem therians, such
as Nanolestes, Peramus, and Kielantherium, the para-
style is larger than the stylocone (Clemens and Mills
1971; Martin 2002; Lopatin and Averianov 2007). In
the stem therian Juramaia and basal eutherians Pro-
kennalestes and Murtoilestes the stylocone is slightly
larger than the parastyle (Kielan-Jaworowska and
Dashzeveg 1989; Averianov and Skutschas 2001;
Luo et al. 2011). Among the Trinity therians the sty-
locone is larger than the parastyle in Atokatheridium
and Oklatheridium. In Holoclemensia and P
appoth-
erium there is a stylar cusp in D position. The upper
molar stylar cusps have no occlusal relationships
with the lower molar structures and their function
is uncertain. Apparently development of these cusps
has little if any phylogenetic significance (Clemens
and Lillegraven 1986).
Penultimate and antepenultimate upper mo-
lars deep ectoflexus. A deep ectoflexus on penul-
timate and preceding molar has been proposed as
a metatherian synapomorphy (Table 2, character
51). These molars are M1–2 in the stem therians
and eutherians and M2–3 in the metatherians. In
metatherians this condition is best exemplified by
deltatheroidans (Rougier et al. 2004; Averianov et al.
2010). However, this condition is present also in stem
therians (Peramus, Juramaia), and basal eutherians
(Prokennalestes, Murtoilestes, Kulbeckia) (Clemens
and Mills 1971; Kielan-Jaworowska and Dashzeveg
1989; Averianov and Skutschas 2001; Archibald and
A.O. Averianov
174
Averianov 2003; Luo et al. 2011). In zhelestids the
ectoflexus on the antepenultimate upper molar (M1)
is greatly reduced to absent (Nesov et al. 1998; Ave-
rianov and Archibald 2005; Archibald and Averianov
2012). Among the Trinity therians this character is
developed in Oklatheridium and, to a lesser extent,
in Atokatheridium (condition for Pappotherium is
unknown). A derived condition, with reduced ecto-
flexus on the antepenultimate upper molar (M1), is
present in Holoclemensia. This is another, possible in-
dependently acquired, eutherian-like characteristic
of that taxon.
Postmetacrista cusp. The absence of the post-
metacrista cusp has been suggested as a eutherian
synapomorphy (Table 2, character 56), while earlier
Slaughter (1971) considered this cusp as a character
supporting eutherian affinities for Pappotherium. In
addition to Pappotherium, this cusp is present in Kiel-
antherium, Juramaia, Prokennalestes, and Murtoilestes
(Kielan-Jaworowska and Dashzeveg 1989; Averianov
and Skutschas 2001; Lopatin and Averianov 2007;
Luo et al. 2011). This character is likely a plesiomor-
phy for the stem therians and basal eutherians.
Prevallum and postvallum shear. The main
shearing surfaces of the upper and lower tribosphenic
molars, preparacrista – protocristid and postmeta-
crista – paracristid, are unequally developed in eu-
therians and metatherians. In eutherians there is an
emphasis on the preparacrista – protocristid (preval-
lum/postvallid) shear, while in metatherians – on the
postmetacrista – paracristid (postvallum/prevallid)
shear. This is manifested, in particular, in better de-
velopment of the paracone and metaconid in eutheri-
ans and the metacone and paraconid in metatherians
(Table 2, characters 52–54, 57, 84, 93, and 94). In de-
rived therians, this system of the first-rank shearing
surfaces has been enhanced by additional, double-
rank shearing surfaces: preprotocrista – protocristid
(prevallum/postvallid) and postprotocrista – parac-
ristid (postvallum/prevallid) (Table 2, characters
59, 60, and 73). The Early Cretaceous aegialodontid
Kielantherium already has and emphasis on the post-
vallum/prevallid shear, with strong postmetacrista
and paraconid higher than the metaconid (Lopatin
and Averianov 2007). This metatherians-like char-
acteristic was possible acquired by Kielantherium
independently from the metatherians, as well as its
dental formula with four molars, which was sug-
gested previously by Davis and Cifelli (2011). This
is likely because a number of stem therians also have
paraconid higher than metaconid: Amphibetulimus,
Peramus, Mozomus, and Arguimus (Averianov et al.
in press). In Kielantherium there is a fully developed
second-rank prevallum/postvallid shear, with the
preprotocrista extending labially towards the para-
stylar region. The second-rank postvallum/prevallid
shear is not developed, however. The postprotocrista
terminates at the base of the metacone. The acquisi-
tion of the second-rank postvallum/prevallid shear-
ing surface has been postulated as a synapomorphy
for Theria, Eutheria, or Metatheria (Table 2, charac-
ter 60). It is present in a stem therian Juramaia and
basal eutherians Prokennalestes, Murtoilestes, and
Bobolestes, where the postprotocrista terminates near
the labial end of the metacone (Kielan-Jaworowska
and Dashzeveg 1989; Averianov and Skutschas 2001;
Averianov and Archibald 2005; Luo et al. 2011). The
primitive condition, exemplified by Kielantherium,
is characteristic for all Trinity therians. Two taxa of
Trinity therians (Atokatheridium and Oklatheridium)
have emphasis on the postvallum/prevallid shear,
with strong postmetacrista and paraconid higher
than metaconid. This apparently suggests metathe-
rians affinity for these taxa. In other Trinity therians
(Kermackia, Holoclemensia, and Pappotherium), the
paraconid is smaller than metaconid.
Upper molars protocone size. The mesiodistal
expansion of the protocone has been suggested as a
eutherian or metatherian synapomorphy (Table 2,
characters 70, 71). In Kermackia and Holoclemensia
the protoconal region is known only for the ultimate
molars (M3) where it can be reduced compared with
the preceding molars. On M2 of Pappotherium the
protocone is extremely narrow mesiodistally. This has
been used as an argument for deltatheroidan affinities
of this taxon (Davis and Cifelli 2011). However, more
likely, it is retention of the primitive therian condi-
tion. The protocone of Pappotherium is very low, par-
alleling the condition of stem therians Kielantherium
and
Juramaia (Lopatin and A
verianov 2007; Luo et
al. 2011). In basal eutherians, such as Prokennalestes
and Murtoilestes, the protocone is significantly higher
(Kielan-Jaworowska and Dashzeveg 1989; Averianov
and Skutschas 2001). The protoconal region in Ato-
katheridium (preserved in M2–3) and Oklatheridium
(M3) is more expanded mesiodistally compared with
deltatheroidans. The protoconal region was likely
narrow on M1 of Oklatheridium where it is incom-
pletely preserved. The wide protoconal region of M3
in Oklatheridium correlates with the wide talonid of
Tribosphenic mammals from the Lower Cretaceous of USA
175
the middle lower molar (m2 or 3) attributed to that
taxon. This character advocates against close rela-
tionships of Oklatheridium and deltatheroidans.
Upper molar conules. In Kielantherium the proto-
cone is a single cusp in the protoconal region (Lopa-
tin and Averianov 2007). In more derived therians
one or two cusps (conules) have been added on the
protoconal cristae (Table 2, characters 74–76), while
Rougier et al. (1998) and Luo et al. (2003) cited lack
of conules as a marsupial synapomorphy (Table 2,
character 72). The conules are totally lacking on M3
of Kermackia and the same is likely true for the other
upper molars in that taxon which are not known. In
Pappotherium the conules are very small and lack in-
ternal cristae; the metaconule is absent on M3. This
condition is similar to that of a stem therian Juramaia
Luo et al. 2011. In Holoclemensia the protoconal re-
gion is known only for M3. Both conules are present
there; they are distinctly larger than in Pappotherium,
but still lack the internal cristae. In Atokatheridium
there are small conules with short internal cristae on
M2 and M3 (protoconal region is unknown for M1
and M4). In Oklatheridium there is a large paraco-
nule with postparaconule crista and a smaller, likely
unwinged, metaconule on M3. On M4 there is only
small and unwinged metaconule (protoconal region
is unknown for M1–2). The development of the co-
nules in Atokatheridium and Oklatheridium is more
similar to that in basal eutherians Prokennalestes and
Murtoilestes (Kielan-Jaworowska and Dashzeveg
1989; Averianov and Skutschas 2001) than to condi-
tion of deltatheroidans, where conules are small and
lack internal cristae (Averianov et al. 2010).
Lower molars trigonid angle and protocristid
orientation. In stem therians and some basal euthe-
rians and metatherians the trigonid of lower molars
is more open lingually and the protocristid is more
oblique to the dentary axis compared with more
derived taxa (Table 2, characters 82, 83, and 87). In
Kermackia the trigonid angle of lower molars is 46–
54° and the protocristid is oblique. In Atokatheridium
there is a single complete lower molar (m4) with
trigonid angle 50° and oblique protocristid. In Okla-
theridium the trigonid angle is 45–52° and the pro-
tocristid is more transverse. Both Holoclemensia and
Pappotherium have a smaller trigonid angle (30–42°)
and a transverse protocristid. These are relatively
derived characters, present in a few basal eutherians,
such as Sasayamamylos or Bobolestes (Averianov and
Archibald 2005; Kusuhashi et al. 2013).
Lower molars paraconid vertical crest. A keel-
like mesiolingual edge of the lower molars paraconid,
which corresponds to the mesiolingual cuspule e, has
long been considered as a metatherian feature (Table
2, character 92), although it is present also in a basal
eutherian Murtoilestes (Averianov and Skutschas
2001). Among Trinity therians this character present
in Kermackia and Atokatheridium. Davis et al. (2008)
thought that this crest is absent in Atokatheridium.
At least for the latter taxon this character may sug-
gest metatherian affinities.
Lower molars talonid width. In the early tribos-
phenic mammals, like Kielantherium, talonid was nar-
row, about half of the trigonid width (Dashzeveg and
Kielan-Jaworowska 1984; Lopatin and Averianov
2007). With the further development of the proto-
conal region, the talonid becomes wider, approaching
or exceeding the trigonid in width (Table 2, charac-
ters 97, 98). Among Trinity therians Kermackia has
the low talonid to trigonid width ratio (0.68–0.81),
which is consistent with the phylogenetic position
of this taxon as a stem therian. Holoclemensia has
similar values of this ratio; it varies individually and
between the tooth positions from 0.63 to 0.85. In
Oklatheridium the talonid is only slightly narrower
than the trigonid, with the talonid to trigonid width
ratio of 0.80–0.91. This is markedly different from
the condition of deltatheroidans, where the talonid is
very narrow. Pappotherium is the most derived among
Trinity therians in this respect, with the talonid with
to trigonid width ratio of 0.94 for m1.
Lower molars distal metacristid and cristid
oblique. The distal metacristid is a crest connecting
the metaconid with the hypoconid, which shears
against the paracone (F
ox 1975). It is present in stem
therians that have the paracone the largest cusp of the
upper molars and the protocone absent or small. With
further development of the protocone it starts to shear
against the metaconid (wear facet 5), which led to
disconnection of the distal metacristid from the meta-
conid (Crompton 1971; Davis 2011a). Davis (2011b:
677) redefined distal metacristid “as an oblique crest
on the posterior face of the metaconid, but not neces-
sarily reaching the apex of the cusp.” However, in this
definition the distal metacristid would not differ from
the cristid obliqua. Here I follow the definition of the
distal metacristid by Fox (1975) as a continuous crest
between the metaconid apex and the hypoconid. The
disrupted crest, not reaching the metaconid apex, is
the cristid obliqua. Several purported synapomorphies
A.O. Averianov
176
are related to the distal metacristid and orientation
of the cristid obliqua (Table 2, characters 101–104).
Among Trinity therians the distal metacristid is
well-developed in the stem therian Kermackia. Ato-
katheridium and Oklatheridium show a transitional
stage where some teeth still have a faint distal metac-
ristid while in other teeth it is disconnected from the
metaconid apex (cristid obliqua). In this respect both
taxa are different from deltatheroidans which have
the distal metacristid. The next stage is exemplified
by Holoclemensia, where the cristid obliqua is rarely
ascending on the trigonid wall above the protocristid
notch. Pappotherium has the most derived condition,
with short cristid obliqua, although this could be
accentuated by the wear of the single known speci-
men. In Holoclemensia the cristid obliqua terminates
lingual to the protocristid notch which is correlated
with the narrow talonid relative to the trigonid. In
Pappotherium, which have the talonid nearly equal to
the trigonid in width, this crest terminates labial to
the protocristid notch (some labial shift of this crest
could be caused by the wear of the single known speci-
men). The cristid obliqua contacting the trigonid at
the protocristid notch or more labial has been cited
as a synapomorphy for either Eutheria or Metatheria
(Table 2, characters 103, 104). Evidently this trait
was developed independently in these lineages in cor-
relation with the widening of the talonid.
Lower molars hypoconulid and entoconid ap-
proximation. In metatherians the hypoconulid and
entoconid are closely approximated (“twinned”) (Ta-
ble 2, character 111). This character has been used
as an argument for assigning Holoclemensia to the
Marsupialia since original description of this taxon
(Slaughter 1968b). However, as was shown by Jacobs
et al. (1989), in Holoclemensia the hypoconulid and
entoconid are not as close as in the Late Cretaceous
stem marsupials. The approximation of these cusps
is correlated with the widening of the talonid and
also characteristic for some Late Cretaceous euthe-
rians, including zhelestids (Archibald and Averianov
2012). But none of the Cretaceous eutherians show a
peculiar metatherian condition, with the hypoconu-
lid and entoconid almost aligned mesiodistally.
CONCLUSIONS
There are five tribosphenic taxa in the verte-
brate fauna of the Antlers Formation of Texas and
Oklahoma, USA (Table 3). The most primitive
taxon is a stem therian Kermackia texana, which
has primitive therian postcanine formula with three
molars, replacement in the fifth premolar position,
upper molars with a small protoconal region with
low protocone and no conules, lower molars with
great trigonid angle, oblique protocristid, paraconid
smaller than metaconid (except m3), strong distal
metacristid, narrow talonid, small talonid basin, and
small entoconid (absent on m3). Kermackia has at
least one metatherian character – a keel-like vertical
crest of the paraconid. Holoclemensia texana has such
plesiomorphic therian characters as a tall trenchant
penultimate upper premolar (P4), replacement in
the fifth premolar locus, and three molars. It is more
derived compared with Kermackia in larger pro-
toconal region with higher protocone and conules
present, lack of distal metacristid, smaller trigonid
angle, transverse protocristid, and wide talonid with
greater talonid basin. Holoclemensia has certain sim-
ilarities with Eutheria: possible protoconal bulge on
P4, M1 with reduced ectoflexus, semimolariform p5,
and low trigonid angle with transverse protocristid.
However, all these traits were likely derived inde-
pendently in different eutherian lineages. Moreover,
it differs from basal eutherians by the postprotocrista
not extending labially past the metacone base (lack
of the second rank postvallum/prevallid shear)
and conules lacking the internal cristae. Therefore
Holoclemensia is considered here as a stem therian
rather than eutherian. A peculiar large stylar cusp C
is an autapomorphy of this taxon (Davis and Cife-
lli 2011). Pappotherium pattersoni has the following
therian plesiomorphic characters: replacement in the
fifth premolar position, premolariform p5, and three
molars. It is more derived than Holoclemensia in hav-
ing wider and shorter talonid. By low trigonid angle,
transverse protocristid, and the cristid obliqua labial
to the protocristid notch (possible wear artifact)
Pappotherium is similar with Eutheria. It cannot be
attributed to the Eutheria because of narrow proto-
conal region, low protocone, small conules lacking
internal cristae, postprotocrista not extending labi-
ally past the metacone base, and small talonid basin.
Pappotherium is considered here as a stem therian.
The two remaining taxa, Atokatheridium boreni and
Oklatheridium szalayi, are considered as stem mar-
supials because of having four molars and emphasis
on the postvallum/prevallid shear (large metacone
on M2, strong postmetacrista, paraconid higher than
metaconid). In Atokatheridium a small stylar cusp C
Tribosphenic mammals from the Lower Cretaceous of USA
177
is variable present. These taxa cannot be attributed
to the Deltatheroida because of large protoconal
region with winged conules. Oklatheridium is fur-
ther different from Deltatheroida by wider talonid
and better developed entoconid, which is small or
reduced in deltatheroidans (Averianov et al. 2010).
Condition of these characters is uncertain for Ato-
katheridium, as the single known complete lower mo-
lar of this taxon, with narrow talonid and entoconid
lacking, is likely a m4 which talonid is supposed to
be reduced. The Early Cretaceous Trinity Fauna of
North America shows unparalleled diversity of early
therian taxa, including a basal stem therian (Ker-
mackia), two taxa near the eutherian-metatherian
dichotomy (Holoclemensia and Pappotherium), and
two taxa of basal metatherians (Atokatheridium and
Oklatheridium).
ACKNOWLEDGEMENTS
I am grateful to Louis Jacobs, Dale Winkler (SMP–
SMU), Richard Cifelli (OMNH), Kenneth Angielczyk,
and William Simpson (CNHM) for the access to the
specimens under their care. I am especially grateful to Dale
Winkler and Rich Cifelli for providing the casts of the most
important specimens. I thank Brian Davis (University of
Louisville) for reading of an earlier version of this manu-
script and suggestions, although not all his suggestions are
followed here. I thank J. David Archibald (San Diego Uni-
versity) for review of the paper and linguistic corrections.
This work was supported by the Russian Foundation for
Basic Research (projects 13-04-01401 and 13-04-00525).
REFERENCES
Aplin K.P. and Archer M. 1987. Recent advances in mar-
supial systematics with a new syncretic classification.
In: M. Archer (Ed.). Possums and Opossums: Studies
in Evolution. Surrey Beatty and Sons, Chipping Nor-
ton, South Wales and the Royal Society of New South
Wales, Sydney: xv–lxxii.
Archer M. 1984. The Australian marsupial radiation. In:
M. Archer and G. Clayton (Eds.). Vertebrate Zoogeog-
raphy and Evolution in Australasia. Hesperian Press,
Carlisle: 633–808.
Archibald J.D. and Averianov A.O. 2003. The Late Cre-
taceous placental mammal Kulbeckia. Journal of Verte-
brate Paleontology, 23(2): 404–419.
Archibald J.D. and Averianov A.O. 2006. Late Cretaceous
asioryctitherian eutherian mammals from Uzbekistan
and phylogenetic analysis of Asioryctitheria. Acta Pa-
laeontologica Polonica, 51(2): 351–376.
Archibald J.D. and Averianov A.O. 2012. Phylogenetic
analysis, taxonomic revision, and dental ontogeny of the
Cretaceous Zhelestidae (Mammalia: Eutheria). Zoologi-
cal Journal of the Linnean Society, 164(2): 361–426.
Averianov A.O. and Archibald J.D. 2005. Mammals from
the mid-Cretaceous Khodzhakul Formation, Kyzyl-
kum Desert, Uzbekistan. Cretaceous Research, 26(4):
593–608.
Averianov A.O. and Archibald J.D. 2013. Variation and
taxonomy of Asiamerican eutherian mammal Paranyc-
toides. Canadian Journal of Earth Sciences, 50(9):
895–903.
Averianov A.O., Archibald J.D. and Ekdale E.G. 2010.
New material of the Late Cretaceous deltatheroidan
mammal Sulestes from Uzbekistan and phylogenetic
reassessment of the metatherian-eutherian dichotomy.
Journal of Systematic Palaeontology, 8(3): 301–330.
Averianov A.O., Martin T., Lopatin A.V. and Krasno-
lutskii S.A. In press. Stem therian mammal Amphib-
etulimus from the Middle Jurassic of Siberia. Palaeon-
tologische Zeitschrift.
Averianov A.O. and Skutschas P.P. 1999. Phylogenetic
relationships within basal tribosphenic mammals. Pro-
ceedings of the Zoological Institute of the Russian Acad-
emy of Sciences, 281: 55–60.
Averianov A.O. and Skutschas P.P. 2001. A new genus of
eutherian mammal from the Early Cretaceous of Trans-
baikalia, Russia. Acta Palaeontologica Polonica, 46(3):
431–436.
Table 3. Distribution of the tribosphenic mammals in the localities of the Antlers Formation of Texas and Oklahoma, USA.
Taxon Butler Farm Greenwood Canyon Tomato Hill Pecan Valley Estates
Kermackia texana
+++–
Holoclemensia texana
++++
Pappotherium pattersoni
+–––
Atokatheridium boreni
–++–
Oklatheridium szalayi
–++–
A.O. Averianov
178
Butler P.M. 1977. Evolutionary radiation of the cheek
teeth of Cretaceous placentals. Acta Palaeontologica
Polonica, 22(3): 241–269.
Butler P.M. 1978. A new interpretation of the mammalian
teeth of tribosphenic pattern from the Albian of Texas.
Breviora, 446: 1–27.
Butler P.M. 1990. Early trends in the evolution of tribos-
phenic molars. Biological Reviews, 65: 529–552.
Butler P.M. 1992. Tribosphenic molars in the Cretaceous.
In: P. Smith and E. Tchernov (Eds.). Structure, Func-
tion and Evolution of Teeth. Freund Publishing House,
Tel Aviv: 125–138.
Butler P.M. and Clemens W.A. 2001. Dental morphology
of the Jurassic holotherian mammal Amphitherium, with
a discussion of the evolution of mammalian post-canine
dental formulae. Palaeontology, 44(1): 1–20.
Cifelli R.L. 1990. Cretaceous mammals of southern Utah.
III. Therian mammals from the Turonian (early Late
Cretaceous). Journal of Vertebrate Paleontology, 10(3):
332–345.
Cifelli R.L. 1993a. Early Cretaceous mammal from North
America and the evolution of marsupial dental charac-
ters. Proceedings of the National Academy of Sciences,
90: 9413–9416.
Cifelli R.L. 1993b. Theria of metatherian-eutherian grade
and the origin of marsupials. In: F.S. Szalay, M.J. No-
vacek and M.C. McKenna (Eds.). Mammal Phylogeny:
Mesozoic Differentiation, Multituberculates, Mono-
tremes, Early Therians, and Marsupials. Springer-
Verlag, New York: 205–215.
Cifelli R.L. 1997. First notice on Mesozoic mammals from
Oklahoma. Oklahoma Geological Notes, 57: 4–17.
Cifelli R.L. 2004. Marsupial mammals from the Albian-
Cenomanian (Early-Late Cretaceous) boundary, Utah.
Bulletin of the American Museum of Natural History,
285: 62–79.
Cifelli R.L. and Madsen S.K. 1998. Triconodont mam-
mals from the medial Cretaceous of Utah. Journal of
Vertebrate Paleontology, 18(2): 403–411.
Cifelli R.L. and Muizon C. de 1997. Dentition and jaw
of Kokopellia juddi, a primitive marsupial or near mar-
supial from the medial Cretaceous of Utah. Journal of
Mammalian Evolution, 4(4): 241–258.
Cifelli R.L. and Muizon C. de 1998. Marsupial mammal
from the Upper Cretaceous North Horn Formation,
central Utah. Journal of Paleontology, 72(3): 532–537.
Clemens W.A. 1966. F
ossil mammals of the type Lance
Formation Wyoming. Part II. Marsupialia. University of
California Publications in Geological Sciences, 62: 1–122.
Clemens W.A. 1968. Origin and evolution of marsupials.
Evolution, 22(1): 1–18.
Clemens W.A. 1970. Mesozoic mammalian evolution. An-
nual Review of Ecology and Systematics, 1: 357–390.
Clemens W.A. 1979. Marsupialia. In: J.A. Lillegraven,
Z. Kielan-Jaworowska and W.A. Clemens (Eds.).
Mesozoic Mammals: The First Two-thirds of Mamma-
lian History. University of California Press, Berkeley:
192–220.
Clemens W.A. and Lillegraven J.A. 1986. New Late Cre-
taceous, North American advanced therian mammals
that fit neither the marsupial nor eutherian molds. In:
K.M. Flanagan and J.A. Lillegraven (Eds.). Vertebrates,
Phylogeny and Philosophy. Contributions to Geology,
University of Wyoming, Special Paper: 55–86.
Clemens W.A. and Mills J.R.E. 1971. Review of Peramus
tenuirostris Owen (Eupantotheria, Mammalia). Bulletin
of the British Museum of Natural History (Geology), 20:
89–113.
Crompton A.W. 1971. The origin of the tribosphenic mo-
lar. In: D.M. Kermack and K.A. Kermack (Eds.). Early
Mammals. Zoological Journal of the Linnean Society:
65–87.
Crompton A.W. and Kielan-Jaworowska Z. 1978. Molar
structure and occlusion in Cretaceous therian mam-
mals. In: P.M. Butler and K.A. Joysey (Eds.). Studies
in the Development, Function and Evolution of Teeth.
Academic Press, London: 249–287.
Dashzeveg D. and Kielan-Jaworowska Z. 1984. The
lower jaw of an aegialodontid mammal from the Early
Cretaceous of Mongolia. Zoological Journal of the Lin-
nean Society, 82: 217–227.
Davis B.M. 2011a. Evolution of the tribosphenic molar
pattern in early mammals, with comments on the “dual-
origin” hypothesis. Journal of Mammalian Evolution,
18(4): 227–244.
Davis B.M. 2011b. A novel interpretation of the tribos-
phenidan mammal Slaughteria eruptens from the Lower
Cretaceous Trinity Group, and implications for dental
formula in early mammals. Journal of Vertebrate Paleon-
tology, 31(3): 676–683.
Davis B.M. and Cifelli R.L. 2011. Reappraisal of the
tribosphenidan mammals from the Trinity Group (Ap-
tian–Albian) of Texas and Oklahoma. Acta Palaeonto-
logica Polonica, 56(3): 441–462.
Davis B.M., Cifelli R.L. and Kielan-Jaworowska Z.
2008. Earliest evidence of Deltatheroida (Mammalia:
Metatheria) from the Early Cretaceous of North Amer-
ica. In: E.J. Sargis and M. Dagosto (Eds.). Mammalian
Evolutionary Morphology. A Tribute to Frederick S
Szalay. (Vertebrate Paleobiology and Paleoanthropol-
ogy Series) Springer: 3–24.
Fox R.C. 1975. Molar structure and function in the Early
Cretaceous mammal Pappotherium: Evolutionary im-
plications for Mesozoic Theria.
Canadian Journal of
Earth Sciences, 12(3): 412–442.
Fox R.C. 1980. Picopsis pattersoni, n. gen. and sp., an
unusual therian from the Upper Cretaceous of Al-
berta, and the classification of primitive tribosphenic
mammals. Canadian Journal of Earth Sciences, 17(11):
1489–1498.
Tribosphenic mammals from the Lower Cretaceous of USA
179
Gheerbrant E. and Astibia H. 2012. Addition to the Late
Cretaceous Laño mammal faunule (Spain) and to the
knowledge of European “Zhelestidae” (Lainodontinae
nov.). Bulletin de la Société géologique de France, 183(6):
537–546.
Hershkovitz P. 1982. The staggered marsupial lower third
incisor (I
3
). Geobios, 15(Supplement 1): 191–200.
Hershkovitz P. 1995. The staggered marsupial third lower
incisor: hallmark of cohort Didelphimorphia, and de-
scription of a new genus and species with staggered i3
from the Albian (Lower Cretaceous) of Texas. Bonner
Zoologische Beiträge, 45: 153–169.
Hopson J.A. and Crompton A.W. 1969. Origin of mam-
mals. In: T. Dobzhansky, M.K. Hecht and V.C. Steere
(Eds.). Evolutionary Biology. Appleton-Century-
Crofts, New York: 25–72.
Hu Y., Meng J., Li C. and Wang Y. 2010. New basal eu-
therian mammal from the Early Cretaceous Jehol biota,
Liaoning, China. Proceedings of the Royal Society B:
Biological Sciences, 277(1679): 229–236.
Illiger C. 1811. Prodromus systematis mammalium et avi-
um additis terminis zoographicis utriusque classis. C.
Salfeld, Berlin.
Jacobs L.L., Winkler D.A. and Murry P.A. 1989. Modern
mammal origins: evolutionary grades in the Early Cre-
taceous of North America. Proceedings of the National
Academy of Sciences, 86: 4992–4995.
Ji Q., Luo Z.-X., Yuan C.-X., Wible J.R., Zhang J.-P. and
Georg J.A. 2002. The earliest known eutherian mam-
mal. Nature, 416(6883): 816–822.
Kielan-Jaworowska Z. 1975. Evolution of the therian
mammals in the Late Cretaceous of Asia. Part I. Del-
tatheridiidae. Palaeontologia Polonica, 33: 103–132.
Kielan-Jaworowska Z. and Cifelli R.L. 2001. Primitive
boreosphenidan mammal (?Deltatheroida) from the
Early Cretaceous of Oklahoma. Acta Palaeontologica
Polonica, 46(3): 377–391.
Kielan-Jaworowska Z., Cifelli R.L. and Luo Z.-X. 2004.
Mammals from the Age of Dinosaurs: Origins, Evolu-
tion, and Structure. New York, Columbia University
Press, 630 p.
Kielan-Jaworowska Z. and Dashzeveg D. 1989. Euthe-
rian mammals from the Early Cretaceous of Mongolia.
Zoologica Scripta, 18: 347–355.
Kielan-Jaworowska Z., Eaton J.G., Bown T.M. 1979.
Theria of metatherian-eutherian grade. In: J.A. Lil-
legraven, Z. Kielan-Jaworowska and W.A. Clemens
(Eds.). Mesozoic Mammals: The First Two-thirds of
Mammalian History. University of California Press,
Berkeley: 182–191.
Kobayashi Y., Winkler D.A. and Jacobs L.L. 2002.
Origin of the tooth-replacement pattern in therian
mammals: evidence from a 110 Myr old fossil. Proceed-
ings of the Royal Society of London, Series B: Biological
Sciences, 269(1489): 369–373.
Kusuhashi N., Tsutsumi Y., Saegusa H., Horie K., Ikeda
T., Yokoyama K. and Shiraishi K. 2013. A new Early
Cretaceous eutherian mammal from the Sasayama
Group, Hyogo, Japan. Proceedings of the Royal Soci-
ety B: Biological Sciences, 280(1759): DOI: 10.1098/
rspb.2013.0142.
Li C., Setoguchi T., Wang Y., Hu Y. and Chang Z.-L.
2005. The first record of “eupantotherian” (Theria,
Mammalia) from the late Early Cretaceous of west-
ern Liaoning, China. V
ertebrata PalAsiatica, 43(4):
245–255.
Lillegraven J.A. 1969. Latest Cretaceous mammals of up-
per part of Edmonton Formation of Alberta, Canada,
and review of marsupial-placental dichotomy in mam-
malian evolution. University of Kansas Paleontological
Contributions, 50: 1–122.
Linnaeus C. 1758. Systema naturae per regna tria naturae,
secundum classes, ordines, genera, species, cum charac-
teribus, differentiis, synonymis, locis. Vol. 1: Regnum
animale. Editio decima, reformata. Laurentii Salvii,
Stockholm.
Lopatin A.V. and Averianov A.O. 2006. Revision of a
pretribosphenic mammal Arguimus from the Early
Cretaceous of Mongolia. Acta Palaeontologica Polonica,
51(2): 339–349.
Lopatin A.V. and Averianov A.O. 2007. Kielantherium, a
basal tribosphenic mammal from the Early Cretaceous
of Mongolia, with new data on the aegialodontid denti-
tion. Acta Palaeontologica Polonica, 52(3): 441–446.
Luckett W.P. 1993. An ontogenetic assessment of dental
homologies in therian mammals. In: F.S. Szalay, M.J.
Novacek and M.C. McKenna (Eds) Mammal Phy-
logeny: Mesozoic Differentiation, Multituberculates,
Monotremes, Early Therians, and Marsupials. Spring-
er-Verlag, Inc., New York: 182–204.
Luo Z.-X., Ji Q., Wible J.R. and Yuan C.-X. 2003. An
Early Cretaceous tribosphenic mammal and metathe-
rian evolution. Science, 302(5652): 1934–1940.
Luo Z.-X., Kielan-Jaworowska Z. and Cifelli R.L. 2004.
Evolution of dental replacement in mammals. Bul-
letin of the Carnegie Museum of Natural History, 36:
159–175.
Luo Z.-X. and Wible J.R. 2005. A Late Jurassic digging
mammal and early mammalian diversification. Science,
308(5718): 103–107.
Luo Z.-X., Yuan C.-X., Meng Q.-J. and Ji Q. 2011. A Ju-
rassic eutherian mammal and divergence of marsupials
and placentals. Nature, 476(7361): 442–445.
Marshall L.G. and Kielan-Jaworowska Z. 1992. Re-
lationships of the dog-like marsupials, deltatheroi-
dans and early tribosphenic mammals. Lethaia, 25:
361–374.
Martin T. 2002. New stem-line representatives of Zatheria
(Mammalia) from the Late Jurassic of Portugal. Journal
of Vertebrate Paleontology, 22(2): 332–348.
A.O. Averianov
180
McKenna M.C. 1975. Towards a phylogenetic classifica-
tion of the Mammalia. In: W.P. Luckett and F.S. Szalay
(Eds.). Phylogeny of the Primates. Plenum Press, New
York: 21–46.
Mills J.R.E. 1964. The dentitions of Peramus and Amphith-
erium. Proceedings of the Linnean Society of London,
175(2): 117–133.
Nesov L.A., Archibald J.D., Kielan-Jaworowska Z.
1998. Ungulate-like mammals from the Late Creta-
ceous of Uzbekistan and a phylogenetic analysis of
Ungulatomorpha. In: K.C. Beard and M.R. Dawson
(Eds.). Dawn of the Age of Mammals in Asia. Bulletin
of the Carnegie Museum of Natural History: 40–88.
Novacek M.J. 1999. 100 million years of land vertebrate
evolution: the Cretaceous-Early Tertiary transition.
Annals of the Missouri Botanical Garden, 86: 230–258.
O’Leary M.A., Bloch J.I., Flynn J.J., Gaudin T.J.,
Giallombardo A., Giannini N.P., Goldberg S.L.,
Kraatz B.P., Luo Z.-X., Meng J., Ni X., Nova-
cek M.J., Perini F.A., Randall Z.S., Rougier G.W.,
Sargis E.J., Silcox M.T., Simmons N.B., Spauld-
ing M., Velazco P.M., Weksler M., Wible J.R. and
Cirranello A.L. 2013. The placental mammal ancestor
and the post–K-Pg radiation of placentals. Science,
339(6120): 662–667.
Parker T.J. and Haswell W.A. 1897. A Text-book of Zool-
ogy, Volume 2. MacMillan and Company, London.
Patterson B. 1951. Early Cretaceous mammals from
Northern Texas. American Journal of Science, 249(1):
31–46.
Patterson B. 1955. A symmetrodont mammal from the
Early Cretaceous of northern Texas. Fieldiana: Zoology,
37: 689–693.
Patterson B. 1956. Early Cretaceous mammals and the
evolution of mammalian molar teeth. Fieldiana: Geol-
ogy, 13(1): 1–105.
Rougier G.W., Martinelli A.G., Forasiepi A.M. and
Novacek M.J. 2007. New Jurassic mammals from Pa-
tagonia, Argentina: a reappraisal of australosphenidan
morphology and interrelationships. American Museum
Novitates, 3566: 1–54.
Rougier G.W., Wible J.R. and Novacek M.J. 1998.
Implications of Deltatheridium specimens for early
marsupial history. Nature, 396(6710): 459–463.
Rougier G.W., Wible J.R. and Novacek M.J. 2004. New
specimen of Deltatheroides cretacicus (Metatheria,
Deltatheroida) from the Late Cretaceous of Mongolia.
Bulletin of the Carnegie Museum of Natural History, 36:
245–266.
Sigogneau-Russell D., Dashzeveg D. and Russell D.E.
1992. Further data on Prokennalestes (Mammalia,
Eutheria, inc. sed.) from the Early Cretaceous of Mon-
golia. Zoologica Scripta, 21: 205–209.
Slaughter B.H. 1965. A therian from the Lower Creta-
ceous (Albian) of T
exas. Postilla, 93: 1–18.
Slaughter B.H. 1968a. Earliest known eutherian mammals
and the evolution of premolar occlusion. Texas Journal
of Science, 20: 3–12.
Slaughter B.H. 1968b. Earliest known marsupials. Sci-
ence, 162: 254–255.
Slaughter B.H. 1968c. Holoclemensia instead of Clemen-
sia. Science, 162: 1306.
Slaughter B.H. 1969. Astroconodon, the Cretaceous tri-
conodont. Journal of Mammalogy, 50: 102–107.
Slaughter B.H. 1971. Mid-Cretaceous (Albian) therians
of the Butler Farm local fauna, Texas. In: D.M. Kermack
and K.A. Kermack (Eds.). Early Mammals. Zoological
Journal of the Linnean Society, London: 131–143.
Slaughter B.H. 1981. The Trinity therians (Albian, mid-
Cretaceous) as marsupials and placentals. Journal of
Paleontology, 55: 682–683.
Slaughter B.H., Pine R.H. and Pine N.E. 1974. Eruption
of cheek teeth in Insectivora and Carnivora. Journal of
Mammalogy, 55: 115–125.
Turnbull W.D. 1971. The Trinity therians: their bear-
ing on evolution in marsupials and other therians. In:
A.A. Dahlberg (Ed.). Dental Morphology and Evolu-
tion. University of Chicago Press, Chicago: 151–179.
Turnbull W.D. 1995. Trinity mammal jaws from the late
Early Cretaceous of Texas. In: R.J. Radlonski and
H. Renz (Eds.). Proceedings of the Tenth International
Symposium on Dental Morphology. Christine und Mi-
chael Brünne, Berlin: 261–265.
Turnbull W.D. and Cifelli R.L. 1999. Triconodont mam-
mals of the Aptian-Albian Trinity Group, Texas and
Oklahoma. In: J.T. Mayhall and T. Heikkinen (Eds.).
Dental Morphology ‘98 Proceedings of the 11th Inter-
national Symposium on Dental Morphology. Univer-
sity of Oulu Press, Oulu: 252–272.
Vandebroek G. 1961. The comparative anatomy of the
teeth of lower and non specialized mammals. In: G.
Vandebroek (Ed.). International Colloquium on the
Evolution of Lower and Non-specialized Mammals.
Koninklijke Vlaamse Academie voor Wetenschappen,
Letteren en Schone Kunsten van Belgie, Brussels: part
I, 215–320; part II, 244 plates, 211–181.
Vullo R., Gheerbrant E., Muizon C., de and Néraudeau D.
2009. The oldest modern therian mammal from Europe
and its bearing on stem marsupial paleobiogeography.
Proceedings of the National Academy of Sciences USA,
106(47): 19910–19915.
Wible J.R., Novacek M.J. and Rougier G.W. 2004. New
data on the skull and dentition in the Mongolian Late
Cretaceous eutherian mammal Zalambdalestes
. Bul-
letin of the American Museum of Natural History, 281:
1–144.
Wible J.R., Rougier G.W
., Novacek M.J. and Asher R.J.
2007. Cretaceous eutherians and Laurasian origin for
placental mammals near the K/T boundary. Nature,
447(7147): 1003–1006.
Tribosphenic mammals from the Lower Cretaceous of USA
181
Wible J.R., Rougier G.W., Novacek M.J. and Asher R.J.
2009. The eutherian mammal Maelestes gobiensis from
the Late Cretaceous of Mongolia and the phylogeny of
Cretaceous Eutheria. Bulletin of the American Museum
of Natural History, 327: 1–123.
Wible J.R., Rougier G.W., Novacek M.J. and McKen-
na M.C. 2001. Earliest eutherian ear region: a petrosal
referred to Prokennalestes from the Early Cretaceous
of Mongolia. American Museum Novitates, 3322: 1–44.
Wilson G.P. and Riedel J.A. 2010. New specimen reveals
deltatheroidan affinities of the North American Late
Cretaceous Mammal Nanocuris. Journal of Vertebrate
Paleontology, 30(3): 872–884.
Winkler D.A., Jacobs L.L., Kobayashi Y. and Pol-
cyn M.J. 2011. CT reconstructions and relationships
of the Early Cretaceous tribosphenidan mammal,
Slaughteria eruptens (Trinity Group Texas, USA). Pa-
laeontologia Electronica, 14(3): 21A:12p.
Winkler D.A., Murry P.A. and Jacobs L.L. 1990. Early
Cretaceous (Comanchean) vertebrates of central Texas.
Journal of Vertebrate Paleontology, 10(1): 95–116.
Zan S., Wood C.B., Rougier G.W., Jin L., Chen J. and
Schaff C.R. 2006. A new “middle” Cretaceous zalamb-
dalestid mammal, from a new locality in Jilin Province,
northeastern China. Journal of the Paleontological Soci-
ety of Korea, 22(1): 153–172.
Zangerl R. and Denison R.H. 1950. Discovery of Early
Cretaceous mammals and frogs in Texas. Science,
112(2898): 61.
Submitted December 12, 2014; accepted March 31, 2015.
