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In non-mammalian amniotes, the parasphenoid is a midline dermal element with a narrow rostral portion, the cultriform process, linked to the interorbital septum and an expanded distal portion, the alae or wings, forming part of the ventral skull base. In mammals, the parasphenoid has not been found in extant monotremes and only a handful of reports of a reduced parasphenoid (a remnant of the cultriform process) have been made for extant marsupials and placentals. Most reports are in serially-sectioned perinatal specimens where the contrast between the intramembranous origin of the parasphenoid and the overlying endochondral basisphenoid facilitates delimiting the different elements forming the skull base. The only report of a parasphenoid remnant in adult marsupials is in the white-eared opossum, Didelphis albiventris, and it was published more than 100 years ago. Here, we report the results of a survey of 576 specimens of Didelphidae and 115 other Marsupialia in the extant collections of the Section of Mammals, Carnegie Museum of Natural History. We observed what we interpret as a parasphenoid remnant in some juveniles and adults from ten of the 27 didelphid species studied: Didelphis albiventris, Didelphis marsupialis, Didelphis virginiana, Marmosa murina, Monodelphis arlindoi, Monodelphis domestica, Philander opossum, Thylamys elegans, Thylamys pusilla, and Thylamys venustus. This element was variable in its presence within the collection, as well as in its size, form, and position. In our largest specific sample, the Virginia opossum, Didelphis virginiana, a parasphenoid was present in 55% of 238 specimens. It is uncertain if the variable occurrence reflects a true absence of the parasphenoid or its loss during specimen preparation. Outside of Didelphidae, we noted a substantial parasphenoid in the microbiothere Dromiciops gliroides, contributing to a midline septum that partially divides the nasopharynx into two channels, and a probable small one in the macropodid Thylogale sp. In extinct mammals and non-mammalian cynodonts, a midline mesocranial ridge interpreted by prior authors as composed of or including a parasphenoid has a wide distribution, supporting the presence of this structure as primitive for Mammalia. It is suggested here that the Miocene platypus Obdurodon has a well-developed parasphenoid further supporting the presence of a parasphenoid as a plesiomorphic feature for Mammalia that is independently lost in some therians and apparently in extant monotremes.
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THE MAMMALIAN PARASPHENOID:
ITS OCCURRENCE IN MARSUPIALS
John R. Wible
Curator, Section of Mammals, Carnegie Museum of Natural History
5800 Baum Boulevard, Pittsburgh, Pennsylvania 15206
wiblej@carnegiemnh.org
SaRah l. Shelley
Postdoctoral Fellow, Section of Mammals, Carnegie Museum of Natural History
5800 Baum Boulevard, Pittsburgh, Pennsylvania 15206
shelleys@carnegiemnh.org
GuilleRmo W. RouGieR
[Research Associate, Section of Mammals, Carnegie Museum of Natural History]
Department of Anatomical Sciences and Neurobiology,
University of Louisville, Louisville, Kentucky 40292
grougier@louisville.edu
ANNALS OF CARNEGIE MUSEUM
Vol. 85, numbeR 2, PP. 113–164 31 DecembeR 2018
ABSTRACT
In non-mammalian amniotes, the parasphenoid is a midline dermal element with a narrow rostral portion, the cultriform process, linked to the
interorbital septum and an expanded distal portion, the alae or wings, forming part of the ventral skull base. In mammals, the parasphenoid has not
been found in extant monotremes and only a handful of reports of a reduced parasphenoid (a remnant of the cultriform process) have been made
for extant marsupials and placentals. Most reports are in serially-sectioned perinatal specimens where the contrast between the intramembranous
origin of the parasphenoid and the overlying endochondral basisphenoid facilitates delimiting the different elements forming the skull base. The
only report of a parasphenoid remnant in adult marsupials is in the white-eared opossum, Didelphis albiventris, and it was published more than
100 years ago. Here, we report the results of a survey of 576 specimens of Didelphidae and 115 other Marsupialia in the extant collections of
the Section of Mammals, Carnegie Museum of Natural History. We observed what we interpret as a parasphenoid remnant in some juveniles
and adults from ten of the 27 didelphid species studied: Didelphis albiventris, Didelphis marsupialis, Didelphis virginiana, Marmosa murina,
Monodelphis arlindoi, Monodelphis domestica, Philander opossum, Thylamys elegans, Thylamys pusilla, and Thylamys venustus. This element
was variable in its presence within the collection, as well as in its size, form, and position. In our largest specific sample, the Virginia opossum,
Didelphis virginiana, a parasphenoid was present in 55% of 238 specimens. It is uncertain if the variable occurrence reflects a true absence of
the parasphenoid or its loss during specimen preparation. Outside of Didelphidae, we noted a substantial parasphenoid in the microbiothere
Dromiciops gliroides, contributing to a midline septum that partially divides the nasopharynx into two channels, and a probable small one in the
macropodid Thylogale sp.
In extinct mammals and non-mammalian cynodonts, a midline mesocranial ridge interpreted by prior authors as composed of or includ-
ing a parasphenoid has a wide distribution, supporting the presence of this structure as primitive for Mammalia. It is suggested here that the
Miocene platypus Obdurodon has a well-developed parasphenoid further supporting the presence of a parasphenoid as a plesiomorphic feature
for Mammalia that is independently lost in some therians and apparently in extant monotremes.
Key WoRDS: basisphenoid, Didelphis, Didelphidae, Dromiciops, marsupials, nasopharynx, Obdurodon, parasphenoid
INTRODUCTION
In his Lectures on the Elements of Comparative Anatomy,
Huxley (1864) coined the term parasphenoid for the mid-
line dermal element found beneath the skull base in sh
and amphibians and said to be absent in reptiles, birds, and
mammals. A well-developed parasphenoid in reptiles and
birds was subsequently described by Parker and Bettany
(1877). As shown in an embryo of the sand lizard, Lac-
erta agilis (Fig. 1A), the parasphenoid in these amniotes
typically has an anterior midline rod (rostrum or cultriform
process), which underlies the interorbital septum, and a
posterolateral pair of wings (alae) beneath the skull base
(Gaupp 1906). In the adult sand lizard, the posterior part of
the parasphenoid fuses to the basisphenoid, while the cul-
triform process remains unfused (Gaupp 1906). The rst
mention of a parasphenoid in a mammal was by Parker
(1885). He observed a small dermal bone on the midline
ventral to the basisphenoid in two juveniles and two adults
of the Philippine colugo, the dermopteran Cynocephalus
volans (= Galeopithecus philippensis) (Fig. 1B). Parker
(1885: 260) reported this bone as “the exact counterpart of
the parasphenoid of the Lacertilia,” which given its posi-
tion must have referred to the cultriform process. In the
young colugos, he specically stated that the parasphenoid
was distinct from the basisphenoid; however, he did not
repeat this description for the adults, but his illustration
(plate 39, g. 8) suggests the two bones are distinct. He
described the parasphenoid in the adult colugos as slender
and “acicular” (needle-shaped) and gured it as tapered at
both ends. In 1908, Fuchs reported the second occurrence
of a parasphenoid in a mammal, in embryos of unidentied
species of the marsupial Didelphis (=Didelphys).
In the youngest embryo of Didelphis sp. studied by
Fuchs (1908: g. 1, 1910: g. 14), the parasphenoid lay
on the midline dorsal to the nasopharynx, separated from
114 annalS of caRneGie muSeum Vol. 85
the overlying chondrocranium by connective tissue (Fig.
2); this intramembranous ossication was rod-shaped and
0.24 mm in length. In a second, older embryo that Fuchs
attributed to the same unidentied species, rather than rod-
shaped, the parasphenoid was a at lamella, 0.21 mm in
length, that was fused to the basisphenoid at its posterior
end. In 1911, Fuchs (1911: g. 15, also 1915: g. 167)
reported and gured a parasphenoid in two adults of the
white-eared opossum, Didelphis albiventris (= Didelphys
azarae) (Fig. 3). It was rod-shaped, 2.5 to 3 mm long, and
situated at the anterior end of the basisphenoid. The pos-
terior end of the parasphenoid was fused to the basisphe-
noid, but anteriorly it ended as a freestanding spine. Fuchs
(1911) also reported that the parasphenoid was absent in an
adult Virginia opossum, Didelphis virginiana (=Didelphys
virginiana), and a philander (presumably an unidentied
species of Philander).
For much of the next quarter century, few authors com-
mented on the observations of a parasphenoid in mammals
made by Parker and Fuchs. An exception was Kampen
(1922: 54) who wrote regarding these authors “ich kann
das Vorkommen aber sowohl bei Didelphys [sic] wie bei
Galeopithecus [sic] bestätigen. [I can conrm the occur-
rence in both Didelphys [sic] as in Galeopithecus [sic].]”
Oddly, Kampen did not provide any rationale as to the ba-
sis of his conrmation of their observations.
Rather than conrmation, Broom (1935) questioned
Fuchs’ identication of a parasphenoid in Didelphis sp.
Yet, as Broom (1935) did not cite any of the four papers
written by Fuchs on the topic (1908, 1910, 1911, 1915), it
is uncertain if Broom was referring to Fuchs’ observation
in the embryos, adults, or both. Broom (1935: 31) stated
“Though this [Fuchs’] observation was made many years
ago it has never so far as I am aware been conrmed. I
Fig. 1.—Skulls in ventral view highlighting the parasphenoid: A, Gaupp’s (1906: g. 383) illustration of a 47 mm long embryo of the sand lizard
Lacerta agilis. Dermal bones have been removed from the specimen’s left side to show the chondrocranium (gray). The well-developed parasphenoid
has a midline anteriorly directed cultriform process and paired posterolateral alae or wings. B, Parker’s (1885: plate 37, g. 6) illustration of a young
Cynocephalus volans (= Galeopithecus philippensis) 20 cm long to root of tail. Cartilage (puce); ossifying chondrocranium (orange); bone (beige). The
reduced parasphenoid is a midline ridge ventral to the basisphenoid.
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 115
have myself years ago searched for it in young specimens
of Didelphys [sic] without success.” Additionally, Broom
(p. 31) noted “Any membrane bones in early ossication
may have little bony centres at their edges which are not in
contact with the more central mass.” He conjectured that
the small ossication seen by Fuchs was merely a detached
part of the more rostrally placed vomer. In his inuential
The Development of the Vertebrate Skull, De Beer (1937)
dismissed Fuchs’ (1908) report on Didelphis sp., because
the same observation was not repeated in other Didel-
phis by Broom (1935) and Toeplitz (1920) (see below).
De Beer (1937) also did not mention the observation of a
parasphenoid in the Philippine colugo by Parker (1885),
even though De Beer cited that paper for other purposes.
Toeplitz (1920) reported on the developing skull in four
pouch young of the common opossum, Didelphis marsu-
pialis; she made no mention of the parasphenoid, but also
did not cite any of Fuch’s papers and, therefore, may have
been unaware of the purported existence of that bone in
Didelphis sp. Given the small size of the parasphenoid in
the Didelphis sp. embryos studied by Fuchs (1908, 1910),
it might be easily overlooked in the study of serial sections
of other embryos.
Coming to the defense of both Fuchs and Parker in 1940
were two paleontologists, Parrington and Westoll. They
acknowledged the presence of a well-developed paras-
phenoid resembling the primitive condition for amniotes
retained in reptiles and synapsids, including non-mamma-
lian cynodonts (Fig. 4A). They proposed an evolutionary
scenario for structures on the skull base in non-mammalian
cynodonts and mammals (Fig. 4) that showed a gradual
reduction of the parasphenoid and then loss “altogether
in normal mammals” (p. 352). They concluded (p. 339)
“that the only satisfactory trace of any parasphenoid el-
ement in mammals, so far as is yet known, is the small
splint of bone found applied to the basisphenoid in certain
individuals of Galeopithecus [sic] and Didelphys [sic].
Considering the relations of this small bone, it is very re-
markable that its claims to be the parasphenoid have been
so overlooked in favour of the extremely dubious claims
of the vomer.” Although they acknowledged the loss of the
parasphenoid in most mammals, they stated (p. 352) “It is
not unlikely that it could be found in other mammals by
systematic searching,” because this part of the skull had
not received adequate attention. The careful reading of the
fossil and extant record by Parrington and Westoll (1940)
Fig. 2.—Fuch’s (1908: g. 1) illustration, modied here, of a cross section through the head of an unidentied species of Didelphis (= Didelphys) embryo
directly in front of the hypophysis. The parasphenoid is ventral to the central stem of the chondrocranium. Bone (black), cartilage (stippled blue), nerves
(stippled yellow), pterygoid muscle (red).
116 annalS of caRneGie muSeum Vol. 85
did not support Broom’s (1935) claim that the parasphe-
noid reported by Fuchs for Didelphis was a detached por-
tion of the vomer. In fact, it is hard to imagine Broom’s
suggestion ever had much credence as Toeplitz’s (1920:
tafelgur 4) illustration of the chondrocranium of Didel-
phis marsupialis shows that the gap between the rear of
the vomer and the inferred position of Fuchs’ parasphe-
noid was too great to support the latter ossication being
derived from the former. In the adult Didelphis albiventris
(Fig. 3), for example, the vomer does not reach posterior to
the choanae, and therefore that bone is separated from the
parasphenoid by the length of the presphenoid.
Since 1940, only a handful of additional reports of a
parasphenoid splint in extant mammals have appeared. As
an independent dermal element, Reinbach (1951) noted a
parasphenoid in an embryo of Didelphis marsupialis, the
same taxon in which Toeplitz (1920) did not report one,
as well as in an embryo of the dwarf armadillo, Zaedyus
pichiy (= Z. minutus) (see also Reinbach 1955) and later an
embryo of Homo sapiens (Reinbach 1967). Kuhn (1971)
made the same observation in an embryo of the African
palm civet, Nandina binotata, as did Presley and Steel
(1978) in their developmental stages of Didelphis vir-
giniana and Sánchez-Villagra and Forasiepi (2017) in a
Didelphis sp. Starck (1956) found a parasphenoid splint
fused to the basisphenoid in a subadult Bactrian camel,
Camelus bactrianus. Lastly, Jollie (1962: g. 3.6) ob-
served and illustrated a splint-like parasphenoid spanning
the suture between the pre- and basisphenoid in a “half-
grown” opossum (presumably a species of Didelphis), but
this bone was not in his gured adult (g. 3.5C).
Few observations of a parasphenoid in fossil mam-
maliaforms have been made since 1940, but included are
representatives of diverse lineages. These reported median
crests vary in extent, thickness, and position, but share a
common attribute, fusion with the basisphenoid, which
highlights the problem of identifying this element as a sep-
arate entity. In basal mammaliaforms, a freestanding cul-
triform process of the parasphenoid, with its posterior end
fused to the basisphenoid, resembling that in non-mam-
malian cynodonts occurs in Early Jurassic Morganucodon
(Kermack et al. 1981). A similar median crest not set off
by sutures occurs in Late Triassic Adelobasileus (Lucas
and Luo 1993), Early Jurassic Sinoconodon (Crompton
and Luo 1993), and Late Jurassic Haldanodon (Ruf et al.
2013), but was identied as part of the basisphenoid by
all of these authors. Among mammals, Kermack (1963)
described for the late Jurassic triconodontid Triconodon
mordax a composite bone formed by the fusion of the para,
basi-, pre-, and alisphenoids plus the pterygoids, with the
parasphenoid represented by the cultriform process. Miao
(1988: 45) described “a small splint of bone” arising from
the midline of the basisphenoid in the late Paleocene mul-
tituberculate Lambdopsalis and interpreted it as a paras-
phenoid remnant despite the lack of delimiting sutures. In
his dissertation on the Early Cretaceous prototribosphe-
nidan Vincelestes, Rougier (1993) interpreted a midline
keel in the mesocranium as a parasphenoid (Fig. 5B), al-
though it was not separated from the basisphenoid by a
suture. Similar structures have been reported in the Late
Cretaceous eutherians Zalambdalestes (Fig. 5C) and Mae-
lestes and interpreted as possible parasphenoids (Wible et
al. 2004, 2009). Lastly, the late Miocene meridiolestidan
Necrolestes has a raised ridge dividing the mesocranium,
with a rod-shaped element in the posterior half interpreted
as a parasphenoid by Wible and Rougier (2017; Fig. 5A).
Given the large role that Didelphis has played in the
history of the parasphenoid in mammals and given the
large number of specimens of that taxon in the Section of
Mammals, Carnegie Museum of Natural History, we de-
cided to study that sample to understand the range of mor-
phologies and their distribution of this enigmatic structure.
What Fuchs (1911, 1915) gured for an adult Didelphis al-
biventris (Fig. 3) was both small enough to be overlooked
by those not specically looking for it and large enough
to be noted by those that were. A case in point is the prior
work of the senior author; Wible (2003) previously pub-
lished on the skull morphology of the Monodelphis sample
Fig. 3.—Fuch’s (1915: g. 167) illustration, modied here, of the
adult skull of Didelphis albiventris (= Didelphys azarae) showing the
parasphenoid.
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 117
in the Section of Mammals and failed to notice a parasphe-
noid, which we correct here. Armed with the search image
provided by Fuchs (1911, 1915), we report here the results
of our study of Didelphis and other marsupials in the Carn-
egie Museum of Natural History.
MATERIALS AND METHODS
We examined 576 specimens of Didelphidae and 115 oth-
er Marsupialia (1 Microbiotheria, 25 Dasyuromorphia, 1
Peremelemorphia, and 88 Diprotodontia) in the Section
of Mammals, Carnegie Museum of Natural History (CM).
Our largest generic sample was Didelphis at 324, and larg-
est specic sample was Didelphis virginiana at 238. The
CM numbers and summary observations of each specimen
are in the Appendices. Of the 17 genera and 87 species
of Didelphidae reported by Wilson and Reeder (2005), we
sampled 11 genera and 27 species, and of the 74 genera
and 244 species of other marsupials (Wilson and Reeder
2005), we sampled 19 genera and 23 species.
We identied each specimen as pouch young, juvenile,
or adult. Pouch young were identied by size, the uniform
nature of their pelt, and dentition with a deciduous upper
third premolar and either no upper molars or the rst mo-
lar erupting; this is equivalent to the immature age class
of Gardner (1973). Juveniles minimally had the upper
Fig. 4.—Parrington and Westoll’s (1940: g. 16) diagram, modied here, showing six possible stages in the evolution of the mammalian palate, high-
lighting the parasphenoid (pink) and vomer (blue). A-D, represent different non-mammalian cynodont conditions (only C was attributed to a named
group, Ictidosauria); E, based on the condition in Cynocephalus volans reported by Parker (1885); F, typical mammalian condition. Abbreviations:
ALSP, alisphenoid; ANG, angular; AR T, articular + prearticular; BOC, basioccipital; BPT, basipterygoid process; BSP, basisphenoid; D, dentary;
ECPT, ectopterygoid; EPPT, epipterygoid; EXOC, exoccipital; MK, Meckel’s cartilage; MX, maxilla; OPOT, opisthotic; PAL, palatine; PMX, pre-
maxilla; PRSP, presphenoid; PROT, prootic; PT, pterygoid; QU, quadrate; SQ, squamosal; S T, stapes; TY, tympanic.
118 annalS of caRneGie muSeum Vol. 85
rst molar in place and maximally the upper fourth molar
erupting. Adults had a full complement of upper teeth with
the upper third premolar and all four upper molars in place.
GWR studied a serially-sectioned head of an 11-day old
Didelphis sp. embryo in the laboratory of Marcelo Sán-
chez-Villagra at the Universität Zürich.
In general, for taxonomic identication, we followed
Wilson and Reeder (2005). However, for Marmosa and
Monodelphis, we followed Voss et al. (2014) and Pavan
and Voss (2016), respectively. The latter authors have
assigned some of the specimens attributed to Monodelphis
brevicaudata by Wible (2003) to Monodelphis arlindoi
and Monodelphis glirina. D’Elía et al. (2016) recently
have named two new species of Dromiciops. The single
CM specimen of this taxon is from a locality that is in the
range of one of these new species, Dromiciops bozinovici.
However, the methods of D’Elía et al. (2016) have been
questioned and new morphological and genetic data sup-
porting monotypy for Dromiciops have been published
in Valladares-Gómez et al. (2017), Martin (2018), and
Suárez-Villota et al. (2018). Consequently, we continue to
follow Wilson and Reeder (2005) in recognizing a single
species, Dromiciops gliroides.
Fig. 5.—Skulls above and mesocrania below in ventral view. A, the late Miocene meridiolestidan Necrolestes patagonensis (after Wible and Rougier
2017: g. 12B); B, the Early Cretaceous prototribosphenidan Vincelestes neuquenianus (after Rougier 1993: g. 41); C, the Late Cretaceous eutherian
Zalambdalestes lechei (after Wible et al. 2004: g. 43). Abbreviations: bs, basisphenoid; pal, palatine; pas, parasphenoid; pt, pterygoid; v, vomer.
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 119
Recognition Criteria
A parasphenoid is most readily identied as an independent,
midline dermal element ventral to the bones of the mesocra-
nial axis, which entails the study of histological sections of
ontogenetic stages to conrm (Fig. 2). We were fortunate to
have access to one such specimen, a Didelphis sp. embryo
(Fig. 6A), which had an independent, midline dermal bone
beneath the chondrocranium at the level of the hypophysis
(Fig. 6B). In agreement with Fuchs (1908), we identify this
ossication as the parasphenoid. This specimen’s parasphe-
noid resembled that in the older embryo of Didelphis sp.
studied by Fuchs (1908) as it was dorsoventrally attened
and not rod-shaped as in the earlier stage. We used the pres-
ence of this intramembranous parasphenoid in the embryo
to identify similarly positioned midline structures as para-
sphenoids in the prepared CM specimens, even though the
pattern of ossication of these structures was not knowable.
The parasphenoid of stem mammals can be used as a
model to suggest that what we recognize here as a paras-
phenoid in extant taxa is likely a remnant of the cultriform
process of other amniotes; as such a spine, crest, or pro-
cess bridging or approximating the area of the transverse
suture between the presphenoid and basisphenoid can be
advanced as a parasphenoid, regardless of its ultimate fate
(i.e., fusion to other bones or not). What we recognize as
parasphenoid can be free (as reported previously in em-
bryos of Didelphis, Zaedyus, Nandina, and Homo, and ju-
venile Philippine colugos), be fused to the basisphenoid
(and/or presphenoid), or be involved in the formation of
a complex and multipartite median crest in the nasopha-
ryngeal region. Given that the parasphenoid is embryo-
logically a separate ossication prior to fusing with the
basisphenoid, in theory at some point a transient suture
should be present. However, determining whether a suture
is present is not always possible, because of the nature of
the anatomical domain; the roof of the nasopharynx is a
conned space and we were not always able to visualize
the contact between the dorsal surface of the parasphenoid
and the ventral surface of the basisphenoid.
Preservational Bias
In didelphids, the parasphenoid is typically small and frag-
ile; in fact, we encountered one example where the free
anterior end of the parasphenoid broke off while trying to
clean the area for photography. We have documented at
least two examples where the freestanding, ossied para-
sphenoid was preserved in situ by dried connective tissue
anchoring it to the skull. We raise the distinct possibility
that the absence of the parasphenoid in our sample indeed
reects its loss in specimens during preparation. This is
similar to the well-known artifactual absence of the ptery-
goids (which are much larger and with a far more extensive
sutural contact) in many didelphid specimens in museum
collections. Therefore, reported absence of the parasphe-
noid here should not be taken as an absolute statement (the
specimen never had it), but as a direct observation of what
is in the collection (this specimen, as preserved in the col-
lection, does not have it).
RESULTS
The nasopharyngeal fossa (Davis 1964) or basipharyngeal
canal (Evans 1993) is the space on the skull base housing
the nasopharynx. It communicates with the nasal cavity
via the choanae (internal nasal aperture) and has a bony
Fig. 6.—Cross section through the mesocranium of Didelphis sp. embryo (ZUIT) at the level of the hypophysis. A, complete section; B, closeup of
nasopharynx roof showing the attened intramembranous parasphenoid. Abbreviations: b, brain; CNV, trigeminal nerve ganglion; cs, central stem of
chondrocranium; D, dentary; hp, hypophysis; Mc, Meckel’s cartilage; nph, nasopharynx; pas, parasphenoid; pt, pterygoid; ton, tongue.
120 annalS of caRneGie muSeum Vol. 85
Fig. 7. Didelphis virginiana, CM 75001, adult female skull in ventral view with closeup of mesocranium. This specimen had no evidence of the para-
sphenoid and exhibited the smooth condition for the basisphenoid. Abbreviations: as, alisphenoid; bo, basioccipital; bs, basisphenoid; cf, carotid fora-
men; fo, foramen ovale; f r, frontal; pal, palatine; ppt, postpalatine torus; pr, promontorium of petrosal; ps, presphenoid; pt, pterygoid; ptc, pterygoid
canal; tc, transverse canal foramen.
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 121
Table 1. Occurrence of basisphenoid and parasphenoid conditions in Didelphis.
Taxon n
Basisphenoid Parasphenoid
smooth furrow depres-
sion absent ridge spine double
spine
D. albiventris 23 56.5% 4.3% 39.1% 69.6% 4.3% 26.1% 0%
D. marsupialis 63 57.1% 0% 42.9% 63.5% 19.0% 14.3% 1.6%
D. virginiana 238 26.4% 2.9% 70.3% 45.0% 27.7% 22.7% 5.0%
Total 324 34.3% 2.5% 63.0% 50.3% 24.4% 20.1% 4.6%
Table 2. Co-occurrence of basisphenoid (BS) and parasphenoid (PS) conditions in Didelphis virginiana. N=237; CM 35817
excluded due to missing information on the basisphenoid condition.
PS\BS Smooth Furrow Depression Total
Absent 49 [20.7%] 3 [1.3%] 55 [23.2%] 107 [45.1%]
Ridge 1 [0.4%] 1 [0.4%] 64 [27.0%] 66 [27.8%]
Spine 7 [3.0%] 2 [0.8%] 44 [18.06%] 53 [22.4%]
Double Spine 5 [2.1%] 1 [0.4%] 5 [2.1%] 11 [4.6%]
Total 62 [26.2%] 7 [3.0%] 168 [70.9%]
Table 3. Occurrence of basisphenoid and parasphenoid conditions in Marmosa.
Taxon n
Basisphenoid Parasphenoid
smooth furrow depres-
sion absent ridge spine double spine
Ma. demerarae 5 100% 0% 0% 100% 0% 0% 0%
Ma. mexicana 93 100% 0% 0% 100% 0% 0% 0%
Ma. murina 18 88.9% 5.6% 5.6% 88.9% 11.1% 0% 0%
Ma. rapposa 6 100% 0% 0% 100% 0% 0% 0%
Ma. robinsoni 10 80% 20% 0% 100% 0% 0% 0%
Total 132 97.7% 2.3% 0.8% 98.5% 1.5% 0% 0%
Table 4. Occurrence of basisphenoid and parasphenoid conditions in Monodelphis.
Taxon n Basisphenoid Parasphenoid
smooth furrow depression absent ridge spine double spine
Mo. arlindoi 7 57.1% 0% 42.9% 42.9% 57.1% 0% 0%
Mo. brevicaudata 2 100% 0% 0% 100% 0% 0% 0%
Mo. dimidiata 4 100% 0% 0% 100% 0% 0% 0%
Mo. domestica 28 92.9% 0% 7.1% 64.3% 10.7% 25% 0%
Mo. glirina 2 100% 0% 0% 100% 0% 0% 0%
Mo. osgoodi 1 100% 0% 0% 100% 0% 0% 0%
Mo. touan 5 100% 0% 0% 40% 60% 0% 0%
Total 49 89.8% 0% 10.2% 63.3% 22.4 14.3% 0%
122 annalS of caRneGie muSeum Vol. 85
roof and lateral walls, and a soft tissue oor formed by the
soft palate. In didelphids, the roof is formed by the bones
of the mesocranial axis, the presphenoid and the basisphe-
noid; the lateral walls are formed by the entopterygoid
processes, which are composed of the pterygoids and the
perpendicular plates of the palatines (Wible 2003; Fig. 7).
We observed four conditions for the parasphenoid and
three for the ventral surface of the anterior part of the ba-
sisphenoid in the marsupials studied. These seven condi-
tions are included below, with summary distributions in
Tables 1–6; the primary data are included in Appendices
1–12.
Parasphenoid
The four conditions of the parasphenoid include an ab-
sence and three conditions of presence, which really rep-
resent a continuum differing in the extent of fusion to the
ventral surface of the bones on the mesocranial axis.
(1) Absent: The parasphenoid either as a separate os-
sication or fused to the basisphenoid surface as reported
in Didelphis albiventris by Fuchs (1911, 1915; Fig. 4) is
absent in all specimens of Caluromys, Chironectes, Gra-
cilinanus, Lutreolina, Marmosops, Metachirus, four of
ve species of Marmosa, ve of seven species of Mono-
delphis, and the entire Australian sample, except one
specimen of Thylogale. The remaining didelphids (except
Thylamys venustus) have some specimens exhibiting evi-
dence for the parasphenoid, but absent in others (Fig. 8).
Absence of the parasphenoid ranges from the low of 0%
(always present) in Thylamys venustus (Table 6) to 88.9%
in Marmosa murina (Table 3); in the species with the larg-
est sample size, Didelphis virginiana, 45.0% of 238 speci-
mens lack a parasphenoid (Tables 1–2; Figs. 7, 8A).
(2) Ridge: The parasphenoid presents as a raised ridge
entirely fused to the basisphenoid surface in some speci-
mens of Didelphis (Figs. 8D, 9A), Marmosa murina,
Monodelphis arlindoi, Monodelphis domestica, Philan-
der, and Thylamys. The percentages range from the low
of 4.3% in Didelphis albiventris (Table 1) to 57.1% in
Monodelphis arlindoi (Table 4) with Didelphis virginiana
at 27.7% (Tables 1–2). In the last taxon, the ridge is be-
tween 1 and 3 mm in length (cf. Figs. 8D, 9A). The ante-
rior border of the ridge can approximate the presphenoid/
basisphenoid suture or be more posteriorly positioned be-
tween the posterior part of the pterygoids. The microbio-
there Dromiciops has a ridge on the basisphenoid, which
we consider separately below.
(3) Spine: The spine is the condition described by Fuchs
(1911, 1915) in two adults of Didelphis albiventris, where
the parasphenoid presents as a raised ridge that is prolonged
anteriorly as a freestanding spine (Fig. 3). Among didel-
phids, we found a spine in some specimens of Didelphis
(Figs. 8E–F, 9B–C), Monodelphis domestica (Fig. 10B),
Philander, and Thylamys (Fig. 10C); outside of Didelphi-
dae, a small spine occurred in one specimen of the macropo-
did Thylogale sp., described separately below. The percent-
ages range from the low of 4.3% in Thylamys elegans to
33.3% in Thylamys venustus (one of three specimens; Table
6) with Didelphis virginiana at 22.7% (Tables 1–2). In the
last taxon, the length of the spine measured from its base
fused to the basisphenoid ranges between 1 and 7 mm. The
anterior tip of the spine can be recessed posteriorly from
the presphenoid/basisphenoid suture, even with it (Figs. 8E,
9B–C), or extend anterior to it (Fig. 8F). In Didelphis vir-
giniana, CM 39792, the parasphenoid base is situated on
both the basisphenoid and presphenoid.
(4) Double spine: A spine occurs on both the anterior and
posterior ends of the parasphenoid in some specimens of Di-
delphis marsupialis, Didelphis virginiana (Fig. 11), Philan-
Table 6. Occurrence of basisphenoid and parasphenoid conditions in Thylamys.
Taxon n Basisphenoid Parasphenoid
smooth furrow depression absent ridge spine double spine
T. cinderella 23 100% 0% 0% 82.6% 13.0% 4.3% 0%
T. pusilla 5 100% 0% 0% 60% 20% 20% 0%
T. venustus 3 100% 0% 0% 0% 33.3% 33.3% 33.3%
Total 31 100% 0% 0% 71.0% 16.1% 9.7% 3.2%
Table 5. Occurrence of basisphenoid and parasphenoid conditions in Philander.
Taxon n Basisphenoid Parasphenoid
smooth furrow depression absent ridge spine double spine
P. opossum 54 81.5% 0% 18.5% 46.3% 7.4% 31.5% 14.8%
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 123
der (Fig. 10A), and Thylamys venustus. The percentages are
between 1.6% in Didelphis marsupialis (Table 1) and 33.3%
in Thylamys venustus (one of three specimens; Table 6), with
Didelphis virginiana at 5.0%. In the last taxon, the length of
the double spine is between 1 and 8 mm. As with the spine
condition, the anterior tip of the double spine can be recessed
posteriorly from the presphenoid/basisphenoid suture (Fig.
11), even with it, or extending anterior to it. In Didelphis
virginiana, CM 57439, the base of the short double spine is
entirely on the presphenoid (Fig. 12), and in CM 23792 and
59667, the double spine is not attached to the skull base but is
freestanding.
Ventral Surface of Basisphenoid
(1) Smooth: The ventral surface of the anterior part of the
Fig. 8.—Didelphis virginiana, adult mesocrania in ventral view. A, CM 75001, female, parasphenoid absent with smooth basisphenoid; B, CM 23800,
sex unknown, parasphenoid absent with furrow on basisphenoid indicated by white arrow; C, CM 61364, male, parasphenoid absent with depression
on basisphenoid indicated by white arrow; D, CM 33653, female, parasphenoid present as ridge (indicated by black arrow) with depression on basi-
sphenoid; E, CM 23801, female, parasphenoid present as spine (indicated by black arrow) with depression on basisphenoid; F, CM 10611, male, paras-
phenoid present as spine extending anterior to basisphenoid/presphenoid suture (indicated by black arrow) with depression on basisphenoid. Pterygoid
anges are preserved only in A. Scale = 2 mm.
124 annalS of caRneGie muSeum Vol. 85
basisphenoid in most extant mammals is relatively smooth
and at (e.g., Euphractus, Wible and Gaudin 2004: g.
1B; Solenodon, Wible 2008; g. 18; Ptilocercus, Wible
2011: gs. 4A, C), that is, essentially featureless (Figs. 7,
8A). In the marsupial sample, the smooth condition oc-
curs both with and without evidence for the parasphenoid.
All specimens of Caluromys, Chironectes, Gracilinanus,
Lutreolina, two of four species of Marmosa, Marmosops,
Metachirus, four of seven species of Monodelphis, and the
entire Australian sample, except one specimen of Thylo-
gale sp., have the smooth condition with no evidence for
the parasphenoid. Nearly all the remaining didelphids have
a mixture of conditions of the basisphenoid substrate and
the parasphenoid, including the smooth basisphenoid sur-
face occurring with and without evidence for the paras-
phenoid. In Didelphis virginiana, of the 45.0% that have
no evidence for the parasphenoid, 45.8% have the smooth
condition, while of the 55.0% with evidence for the para-
sphenoid, 11.0% have the smooth condition. The highest
percentage of smooth condition occurring with the para-
sphenoid is in Philander, where 70.0% of the specimens
with a parasphenoid have a smooth basisphenoid.
(2) Furrow: A small number of didelphid specimens
have a narrow, shallow furrow situated on the basisphe-
noid midline (Fig. 8B). This occurs without evidence for
the parasphenoid in one specimen of Didelphis albiventris
and Marmosa murina, two specimens of Marmosa robin-
soni, and three of Didelphis virginiana. In the last taxon,
the furrow is between 1 and 3 mm in length. Only a single
specimen in the sample has the furrow co-occurring with
the parasphenoid, Didelphis virginiana, CM 59677, where
a freestanding parasphenoid occupies the furrow.
(3) Depression: A larger number of didelphid speci-
mens have a more pronounced depression, generally ci-
Fig. 9.—Didelphis virginiana, mesocrania in ventral view in three ontogenetic stages. A, CM 45503, pouch young female, parasphenoid present as spine
(indicated by black arrow) with smooth basisphenoid, scale = 2 mm; B, CM 33664, juvenile male with dP3 and M1-2, parasphenoid present as spine
(indicated by black arrow) with depression on basisphenoid, scale = 5 mm; C, CM 35819, juvenile male with P3 and M4 erupting, parasphenoid present
as spine (indicated by black arrow) with depression on basisphenoid, scale = 5 mm. Pterygoid anges are broken in all three.
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 125
gar-shaped, longer than wide, situated on the basisphenoid
midline (Fig. 8C). A depression occurs both with and
without evidence for the parasphenoid in Didelphis mar-
supialis, Didelphis virginiana, Monodelphis arlindoi, and
Philander, but occurs only with the parasphenoid in Di-
delphis albiventris, Marmosa murina, and Monodelphis
domestica. In Didelphis virginiana, of the 45.0% that have
no evidence for the parasphenoid, 53.6% have a depres-
sion, while of the 55.0% with evidence for the parasphe-
noid, 86.3% have a depression. In this taxon, the depres-
sion ranges between 1 and 8 mm in length. Its anterior
margin can be recessed posteriorly from the presphenoid/
basisphenoid suture (Figs. 8C–E, 9C), even with it (Figs.
8F, 9B), or on the presphenoid. In Didelphis virginiana,
CM 57439, the depression is entirely on the presphenoid
(Fig. 12). Outside of Didelphidae, only one specimen, the
macropodid Thylogale sp., had a depression (see below).
Sexual Dimorphism and Ontogeny
We investigated the occurrence of the parasphenoid and
basisphenoid morphologies in the Didelphis virginiana
sample to assess any evidence of sexual dimorphism. In our
sample of 238 specimens, 112 are identied as male, 105
as female, and 21 are of unknown sex. Of the 96 specimens
of known sex without the parasphenoid, 44.8% are male
and 55.2% are female. Of the 121 specimens of known sex
with the parasphenoid, 57.0% are male and 43.0% are fe-
male. Of the 58 specimens of known sex with a smooth ba-
sisphenoid, the male/female ratio is equal. Of the 88 speci-
mens of known sex with a furrow or depression, 67.0% are
male and 33.0% are female. We conducted a chi-square
test in PAST (version 3.20; Hammer et al. 2001) to test
for signicance in the differences between the presence/
absence of the parasphenoid and basisphenoid morpholo-
gies by sex (degrees of freedom = 1; alpha level p < 0.05).
The null hypothesis is that the data are drawn from popula-
tions with equal sex distributions. The occurrence of the
parasphenoid is not signicantly correlated with sex (p =
0.31128; Chi2 = 1.0253) nor is the occurrence of the basi-
sphenoid morphologies (smooth vs. furrow/depression) (p
= 0.774; Chi2 = 0.082455).
We also investigated the occurrence of the parasphe-
noid and basisphenoid morphologies in the Didelphis vir-
giniana sample to assess any ontogenetic differences. In
our sample of 238 specimens, nine are identied as pouch
young, 123 as juveniles, and 106 as adults. Regarding the
nine pouch young, the parasphenoid is absent in eight with
a spine present in the ninth (Fig. 9A); the basisphenoid is
smooth in seven and has a depression in two. Regarding
the 123 juveniles, the parasphenoid is absent in 43.9% and
present in 56.1%; the basisphenoid is smooth in 28.5% and
with a depression or furrow in 70.7% (one specimen was
unknown for the basisphenoid condition because it was
obscured by soft tissue). In the 106 adults, the parasphe-
noid is absent in 42.5% and present in 57.5%; the basi-
sphenoid is smooth in 14.1% and with a depression or fur-
row in 85.9%. Our observations show that the presence of
the parasphenoid and different basisphenoid morphologies
occur throughout ontogeny.
An ontogenetic difference that we observed in the Di-
delphis virginiana sample concerned the morphology of
the anterior part of the ventral surface of the basisphenoid.
In the pouch young, the ventral surface of the basisphenoid
is generally at across its breadth, which is of relatively
uniform dimension from anterior to posterior (Fig. 9A).
However, in the juveniles (Figs. 9B–C) and adults (Fig.
8), the anterior end of the basisphenoid is much narrower
than the posterior end and has a midline plateau that var-
ies in shape and elevation. It ranges from columnar (Figs.
8A–B) to goblet-shaped with a narrow stem (Fig. 8F). We
observed the same phenomenon in Didelphis albiventris
and Didelphis marsupialis, whereas in the remaining di-
delphids, the basisphenoid is generally atter or rounder
anteriorly. In other didelphids illustrated here, this is most
readily seen in Thylamys venustus (Fig. 10C); Philander
opossum and Monodelphis domestica (Figs. 10B–C) show
a similar condition but the basisphenoid is partially hidden
by the medially expanded pterygoids.
On a qualitative scale, the ontogenetic changes to the
basisphenoid in Didelphis virginiana seem to account for
much of the proportional increase in the length of the me-
socranium (cf. Figs. 9A and 9B–C). The position of the
presphenoid/basisphenoid suture in the pouch young is
proximate to the choanae, which makes the parasphenoid
more integral to the choanae and the division of the nasal
passageway, while in the juveniles and adults, the presphe-
noid/basisphenoid suture is more caudally located with re-
gards to the choanae, increasing the distance between the
parasphenoid and nasal passageway.
Occurrences in Non-Didelphid Marsupials
Only two marsupial specimens outside of Didelphidae in
our sample have evidence for a parasphenoid, the micro-
biothere Dromiciops gliroides, CM 40621, and the macro-
podid Thylogale sp., CM 13070.
Hershkovitz (1992:199) reported that “A prolongation
of the nasal septum or vomer extends through the mesop-
terygoid fossa as a low sagittal crest of the presphenoid and
forepart of the basisphenoid in Dromiciops, and in no other
marsupial.” Carnegie Museum of Natural History has only
one specimen of Dromiciops, an adult female preserving
sutural detail in the mesocranium (Fig. 13). The speci-
men shows that the median crest reported by Hershkovitz
(1992, 1999; the sphenoid crest of Giannini et al. 2004) is
composed of at least three bones. The anteriormost ele-
ment, the vomer, is the shortest; anteroventrally, it abuts a
midline crest on the palatine to fully separate the choanae
into left and right apertures. The middle element, which
is only slightly longer, is part of the presphenoid and is
overlapped laterally by the left and right pterygoids’ con-
126 annalS of caRneGie muSeum Vol. 85
tribution to the roof of the nasopharynx. The third element,
the longest, is on the basisphenoid and differs from the
other two in that it is thickened ventrally into a rod-like
structure. A recent paper by Sánchez-Villagra and Forasie-
pi (2017: gs. 6a–c) included photomicrographs of cross
sections through the meso- and basicranium in a perinatal
Dromiciops gliroides (head length = 19 mm). Although
not labeled, a at ossication is present ventral to the ba-
sisphenoid in the roof of the nasopharynx (Fig. 14, photo-
micrograph provided by Analía Forasiepi), resembling that
identied as the paraphenoid in Didelphis by Fuchs (1908,
1910; Fig. 2) and here (Fig. 6). Wolfgang Maier (personal
communication) reported to us on the sections and con-
rmed that this ossication is the parasphenoid, which is
fused to the basisphenoid posteriorly. Therefore, the third
element of the median crest preserved in CM 40621 is a
composite of the parasphenoid and basisphenoid.
The juvenile Thylogale sp., CM 13070, differs from
all other Australian marsupials in our sample rst in hav-
ing a depression on the basisphenoid and second in hav-
ing a small spine fused to the basisphenoid in the posterior
aspect of the depression (Fig. 15). This spine is smaller
than those occurring in didelphids and does not taper to
a point. We tentatively interpret the Thylogale spine as a
parasphenoid remnant, but a more denitive statement re-
quires that a larger sample be studied. In addition to this
small spine on the anterior basisphenoid, we discovered
in CM 13070 a longer, posteriorly-directed, midline spine
on the vomer, ventral to the presphenoid, just anterior to
the choanae (Fig. 15). After this discovery, we revisited the
marsupial sample to record the incidence of this more an-
teriorly placed spine. We found an anterior spine only in
some diprotodontians in our sample (43 of 88 specimens).
It is present on the vomer in all the macropodiforms and
Fig. 10.—Other Didelphidae, adult mesocrania in ventral view, highlighting the parasphenoid. A, Philander opossum, CM 110578, female, showing the
double spine condition (indicated by black arrow); B, Monodelphis domestica, CM 80032, male, showing the spine condition (indicated by black arrow);
C, Thylamys venustus, CM 5296, sex unknown, showing the spine condition (indicated by black arrow). Scales = 2 mm.
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 127
in Phascolarctos but absent in Vombatus in the vombati-
forms. In the phalangeriforms, we found a spine absent in
Cercartetus, Petaurus, Tarsipes, and Acrobates, and pres-
ent in Trichosurus, Petauroides, and Pseudocheirus. In
these three taxa, the left and right pterygoids meet on the
midline underlying the vomer and the spine is formed on
the posterior margin of the pterygoids. Pseudocheirus dif-
fers in that the spine has a dual origin, the pterygoids and
vomer.
Phylogeny
Wilson and Reeder (2005) recognized 379 species of
extant marsupials distributed in seven orders. The CM
collection holds only 50 species from ve orders; unrep-
resented are the orders Paucituberculata and Notorycte-
morphia. Despite the limitations in our sample size, both
regarding species coverage and numbers of specimens per
species, and preservational bias (see Materials and Meth-
ods), we assessed the distribution of the parasphenoid as
preserved in the CM sample in a phylogenetic context. As
no published phylogenetic analysis included all the taxa
in our sample, we compiled a tree based on the recent lit-
erature (Fig. 16). We follow Voss and Jansa (2009), Giarla
et al. (2010), Voss et al. (2014), and Pavan and Voss (2016)
for relationships within Didelphimorphia, Westerman et al.
(2016) for relationships within Dasyuromorphia, Meredith
et al. (2008, 2009) for relationships within Diprotodontia,
and Mitchell et al. (2014) for relationships between the ma-
jor groups. On that tree, we highlighted the incidence at the
specic level of the parasphenoid, whether ridge, spine, or
double spine, and no matter what the percentage of occur-
rence. If our sample truly reects the morphological pattern,
a spotty distribution is revealed, supporting either multiple
losses or reacquisitions of the parasphenoid. However, we
acknowledge that imparting any phylogenetic component to
these data is premature and awaits a dedicated survey with
larger sample sizes from a broader taxonomic spectrum.
DISCUSSION
Prior to our study, the only report of a parasphenoid in
adult marsupials was a parasphenoid spine fused to the ba-
sisphenoid in two Didelphis albiventris by Fuchs (1911,
Fig. 11.—Didelphis virginiana, CM 35817, juvenile with dP3, P3 erupting, and M1-2, skull in oblique ventral view highlighting the double spine condi-
tion of the parasphenoid. Pterygoid anges are broken. Scale = 5 mm.
128 annalS of caRneGie muSeum Vol. 85
1915; Fig. 3). We have made similar observations (Figs.
8D–E, 9–10), that is, a ridge, spine, or double spine fused
to the basisphenoid, in juveniles and/or adults from ten of
the 27 didelphid species studied: Didelphis albiventris,
Didelphis marsupialis, Didelphis virginiana, Marmosa
murina, Monodelphis arlindoi, Monodelphis domestica,
Philander opossum, Thylamys elegans, Thylamys pusilla,
and Thylamys venustus. Of these ten species, only one,
Thylamys venustus, has 100% incidence of the parasphe-
noid, but with n = 3 (Table 6); the others have a variable
incidence, ranging from 11.1% presence in Marmosa mu-
rina (Table 3) to 57.1% in Monodelphis arlindoi (Table 4).
However, sample sizes for most of the 27 didelphid spe-
cies studied are generally small, with only four represented
by more than 50 specimens. It seems likely that with ad-
ditional study the incidence of this structure will continue
to be variable within species, because of the remarkable
range of morphologies we encountered concerning its size,
shape, and position as well as that of the skull base sub-
strate.
In addition to replicating Fuchs’ (1911, 1915) observa-
tion in adult Didelphis, our study provides support for his
identication of this structure as a parasphenoid remnant.
There are two possible explanations for this structure as it
occurs in our sample: as an independent element fused to
the skull base or as an outgrowth from the skull base. Em-
bryology clearly supports the former, as in the few avail-
able histological studies of didelphids (i.e., Didelphis sp.,
Fuchs 1908, 1910; Sánchez-Villagra and Forasiepi 2017;
Didelphis marsupialis, Reinbach 1951; Didelphis virgin-
iana, Presley and Steel 1978), the element in question is of
independent intramembranous origin (Fig. 6). The vomer
and parasphenoid are the only candidate midline dermal
elements (Parrington and Westoll 1940), and the vomer is
already accounted for positioned far anteriorly in the nasal
cavity (Didelphis marsupialis, Toeplitz 1920; Monodel-
phis domestica, Rowe et al. 2005). The fact that we found
two instances, in a juvenile and an adult Didelphis virgin-
iana, where the double spine condition was held to the ba-
sisphenoid only by connective tissue is further support for
the independent origin of the remaining instances where
the structure is fused to varying degrees to the basisphe-
noid and/or presphenoid.
We also have reported the presence of a parasphenoid in
two non-didelphid marsupials, the microbiothere Dromi-
ciops gliroides and the macropodid Thylogale sp. In the
former, the nasopharyngeal fossa is divided by a midline
septum, which in the one specimen in our sample has su-
tures delimiting three contributing elements, vomer, pre-
sphenoid, and basisphenoid (Fig. 13). Photomicrographs
of a perinatal Dromiciops published by Sánchez-Villagra
and Forasiepi (2017: gs. 6a–c) show that the last of these
three elements includes the parasphenoid (Fig. 14), which
is fused to the basisphenoid posteriorly. In Thylogale sp.,
the element in question, a tiny splint of bone in a depression
on the basisphenoid (Fig. 15), has a general resemblance
to the didelphid parasphenoid. However, as none of the 31
other macropodids in our sample had any surface features
on the basisphenoid whatsoever, we tentatively identify
this structure as a parasphenoid in Thylogale sp.
Among marsupials, Didelphis has been the subject of
more treatments on aspects of cranial anatomy than any
other taxon. In the mesocranium, soft tissues have been
studied extensively, including the muscles of mastication,
pharynx, soft palate, and tongue (e.g., Coues 1872; Kon-
stanecki 1891; Hiiemae and Jenkins 1969; Turnbull 1970;
Crompton et al. 1977; Hiiemae and Crompton 1985; Diogo
et al. 2016). These studies show that, as is typical in mam-
mals (Smith 1992), the nasopharynx lies ventral to the ba-
sisphenoid with the rear of that space at a level posterior to
the hypophyseal fossa (see Hiiemae and Jenkins 1969: g.
10D). There are no muscles attached to the ventral surface
of the basisphenoid (see Hiiemae and Jenkins 1969: g.
Fig. 12.—Didelphis virginiana, CM 57439, adult male, mesocranium in
ventral view showing the elongate depression on the basisphenoid ex-
tending anteriorly onto the presphenoid and the small double spine of
the parasphenoid fused to the presphenoid (indicated by black arrow).
Pterygoid anges are broken. Scale = 5 mm.
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 129
8); the closest are the pharyngeal muscles, the pterygopha-
ryngeus and palatopharyngeus, which arise from the ptery-
goid and soft palate, respectively (in Didelphis virginiana
these muscles occur in place of the superior pharyngeal
constrictor, which is absent; Diogo et al. 2016). Therefore,
the parasphenoid remnant in Didelphis does not provide
muscle attachment, but merely lies in the roof of the na-
sopharynx. The function of such a structure that in our
sample is so variably present and expressed regarding size
and position is unclear to us. Histological sections in an
embryo Didelphis marsupialis (Reinbach 1951: g. 4) and
Didelphis sp. (Fig. 6) show the parasphenoid embedded
in a layer of soft tissue; at the bare minimum, the bone’s
presence provides ancillary support for a subdivision of
the roof of the nasopharynx. No doubt the more substan-
tial septum occurring in Dromiciops (Figs. 13–14) adds
epithelial surface area in the nasopharynx, which might
warm and/or humidify respired air, and the prolongation
of the nasal septum into the nasopharynx might enhance
respiration by smoothing and directing airow. In fact, the
delicate spine on the vomer and/or pterygoid that we found
in some diprotodontians (Fig. 15) might have similar func-
Fig. 13.—Dromiciops gliroides, CM 40621, adult female, skull in oblique ventrolateral view with closeup of the mesocranium. The posteroventral edges
of the left and right pterygoid bones are broken and most of the pterygoid anges are missing. The three elements contributing to the midline crest in the
basipharyngeal canal are indicated. Abbreviations: bs, basisphenoid; pas, parasphenoid; ps, presphenoid; pt, pterygoid; v, vomer.
130 annalS of caRneGie muSeum Vol. 85
tions on a smaller scale because it is continuous with and
prolongs the nasal septum. However, we cannot postulate
the same explanations for the didelphid parasphenoid rem-
nant as it is so broadly separated from the nasal septum and
would add little epipthelial surface area.
If the presence of parasphenoid is regarded as a primi-
tive mammalian feature, a view we support here, the para-
sphenoid may not be functionally signicant, but rather
an atavistic remnant of a more prominent primitive fea-
ture. The cultriform process of early non-mammalian
cynodonts (Fig. 17A) is the likely homolog of the mam-
malian parasphenoid, the alae covering the basisphenoid
ventrally being lost. In advanced non-mammalian cyn-
odonts (e.g., brasilodontids, Rodrigues et al. 2013; Ruf
et al. 2014; pachygenelids, Martinelli and Rougier 2007;
Figs. 17B–C), the cultriform process bridges the mesocra-
nium as a narrow, knife-like bony projection dividing the
interpterygoid vacuity and providing ventral support to the
interorbital septum (Martinelli and Rougier 2007; Cromp-
ton et al. 2017). With the progressive expansion of the ros-
tral portion of the braincase, the presphenoid eventually
reaches the ventral level of the skull base, wedging itself
between the pterygoids and establishing an extensive con-
tact with the basisphenoid. This transformation obliterated
the interorbital septum (Martinelli and Rougier 2007; Fig.
17D) and likely rendered the parasphenoid functionally re-
dundant, except perhaps for playing a role in the division
of the nasopharynx.
We nish by setting the record straight regarding the
incidence of the parasphenoid in mammals as there is
currently confusion and controversy, ranging from the
element said to be broadly present to entirely absent. In
his book Vertebrate Paleontology and Evolution, Carroll
(1988: 403) stated that “the parasphenoid appears as a sep-
arate ossication in most mammals.” In a recent review ar-
ticle on the parasphenoid in vertebrates, Atkins and Franz-
Odendaal (2016) reported that among mammals this bone
is present in monotremes and marsupials but is absent in
placentals. The well-known German morphologist Diet-
rich Starck in his 1967 review article on the mammalian
skull in the Traité de Zoologie summarized the literature to
that time noting the few instances that a parasphenoid was
described: in one marsupial (Didelphis, Fuchs 1908) and
three placentals (Cynocephalus, Parker 1885; Zaedyus,
Reinbach 1951; Camelus, Starck 1956). In The Mamma-
lian Skull, Moore (1981: 102) wrote “the parasphenoid is
lacking in the mammalian skull.”
Regarding extant monotremes, none of the many au-
thors reporting on ontogenetic stages for either Tachyglos-
sus or Ornithorhynchus (e.g., Gaupp 1908; Watson 1916;
De Beer and Fell 1936; Kuhn 1971; Presley and Steel
1978; Zeller 1989) have found a midline element beneath
the basisphenoid that could be interpreted as a parasphe-
noid. In his monograph on skull development of Ornitho-
rhynchus, Zeller (1989) reiterated the absence of a para-
sphenoid in extant monotremes, but noted that its absence
was a departure from the expected primitive mammalian
and therian conditions. Kuhn (1971) in his monograph on
skull development of Tachyglossus made a curious obser-
vation; he found a very thick layer of connective tissue
in the area where a parasphenoid would be expected but
no bone. He stated (p. 142) “Man hat den Eindruck daß
es im Gebiet vor dem Canalis craniopharyngeus noch zu
Verknöcherung in dieser Schicht kommen könnte. [One
has the impression that in the area in front of the Cana-
lis craniopharyngeus ossication could still come in this
layer.]” Ultimately, Kuhn (1972) seemed surprised that he
did not nd a parasphenoid in the Tachyglossus specimens
Fig. 14.—Photomicrograph of cross-section of Dromiciops gliroides (Universität Tübingen, collection of W. Maier from the former Zoologisches Insti-
tut; head length = 19 mm; section 24.01.01) in the mesocranium. The at intramembranous ossication in the roof of the nasopharynx is interpreted as
the parasphenoid. Abbreviations: b, brain; cs, central stem of chondrocranium (cartilage between pre- and basisphenoid); D, dentary; nph, nasopharynx;
on, optic nerve; pas, parasphenoid; pt, pterygoid; ton, tongue.
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 131
that he studied and left the door open about the occurrence
of this bone in monotremes.
There is a source for confusion on the parasphenoid
in monotremes in the older literature. In his monograph
on the development of the skull of Tachyglossus, Gaupp
(1908) used the term parasphenoid and described one in
the echidna. However, this was a paired element, not a
midline one. Gaupp (1908) used parasphenoid as equiva-
lent to his Säugerpterygoid (Gaupp 1905), which accord-
ing to Parrington and Westoll (1940) and Presley and Steel
(1978) is the pterygoid bone. Clark and Smith (1993) re-
peated Gaupp’s observation of this (paired) parasphenoid
in the echidna, and Atkins and Franz-Odendaal (2016)
used Clark and Smith (1993) as the source for the pres-
ence of a parasphenoid in monotremes. Contra Clark and
Smith (1993) and Atkins and Franz-Odendaal (2016), a
Fig. 15.—Thylogale sp., CM 13070, skull of juvenile of unknown sex in ventral view with closeup of mesocranium angled to show the rear of the nasal
cavity. The probable parasphenoid spine (indicated by the black arrow) is situated in the rear of a depression on the basisphenoid; anterior to it is the
posteriorly directed midline spine on the vomer (indicated by the white arrow).
132 annalS of caRneGie muSeum Vol. 85
parasphenoid is not known to date for extant monotremes.
Although not known in extant monotremes, we raise
the possibility that a parasphenoid occurs in the Miocene
platypus Obdurodon. In illustrations of the skull (Archer et
al. 1993: g. 7.3; Musser and Archer 1998: g. 1b), a well-
developed midline ridge divides the mesocranium, extend-
ing from the choanae to the level of the carotid foramina.
Labeled as presphenoid by Archer et al. (1993: g. 7.3),
this structure resembles the well-developed midline sep-
tum in Dromiciops (Fig. 13) and the Miocene meridolesti-
dan Necrolestes (Fig. 5A), both of which are interpreted as
including a parasphenoid. The sagittal slice movie of the
Fig. 16.—Phylogenetic tree depicting the relationships of the taxa in our sample, highlighting (in pink) the occurrence of the parasphenoid at the spe-
cic level, compiling together the ridge, spine, and double spine conditions. The relationships in the tree are based on Voss and Jansa (2009), Giarla
et al. (2010), Voss et al. (2014), and Pavan and Voss (2016) within Didelphimorphia, Westerman et al. (2016) within Dasyuromorphia, Meredith et al.
(2008, 2009) within Diprotodontia, and Mitchell et al. (2014) between the major groups.
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 133
Fig. 17.—Mesocrania in ventral view. A, the probainognathian Probainognathus jenseni; B, the pachygenelid Chaliminia musteloides; C, the brasilo-
dontid Brasilitherium riograndensis; and D, the morganucodontid Morganucodon sp. Redrawn from Martinelli and Rougier (2007: gs. 5C, D, E, G).
Not to scale. Abbreviations: bs, basisphenoid; cp, cultriform process; pt, pterygoid.
134 annalS of caRneGie muSeum Vol. 85
CT scan of Obdurodon on the DigiMorph website (http://
www.digimorph.org/specimens/Obdurodon_dicksoni/)
appears to support this ridge as a separate element as a
suture delimits it from the overlying skull base (see slices
244-248). If, as supported here, the presence of the para-
sphenoid is primitive for Mammalia, its occurrence in an
extinct monotreme would not be surprising.
Regarding extant marsupials, we have shown in this pa-
per that the parasphenoid has a spotty distribution within
the clade, both above and below the specic level (Fig.
16; Tables 1–6; Appendices 1–12). The only source used
by Atkins and Franz-Odendaal (2016) that included any
information on marsupials was Kardong (2006), a com-
parative vertebrate anatomy textbook. Kardong (2006) did
not discuss the distribution of the parasphenoid in mam-
mals, but illustrated a skull in ventral view of Didelphis
(his g. 7.51b) after Carroll (1988: g. 18–3b). The at
anterior part of the basisphenoid has a label indicating a
parasphenoid; although the label is in the same area as the
element indicated by Fuchs (1911, 1915; Fig. 3), there is
no raised structure showing. It was a giant leap by Atkins
and Franz-Odendaal (2016) to take this gure as evidence
that marsupials have a parasphenoid. Contra Atkins and
Franz-Odendaal (2016), a parasphenoid remnant is known
to occur in some but not all extant marsupials, and is both
variably present and expressed in size and position.
Regarding extant placentals, Starck (1967) was correct
in his summary of the few instances of reports of a para-
sphenoid in this group, although observations in a human
embryo and embryo of Nandinia were subsequently added
by Reinbach (1967) and Kuhn (1971), respectively. Ad-
ditionally, a parasphenoid has been said to occur in two
stem placentals, Late Cretaceous Zalambdalestes (Wible
et al. 2004; Fig. 5C) and Maelestes (Wible et al. 2009).
For their observation of the total absence of a parasphe-
noid in placentals, Atkins and Franz-Odendaal (2016) used
as support the textbook Human Osteology by White et al.
(2011), presumably because it does not contain an entry for
parasphenoid. Obviously, that source was not sufcient to
characterize Placentalia.
The fossil record of non-therian and non-monotreme
mammals has improved dramatically in the last twenty
years (Kielan-Jaworowska 2013) and complete or partial
skulls are now known for most of the major groups repre-
senting stem-therian diversity. Utilizing the same criteria
applied here for didelphids would lead to recognize crests
and ridges in suitable position to be called parasphenoid in
morganucodontids, docodonts, triconodonts, multituber-
culates, and meridiolestids. A bona de cultriform process
bisecting an interpterygoid vacuity is also present in the
close sister groups of Mammaliaformes (Martinelli and
Rougier 2007; Crompton et al. 2017), but a distinct suture
delimiting an independent bone is missing and its fusion
to the basisphenoid in adult stages seems to be a condition
acquired early in cynodont phylogeny.
In summary, we regard the presence of the parasphenoid
as a primitive feature for Mammalia. However, given the
extensive ontogenetic study of monotremes to date, we ac-
cept the absence of the parasphenoid in the extant members
of this group as an autapomorphy. However, if the Miocene
platypus Obdurodon has a parasphenoid as suggested here,
this element could have been lost independently in the ex-
tant platypus and echidnas. We have shown in this report
a variable distribution for the parasphenoid within extant
Marsupialia and expressed that more research on this struc-
ture is needed to better characterize its incidence. The same
must be said for extant Placentalia where an even smaller
percentage of the vaster diversity has been investigated in
both pre- and postnatal stages for a structure thus far record-
ed for only ve extant taxa.
ACKNOWLEDGMENTS
In the Section of Mammals, Carnegie Museum of Natural History, we
thank Suzanne McLaren, Lisa Miriello, and Marion Burgwin for help
with the marsupial database and specimens, and Paul Bowden for his
masterful artwork. We also thank Robert Voss, American Museum of
Natural History, for his continued research on the small opossums in the
CM collection; Rebecca German, Northeast Ohio Medical University,
for leads on possible functional implications; Marcelo Sánchez-Villagra,
Universität Zürich, for access to the embryo of Didelphis sp. in Figure
6; Analía Forasiepi, IANIGLA, CCT-Mendoza, CONICET, for the pho-
tomicrographs of the perinatal Dromiciops gliroides in Figure 14; and
Wolfgang Maier, Universität Tübingen, for conrming the presence of
the parasphenoid in cross sections of the perinatal Dromiciops gliroides.
The contents of this manuscript were improved by reviews by A. Forasie-
pi and W. Maier. Support for this research is from National Science Foun-
dation Grant DEB 1654949, the R.K. Mellon North American Mammal
Research Institute, and PICT-2016-3682 from the Agencia de Promoción
Cientifíca y Técnica, Argentina.
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aPPenDix 1
Caluromys
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Caluromys derbianus
51988 M juvenile 0 0
119051 ? adult 0 0
Caluromys philander
4680 F adult 0 0
52689 M adult 0 0
52690 F adult 0 0
aPPenDix 2
Chironectes
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Chironectes minimus
4455 F adult 0 0
6047 F adult 0 0
98580 F adult 0 0
119053 F adult 0 0
138 annalS of caRneGie muSeum Vol. 85
aPPenDix 3
Didelphis
(continued on next page)
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis albiventris
5277 M juvenile 0 0
42772 F adult 0 0
52695 M juvenile 0 0
78203 M adult 0 0
80002 M juvenile 0 0
80005 F adult 0 0
80009 ? adult 0 0
80010 M adult 0 0
80011 ? adult 0 0
80007 F adult 0 1
5086 F adult 0 2
42774 M juvenile 0 2
80004 F juvenile 0 2
80008 M juvenile 0 2
80013 F juvenile 0 2
5263 M juvenile 1 2
5284 M juvenile ^2 0
80012 M juvenile 2 0
80006 F adult 2 0
42773 F juvenile 2 2
78204 F adult 2 2
80003 M juvenile 2 2
Didelphis marsupialis
677 ? adult 0 0
1024 M juvenile 0 0
1026 M adult 0 0
1039 ? juvenile 0 0
1753 M adult 0 0
1959 M juvenile 0 0
3943 F juvenile 0 0
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 139
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis marsupialis (continued)
6341 M adult 0 0
6350 M adult 0 0
52696 F adult 0 0
52697 F adult 0 0
52698 F juvenile 0 0
52706 F adult 0 0
52710 M juvenile 0 0
52713 F juvenile 0 0
52716 F adult 0 0
52724 F adult 0 0
68341 M adult 0 0
69802 F adult 0 0
78209 ? adult 0 0
97165 ? juvenile 0 0
110564 F adult 0 0
119056 F juvenile 0 0
119057 F juvenile 0 0
705 M adult 0 2
1005 F adult 0 2
1027 F adult 0 2
1962 M adult 0 2
3587 F adult 0 2
6337 M adult 0 2
52701 M adult 0 2
52704 F adult 0 2
52705 F adult 0 2
52712 M juvenile 0 2
55553 M adult 0 2
55554 M adult 0 2
63501 F juvenile 0 2
63502 F juvenile 0 2
aPPenDix 3
Didelphis
(continued from previous page)
140 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis marsupialis (continued)
110566 F adult 0 2
110567 F juvenile 0 2
6048 M adult 1 0
63170 M adult 1 0
110568 F adult 1 0
119054 F juvenile 1 0
712 ? adult 1 2
6346 M adult 1 2
10577 M adult 1 2
52700 F adult 1 2
52702 F adult 1 2
52707 M adult 1 2
52726 F juvenile 1 2
110563 F juvenile 1 2
656 ? adult 2 0
1023 M adult 2 0
52711 M juvenile 2 0
52715 F adult 2 0
52725 F adult 2 0
92705 F adult 2 0
110565 M adult 2 0
112151 M juvenile 2 0
52703 M juvenile ^2 2
52708 M adult 2 2
52709 M adult 2 2
Didelphis virginiana
634 F juvenile 0 0
7885 M juvenile 0 0
8449 F adult 0 0
10214 M juvenile 0 0
aPPenDix 3
Didelphis
(continued from previous page)
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 141
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis virginiana (continued)
12972 M juvenile 0 0
13002 F juvenile 0 0
17982 M adult 0 0
18230 F adult 0 0
18231 M juvenile 0 0
18311 F juvenile 0 0
23789 M juvenile 0 0
23793 M juvenile 0 0
23798 F juvenile 0 0
23808 M pouch young 0 0
23809 M pouch young 0 0
23811 M pouch young 0 0
23812 F pouch young 0 0
23813 F pouch young 0 0
23814 F pouch young 0 0
27660 M adult 0 0
27662 F juvenile 0 0
30488 M adult 0 0
30490 F adult 0 0
30495 F juvenile 0 0
30496 F adult 0 0
30503 M juvenile 0 0
30509 F adult 0 0
30511 F juvenile 0 0
30512 M adult 0 0
30517 M juvenile 0 0
30519 F juvenile 0 0
33651 M juvenile 0 0
33652 F juvenile 0 0
33655 M juvenile 0 0
33656 F juvenile 0 0
aPPenDix 3
Didelphis
(continued from previous page)
142 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis virginiana (continued)
33667 M juvenile 0 0
33669 ? adult 0 0
35820 M juvenile 0 0
39795 ? juvenile 0 0
50268 F adult 0 0
55556 ? adult 0 0
59659 F adult 0 0
59999 M juvenile 0 0
61886 M juvenile 0 0
75001 F adult 0 0
81771 ? adult 0 0
110564 F juvenile 0 0
110571 M juvenile 0 0
119058 M juvenile 0 0
7889 F juvenile 0 1
23800 ? adult 0 1
92405 F adult 0 1
1418 ? juvenile 0 2
2224 M juvenile 0 2
6416 F adult 0 2
10031 M juvenile 0 2
10447 F juvenile 0 2
16473 F adult 0 2
16476 ? adult 0 2
16477 F adult 0 2
18127 M juvenile 0 2
18375 F juvenile 0 2
18621 ? adult 0 2
19375 F juvenile 0 2
21410 F adult 0 2
22178 F juvenile 0 2
aPPenDix 3
Didelphis
(continued from previous page)
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 143
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis virginiana (continued)
22565 F adult 0 2
23791 F adult 0 2
23795 ? adult 0 2
23799 M adult 0 2
23802 ? juvenile 0 2
23803 F juvenile 0 2
23805 M adult 0 2
23806 F adult 0 2
23807 M pouch young 0 2
23810 F pouch young 0 2
27650 M adult 0 2
27654 M adult 0 2
27655 F adult 0 2
27656 F adult 0 2
30475 F juvenile 0 2
30478 M adult 0 2
30492 F juvenile 0 2
30497 F juvenile 0 2
30498 F adult 0 2
30499 F juvenile 0 2
30510 F adult 0 2
30515 M adult 0 2
30516 M adult 0 2
30518 M juvenile 0 2
33648 M juvenile 0 2
33660 F juvenile 0 2
33661 F adult 0 2
33665 M juvenile 0 2
33668 F juvenile 0 2
35824 M adult 0 2
35825 M juvenile 0 2
aPPenDix 3
Didelphis
(continued from previous page)
144 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis virginiana (continued)
39790 M juvenile 0 2
39792 M adult 0 2
40594 M juvenile 0 2
55557 F adult 0 2
59651 F adult 0 2
60000 F juvenile 0 2
81783 M juvenile 0 2
83428 ? adult 0 2
102670 M juvenile 0 2
102689 M juvenile 0 2
33647 M juvenile 1 0
55555 M adult 1 1
1417 ? juvenile 1 2
7813 M juvenile 1 2
9739 F juvenile 1 2
9740 F juvenile 1 2
11298 ? juvenile 1 2
12904 M adult 1 2
12971 M juvenile 1 2
14998 F juvenile 1 2
16474 F juvenile 1 2
16475 F juvenile 1 2
16478 M adult 1 2
17529 M adult 1 2
18622 ? adult 1 2
19351 F juvenile 1 2
19705 M juvenile 1 2
22153 F adult 1 2
22172 F adult 1 2
22501 ? juvenile 1 2
22564 ? adult 1 2
aPPenDix 3
Didelphis
(continued from previous page)
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 145
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis virginiana (continued)
22572 M adult 1 2
23797 M adult 1 2
23804 F adult 1 2
27649 F juvenile 1 2
27658 M adult 1 2
30474 F juvenile 1 2
30476 M adult 1 2
30480 M juvenile 1 2
30481 F juvenile 1 2
30482 M adult 1 2
30483 M adult 1 2
30486 F adult 1 2
30489 M adult 1 2
30493 M adult 1 2
30494 F juvenile 1 2
30500 F adult 1 2
30502 F adult 1 2
30505 F adult 1 2
30507 M adult 1 2
30508 M adult 1 2
33364 F adult 1 2
33653 F adult 1 2
33654 F adult 1 2
33658 M juvenile 1 2
33659 M juvenile 1 2
33663 F juvenile 1 2
33666 M juvenile 1 2
35821 F juvenile 1 2
35823 F adult 1 2
37234 F juvenile 1 2
37236 M adult 1 2
aPPenDix 3
Didelphis
(continued from previous page)
146 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis virginiana (continued)
39789 M juvenile 1 2
39793 F adult 1 2
39794 M adult 1 2
55199 F juvenile 1 2
59675 F adult 1 2
61364 M adult 1 2
61916 M juvenile 1 2
81780 F juvenile 1 2
81786 M juvenile 1 2
90002 F adult 1 2
93570 M juvenile 1 2
95915 M juvenile 1 2
106577 M juvenile 1 2
110570 F adult 1 2
13001 F juvenile 2 0
18376 M juvenile 2 0
23792 F juvenile *2 0
30514 M adult 2 0
35826 F adult 2 0
45503 F pouch young 2 0
59998 M adult 2 0
81785 F juvenile 2 0
94311 M adult 2 0
110572 M juvenile 2 0
117001 F adult 2 0
118516 F juvenile 2 0
23796 ? juvenile 2 1
35827 M adult 2 1
59667 F adult *2 1
7655 M adult 2 2
8486 F adult 2 2
aPPenDix 3
Didelphis
(continued from previous page)
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 147
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis virginiana (continued)
39789 M juvenile 1 2
39793 F adult 1 2
39794 M adult 1 2
55199 F juvenile 1 2
59675 F adult 1 2
61364 M adult 1 2
61916 M juvenile 1 2
81780 F juvenile 1 2
81786 M juvenile 1 2
90002 F adult 1 2
93570 M juvenile 1 2
95915 M juvenile 1 2
106577 M juvenile 1 2
110570 F adult 1 2
13001 F juvenile 2 0
18376 M juvenile 2 0
23792 F juvenile *2 0
30514 M adult 2 0
35826 F adult 2 0
45503 F pouch young 2 0
59998 M adult 2 0
81785 F juvenile 2 0
94311 M adult 2 0
110572 M juvenile 2 0
117001 F adult 2 0
118516 F juvenile 2 0
23796 ? juvenile 2 1
35827 M adult 2 1
59667 F adult *2 1
7655 M adult 2 2
8486 F adult 2 2
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis virginiana (continued)
10199 F juvenile 2 2
10611 M adult 2 2
12903 M juvenile 2 2
17556 F juvenile 2 2
18623 ? juvenile 2 2
18753 M juvenile 2 2
19665 M juvenile 2 2
23790 F juvenile 2 2
23794 M juvenile 2 2
23801 F adult 2 2
27653 F adult 2 2
27657 F juvenile 2 2
27659 M adult 2 2
27661 M adult 2 2
27663 M juvenile 2 2
27664 F adult 2 2
30477 M adult 2 2
30479 M adult 2 2
30484 M juvenile 2 2
30485 F juvenile 2 2
30487 M juvenile 2 2
30491 M juvenile 2 2
30501 M adult 2 2
30504 F adult 2 2
30506 M adult 2 2
30513 M adult 2 2
33625 M juvenile 2 2
33657 F juvenile 2 2
33662 M juvenile 2 2
33664 M juvenile 2 2
35817 M juvenile 2 2
aPPenDix 3
Didelphis
(continued from previous page)
148 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Didelphis virginiana (continued)
35818 M juvenile 2 2
35819 M juvenile 2 2
35822 M juvenile 2 2
35828 M adult 2 2
37238 M adult 2 2
39397 ? adult 2 2
39791 F juvenile 2 2
45501 ? juvenile 2 2
57439 M juvenile 2 2
60769 F juvenile 2 2
61917 F adult 2 2
81782 F juvenile 2 2
81784 F adult 2 2
89169 M adult 2 2
102688 M juvenile 2 2
106403 M adult 2 2
3214 ? juvenile 2 ?
aPPenDix 3
Didelphis
(continued from previous page)
aPPenDix 4
Gracilinaus
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Gracilinanus agilis
1854 M juvenile 0 0
80015 F adult 0 0
Gracilinanus dryas
70720 F adult 0 0
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 149
aPPenDix 5
Lutreolina
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Lutreolina crassicaudata
42775 M adult 0 0
42776 F adult 0 0
42778 M adult 0 0
aPPenDix 6
Marmosa
(continued on next page)
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Marmosa sp.
5244 F adult 0 0
86374 F juvenile 0 0
Marmosa demerarae
63503 M adult 0 0
63504 M adult 0 0
63505 F juvenile 0 0
68342 F adult 0 0
68343 M juvenile 0 0
Marmosa mexicana
90003 M juvenile 0 0
110581 M adult 0 0
110582 M adult 0 0
110583 M adult 0 0
110584 F adult 0 0
110585 M adult 0 0
110586 M adult 0 0
110587 F adult 0 0
110588 M adult 0 0
150 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Marmosa mexicana (continued)
110589 F adult 0 0
110590 M adult 0 0
112861 F adult 0 0
112862 F adult 0 0
112863 M adult 0 0
112864 M adult 0 0
112865 F adult 0 0
112867 M adult 0 0
112868 F adult 0 0
112869 M adult 0 0
112870 M adult 0 0
112871 F adult 0 0
112872 F adult 0 0
112873 M adult 0 0
112874 F adult 0 0
112875 M adult 0 0
112876 M adult 0 0
112877 F adult 0 0
114482 M adult 0 0
114483 M adult 0 0
114484 M adult 0 0
114485 M adult 0 0
114486 M adult 0 0
114487 F juvenile 0 0
114488 F juvenile 0 0
114489 M adult 0 0
114490 M adult 0 0
114491 F adult 0 0
114492 F adult 0 0
114493 M adult 0 0
114494 M adult 0 0
aPPenDix 6
Marmosa
(continued from previous page)
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 151
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Marmosa mexicana (continued)
114495 F adult 0 0
114496 M adult 0 0
114497 M juvenile 0 0
114498 M juvenile 0 0
114499 F adult 0 0
114500 M adult 0 0
114501 F adult 0 0
114502 M adult 0 0
114503 M adult 0 0
114504 M adult 0 0
114505 M juvenile 0 0
114506 F adult 0 0
114507 M adult 0 0
114508 F adult 0 0
114509 F adult 0 0
114510 M adult 0 0
114512 F adult 0 0
114513 F adult 0 0
114514 M adult 0 0
114515 M adult 0 0
114516 M adult 0 0
114517 M adult 0 0
114518 M adult 0 0
114519 M adult 0 0
114520 M adult 0 0
114521 M adult 0 0
114522 F adult 0 0
114523 M adult 0 0
114524 M adult 0 0
114525 M adult 0 0
114526 F adult 0 0
aPPenDix 6
Marmosa
(continued from previous page)
152 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Marmosa mexicana (continued)
114527 M adult 0 0
114528 M adult 0 0
114529 M adult 0 0
114530 F adult 0 0
114531 M adult 0 0
118517 F adult 0 0
118518 F adult 0 0
119059 M adult 0 0
119060 F adult 0 0
119061 F adult 0 0
119063 M adult 0 0
119064 F adult 0 0
119066 M juvenile 0 0
119680 M adult 0 0
119681 F adult 0 0
119688 M adult 0 0
119689 M juvenile 0 0
119690 F juvenile 0 0
119691 F adult 0 0
119692 F adult 0 0
120175 M adult 0 0
119065 F adult 0 2
Marmosa murina
1551 F adult 0 0
63507 F adult 0 0
68345 M juvenile 0 0
68346 F adult 0 0
68347 M juvenile 0 0
68348 M juvenile 0 0
68349 M juvenile 0 0
68351 M juvenile 0 0
aPPenDix 6
Marmosa
(continued from previous page)
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 153
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Marmosa murina (continued)
68352 F juvenile 0 0
68353 F adult 0 0
68354 M adult 0 0
68355 F adult 0 0
68356 F adult 0 0
68357 M juvenile 0 0
78214 F juvenile 0 0
63508 F juvenile 0 1
68344 M juvenile 1 0
68350 M adult 1 2
Marmosa rapposa
2754 M juvenile 0 0
4947 ? adult 0 0
4941 M adult 0 0
4951 M adult 0 0
5040 ? adult 0 0
5049 F adult 0 0
Marmosa robinsoni
2630 M juvenile 0 0
3100 M adult 0 0
3101 M adult 0 0
3107 M adult 0 0
3140 M adult 0 0
3141 M adult 0 0
91639 M adult 0 0
112152 M adult 0 0
6335 M adult 0 1
1008 F adult 0 1
aPPenDix 6
Marmosa
(continued from previous page)
154 annalS of caRneGie muSeum Vol. 85
aPPenDix 7
Marmosops
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Marmosops dorothea
4979 M juvenile 0 0
aPPenDix 8
Metachirus
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Metachirus nudicaudatus
12173 F adult 0 0
52728 M adult 0 0
78215 F adult 0 0
aPPenDix 9
Monodelphis
(continued on next page)
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Monodelphis arlindoi
68358 F adult 0 0
68359 F adult 0 0
52729 F adult 0 2
63510 F adult 1 0
63511 F adult 1 0
63509 M adult 1 2
68361 F adult 1 2
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 155
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Monodelphis brevicaudata
52730 M adult 0 0
68360 F juvenile 0 0
Monodelphis dimidiata
86608 F adult 0 0
86609 F adult 0 0
86610 F adult 0 0
86611 M adult 0 0
Monodelphis domestica
5010 M adult 0 0
80016 M adult 0 0
80017 F adult 0 0
80018 F adult 0 0
80019 F juvenile 0 0
80024 M adult 0 0
80025 F adult 0 0
80026 M adult 0 0
80027 M adult 0 0
80029 M adult 0 0
80034 F adult 0 0
80035 M juvenile 0 0
80036 M adult 0 0
80037 M adult 0 0
80038 F adult 0 0
80039 M juvenile 0 0
101529 M adult 0 0
101531 F adult 0 0
80023 M adult 1 0
80031 F adult 1 0
5025 F juvenile 1 2
80020 M juvenile 2 0
80028 F adult 2 0
aPPenDix 9
Monodelphis
(continued from previous page)
156 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Monodelphis domestica (continued)
80030 F juvenile 2 0
80032 M adult 2 0
80033 F adult 2 0
80040 F adult 2 0
80021 M adult 2 2
Monodelphis glirina
4681 M adult 0 0
5061 F adult 0 0
Monodelphis osgoodi
5242 M adult 1 0
Monodelphis touan
76732 M adult 0 0
76734 M juvenile 0 0
76730 M adult 1 0
76733 M juvenile 1 0
76731 M adult 1 0
aPPenDix 9
Monodelphis
(continued from previous page)
aPPenDix 10
Philander
(continued on next page)
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Philander opossum
1931 M adult 0 0
1957 F juvenile 0 0
1988 M adult 0 0
1989 F adult 0 0
4984 M adult 0 0
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 157
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Philander opossum (continued)
4993 M juvenile 0 0
4995 F juvenile 0 0
52733 F adult 0 0
55559 M adult 0 0
61833 ? adult 0 0
63512 F juvenile 0 0
63514 F juvenile 0 0
63518 M juvenile 0 0
68362 M juvenile 0 0
68363 F adult 0 0
68364 F juvenile 0 0
69803 F adult 0 0
76748 M adult 0 0
110577 F juvenile 0 0
110579 M adult 0 0
110580 M juvenile 0 0
119067 F adult 0 0
119073 F juvenile 0 0
55558 M adult 0 2
63513 F juvenile 0 2
76740 M juvenile 1 0
76745 M juvenile 1 0
76739 M adult 1 0
63515 F juvenile 1 2
1997 ? adult ^2 0
52731 M adult 2 0
52732 M juvenile 2 0
55561 M adult ^2 0
63516 M adult 2 0
63517 F adult ^2 0
68365 F adult ^2 0
aPPenDix 10
Philander
(continued from previous page)
158 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Philander opossum (continued)
68367 M juvenile 2 0
68368 F juvenile 2 0
76736 F adult 2 0
76737 F juvenile 2 0
76738 M juvenile 2 0
76741 M juvenile 2 0
76742 F adult 2 0
76744 M adult 2 0
76746 F adult 2 0
110578 F adult 2 0
118571 M adult 2 0
12172 F juvenile 2 2
52734 F adult 2 2
52735 F adult 2 2
68366 F juvenile 2 2
76735 M juvenile 2 2
76743 F juvenile 2 2
76747 M juvenile 2 2
aPPenDix 10
Philander
(continued from previous page)
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Thylamys cinderella
42779 F adult 0 0
42780 F adult 0 0
42781 F adult 0 0
42783 M adult 0 0
aPPenDix 11
Thylamys
(continued on next page)
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 159
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Thylamys cinderella (continued)
42784 F adult 0 0
42785 M adult 0 0
42787 M adult 0 0
42788 M adult 0 0
42791 F adult 0 0
42792 F adult 0 0
42795 F adult 0 0
42796 M adult 0 0
42808 F adult 0 0
42809 M juvenile 0 0
42810 F adult 0 0
86370 F adult 0 0
86371 F adult 0 0
86372 F juvenile 0 0
86373 M juvenile 0 0
42782 M adult 1 0
42804 M adult 1 0
42806 F adult 1 0
42805 M adult 2 0
Thylamys pusillus
42799 F juvenile 0 0
42800 M juvenile 0 0
42803 F juvenile 0 0
42797 F adult 1 0
42802 F juvenile 2 0
Thylamys venustus
5231 M adult 1 0
5227 ? adult 2 0
5296 ? adult 2 0
aPPenDix 11
Thylamys
(continued from previous page)
160 annalS of caRneGie muSeum Vol. 85
aPPenDix 12
Additonal Marsupials
(continued on next page)
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Dromiciops gliroides
40621 F adult ?1 N/A
Antechinus stuartii
50816 F adult 0 0
50817 M adult 0 0
50818 M juvenile 0 0
50821 M juvenile 0 0
50822 M juvenile 0 0
50823 F juvenile 0 0
50824 M juvenile 0 0
50825 F juvenile 0 0
50826 F adult 0 0
50827 M adult 0 0
50829 F adult 0 0
50832 M juvenile 0 0
50833 F adult 0 0
50834 M adult 0 0
50836 M adult 0 0
50837 F adult 0 0
50839 M adult 0 0
Dasyuroides brynei
50840 M adult 0 0
50841 M adult 0 0
Dasyurus maculatus
50842 F adult 0 0
Sarcophilus harrisii
1832 ? adult 0 0
20974 ? adult 0 0
40598 F adult 0 0
59513 M adult 0 0
Thylacinus cynocephalus
20975 ? juvenile 0 0
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 161
aPPenDix 12
Additonal Marsupials
(continued from previous page)
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Perameles nasuta
20977 M adult 0 0
Acrobates pygmaeus
111905 F adult 0 0
111906 ? adult 0 0
111907 ? adult 0 0
111908 F adult 0 0
111909 M adult 0 0
111910 F adult 0 0
111911 F adult 0 0
Petaurus breviceps
116682 M adult 0 0
Petauroides volans
50868 F adult 0 0
50869 M adult 0 0
50870 M adult 0 0
50871 F adult 0 0
50872 F adult 0 0
50873 M adult 0 0
50874 F adult 0 0
50878 F juvenile 0 0
Pseudocheirus peregrinus
50860 F adult 0 0
50862 F adult 0 0
50863 F adult 0 0
50864 M juvenile 0 0
50865 F juvenile 0 0
Tarsipes rostratus
111895 M adult 0 0
111896 F adult 0 0
111897 M adult 0 0
111898 M adult 0 0
162 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Tarsipes rostratus (continued)
111899 F adult 0 0
111900 F adult 0 0
111901 F adult 0 0
111902 M adult 0 0
111903 F adult 0 0
111904 M adult 0 0
Cercartetus nanus
50847 F adult 0 0
111890 M adult 0 0
111891 F adult 0 0
111892 M adult 0 0
111893 F adult 0 0
111894 F adult 0 0
Trichosurus vulpecula
50848 F adult 0 0
50849 F adult 0 0
50850 M adult 0 0
50851 F adult 0 0
50854 M adult 0 0
50855 F adult 0 0
50856 M adult 0 0
50857 F adult 0 0
Phascolarctos cinereus
1804 ? adult 0 0
13067 ? adult 0 0
13068 ? adult 0 0
20928 ? juvenile 0 0
50858 F adult 0 0
50859 ? adult 0 0
Vombatus ursinus
50880 M adult 0 0
aPPenDix 12
Additonal Marsupials
(continued from previous page)
2018 Wible, Shelley, anD RouGieR—The PaRaSPhenoiD in maRSuPialS 163
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Vombatus ursinus (continued)
50881 M adult 0 0
Macropus eugenii
50885 F adult 0 0
Macropus giganteus
17452 F juvenile 0 0
22651 M juvenile 0 0
30406 M juvenile 0 0
20639 ? adult 0 0
20982 ? adult 0 0
20983 ? adult 0 0
30407 M adult 0 0
Macropus robustus
50886 F juvenile 0 0
Macropus rufogriseus
1317 M adult 0 0
50887 F juvenile 0 0
50888 F adult 0 0
50889 M adult 0 0
50890 F adult 0 0
50891 M adult 0 0
50892 F adult 0 0
50893 M juvenile 0 0
50894 F adult 0 0
50895 F adult 0 0
50896 M adult 0 0
Macropus rufus
13059 M juvenile 0 0
13060 ? juvenile 0 0
61354 F juvenile 0 0
Thylogale sp.
13069 ? juvenile 0 0
aPPenDix 12
Additonal Marsupials
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164 annalS of caRneGie muSeum Vol. 85
CM # Sex Life stage Parasphenoid Substrate
0-absent 0-smooth
1-ridge 1-furrow
2-spine 2-depression
Thylogale sp. (continued)
13070 ? juvenile ?2 2
Thylogale thetis
50882 M juvenile 0 0
50883 F juvenile 0 0
Wallabia bicolor
20980 F adult 0 0
20981 ? juvenile 0 0
50901 F juvenile 0 0
50898 F adult 0 0
50899 F adult 0 0
50900 F adult 0 0
aPPenDix 12
Additonal Marsupials
(continued from previous page)
... On the other hand, Gaupp (1908) observed what he interpreted as paired centers in one stage of the echidna Tachyglossus aculeatus (= Echidna aculeata) even though there was a weak median connector that he interpreted as a later addition; Kuhn (1971) cautioned that dual centers though likely in the echidna are not proven by this single stage. Among extant mammals, the parasphenoid is absent in monotremes (Kuhn 1971;Zeller 1989), has a spotty distribution in placentals but recently has been shown to be widely distributed in didelphid marsupials (Wible et al. 2018). Figure 2 shows the cranium of an embryo sand lizard, Lacerta agilis, taken from Gaupp (1906). ...
... The basisphenoid was reported to have a thick midline crest, slightly bulbous at its posterior end, extending well posterior to the choanae; Musser and Archer (1998) contrasted this prominent crest with the similarly situated thin one in Ornithorhynchus (Fig. 4B). Wible et al. (2018) suggested that this so-called basisphenoid crest in Obdurodon is formed by a separate parasphenoid based on the sagittal slice movie of the CT scans of QM F20568 on the Digi-Morph website (http://www.digimorph.org/specimens/ Obdurodon_dicksoni). Thanks to Drs. ...
... Mike Archer and Ted Macrini, I have studied the CT scans of this specimen and report what appears to be a separate bone on the midline dividing the nasopharyngeal passage posterior to the choanae (Fig. 9). As noted by Wible et al. (2018), in its position and size it is reminiscent of the parasphenoid reconstructed in the Miocene meridolestidan Necrolestes by Wible and Rougier (2017). The CT scans show that the midline bone in Obdurodon is not only posterior to the choanae but extends anteriorly dorsal to the palatine bones (Fig. 9B), separating the left and right nasopharyngeal meatuses. ...
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The os paradoxum or dumb-bell-shaped bone is a paired bone occurring in the middle of the specialized bill of the platypus Ornithorhynchus anatinus. It has been variously considered as a neomorph of the platypus, as the homologue of the paired vomer of sauropsids, or as a part of the paired premaxillae. A review of the near 200-year history of this element strongly supports the os paradoxum as a remnant of the medial palatine processes of the premaxillae given its ontogenetic continuity with the premaxillae and association with the vomeronasal organ and cartilage, incisive foramen, and cartilaginous nasal septum. In conjunction with this hypothesis, homologies of the unpaired vomer of extant mammals and the paired vomer of extant sauropsids are also supported. These views are reinforced with observations from CT scans of O. anatinus, the Miocene ornithorhynchid Obdurodon dicksoni, and the extant didelphid marsupial Didelphis marsupialis. At the choanae, Obdurodon has what appears to be a separate parasphenoid bone unknown in extant monotremes.
... altimontis AMNH 96250. Parasphenoids have been reported in two Late Cretaceous eutherians, Maelestes Wible et al., 2007, and Zalambdalestes Gregory and Simpson, 1926(Wible et al. 2004, 2009 and in some extant placentals (Wible et al. 2018), but these are not as tall or elongate as that in L. haydeni. ...
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Leptictis haydeni Leidy, 1868, from the early Oligocene of South Dakota is the type species of the genus and is known only from the well-preserved holotype cranium. The anatomy of its basicranium is described and illustrated based on CT scan data and the primary neurovascular structures are reconstructed. Comparisons are made with a cranium of Leptictis dakotensis (Leidy, 1868) also based on CT scan data. Numerous differences between the two are identified, including the shape of the hypophyseal fossa, the size and orientation of the posterior clinoid process, the depth of the sulcus for the capsuloparietal emissary vein, the size of the petrosal contribution to the middle cranial fossa and to the epitympanic recess, the position of the exit of the auditory tube from the middle ear, the size of the entotympanic, the presence of a styliform process on the entotympanic, and the shape of the ectopterygoid process of the alisphenoid, which added to the few prior reported dental differences justify retaining separate species. The ramus inferior of the stapedial artery, identified by prior authors as present in L. dakotensis, is shown to be absent in both species. Additional comparisons are made with the early Eocene palaeoryctid Eoryctes melanus Thewissen and Gingerich, 1989, also based on CT scans. These three taxa share details of the tympanic processes and epitympanic wings of the bones of the middle ear, the pattern of the dural sinuses and the large size of the sigmoid sinus, the well-developed exposure of the parietal on the occiput, and the unusual course of the nerve of the pterygoid canal, suggestive of a possible close phylogenetic relationship.
... The prenatal specimens (C. volans, DUCEC 804 and "Cynocephalus," DUCEC 8310) have a tiny, independent dermal ossification here, the parasphenoid (see Parker, 1885;Wible et al., 2018), that is presumably fused to the basisphenoid in the older specimens (C. volans, DUCEC 806 and "Cynocephalus," DUCEC 839), including AMNH 187861. ...
Article
The placental order Dermoptera, which includes two extant species, the Philippine and Sunda flying lemurs, Cynocephalus volans and Galeopterus variegatus, respectively, is generally held to be the sister group of Primates. Yet, little has been reported on their cranial anatomy. Here, the anatomy of the ear region is described and illustrated for a juvenile and adult C. volans based on CT scans. The inclusion of a juvenile is essential as nearly all cranial sutures are fused in the adult. Soft tissues are reconstructed based on sectioned histological pre- and postnatal specimens previously reported by the author. Numerous unusual features are identified, including: a small parasphenoid beneath the basisphenoid, a tensor tympani fossa on the epitympanic wing of the squamosal, a cavum supracochleare for the geniculate ganglion of the facial nerve that is not enclosed in the petrosal bone, a secondary facial foramen between the petrosal and squamosal, a secondary posttemporal foramen leading to the primary one, a subarcuate fossa that is floored in part by a large contribution from the squamosal, a body of the incus larger than the head of the malleus, and a crus longum of the incus that lacks an osseous connection to the lenticular process. Documentation of the anatomy of the Philippine flying lemur ear region is an essential first step in morphological phylogenetic analyses where features of the basicranium are widely sampled.
... I provide a general overview of this bone in mammals and address the unusual features present in M. domestica. For discussion of the broader homologies of the mammalian vomer, see Wible et al. (2018) and Wible (2022). ...
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Full-text available
The individual bones of the adult cranium of the gray short-tailed opossum, Monodelphis domestica (Wagner, 1842) are described and illustrated in multiple views based on CT scans. The author previously reported on the outer bony surfaces of the skull of Monodelphis Burnett, 1830, and the current contribution is a companion piece, paying particular attention to the inner bony surfaces (within the endocranium and nasal cavity) and the facets between individual cranial elements, including the ethmo-and frontoturbinals. Comments are provided on the internal nasal floor skeleton, which in M. domestica includes a fused conglomerate formed by the medial pala-tine processes of the premaxillae, the vomer, the ethmoid, the presphenoid, and the orbitosphenoids. This conglomerate includes horizontal shelves just dorsal to the hard palate, and occurs widely in marsupials but is currently unknown in monotremes and placentals.
... Nothing in the CT scans of the two specimens studied here suggests that this is a separate element. Nevertheless, one of the authors of this report has recently published on the occurrence of a little known midline bone called the parasphenoid that occurs in some extant mammals and is thought to be present in some extinct mammals (Wible et al. 2018). We suggest that this midline crest in Metacheiromys likely is a parasphenoid fused to the basisphenoid. ...
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Cranial skeletal material of the Eocene palaeanodont Metacheiromys marshi was examined using high-resolution CT scans. The present study represents the first time that CT scans have been conducted on skulls of this extinct fossorial mammal. The bony osteology of the auditory region is described in detail, including the ectotympanic and entotympanic, the petrosal in both tympanic and endocranial views, and the middle ear ossicles. The results of this investigation confirm a number of derived resemblances between palaeanodonts and xenarthrans, including a large entotympanic element in the medial wall of the auditory bulla, the presence of an anteroventral process of the tegmen tympani, and a posttemporal canal. However, the present study also provides novel derived auditory features linking palaeanodonts and pangolins, consistent with current understanding of palaeanodont phylogenetic relationships, including the absence of an ectotympanic styliform process, a posterolaterally oriented aperture to the cochlear fossula, and a convex mallear head / concave incudal head. Several autapomorphic features characterizing the auditory osteology of Metacheiromys are also noted. The presence of a large, spherical mallear head, and of a capacious tympanic cavity extended into sinuses in surrounding bones, likely represent adaptations for fossoriality, consistent with palaeobiological inferences drawn from the postcranial anatomy of Metacheiromys .
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The current literature on marsupial phylogenetics includes numerous studies based on analyses of morphological data with limited sampling of Recent and fossil taxa, and many studies based on analyses of molecular data with dense sampling of Recent taxa, but few studies have combined both data types. Another dichotomy in the marsupial phylogenetic literature is between studies focused on New World taxa and those focused on Sahulian taxa. To date, there has been no attempt to assess the phylogenetic relationships of the global marsupial fauna based on combined analyses of morphology and molecular sequences for a dense sampling of Recent and fossil taxa. For this report, we compiled morphological and molecular data from an unprecedented number of Recent and fossil marsupials. Our morphological data consist of 180 craniodental characters that we scored for 97 terminals representing every currently recognized Recent genus, 42 additional ingroup (crown-clade marsupial) terminals represented by well-preserved fossils, and 5 outgroups (nonmarsupial metatherians). Our molecular data comprise 24.5 kb of DNA sequences from whole-mitochondrial genomes and six nuclear loci (APOB, BRCA1, GHR, RAG1, RBP3 and VWF) for 97 marsupial terminals (the same Recent taxa scored for craniodental morphology) and several placental and monotreme outgroups. The results of separate and combined analyses of these data using a wide range of phylogenetic methods support many currently accepted hypotheses of ingroup (marsupial) relationships, but they also underscore the difficulty of placing fossils with key missing data (e.g., Evolestes), and the unique difficulty of placing others that exhibit mosaics of plesiomorphic and autapomorphic traits (e.g., Yalkaparidon). Unique contributions of our study are (1) critical discussions and illustrations of marsupial craniodental morphology including features never previously coded for phylogenetic analysis; (2) critical assessments of relative support for many suprageneric clades; (3) estimates of divergence times derived from tip-and-node dating based on uniquely taxon-dense analyses; and (4) a revised, higher-order classification of marsupials accompanied by lists of supporting craniodental synapomorphies. Far from the last word on these topics, this report lays the foundation for future research that may be enabled by the discovery of new fossil taxa, better-preserved material of previously described taxa, novel morphological characters (e.g., from the postcranium), and improved methods of phylogenetic analysis.
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Andinodelphys cochabambensis Marshall & Muizon, 1988 is one of the best preserved metatherian species from the early Palaeocene fauna of Tiupampa (Bolivia). It is represented by five almost complete skulls, three of them being securely associated to sub-complete to partial skeleton. Four skulls could be extracted from a block including several intermingled skeletons. The present paper provides a thorough description of the dental, cranial, and dentary anatomy of A. cochabambensis. The cranial anatomy of A. cochabambensis is similar to that of Pucadelphys andinus. The skull of Andinodelphys however differs from that of Pucadelphys in its larger size and proportionally longer rostrum. Other differences include the presence, in Andinodelphys, of large anteriorly protruding I1s, small palatal vacuities, a transverse canal, and a small hypotympanic sinus. Andinodelphys has the same dental formula as Pucadelphys (I 5/4, C 1/1, P 3/3, M4/4), the plesiomorphic condition for metatherians. Furthermore, both genera share the lack a tympanic process of the alisphenoid, a deep groove for the internal carotid artery at the anterior apex of the promontorium, a small prootic canal perforating the lateral edge of the petrosal and opening laterally in the deep sulcus for the prootic sinus, and a vestigial anterior lamina of the petrosal. Dentally Andinodelphys closely resembles Pucadelphys, the two genera differing in the larger size of the former and in the inconstant presence in the former of a twinned stylar cusp C. Although 25% smaller, the cheek teeth of Andinodelphys closely resemble those of Itaboraidelphys camposi from the early Eocene of Itaboraí (Brazil). As far as dental morphology is concerned, both genera are likely to have diverged from a direct common ancestor, probably Andinodelphys-like, with Itaboraidelphys displaying more derived dental structures. Two isolated petrosal from Itaboraí (Type 2 petrosals) are morphologically close to those of Andinodelphys but distinctly larger. In this paper, a previous interpretation including the teeth of Itaboraidelphys and these petrosals in the same taxon is followed. A phylogenetic analysis retrieved Itaboraidelphys as a sister taxon of the clade Pucadelphys + Andinodelphys, thus lending support to inclusion of the former in the Pucadelphyidae. Three sets of parsimony analyses were performed. A first set of analyses (with all characters) retrieved a strict consensus tree with a clade as follows: (pucadelphyids, (deltatheroidans (stagodontids, Gurlin Tsav skull-GTS), sparassodonts)). An implied weighting analysis with the same data matrix placed the stagodontids in an early diverging position but retained a clade (pucadelphyids, (deltatheroidans, (GTS, sparassodonts))), the deltatheroidans, being therefore inserted in the pucadelphydans. This result implies an independent arrival of pucadelphyids and sparassodonts to South America, which consequently must have been present in North America in the Late Cretaceous. Possible North American sparassodonts could be the poorly known genera Atokatheridium and Olklatheridium (currently referred to deltatheroidans) and the pucadelphyids may have been present in the Late Cretaceous of North America with the genus Aenigmadelphys. However, this hypothesis is less parsimonious (with regard to palaeobiogeography) than a single southward migration of an ancestral Pucadelphyda (Pucadelphyidae + Sparassodonta). Because the result of this first set of analyses may have been induced by heavily homoplastic dental characters related to hypercarnivory, a second set of analyses was performed excluding all the dental characters. The strict consensus is poorly resolved but retains monophyletic Marsupialia and Sparassodonta. An implied weighting analysis retrieved a monophyletic Pucadelphyda but split the deltatheroidans, the polyphyly of which is regarded as a possible artefact related to the lack of dental characters. The GTS is sister taxon to Pucadelphyda. Because the polyphyly of deltatheroidans contradicts all previous hypotheses, a third set of analyses has been performed excluding only those molar characters that supported the close relationships of the hypercarnivorous clades (deltatheroids, stagodontids, and sparassodonts). The strict consensus tree retrieved monophyletic deltatheroidans, Marsupialia and sparassodonts. An implied weighting analysis resulted in deltatheroidans forming a paraphyletic stem assemblage of Metatheria and monophyletic Pucadelphyda. The GTS was no longer related to sparassodonts but was the sister taxon of a clade including the North American taxa of the data matrix, Asiatherium, and Marsupialia. This topology, which is favoured here, supports (as well as that of the second set of analyses) a single pucadelphydan southward migration, probably in the Late Cretaceous, with a Tiupampian radiation of South American carnivorous metatherians.
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The long-recognized monotypic status of the relictual marsupial genus Dromiciops was recently challenged by a controversial reanalysis of previously published mtDNA data that were combined with a new morphological study to conclude that the genus contains 3 species: D. bozinovici, D. mondaca, and D. gliroides. We present here new phylogenetic and coalescent species delimitation analyses to test the multispecific status of Dromiciops relative to the proposed 3 new species. Our molecular analysis is based on partial sequences of 4 nuclear (RAG1, ApoB, vWF, and IRBP) and 2 mitochondrial (12S RNA and Cytb) genes. Genetic distances showed low differentiation among the proposed Dromiciops species, consistent with typical levels of intraspecific variation. Phylogenetic analyses yielded only moderate support for monophyly of D. bozinovici, while depicting polyphyly in D. gliroides and D. mondaca. Species delimitation analyses did not recover the proposed 3-species scenario, and the taxonomic index of congruence among these methods (Ctax = 0.5-1.0) supported monotypic status for Dromiciops. Taking into consideration all the genetic analyses and previously reported morphological analyses, we conclude that all Dromiciops lineages belong to a single species.
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We analyzed the variation in cranial morphology of the marsupial Dromiciops gliroides along its distribution in south-central Chile. We evaluated whether the cranial morphological variation is congruent with the phylogeographic structure previously observed in this species. We built three-dimensional models of 69 crania on which we digitized 30 landmarks. We used standard geometric morphometric methods to extract and analyze the shape and size components of the crania. Our data showed a subtle but consistent cranial size and shape variation along the studied distributional range, suggesting a geographic variation pattern rather than a phylogeographic structuring. Indeed, our multivariate analyses recovered a subtle morphological differentiation between island and mainland populations, contrary to what is suggested by a former phylogeographic study. We detected that either the cranial size variation, as well as the insularity and the latitude could be important factors underlying the cranial shape changes. We suggest that an interplay of historical and contemporary processes could be shaping the morphological pattern observed in this marsupial.
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