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Since the last description of the ornithurine bird Ambiortus dementjevi from Mongolia, a wealth of Early Cretaceous birds have been discovered in China. Here we provide a detailed comparison of the anatomy of Ambiortus relative to other known Early Cretaceous ornithuromorphs from the Chinese Jehol Group and Xiagou Formation. We include new information on Ambiortus from a previously undescribed slab preserving part of the sternum. Ambiortus is superficially similar to Gansus yumenensis from the Aptian Xiagou Forma� tion but shares more morphological features with Yixianornis grabaui (Ornithuromorpha: Songlingorni� thidae) from the Jiufotang Formation of the Jehol Group. In general, the mosaic pattern of character distri� bution among early ornithuromorph taxa does not reveal obvious relationships between taxa. Ambiortus was placed in a large phylogenetic analysis of Mesozoic birds, which confirms morphological observations and places Ambiortus in a polytomy with Yixianornis and Gansus.
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ISSN 00310301, Paleontological Journal, 2013, Vol. 47, No. 11, pp. 1270–1281. © Pleiades Publishing, Ltd., 2013.
1270
1
INTRODUCTION
Ambiortus dementjevi
Kurochkin, 1982 was one of
the first described Early Cretaceous ornithuromorph
birds. It comes from the Khurilt Ulaan Bulag locality
of the Andaikhudag Formation (Hauterverian—Bar
remian) in the Central Mongolian Altai (Kurochkin,
1982, 1985, 1999, 2000). Although dwarfed by the cur
rent Mesozoic bird collections in China, several other
isolated Mesozoic bird taxa are also known from Mon
golia, including
Apsaravis ukhaana
Norell et Clarke,
2001,
Hollanda luceria
Bell et al., 2010,
Nanantius val
ifanovi
Kurochkin, 1996,
Elsornis keni
Chiappe et al.,
2006, and several specimens of
Gobipteryx minuta
Elzanowski, 1974 (Elzanowski, 1974; Kurochkin,
1996; Norell and Clarke, 2001; Chiappe et al., 2006;
Bell et al., 2010); these taxa span the ornithothoracine
clade, making Mongolia one of the richest places for
Mesozoic birds in the world. Only enantiornithines
(
Nanantius
,
Gurilynia
nessovi
Kurochkin, 1999 and
Elsornis
) and ornithuromorphs (
Apsaravis, Hollanda,
Ambiortus
) are known and, except for
Ambiortus
, these
taxa are all from the Late Cretaceous; no primitive
longtailed birds or basal pygostylians (e.g. Sapeorni
thiformes, Confuciusornithiformes), which form
major components of the rich Early Cretaceous Jehol
avifauna, are known. The holotype and only known
specimen of
Ambiortus dementjevi
is a wellpreserved
1
The article is published in the original.
and articulated partial skeleton, preserving several cervi
cal and thoracic vertebrae, and parts of the left thoracic
girdle and wing (specimen PIN, nos. 3790/271273;
Figs. 1–3). The specimen preserves morphologies that
were at first indicative of a fairly derived ornithuro
morph bird (e.g. curved scapula, bent acromion pro
cess, welldeveloped procoracoid process); the taxon
was originally considered a paleognathous bird, how
ever its position within Aves has shifted with the dis
covery of new taxa from the Jehol Biota. Most recently
in a large cladistic analysis aimed towards Mesozoic
birds as a whole,
Ambiortus
is resolved as a basal orni
thuromorph (O’Connor et al., 2011a).
When
Ambiortus
was first described (Kurochkin,
1982), the Mesozoic record of fossil birds was
extremely sparse (Kurochkin, 1999).
Gansus yumen
ensis
Hou et Liu, 1984 was the first Mesozoic bird
described from China (Hou and Liu, 1984). The holo
type specimen was collected from the Early Creta
ceous Aptian Xiagou Formation in Gansu Province,
northwestern China (Hou and Liu, 1984); known
from only a single foot, this taxon was never compared
with
Ambiortus
because of the lack of overlapping
material. Even a decade later, only a small handful of
Early Cretaceous birds were known: primarily
Con
fuciusornis
Hou et al., 1995 and a handful of fragmen
tary enantiornithines (Hou, 1997). Two ornithurines,
Chaoyangia beishanensis
Hou et Zhang 1993 and
Lia
oningornis longidigitrus
Hou, 1996, had also been
described (Hou et al., 1996), but the former lacked
The Phylogenetic Position of
Ambiortus
:
Comparison with Other Mesozoic Birds from Asia
1
J. K. O’Connor
a
and N. V. Zelenkov
b
a
Key Laboratory of Evolution and Systematics, Institute of Vertebrate Paleontology and Paleoanthropology,
142 Xizhimenwai Dajie, Beijing China 10044
b
Borissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya ul. 123, Moscow, 117997 Russia
email: jingmai.oconnor@gmail.com, nzelen@paleo.ru
Received August 6, 2012
Abstract
—Since the last description of the ornithurine bird
Ambiortus dementjevi
from Mongolia, a wealth of
Early Cretaceous birds have been discovered in China. Here we provide a detailed comparison of the anatomy
of
Ambiortus
relative to other known Early Cretaceous ornithuromorphs from the Chinese Jehol Group and
Xiagou Formation. We include new information on
Ambiortus
from a previously undescribed slab preserving
part of the sternum.
Ambiortus
is superficially similar to
Gansus yumenensis
from the Aptian Xiagou Forma
tion but shares more morphological features with
Yixianornis grabaui
(Ornithuromorpha: Songlingorni
thidae) from the Jiufotang Formation of the Jehol Group. In general, the mosaic pattern of character distri
bution among early ornithuromorph taxa does not reveal obvious relationships between taxa.
Ambiortus
was
placed in a large phylogenetic analysis of Mesozoic birds, which confirms morphological observations and
places
Ambiortus
in a polytomy with
Yixianornis
and
Gansus.
Keywords
: Ornithuromorpha,
Ambiortus
, osteology, phylogeny, Early Cretaceous, Mongolia
DOI: 10.1134/S0031030113110063
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
THE PHYLOGENETIC POSITION OF
AMBIORTUS
1271
overlapping material with
Ambiortus
and the unusual
morphology of the latter has recently proven to be
enantiornithine (O’Connor, 2012). In the last major
study to address
Ambiortus
, the taxon was compared to
the Inner Mongolian bird
Otogornis genghisi
Dong,
1993 from the Lower Cretaceous Yijinghouluo For
mation (Kurochkin, 1999). This taxon, known from a
partial thoracic girdle and pair of wings, was originally
identified as an enantiornithine (Dong, 1993),
although when fully described was unassigned to a spe
cific clade (Hou, 1994). The comparative study, how
ever, concluded that both taxa were paleognathous
birds (Kurochkin, 1999). Although when comparative
material was limited
Ambiortus
and
Otogornis
may have
born some superficial similarity (Kurochkin, 1999), a
relationship between these two taxa and their place
ment within Paleognathae is no longer supported; this
is primarily due to lack of evidence and a greater
understanding of Early Cretaceous ornithuromorph
morphology. For example, Kurochkin (2000) noted
that the presence of a Ushaped furcula and convex
scapular cotyla on the coracoid indicated that
Ambior
tus
was a neornithine, features now known to be
present in most basal ornithuromorphs. In light of
more recent finds and a greater understanding
of Enantiornithes,
Otogornis
is considered a member
of this large clade (Zhou et al., 2008), although the
taxon has been difficult to place in a phylogenetic con
text and its taxonomic position within Enantiornithes
is unstable (O’Connor, 2009). The short and robust
shape of the humerus, absence of a procoracoid pro
cess on the coracoid and straight scapula, all support
the enantiornithine affinity of this taxon (Zhou and
Hou, 2002; O’Connor, 2009). Morphologies that sug
gested this taxon may be more advanced and in fact a
paleognath bird (Kurochkin, 1999) are uncorrobo
rated by the specimen; furthermore, the clearest char
acters that define Paleognathae are from the skull,
which is preserved in neither
Ambiortus
nor
Otogornis
.
Record of the early radiation of Ornithuromorpha,
the clade that includes modern birds (Neomithes), has
grown rapidly during the last decade (Chiappe, 2007;
O’Connor et al., 2010; Brocklehurst et al., 2012).
Where previously the global record was dominated by
largely fragmentary specimens (e.g.
Vorona berivotren
sis
Forster et al., 1996,
Vegavis iaai
Clarke et al., 2005)
and even in China known taxa were based on incom
plete and poorly preserved specimens (e.g.
Chaoyan
gia
,
Gansus
,
Songlingornis
linghensis
Hou, 1997),
recent discoveries from the Early Cretaceous Jehol
Group and Xiagou Formation are largely complete
and wellpreserved (e.g.
Yanornis martini
Zhou et
Zhang, 2001,
Yixianornis grabaui
Zhou et Zhang,
2001,
Longicrusavis houi
O’Connor et al., 2010,
Jian
changornis microdonta
Zhou et al., 2009,
Schizooura lii
Zhou et al., 2012,
Archaeorhynchus spathula
Zhou et
Zhang, 2006,
Hongshanornis longicresta
Zhou et
Zhang, 2005, new specimens of
Gansus
), revealing a
wealth of data (You et al., 2006; Zhou et al., 2009;
O’Connor et al., 2011a; Zhou et al., 2012). Because
scientific understanding of Mesozoic birds has
changed rapidly over the past three decades, reexami
nation of incomplete materials in light of recent infor
mation has the potential to reveal important new
information (O’Connor et al., 2011b; O’Connor and
Zhou, 2013). The holotype of
Ambiortus dementjevi
is
one of the most complete Cretaceous ornithuromorph
specimens known from outside of China, yet it has not
been reexamined in light of the current taxonomic
and morphological diversity. Here we redescribe
Ambiortus
, including previously unpublished data, and
compare it to recently described taxa, revealing new
information regarding the phylogenetic placement of
this taxon and the distribution of ornithuromorph lin
eages in Asia as a whole.
Terminology in this paper primarily follows
Baumel and Witmer (1993); Latin is retained for mus
cles (Baumel et al., 1993), while English equivalents
are used for osteological features.
Institutional abbreviations: CAGS, Chinese Acad
emy of Geological Sciences, Beijing, China; FRDC,
Fossil Research and Development Center, Third
Geology and Mineral Resources Exploration Acad
emy, Gansu Provincial Bureau of Geo–Exploration
and Mineral Development, Lanzhou, China; IVPP,
Institute of Vertebrate Paleontology and Paleoanthro
pology, Beijing, China; PIN, Borissiak Paleontologi
cal Institute of Russian Academy of Sciences, Mos
cow, Russia.
SYSTEMATIC PALEONTOLOGY
AVES
ORNITHUROMORPHA
Genus
Ambiortus
Kurochkin, 1982
D i a g n o s i s. An ornithuromorph bird the size of
extant teal
Anas crecca
, with the unique combination
of the following features: a wide procoracoid process
perpendicular to the shaft; scapular blade long and
thin; scapular acromion hooked; lateral trabecula of
the sternum mediolaterally wide, with a concave
medial margin and convex lateral margin so that the
distal end of the process appears to curve medially;
ventral edge of the proximal end of the humerus
strongly developed and with a distinct tubercle on its
cranial surface; transverse groove is short, fossalike,
and runs dorsoventrally; pneumotricipital fossa of the
humerus not developed; deltopectoral crest projected
dorsally; bicipital crest distally abruptly ending
(revised from Kurochkin, 2000).
Generic composition. Type species only.
C o m p a r i s o n s. From the superficially similar
neornithine birds of the family Lithornithidae
Ambior
tus
differs in the presence of the following features:
welldeveloped procoracoid process of the coracoid;
flat (apparently nonexcavated) sulcus m. supracora
coidei of the coracoid; mediolaterally wide and bowed
lateral sternal trabeculae; dorsally projected deltopec
1272
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
O’CONNOR, ZELENKOV
toral crest of the humerus; distal end of bicipital crest
of the humerus abrupt; and articular surface of the
humeral head facing proximally and caudally, but not
cranially (humeral head not fully globeshaped).
Ambiortus
differs from all other Cretaceous birds by
the apomorphic condition of the caudal portion of the
sternum (see above) and from all Cretaceous birds
except
Apsaravis
in the morphology of its proximal
scapula. The acromion of
Ambiortus
is welldeveloped;
the caudal portion is robust while its apex is sharply
tapered in mediolateral view. The longitudinal axes of
the caudal and cranial halves of this process have dif
ferent orientations (craniodorsal and cranial, respec
tively) so that the dorsal margin of the acromion is not
straight but bent.
Apsaravis
shows a somewhat similar
morphology of the proximal scapula but the bend in
the acromion demarcates an acute angle in
Apsaravis
while this angle is obtuse in
Ambiortus
, and the process
is untapered cranially in
Apsaravis
.
Ambiortus
differs from all Cretaceous ornithuro
morph except
Gansus, Yixianornis
and
Yanornis
by the
presence of a wide procoracoid process perpendicular
to the shaft.
Ambiortus
further differs from
Yanornis
by
having a much less robust furcula, and from
Gansus
by
lacking a delicate omal projection on the lateral pro
cess of the coracoid and by the abrupt distal margin of
the bicipital crest of the humerus.
Ambiortus
further
differs from
Yixianornis
by the presence of a slight
groove on the distal half of the lateral surface of the
scapula and the curved sternal margin of the furcula.
Ambiortus dementjevi
Kurochkin, 1982
Ambiortus dementjevi
: Kurochkin, 1982, p. 453, Figs. 1, 2;
1985, p. 272, Fig. 1; 1999, p. 272, Figs. 1–5; 2000, p. 549.
Figs. 27.7, 27.8.
H o l o t y p e. PIN, nos. 3790/271, 273, partial
skeleton preserved in three slabs.
D e s c r i p t i o n (comparative).
Axial skeleton.
As
described by Kurochkin (1982, 1985, 1999), only cer
vical and thoracic vertebrae are preserved in
Ambior
tus
; the entire series is in articulation but poorly pre
served (Figs. 1, 2). Approximately seven cervical verte
brae are present; the most cranial cervical vertebrae
are missing and the total number of cervicals is
(a)
(b)
Fig. 1.
Ambiortus dementjevi
, holotype PIN, no. 3790/271; photographs in dorsal (a) and ventral (b) views. Scale bar, 1 cm.
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
THE PHYLOGENETIC POSITION OF
AMBIORTUS
1273
unknown. A slight disarticulation between the fourth
and fifth preserved cervical vertebrae suggests the
articular surfaces were amphicoelous, as originally
reported by Kurochkin (1985). However, Kurochkin
(1999) reported on a cervical that was prepared free of
the matrix that was fully heteroceolous. Heterocoely
limited to the cranial cervical vertebrae (caudal cervi
cals amphicoelous) is present in a number of orni
thothoracine taxa (e.g.
Yixianornis
,
Gansus, Pengornis
houi
Zhou et al., 2008)—given the incomplete preser
vation of the cranial cervical series, this cannot be
ruled out in
Ambiortus.
An opisthocoelous condition,
like that present in some neornithines (potentially ple
siomorphic to the clade), also cannot be ruled out. The
costal processes are delicate and rodlike, fully fused
and nearly as long as the vertebral centra. The caudal
cervicals appear to be in ventral view; this surface is
not strongly keeled (as in most enantiornithines and
some ornithuromorphs,
Apsaravis
and
Gansus
) and
developed carotid processes appear to be absent.
The proximal three to four thoracic vertebrae are
preserved in articulation with the cervical vertebrae
(Figs. 1, 2). They are preserved completely in articula
tion, not revealing the morphology of their articular
surfaces. Although poor preservation makes it hard to
assess morphological details, deep, broad fossae are
visible excavating the lateral surface of the centra, as in
other ornithuromorphs; similar fossae are present in
enantiornithines, however in this group they are more
narrow and deep than broad.
Coracoid.
The left coracoid is nearly complete
(right not preserved); only the medial angle is incom
plete (Figs. 1, 2). The acrocoracoid is short, straight
and slightly tapered inward (medially) proximally. The
ventromedial surface of the acrocoracoid bears a prox
imodistal groove (also visible in
Archaeorhynchus
,
specimen IVPP, no. V17091 and
Gansus
(specimen
CAGSIG04CM003) and just proximal to the gle
noid, the acrocoracoid bears a small ovalshaped con
cave facet interpreted as the impression of the acroco
racohumeralis ligament (also present in
Yixianornis
)
(Kurochkin, 1985, 1999). The presence of the well
developed facet for the attachment of the acrocoraco
humeral ligament strongly indicates that the modern
type ligamentbased force balance system of the
shoulder joint (Baier et al., 2007) was present in the
Early Cretaceous ornithuromorphs. The glenoid is
nearly flat; its ventral margin forms a labrum, separat
ing the facet from the neck. Just distal to the head
(slightly overlapping with the distal margin of the gle
noid facet), a welldeveloped procoracoid process is
present (Kurochkin, 1982, 1985, 1999); this feature
may be an synapomorphy of Ornithuromorpha (Fig. 3;
absent in
Apsaravis
; (Clarke and Norell, 2002). The
procoracoid is located approximately 30% from the
proximal end on the proximodistal axis, as in
Yixian
ornis
(32%) and
Gansus
(30%), however it is slightly
more proximally located in
Yanornis
(26%) and more
distally located in
Archaeorhynchus
(40%) and
Schizooura
(49%) (Fig. 3). The process is damaged but
appears to be dorsomedially oriented and quadrangu
lar with a flat medial margin. A similar morphology of
the procoracoid is also observed in
Ganus
(specimen
CAGSIG04CM004, 012),
Yixianornis
(IVPP,
no. V13631) and
“Yanornis”
sp., specimen IVPP,
no. V13278 (Fig. 4). The basal ornithuromorphs
Schizooura
and
Archaeorhynchus
, have more disparate
procoracoid morphologies: long and craniomedially
tapered in the former and small, short, and medially
tapered in the latter (Figs. 3a, 3b) (Zhou et al., 2012;
Zhou et al., 2013). The procoracoid process is reduced
in the neornithine lithornithids. The sulcus of the tri
osseal canal (sulcus m. supracoracoidei) is not exca
(a) (b)
acr
pro
l cor
l sca
l hum
cv
fur
pro
gl
thv
k
al
cmc
rdl?
stn
rib
rad
uln
l cor
l sca
cv
l hum
acr
Fig. 2.
Interpretive drawing of the holotype of
Ambiortus
dementjevi
PIN, no. 3790/271 in dorsal (a) and ventral (b)
views. Dark grey indicates where the slab is perforated
(allowing some bones to be viewed in both views); medium
grey indicates matrix; light grey indicates poorly preserved
bone. Designations: (
al
) alular metacarpal; (
acr
) acro
mion; (
cmc
) carpometacarpus; (
cv
) cervical vertebrae;
(
lcor
) left coracoid; (
gl
) glenoid facet; (
l hum
) humerus;
(
k
) sternal keel; (
pro
) procoracoid process; (
rad
) radius;
(
rdl?
) carpal bone; (
rib
) sternal ribs; (
l sca
) scapula;
(
stn
)sternum; (
thv
) thoracic vertebrae; (
uln
) ulna. Scale
bar, 1 cm.
1274
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
O’CONNOR, ZELENKOV
vated in
Ambiortus
; it is almost flat and might have
been very slightly concave. The articular facet for the
scapula is located on the dorsal surface, lateral to the
procoracoid process; although obscured by articula
tion with the scapula, the surface appears to be a small,
circular, and deeply concave. A slit is visible between
the shaft and the basal (dorsal) part of the procoracoid
process; this may be due to crushing but it is also pos
sible that a slitlike foramen n. supracoracoidei was
present (as in storks, for example; the foramen is ple
siomorphically present in Neornithes, including
Lithornithidae). In
Ambiortus
, the lateral margin of
the coracoid is strongly concave, while the medial
margin is only gently concave, as in
Gansus.
The distal
half of the lateral margin expands to form a lateral pro
cess (Kurochkin, 1999). This feature is widespread
within Ornithuromorpha (present in
Gansus
,
Yanornis,
Yixianornis, Songlingornis, Longicrusavis
,
Ichthyornis
),
but absent in basal taxa (e.g.
Schizooura, Jianchangor
nis
and
Archaeorhynchus
). In
Gansus
—and possibly
Ichthyornis
(Marsh, 1880; Clarke, 2004)—the lateral
corner of this process bears a delicate omal projection
(specimen CAGSIG04–CM004, Fig.3d; absent in
specimen 04CM012), similar to the morphology
observed in some neornithines with aquatic habits
(e.g.
Puffinus, Scolopax
). This feature does not appear
present in
Ambiortus.
The dorsal surface of the cora
coid, although not visible, is inferred to be nearly flat,
lacking the deep, narrow excavation present in
Apsa
ravis
and some enantiornithines (e.g.
Enantiornis
)
(Clarke and Norell, 2002; O’Connor, 2009); the pres
ence of a broad and shallow fossa for the m. sternoco
racoidei, like that in
Gansus, Yixianornis
, and
Yanor
nis
, cannot be determined in
Ambiortus
.
Scapula.
The left scapula is incomplete in
Ambior
tus
, missing the distal end (Figs. 1, 2); the scapular
shaft is elongate and curved (Kurochkin, 1999), typi
cal of Ornithuromorpha (e.g.
Longicrusavis
,
Yixianor
nis, Yanornis, Gansus
; Fig. 5). The shaft is mediolater
ally compressed and the distal half of the lateral sur
face bears a slight groove interpreted for muscle
attachment (Kurochkin, 1999) that is also present in
Gansus, Hongshanornis
and
Yanornis
(absent in
Yix
ianornis
). The acromion is welldeveloped; the caudal
(proximal) portion is robust while the cranial (distal)
half is sharply tapered in mediolateral view. The longi
tudinal axes of the caudal and cranial halves of this
process have different orientations (craniodorsal and
cranial, respectively) so that the dorsal margin of the
acromion is not straight but bent. As was first noted by
Kurochkin (1985), this is very similar to the morphol
ogy observed in Lithornithidae (Fig. 4d; Houde,
1988).
Apsaravis
also shows a similar morphology but
the two taxa differ in that the bend in the acromion
demarcates an acute angle in
Apsaravis
(obtuse in
Ambiortus
and
Lithornis
) and the process is untapered
cranially (Clarke, Norell, 2002). In dorsal view, the
tapered portion of the acromion is spatulate, inter
preted as the articular facet for the furcula (Fig. 2b).
The acromion process in
Gansus
is similar in that it is
welldeveloped, however this taxon differs in that the
process is rectangular, unbent and untapered (in lat
eral view, specimen CAGSIG04CM017) (You
et al., 2006); these taxa greatly differ from the short
(a) (b) (c) (d)
Fig. 4.
Comparative drawings of ornithuromorph scapulae:
(a)
Ambiortus dementjevi
; (b)
Yixianornis grabaui
; (c)
Gan
sus yumenensis
; (d)
Lithornis plebus
, USNM, no. 336534
(from Houde, 1988). Scale bars, 1 cm. Grey areas not pre
served.
(a) (b) (c) (d) (e) (f)
Fig. 3.
Comparative drawings of ornithuromorph coracoids (right, ventral view): (a)
Archaeorhynchus spathula
; (b)
Schizooura lii
;
(c)
Yixianornis grabaui
; (d)
Gansus yumenensis
; (e)
Yanornis martini
; (f)
Ambiortus dementjevi
—reconstructed portion marked
with dash line. Scale bars, 1 cm.
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
THE PHYLOGENETIC POSITION OF
AMBIORTUS
1275
and bluntly tapered morphology in
Yixianornis
(extremely reduced in
Ichthyornis
; Clarke, 2004), or
the short and sharply tapered morphology in
Hongsh
anornis.
The glenoid facet is flat, as in
Gansus
and
Hongshanornis
(slightly concave in
Ichthyornis
) and its
plane is somewhat inclined in relation to the plane of
the shaft, as in most neornithines, including Lithorni
thidae (Kurochkin, 1999). The coracoidal tubercle,
not visible in
Ambiortus
(contra Kurochkin, 1999), is
developed as a slight convexity proximomedial to the
glenoid in other Early Cretaceous taxa (e.g.
Gansus
,
Yixianornis, Hongshanornis
), contrasting with the
condition in
Ichthyornis
(Clarke, 2004).
Furcula
—only the omal halves of the clavicular
rami are preserved in
Ambiortus
(Figs. 1, 2). The rami
are delicate and have oval crosssections, with the long
axis lateroventralmediodorsally oriented. The omal
tips are slightly medially oriented and the rami are
somewhat curved throughout, suggesting the furcula
was ushaped (Fig. 5). The distal ends are blunt and
not developed into distinct acromial or acrocoracoid
processes (Kurochkin, 1999). According to Kuroch
kin (1999), before preparation there existed a void of
the interclavicular symphysis that indicated the pres
ence of a small boss where otherwise there might exist
a hypocleidium (furcular apophysis). Ornithuromor
pha encompasses a large range of furcular morpholo
gies (Fig. 5);
Ambiortus
is most similar to
Gansus
(Fig. 5c; specimen CAGSIG04CM012) and the
hongshanornithids (Fig. 5a).
Archaeorhynchus
(Fig. 5b) and
Jiuquanornis
Wang et al., 2013 (speci
men FRDC05CM021) from the Xiagou Formation
(You et al., 2010) are also overall very similar, only
more robust and with welldeveloped acromial pro
cesses (tapered in the former, blunt and caudally pro
jecting in the latter) (Zhou et al., 2012).
Yixianornis
and
Songlingornis
both possess a straight (as opposed
to curved) sternal (ventral) margin (Clarke et al.,
2006), and the omal tips of the clavicular rami dis
tinctly taper into small acromial processes in
Yixianor
nis
(Fig. 5d). Although contacting the matrix, it
appears the dorsal surface of the omal tips may have
bore a flat articular surface, which would fit interpre
tations regarding the flat facet on the acromion pro
cess of the scapula (Kurochkin, 1999). The furcula is
robust in
Yanornis
(Fig. 5f) and
Zhongjianornis yangi
Zhou et al., 2009, and
Schizooura
has a Vshaped fur
cula with a hypocleidium (Fig. 6g), very different from
other ornithuromorphs but similar to enantiornithines
(especially
Pengornis
) (Zhou et al., 2012).
Sternum
—the left half of the rostral most portion
of the sternum is preserved in the main slab of
Ambior
tus
, specimen PIN, no. 3790/271 (Figs. 1a, 2a), and
the left caudal half of the sternum is preserved as an
impression in the specimen PIN, no. 3790/273 (previ
ously undescribed; Fig. 6a, 6c). The rostral margin is
parabolic; the single preserved coracoidal sulcus is
strongly angled laterocaudally so that the rostral mar
gin of the sternum would have formed a tall arch
(Fig. 2a) (Kurochkin, 1999). The sternal rostrum in
Gansus
is similar with an inner angle estimated at 110
°
(specimen CAGSIG04CM012). The relative
position of the coracoidal sulci is unclear and it cannot
be determined if they were crossed, as in
Ichthyornis
(Clarke, 2004). The welldeveloped coracoidal sulci in
Gansus
and
Yixianornis
were certainly closely spaced
(a) (b) (c) (d)
(e) (f) (g)
Fig. 5.
Comparative drawings of ornithuromorph furcula: (a)
Longicrusavis houi
; (b)
Archaeorhynchus spathula
; (c)
Gansus yume
nensis
; (d)
Yixianornis grabaui
; (e)
Ambiortus dementjevi
; (f)
Yanornis martini
; (g)
Schizooura lii
. Dark grey indicates matrix; light
grey indicates poorly preserved bone or heavily reconstructed areas. Scale bars, 1 cm.
1276
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
O’CONNOR, ZELENKOV
and potentially may have crossed each other medially
although this also cannot be confirmed in either taxon.
The proximal portion of the base of the keel is pre
served in
Ambiortus
(Fig. 2a), although the extent of
the ventral projection of the keel is unknown; the base
of the keel does not reach the rostral margin, although
the cranioventral margin of the keel may have been
level with the rostral margin, as in
Yixianornis
and
Lithornis.
The keel extends to the rostral margin in
Gansus
(specimen CAGSIG04CM003),
Yanornis
(specimen IVPP, no. V13278), and
Archaeorhynchus
(specimen IVPP, no. V17091).
The impression of the distal portion of the sternum,
not previously described, indicates the presence of two
pairs of caudal trabeculae as in most Early Cretaceous
ornithuromorphs (
Archaeorhynchus
,
Yanornis, Yixia
nornis, Gansus, Songlingornis
; reduced in
Jianchangor
nis
and
Schizooura
). The lateral trabecula is mediolat
erally wide, with a concave medial margin and convex
lateral margin (autapomorphy) so that the distal end of
the process appears to curve medially (Figs. 6a, 6c).
Yanornis, Yixianornis
, and
Songlingornis
have a similar
morphology (Clarke et al., 2006), with wide lateral
trabeculae, however these taxa possess large distal
(a) (b)
(c) (d)
ribs
stn
lt
it
cf?
mt
ma ph1
ma ph2
ma ph3
uln
rad
Fig. 6.
Counter slabs of the holotype of
Ambiortus dementjevi
: (a), photograph PIN 3790/272; (b) photograph of PIN3790/273;
(c), interpretive drawing of PIN 3790/272; (d), interpretive drawing of 3790/273. Designations: (
cf?
) caudal fenestra; (
it
) inter
mediate trabecula; (
lt
) lateral trabecula; (
ma ph1
) major digit first phalanx; (
ma ph2
) major digit second phalanx; (
ma ph3
) major
digit ungual phalanx; (
mt
) median trabecula; see also Fig. 2. Dark grey indicates matrix; light grey indicates poorly preserved
bone. Scale bars, 1 cm.
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
THE PHYLOGENETIC POSITION OF
AMBIORTUS
1277
expansions and lack the distomedial curvature present
in
Ambiortus
(Fig. 7). In
Gansus
, this process is more
delicate, straight, and does not have strong lateral pro
jection (specimen CAGSIG04CM003) (You
et al., 2006). In
Hongshanornis
the lateral trabeculae
are curved and lack distal expansions, but differ from
Ambiortus
in that they are very narrow and delicate.
The intermediate trabecula in
Ambiortus
is as long as
the lateral trabecula (consistent with other ornithuro
morphs), although much thinner and less recurved. It
appears to enclose a caudal fenestra like that present in
Songlingornis, Yanornis
and
Yixianornis
(Clarke et al.,
2006), however the distal margin of the sternum,
including the distal ends of the caudal trabeculae, are
not fully preserved and the presence of a fenestra cannot
be confirmed with absolute certainty (Figs. 6a, 6c). In
Gansus
the fenestra remains open mediodistally in the
specimen CAGSIG04CM003 but is closed in the
specimen IVPP V15076 (Li et al., 2011), indicating
this feature is affected by ontogeny. The proximolat
eral margin of the sternum (costal margin) in
Ambior
tus
is level (aligned) with the intermediate trabeculae
(autapomorphy); in
Gansus
, the costal margin is level
with the lateral trabeculae. In other taxa with laterally
splayed trabeculae (e.g.
Songlingornis, Yixianornis
) the
level of the costal margin is between the lateral and
intermediate trabeculae—no other taxon displays the
level of lateral projection present in
Ambiortus.
Although the lateral margin is incomplete, a short lat
erally projecting “zyphoid” process (Clarke et al.,
2006) cranial to the caudal trabeculae, like that
present in
Gansus, Yixianornis
and
Songlingornis
,
appears to be absent in
Ambiortus
(as in
Archaeorhyn
chus
and
Jianchangornis
) (Fig. 7).
Humerus.
Only the proximal half of the left
humerus is preserved in
Ambiortus
(Figs. 1, 2). The
humeral head is not as welldefined, proximodorsally
forming a continuous convexity with the deltopectoral
crest (as in
Gansus
). The articular surface of the
humeral head is continuous with the proximal del
topectoral crest; the articular surface of the humeral
head faces proximally and caudally, but not cranially
as in more advance birds and thus the head is not com
pletely globular. The bicipital crest shows very little
cranial projection (Kurochkin, 1985, 1999) (hypertro
phied in some enantiornithines), consistent with other
basal ornithuromorphs (
Gansus
,
Ichthyornis, Yanor
nis
). In profile (cranial view), the bicipital crest is sep
arated from the humeral head by a concavity (
Archae
orhynchus
,
Ichthyornis, Longicrusavis
); distally, the
crest ends abruptly, as in
Ichthyornis
and
Zhongjianor
nis
(gradually diminishes in
Archaeorhynchus
,
Gansus,
Jianchangornis, Longicrusavis, Schizooura
and
Lithor
nis
) (Zhou et al., 2012) (Fig. 8). The proximocranial
surface of the bicipital crest bears a short, deep dors
oventrally oriented groovelike depression, also present
in
Gansus
(specimen CAGSIG04CM012); this
(a) (b) (c)
(d) (e) (f)
Fig. 7.
Comparative drawings of ornithuromorph sterna: (a)
Yanornis martini
; (b)
Yixianornis grabaui
; (c)
Hongshanornis
longi
cresta
; (d)
Archaeorhynchus spathula
; (e)
Gansus yumenensis
(subadult); (f)
Ambiortus dementjevi.
Grey indicates preserved areas
in
Ambiortus.
Not to scale.
1278
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
O’CONNOR, ZELENKOV
surface is interpreted as the transverse ligamental
groove (Kurochkin, 1985, 1999). Some enantiorni
thines, including
Otogornis
, have a circular fossa exca
vating the cranial surface of the humerus (e.g.
Guri
lynia, Martinavis
Martin et al., 2007,
Longipteryx cha
oyangensis
Zhang et al., 2001,
Cathayornis yandica
Zhou et al., 1992) although a transverse ligamental
groove is reportedly present in some enantiornithines
(Chiappe, Walker, 2002). In basal ornithuromorph
taxa, the humeral head is flat on the cranial surface
(
Schizooura, Archaeorhynchus
); the cranial surface is
convex forming a globeshaped humeral head in more
derived taxa (
Gansus, Ichthyornis
). In
Ambiortus
, the
cranial surface is concave, but limited only to the most
proximal portion, so that the proximocranial margin
forms a labum that continues along the proximal quar
ter of the deltopectoral crest. This feature may be
exaggerated by crushing. Just distal to this labum, the
cranial surface is centrally concave.
The dorsally projecting deltopectoral crest in
Ambiortus
is subequal to the shaft in width, rounded
(Kurochkin, 1999), and appears to taper into the shaft
distally as in most ornithuromorph taxa (e.g.
Yanornis
,
Yixianornis, Hongshanornis, Longicrusavis, Jianchang
ornis, Gansus
); the crest projects cranially in
Lithornis
and other neornithine birds. The crest is proportion
ately wider in the hongshanornithids but narrower in
Yanornis; Schizooura
and
Zhongjianornis
share an
unusual morphology in which the crest does not taper
into the shaft distally, rather the dorsodistal corner of
the crest forms a distinct projection (O’Connor and
Zhou, 2013; Zhou et al., 2012). On the caudal surface
the area of the ventral tubercle (and capital incision) is
damaged although we interpret a ventral tubercle
would have been present (Kurochkin, 1999). A sepa
rated dorsal tubercle is absent (Kurochkin, 1999). Just
distal to the humeral head the caudal surface of the
bone is slightly convex.
Ulna and radius.
Only fragments of the antebrach
ium are preserved in the holotype of
Ambiortus
(Figs. 1, 2, 6). The radius is much more narrow than
the ulna.
Carpals and Carpometacarpus.
Ambiortus
preserves
a single proximal carpal, preserved underlying the
proximal end of the carpometacarpus (Figs. 1, 2). The
exposed portion appears rectangular, not Vshaped,
which may suggest that this is the radiale, however, its
size is more consistent with the ulnare (as interpreted
by Kurochkin, 1999); the surface is concave centrally
with another concavity on the surface facing away
from the carpometacarpus.
The hand is very poorly preserved in
Ambiortus
; the
ventral aspect of the carpometacarpus is preserved in the
main slab overlying the radius and ulna (Figs. 1a, 2a).
The carpometacarpus is fully fused proximally, form
ing a welldeveloped carpal trochlea (Kurochkin,
1999), typical of Ornithuromorpha (fuses late in more
basal birds and is often preserved unfused, e.g.
Rapax
avis pani
Morschhauser et al., 2009,
Shenqiornis mengi
Wang et al., 2010). An extensor process, present in
Gansus
, is reportedly present in
Ambiortus
(Kuroch
kin, 1999). This feature cannot be confirmed,
although the dorsal and ventral profiles of the alular
metacarpal are not symmetrical; the thickest region on
the ventral surface is distally located, while it appears
the thickest region on the dorsal surface is proximally
located (visible even though the carpometacarpus is in
ventral view). The cranioventral margin of the alular
(a) (b)
(c)
(d)
(e)
Fig. 8.
Comparative drawings of ornithuromorph humeri: (a)
Gansus yumenensis
; (b)
Yanornis martini
; (c)
Schizooura lii
; (d)
Lon
gicrusavis houi
; (e)
Ambiortus dementjevi.
Scale bars, 1 cm.
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
THE PHYLOGENETIC POSITION OF
AMBIORTUS
1279
metacarpal bears a facet that tapers proximally.
Whether these are true morphologies or the result of
poor preservation cannot be determined.
The alular digit is not preserved in
Ambiortus
, nor is
the minor digit. The major digit, preserved as an
impression (Figs. 6b, 6d; specimen PIN,
no. 3379/272), has three phalanges; the caudal margin
is not very clear but the first phalanx does not appear
as strongly dorsoventrally compressed and caudally
expanded (Kurochkin, 1999) as in most other orni
thuromorphs (
Yanornis, Yixianornis
). The cranial pila
is well developed along the entire length of the pha
lanx. It appears a small internal index process (Steg
mann, 1978) was present but it does not project past
the distal articular surface as it does in
Ichthyornis
(Clarke, 2004). The intermediate phalanx is delicate,
half the thickness of the first, and tapered slightly
(Kurochkin, 1999). The ungual phalanx is small and
relatively uncurved (more curved in
Yixianornis
; pro
portionately larger in
Longicrusavis
and
Yanornis
); the
major digit ungual appears reduced in
Gansus
as well
(specimen CAGSIG04CM004).
Material. Holotype.
Phylogeny
The dataset is a modified version of O’Connor and
Zhou (2012); scorings for
Ambiortus
were modified
based on this study of the specimen and
Lithornis
(scored for the genus) and several newly described
ornithuromorph taxa (e.g.
Schizooura lii, Jianchangor
nis microdonta, Zhongjianornis yangi
) were added to
the dataset. A total of 60 taxa were scored for
245 equally weighted characters, 31 of which were
treated as ordered; Dromaeosauridae was used as the
outgroup. The dataset was analyzed using TNT
(Goloboff et al., 2008); we conducted a heuristic
search retaining the single shortest tree from every
1000 trees (producing four trees 850 steps long) fol
lowed by an additional round of tree bisection and
reconnection (TBR) branch swapping. This analysis
produced 5760 most parsimonious trees (length =
850 steps; CI = 0.385; RI = 0.671; Fig. 9). The Nelson
strict consensus tree is consistent with that published
by O’Connor et al. (2011) in the nonornithothora
cine part of the tree. The enantiornithine clade shows
greater resolution while the ornithuromorph clade
shows less. Relationships are poorly supported, but
notably
Liaoningornis
and
Eoalulavis hoyasi
Sanz
et al., 1996 form a clade, ‘longipterygidae’ is resolved
as
Boluochia zhengi
Zhou 1995 +
Longipteryx
, and
Rapaxavis
forms a clade with
Shanweiniao cooperorum
O’Connor et al., 2009 +
Longirostravis hani
Hou et al.,
2004 (‘Longirostravisidae’). Within Ornithuromor
pha,
Archaeorchynchus
is resolved as the most basal
taxon, with
Jianchangornis
and
Patagopteryx deferrari
isi
Alvarenga et Bonaparte, 1992 forming successive
outgroups to a clade formed by a dichotomy between a
polytomy between
Schizooura, Zhongjianornis
and
Dromaeosauridae
Archaeopteryx
Jixiangornis
Shenzhouraptor
Rahonavis
Jeholornis
Zhongornis
Eoconfuciusornis
Confuciusornis dui
Jinzhouornis zhangjiyingia
Changchengornis
Confuciusornis sanctus
Didactylornis
Sapeornis
Protopteryx
Otogornis
Iberomesornis
Eocathayornis
Longipteryx
Boluochia
Elsornis
Shenqiornis
Rapaxavis
Longirostravis
Shanweiniao
Vescornis
Gobipteryx
Pengornis
Neuquenornis
Eoenantiornis
Concornis
Cathayornis
Liaoningornis
Eoalulavis
Archaeorhynchus
Jianchangornis
Patagopteryx
Schizooura
Zhongjianornis
Chaoyangia
Enaliornis
Yixianornis
Hollanda
Yanornis
Songlingornis
Gansus
Apsaravis
Ambiortus
Hongshanornis
Longicrusavis
Baptornis advenus
Baptornis varneri
Parahesperornis
Hesperornis regalis
Ichthyornis
Limenavis
Lithornis
Gallus
Anas
Vegavis
Neornithes 1/25
Aves 10/100
Pygostylia 3/38
Enantornithes 2/54
Ornithothoraces 3/60
Ornithuromorpha 1/33
Confuciusornithiformes 3/64
Sapeornithiformes 2/64
Fig. 9.
Cladogram of the strict consensus tree
(5760 MPT’s, length 850 steps) of the hypothetical phylo
genetic relationships of these Mesozoic birds. Note that
Ambiortus
,
Gansus
,
Yixianornis
and the other ‘songlingorn
thids’ are grouped together in a polytomy of ornithuro
morph taxa. Major nodes are marked with absolute/rela
tive Bremer support values.
1280
PALEONTOLOGICAL JOURNAL Vol. 47 No. 11 2013
O’CONNOR, ZELENKOV
Chaoyangia
, and the clade that includes all other more
derived birds. This clade is a polytomy between
Ambiortus, Enaliornis
Seeley 1876,
Yixianornis, Gan
sus, Yanornis, Hollanda, Apsaravis, Songlingornis
,
Hongshanornithidae, Hesperornithiformes, and a
polytomy between
Anas, Gallus, Lithornis, Limenavis
patagonica
Clarke et Chiappe, 2001 and
Vegavis
with
Ichthyornis
as the sister taxon.
DISCUSSION
Ambiortus
preserves a number of features that
firmly place the taxon within the derived ornithotho
racine clade: rectangular medially projecting procora
coid; lateral process on coracoid; Ushaped furcula;
curved scapula; rounded deltopectoral crest; and ster
nal keel nearly or reaching the rostral margin of the
sternum.
Ambiortus
is the only definitive ornithuro
morph from Mongolia and the most important Early
Cretaceous specimen from outside China. Geograph
ically, the next closest major fossil avifauna is that of
the Xiagou Formation, which has yielded a large num
ber of specimens of mostly
Gansus.
The Xiagou For
mation, like the Mongolian Andaikhudag Formation
(Shuvalov, 2000), is composed of continental deposits,
as opposed to nearshore lacustrine like the Jehol
Group. Ambiortus superficially resembles
Gansus
,
although separated by differences in sternal, coracoi
dal, and scapular morphology. Although sharing many
morphological features with certain Jehol taxa, these
species show distinct differences in body plan, typi
cally showing more robust body shapes. Given that the
Xiagou Formation (115–105 Ma) and Andaikhudag
Formation, (136–125 Ma) (Kurochkin, 2000) are
separated by somewhere between 10 to 30 Ma, the
superficial similarities in bodyshape between
Gansus
and
Ambiortus
may be related to similar adaptations to
comparable environments, suggesting that
Ambiortus
might have been waterbird as well. This is consistent
with other Cretaceous ornithuromorphs, which tend
to show aquatic niches (O’Connor et al., 2010).
Ambiortus
shares features with a number of orni
thuromorph taxa (
Yixianornis, Lithornis, Gansus
). The
sternum possesses autapomorphies, but shows a high
degree of similarity to the ‘songlingornithids’
Yixian
ornis, Yanornis
and
Songlingornis
; these taxa share the
presence of robust lateral trabeculae and caudal fenes
trae (Fig. 7). Although sternal morphology was once
thought to be fairly conservative, as more ornithuro
morph specimens accumulate the range of sternal
morphologies continues to rise (You et al., 2010);
closely related species tend to show a relatively high
degree of similarity to each other (e.g. Hongshanorni
thidae, Songlingornithidae), which may suggest
Ambiortus
is related to this clade. The shape of the
acromion process of the scapula is very similar to that
observed in Lithornithiformes (Fig. 4), which may also
suggest a close relationship, although this group is
considered to be fairly derived within Aves (Neorni
thes: Paleognathae) (Houde, 1988). As has been the
case with the enantiornithines, the increase in orni
thuromorph taxonomic diversity has not resulted in
greater systematic clarity—rather the known diversity
shows no clear pattern of character acquisition.
Because morphological comparison does not
readily reveal relationships, we placed
Ambiortus
together with other similar taxa (
Lithornis
) into a cla
distic analysis in order to test hypothetical relation
ships and previous hypotheses that this taxon may be a
more derived paleognathous bird (Kurochkin, 1985,
2000). The results conform with our morphological
observations, placing
Ambiortus
in a polytomy that
includes morphologically similar taxa,
Yixianornis,
Yanornis, Songlingornis
(‘Songlingornithidae’) and
Gansus
(Fig. 9). Seventeen character changes occur at
the node that separates the
Ambiortus
polytomy from
more derived birds (
Ichthyornis
+
Neornithes
).
Although several of these features are homoplastic
(characters 116, 134, 172, 191), the node is marked by: a
higher degree of fusion (characters 1 and 47); increased
pneumaticity (characters 36, 120); advances in the mor
phology of the quadrate (character 25: 0 1); the
presence of a dorsal supracondylar process (character
134: 1 2); a welldifferentiated ulnare (character
152: 0 1); the presence of a pisiform process
(character 156: 1 2); the loss of the major digit
claw (character 172); reduction of the pubis (charac
ter 197: 1 2); the presence of two proximal tar
sometatarsal vascular foramen (character 226: 1 2);
the presence of an intercotylar eminence (character 228:
0 1); and the presence of a welldeveloped facet
for metatarsal I on the plantar surface of metatarsal II
(character 234: 0 1). Although most of these fea
tures cannot be scored in the holotype of
Ambiortus
,
this taxon does retain a manual claw on the major
digit. The analysis confirms hypotheses that
Lithornis
is more derived, although the inclusion of this taxon
resulted in a collapse of Ornithurae, Ichthyornithi
formes and Neornithes. These results highlight an
already recognized need to increase character sam
pling in Mesozoic bird datasets (O’Connor and Zhou,
2013).
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... Mei was first described on the basis of an exquisitelypreserved skeleton with a bird-like sleeping posture, which is arguably the most complete Early Cretaceous troodontid specimen known (Xu and Norell, 2004;Pan et al., 2013). Sinusonasus, Daliansaurus, and Liaoningvenator all have a similar size as Sinovenator, and each of them were reported from a single, near com- Hou et al., 1995Hou et al., , 1996Hou et al., , 1997bHou et al., , 1999aHou et al., , 1999bHou et al., , 2004Hou, 1996Hou, , 1997bChiappe et al., 1999Chiappe et al., , 2007Chiappe et al., , 2014Chiappe et al., , 2019bJi et al., 1999Ji et al., , 2002aJi et al., , 2002bZhang et al., 2006Zhang et al., , 2009Zhou and Zhang, 2005, 2006bGao et al., 2008Gao et al., , 2012O'Connor et al., 2009O'Connor et al., , 2011aO'Connor et al., , 2013O'Connor et al., , 2016cWang et al., 2013dWang et al., , 2013e, 2019c;Zheng et al., 2007Zheng et al., , 2013Zheng et al., , 2014 Dames, 1884;Heller, 1959;Wellnhofer, 1974Wellnhofer, , 1988Wellnhofer, , 1993Wellnhofer, , 2009Mayr et al., 2005;Wellnhofer and Marsh, 1872Marsh, , 1877Marsh, , 1880Martin and Tate, 1976;Martin, 1984;Clarke, 2004;Bell and Chiappe, 2015;Field et al., 2018b Belly River Group Case et al., 2007;Turner et al., 2012;Ely and Case, 2019;Cordes-Person, 2020 ...
... Several early-diverging avialan skeletons as well as nests have been discovered in Mongolia. The enantiornithine Holbotia and the ornithuromorph Ambiortus were collected from the Hauterivian-Barremian Andaikhudag Formation in the Central Mongolian Altai, both preserving soft tissue (O'Connor and Zelenkov, 2013;Zelenkov and Averianov, 2016). All other specimens are from Late Cretaceous deposits. ...
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An unabated surge of new and important discoveries continues to transform knowledge of pen-naraptoran biology and evolution amassed over the last 150+ years. This chapter summarizes progress made thus far in sampling the pennaraptoran fossil record of the Mesozoic and Paleocene and proposes priority areas of attention moving forward. Oviraptorosaurians are bizarre, nonparavian pennaraptorans first discovered in North America and Mongolia within Late Cretaceous rocks in the early 20th century. We now know that oviraptorosaurians also occupied the Early Cretaceous and their unquestionable fossil record is currently limited to Laurasia. Early Cretaceous material from China preserves feathers and other soft tissues and ingested remains including gastroliths and other stomach contents, while brooding specimens and age-structured, single-species accumulations from China and Mongolia provide spectacular behavioral insights. Less specialized early oviraptorosaurians like Incisivosaurus and Microvenator remain rare, and ancestral forms expected in the Late Jurassic are yet to be discovered, although some authors have suggested Epidexipteryx and possibly other scansoriopterygids may represent early-diverging oviraptorosaurians. Long-armed scansoriopterygids from the Middle-Late Jurassic of Laurasia are either early-diverging oviraptorosaurians or paravians, and some have considered them to be early-diverging avialans. Known from five (or possibly six) feathered specimens from China, only two mature individuals exist, representing these taxa. These taxa, Yi and Ambopteryx, preserve stylopod-supported wing membranes that are the only known alternative to the feathered, muscular wings that had been exclusively associated with dinosaurian flight. Thus, scansoriopterygid specimens-particularly those preserving soft tissue-remain a key priority for future specimen collection. Dromaeosaurids and troodontids were first discovered in North America and Mongolia in Late Cretaceous rocks. More recent discoveries show that these animals originated in the Late Jurassic, were strikingly feathered, lived across diverse climes and environments, and at least in the case of dromaeosaurids, attained a global distribution and the potential for aerial locomotion at small size.
... Раннемеловые птицы Монголии представлены пока только двумя находками из западной Гоби: раннемеловой орнитуроморфой Ambiortus dementjevi из верхов неокома (Курочкин, 1982а;Kurochkin, 1985;O'Connor, Zelenkov, 2013) и энанциорнисом Holbotia ponomarenkoi из готерива-баррема (Zelenkov, Averianov, 2016). Амбиортус, судя по сходству с китайским Gansus, был околоводной птицей и, возможно, даже ныряющей -по типу современных поганок, в то время как холботия, как и все остальные известные раннемеловые энанциорнисы, была древесной формой. ...
... Хиргис-Нур (Зеленков, Курочкин, 2010). Из Шарги также описан единственный известный азиатский представитель вымершего семейство палелодид -Palaelodus kurochkini Zelenkov, 2013(Zelenkov, 2013a. Палелодиды -родственники современных фламинго и поганок, объединяющие в своем строении морфологические черты обеих этих групп и претендующие на роль переходного звена между этими сильно дивергировавшими современными кладами (Mayr, 2004). ...
... The oldest record of Ornithuromorpha occurs in the middle Lower Cretaceous (Hauterivian-Barremian) in China (Wang et al., 2015) and roughly coeval beds in Mongolia (O'Connor and Zelenkov, 2013). In contrast, several ornithuromorphs, representing different lineages are recorded in early Aptian Jehol deposits (see Zhou et al., 2003;O'Connor et al., 2011;Wang et al., 2015. ...
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The fossil record of Early Cretaceous birds in South America has been restricted to members of Enantiornithes from the Crato Formation (Aptian) of Brazil. Here we describe a new genus and species of bird discovered at Pedra Branca Mine, Nova Olinda County, Ceará State, Brazil, which adds to the avian fossil record from the Crato Formation. The specimen is represented by an isolated foot that is exposed in plantar view. A plantarly displaced metatarsal III with a well-developed hypotarsus supports its referral to Ornithuromorpha, representing the oldest member of the clade reported for Gondwana. Its unique foot conformation indicates that it may belong to an unknown ornithuromorph clade with some cursory similarities to extant flightless ratites. The presence of Early Cretaceous ornithuromorphs in Brazil indicates that the clade was widespread in Gondwana during the Mesozoic. http://zoobank.org/urn:lsid:zoobank.org:pub:08333BA3-F231-4E61-9E89-105C7478AE31
... 89; Wang et al., 2016). Further anatomical features supporting the placement of LNTU-WLMP-18 within euornithines are the rounded deltopectoral crest (O'Connor and Zelenkov, 2013) and coplanar proximal ends of metatarsals II-IV (Wang et al., 2016), and the absence of a tubercle on the dorsal face of metatarsal II (Chiappe, 2002). Within euornithines, LNTU-WLMP-18 was found to be the sister taxon to Archaeorhynchus, and this pairing formed a clade with Parahongshanornis and Eogranivora. ...
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The ontogenetic development of extant birds is characterized by rapid growth, bone fusion and an early onset of flight ability. In contrast, little is known about how these ontogenetic traits evolved in the bird stem lineage, and the available data pertains primarily to Enantiornithes. Here, we describe an almost complete skeleton of a juvenile euornithine bird (LNTU-WLMP-18) from the Early Cretaceous Jiufotang Formation (Aptian), which was discovered near Lamadong Town (Jianchang County, Liaoning, China). Despite its completeness, bone preservation is rather poor. Thus, to increase the contrast between bone tissue and matrix, we used cyan-red-based autofluorescence photography. The specimen is more or less articulated and exposed in ventral aspect. The jaws are edentulous, the coracoid bears a procoracoid process, and the ischium lacks a proximodorsal process. The pedal unguals are short and barely curved, indicating a ground-dwelling lifestyle. Feathers, including long primaries, are present as carbonized traces. Several characters indicate that LNTU-WLMP-18 is a juvenile: the bone surface has a coarsely striated texture and no fusion is evident between the carpals and metacarpals, between the tibia and the astragalus and calcaneum, or among the metatarsals. Although juvenile characters have the potential to impede accurate identification of the specimen, morphological comparisons and cladistic analysis identify LNTU-WLMP-18 as most likely referable to the basal euornithine Archaeorhynchus, which would make the specimen the first juvenile bird from the Jehol Group that could be assigned to a specific taxon. Based on its size and the incomplete ossification of the bone surface, LNTU-WLMP-18 represents the smallest and therefore youngest known individual of this genus. A statistical comparison of limb proportions shows that the forelimbs of LNTU-WLMP-18 are significantly shorter than the hindlimbs, while the forelimbs are longer than the hindlimbs in subadult and adult individuals. This is different from the situation in some Enantiornithes, in which the forelimbs exceed the length of the hindlimbs even in hatchlings. Similar to Enantiornithes, Archaeorhynchus probably exhibit an early onset of flight ability, as indicated by the extensive wing plumage in LNTU-WLMP-18. Finally, the lack of gastroliths in the visceral cavity might indicate a dietary shift in Archaeorhynchus during ontogeny. As a small-bodied, ground-dwelling, seed-eating bird with a precocial ontogeny, Archaeorhynchus filled an ecological niche that later allowed early crown birds to survive the K-Pg mass extinction.
... A remarkable diversity of ornithuromorph birds is known from the somewhat younger, early Aptian (about 125 Ma) deposits in China (reviewed in O'Connor et al., 2011;Mayr, 2017; see also Wang et al., 2013;Liu et al., 2014;Zhou et al., 2014), and one taxon (Ambiortus) is known from the Hauterivian-Barremian (133.9e126.3 Ma) of Mongolia (Kurochkin, 1985;O'Connor and Zelenkov, 2013). The fossil record of Ornithuromorpha becomes especially reach in the terminal ages of the Late Cretaceous, Campanian and Maastrichtian, when several primitive members of the clade (Patagopteryx, Hollanda, Apsaravis, Vorona) coexisted along with more advanced Hesperornithes, Ichthyornithes, as well as modern-looking birds, apparently related to Neornithes and sometimes even included within the crown group Aves (Hope, 2002;Mayr, 2009Mayr, , 2017O'Connor et al., 2011). ...
Article
Ornithuromorph birds (the clade which includes modern avian radiation) first appeared in the Early Cretaceous in Asia and achieved a great diversity during the latest ages of the Late Cretaceous (Campanian and Maastrichtian). The evolutionary history of orithuromorphs during the first 17 MYAs of the Late Cretaceous (Cenomanian to Santonian ages) remains very poorly known, as the fossil record for this time interval is largely restricted to several isolated finds of the classic avian genus Ichthyornis in North America. Here we describe an isolated distal tibiotarsus of an evolutionary advanced bird, morphologically similar to Ichthyornis, from the middle Cenomanian of Saratov Province, European Russia. This is the first documentation of an Ichthyornis-like bird in the Old World. The find further constitutes only the second pre-Campanian record of the Late Cretaceous Ornithuromorpha in Eurasia, the second record of Cenomanian birds in Russia. This discovery shows that Ichthyornis-like birds enjoyed a wide geographical distribution as early as the beginning of the Late Cretaceous. Given that the earliest and the most primitive ornithuromorph birds are known from Asia, the new find supports a Eurasian origin for Ichthyornithidae.
... The coracoidal tubercle is small, sub-rounded and confluent with the glenoid facet (the articular surface for the humerus), which is large and shallowly concave. A deep sulcus is present on the surface of the scapular shaft (Figure 7), also present in Ambiortus (Kurochkin 1982;O'Connor and Zelenkov 2013). ...
Article
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Gansus yumenensis Hou and Liu, 1984 is a basal ornithuromorph bird that has been recovered from the Lower Cretaceous Xiagou Formation in the Changma Basin of Gansu Province in northwestern China. Although it bears important significance in understanding the origin and early evolution of Ornithuromorpha, this taxon has only received preliminary morphological study. Here, we provide a detailed description of the postcranial morphology of Gansus yumenensis based on seven new specimens and new data from previously reported specimens, and update diagnosis for this taxon. Our phylogenetic analysis including new morphological data on Gansusyumenensis resolves all known four genera of Changma ornithuromorphs as more derived taxa than Jehol members of this clade, indicating the difference between Changma and Jehol avifauna.
Conference Paper
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The Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurians that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurians were party to dramatic geographic changes on the Earth’s surface, including the breakup of the supercontinent Pangaea, and the formation of the Atlantic Ocean. These plate tectonic events are thought to have caused vicariance or dispersal of coelurosaurian faunas, influencing their evolution. Unfortunately, few coelurosaurian biogeographic hypotheses have been supported by quantitative evidence. Here, we report the first, broadly sampled quantitative analysis of coelurosaurian biogeography using the likelihood-based package BioGeoBEARS. Mesozoic geographic configurations and changes are reconstructed and employed as constraints in this analysis, including their associated uncertainties. We use a comprehensive time-calibrated coelurosaurian evolutionary tree produced from the Theropod Working Group phylogenetic data matrix. Six biogeographic models in the BioGeoBEARS package with different assumptions about the evolution of spatial distributions are tested against geographic constraints. Our results statistically favor the DIVALIKE+J and DEC+J models, which allow vicariance and founder events, supporting continental vicariance as an important factor in coelurosaurian evolution. Ancestral range estimation indicates frequent dispersal events via the Apulian route (connecting Europe and Africa during the Early Cretaceous) and the Bering land bridge (connecting North America and Asia during the Late Cretaceous). These quantitative results are consistent with commonly inferred Mesozoic dinosaurian dispersals and continental-fragmentationinduced vicariance events. In addition, we recognize the importance of Europe as a dispersal center and gateway in the Early Cretaceous, as well as other vicariance events such as those triggered by the disappearance of land bridges.
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The Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurians that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurians were party to dramatic geographic changes on the Earth's surface, including the breakup of the supercontinent Pangaea, and the formation of the Atlantic Ocean. These plate tectonic events are thought to have caused vicariance or dispersal of coelurosaurian faunas, influencing their evolution. Unfortunately , few coelurosaurian biogeographic hypotheses have been supported by quantitative evidence. Here, we report the first, broadly sampled quantitative analysis of coelurosaurian biogeography using the likelihood-based package BioGeoBEARS. Mesozoic geographic configurations and changes are reconstructed and employed as constraints in this analysis, including their associated uncertainties. We use a comprehensive time-calibrated coelurosaurian evolutionary tree produced from the The-ropod Working Group phylogenetic data matrix. Six biogeographic models in the BioGeoBEARS package with different assumptions about the evolution of spatial distributions are tested against geographic constraints. Our results statistically favor the DIVALIKE+J and DEC+J models, which allow vicariance and founder events, supporting continental vicariance as an important factor in coelurosaurian evolution. Ancestral range estimation indicates frequent dispersal events via the Apulian route (connecting Europe and Africa during the Early Cretaceous) and the Bering land bridge (connecting North America and Asia during the Late Cretaceous). These quantitative results are consistent with commonly inferred Mesozoic dinosaurian dispersals and continental-fragmentation-induced vicariance events. In addition, we recognize the importance of Europe as a dispersal center and gateway in the Early Cretaceous, as well as other vicariance events such as those triggered by the disappearance of land bridges.
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The Coelurosauria are a group of mostly feathered theropods that gave rise to birds, the only dinosaurs that survived the Cretaceous-Paleogene extinction event and are still found today. Between their first appearance in the Middle Jurassic up to the end Cretaceous, coelurosaurs were party to dramatic geographic changes on the Earth's surface, including the breakup of the supercontinent Pangaea, and the formation of the Atlantic Ocean. These plate tectonic events are thought to have caused vicariance or dispersal of coelurosaurian faunas, influencing their evolution. Unfortunately, few coelurosaurian biogeographic hypotheses are supported by quantitative evidence. Here, we report the first, broadly-sampled quantitative analysis of coelurosaurian biogeography using the likelihood-based package BioGeoBEARS. Mesozoic geographic configurations and changes are reconstructed and employed as constraints in this analysis, including their associated uncertainties. We use a comprehensive time-calibrated coelurosaurian evolutionary tree produced from the Theropod Working Group phylogenetic data matrix. Six biogeographic models in the BioGeoBEARS package with different assumptions about the evolution of spatial distribution are tested against the geographic constraints. Our results statistically favour the DIVALIKE+J and DEC+J models, which allow vicariance and founder events, supporting continental vicariance as an important factor in coelurosaurian evolution. Ancestral range estimation indicates frequent dispersal events via the Apulian Route (connecting Europe and Africa during the Early Cretaceous) and the Bering Land Bridge (connecting North America and Asia during the Late Cretaceous). These quantitative results are consistent with commonly inferred Mesozoic dinosaurian dispersals and continental-fragmentation-induced vicariance events. In addition, we recognise the importance of Europe as a dispersal centre and gateway in the Early Cretaceous, as well as other vicariance events like those triggered by the disappearance of land-bridges.
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Many of the earliest discovered ornithurine birds from the Jehol Group in northeastern China are highly fragmentary; this current study on the only known specimen of Liaoningornis longidigitrus, first described by Hou in 1997, indicates the taxon is in fact a member of Enantiornithes. Although based on fragmentary and poorly preserved material, the absence of a well-developed sternum, lack of developed cnemial crests on the tibiotarsi and reduced pedal unguals suggests Liaoningornis should be excluded from the more advanced ornithothoracine clade. The taxon remains distinct from all known enantiornithines, although it shows similarity to the Spanish taxon Eoalulavis hoyasi; shared features of the sternum suggest a close relationship between these two, although disparity from other enantiornithines suggests this may be an artifact of ontogeny. The Liaoningornis specimen is too fragmentary to be able to make strong inferences about its placement within the diverse enantiornithine clade.
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