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A new ornithuromorph (Aves) with an elongate rostrum from the Jehol Biota, and the early evolution of rostralization in birds

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A new species of Early Cretaceous ornithuromorph with an elongate rostrum is described from the Sihedang locality of the Lower Cretaceous Yixian Formation in north-eastern China. Like the longipterygid enantiornithines, rostral elongation in Dingavis longimaxilla gen. et sp. nov. is achieved primarily through the maxilla, whereas neornithines elongate the premaxilla and rostralization is far more extreme than observed in early birds. Notably, in the rostrum of Xinghaiornis, the most ‘longirostrine’ Early Cretaceous ornithuromorph, the premaxilla and maxilla contribute to the rostrum equally. These lineages together highlight the diversity of configurations in which early birds experimented with rostralization of the skull. The 65% upper limit in rostral proportions of Early Cretaceous taxa with elongate maxillae and the fact that this morphology was abandoned in more derived taxa suggests that in Aves this skull configuration provided less structural stability.
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Journal of Systematic Palaeontology
ISSN: 1477-2019 (Print) 1478-0941 (Online) Journal homepage: http://www.tandfonline.com/loi/tjsp20
A new ornithuromorph (Aves) with an elongate
rostrum from the Jehol Biota, and the early
evolution of rostralization in birds
Jingmai K. O'Connor, Min Wang & Han Hu
To cite this article: Jingmai K. O'Connor, Min Wang & Han Hu (2016): A new ornithuromorph
(Aves) with an elongate rostrum from the Jehol Biota, and the early evolution of rostralization
in birds, Journal of Systematic Palaeontology, DOI: 10.1080/14772019.2015.1129518
To link to this article: http://dx.doi.org/10.1080/14772019.2015.1129518
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A new ornithuromorph (Aves) with an elongate rostrum from the Jehol Biota, and
the early evolution of rostralization in birds
Jingmai K. O’Connor *, Min Wang and Han Hu
Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China
(Received 16 June 2015; accepted 24 November 2015)
A new species of Early Cretaceous ornithuromorph with an elongate rostrum is described from the Sihedang locality of the
Lower Cretaceous Yixian Formation in north-eastern China. Like the longipterygid enantiornithines, rostral elongation in
Dingavis longimaxilla gen. et sp. nov. is achieved primarily through the maxilla, whereas neornithines elongate the
premaxilla and rostralization is far more extreme than observed in early birds. Notably, in the rostrum of Xinghaiornis,
the most ‘longirostrine’ Early Cretaceous ornithuromorph, the premaxilla and maxilla contribute to the rostrum equally.
These lineages together highlight the diversity of configurations in which early birds experimented with rostralization
of the skull. The 65% upper limit in rostral proportions of Early Cretaceous taxa with elongate maxillae and the fact that
this morphology was abandoned in more derived taxa suggests that in Aves this skull configuration provided less structural
stability.
http://zoobank.org/urn:lsid:zoobank.org:pub:9D8A429F-BBA7-47EF-BFD0-ADFB7118833A
Keywords: Ornithothoraces; Cretaceous; Jehol; Mesozoic birds; skull
Introduction
The rostrum (facial skeleton) is the most variable portion
of the archosaur skull and extant birds cover nearly the
entire spectrum of viable skull morphospace (Marug
an-
Lob
on & Buscalioni 2003). In neornithines, the rostrum is
defined by the premaxilla (Baumel & Witmer 1993) and
the maxilla is heavily reduced and fused to the premaxilla,
not significantly contributing to the facial skeleton, but in
non-avian theropods and basal birds the rostrum is formed
by both the premaxilla and maxilla. Here we use the term
‘rostrum’ to refer to the facial skeleton following
Marug
an-Lob
on & Buscalioni (2003). In extant avian
theropods, the neornithines, the contribution of the ros-
trum to the skull varies from 30 to <85%, and the beak
encompasses a huge variety of morphologies (Marug
an-
Lob
on & Buscalioni 2003; Gill 2007). The rostrum and its
horny beak, together with the jaw musculature, form the
avian feeding mechanism. While tooth morphology can
be used to infer diet in mammals, neornithines lack teeth
and have adapted the shape of their rostra to suit a diver-
sity of feeding habits (e.g. carnivorous, filter-feeding,
mud-probing, seed-eating), allowing them to access a
wide variety of trophic resources (Gill 2007). However,
thus far this diversity appears to be largely a characteristic
of Neornithes despite the fact that Cretaceous pterosaurs
achieved extreme rostral proportions (Marug
an-Lob
on &
Buscalioni 2003). Rostral proportions in early birds as far
as we know are much more conservative (O’Connor &
Chiappe 2011). The earliest bird, the Late Jurassic
Archaeopteryx, has a mesorostrine skull (rostral contribu-
tion 5070%) in which the rostrum accounts for roughly
half the total length (rostral length is very difficult to pre-
cisely measure from most fossil specimens). Mesorostral
proportions also represent the plesiomorphic condition
within both Archosauria and Theropoda (Marug
an-Lob
on
& Buscalioni 2003). Similar proportions were retained in
other basalmost birds Jeholornis (52%), Confuciusornis
(55%) and Sapeornis (53%), lineages all found only in the
Early Cretaceous Jehol Biota (130.7120 Ma) (Z. Zhou
2006; Z.-H. Zhou & Zhang 2006). Only in the most
diverse clade, the Enantiornithes, were significant excur-
sions in rostral proportions observed (Zhang et al. 2000;
Hou et al. 2004; Morschhauser et al. 2009; O’Connor
et al. 2009). However, even these departures remained
within the mesorostrine morphospace with the rostrum of
Longipteryx representing the upper known limit, contrib-
uting to 65% of the skull length (O’Connor & Chiappe
2011). All Jehol enantiornithines with rostral elongation
are inferred to form a clade, the Longipterygidae
(O’Connor et al. 2009). Although once considered the
most diverse recognized Early Cretaceous enantiornithine
*Corresponding author. Email: jingmai@ivpp.ac.cn
ÓThe Trustees of the Natural History Museum, London 2016. All rights reserved.
Journal of Systematic Palaeontology, 2016
http://dx.doi.org/10.1080/14772019.2015.1129518
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clade, in some recent analyses the group has collapsed
into two clades, the Longipterygidae Boluochia CLongip-
teryx and the Longirostravidae Rapaxavis CShanweiniao
CLongirostravis (O’Connor et al. 2009; S. Zhou et al.
2014).
The Early Cretaceous record of the Ornithuromorpha,
the derived avian lineage that includes living birds, has
steadily grown over the last decade due nearly entirely to
discoveries of largely complete specimens from the Jehol
Group in north-eastern China (S. Zhou et al. 2013b;S.
Zhou et al. 2014; M. Wang et al. 2015). At the last time
rostral proportions were investigated in the Enantior-
nithes, the sister group to the Ornithuromorpha and the
first major avian radiation, no ornithuromorph preserved
rostral proportions similar to those observed in the longip-
terygids; Yanornis had the most elongate rostrum, contrib-
uting approximately 57% of the skull length. However,
new discoveries have expanded the range of known rostral
proportions in the Ornithuromorpha, and the recently
described taxon Xinghaiornis lini has the longest recog-
nized Early Cretaceous avian rostrum, forming approxi-
mately 67% of the total skull length (X.-R. Wang et al.
2013). Here we describe another specimen with relatively
elongate rostral proportions representing a new species,
Dingavis longimaxilla gen. et sp. nov. We compare the
structure of the rostrum in the new specimen to that of
Xinghaiornis and longipterygid enantiornithines, and dis-
cuss the bearing of this discovery on our current under-
standing of rostral evolution in early birds.
Systematic palaeontology
Class Aves Linnaeus, 1758
Pygostylia Chiappe, 2002
Ornithothoraces Chiappe, 1995
Ornithuromorpha Chiappe 2001
Definition. The first ancestor of Neornithes that is not
also an ancestor of the Enantiornithes, and all of its
descendants.
Remarks. We use the formerly node-based taxon Orni-
thuromorpha (Chiappe 2001,2002) to refer to Neornithes
and all taxa that are more closely related to it than to the
Enantiornithes (O’Connor et al. 2015). We are thus pro-
viding this taxon with a stem-based definition. Although
the proposed definition does not strictly equate with the
published node-based definition, it does provide a formal
definition for the current widespread usage of this term in
most recent literature (Bell et al. 2010; O’Connor et al.
2010; S. Zhou et al. 2013a; M. Wang et al. 2015). We feel
that node-based definitions are premature at this time
given the fluctuating morphology of basal bird phyloge-
nies and the rapid rate of discovery of new material. For
example, the avian status of Archaeopteryx is now
debated, with growing evidence this taxon may be more
closely related to troodontids (Xu et al. 2011). Further-
more, it is recognized that the next youngest avifauna, the
Jehol, represents a relatively derived fauna with the earli-
est known ornithuromorphs being already derived mem-
bers of a specialized clade of Early Cretaceous waders,
the Hongshanornithidae (M. Wang et al. 2015). Therefore,
any node-based definition at this time would be expected
to change, especially if any fossils are found that fill the
temporal gap between Archaeopteryx and the Jehol avi-
fauna. We support the use of stem-based definitions until
we achieve greater phylogenetic clarity.
Genus Dingavis gen. nov.
Type species. Dingavis longimaxilla sp. nov.
Etymology. The genus name is in honour of the late dis-
tinguished Chinese geologist Wenjiang Ding, often con-
sidered the ‘father of Chinese geology’, who brought
Amadeus William Grabau to Beijing University in 1920.
Professor Ding was the first person to teach palaeontology
in China and he also served as the chief editor
of Palaeontologia Sinica, one of the earliest Chinese jour-
nals to receive international recognition.
Diagnosis. See diagnosis of type and only species below.
Dingavis longimaxilla sp. nov.
(Figs 13)
Diagnosis. A large basal ornithuromorph with the follow-
ing unique combination of characters: rostrum forms
6365% of total skull length; jugal process of lacrimal
caudolaterally excavated; both upper and lower jaws
edentulous; length of carpometacarpus Cmajor digit
exceeds humeral length by 25%; short alular metacarpal
(13.7% of major metacarpal); tarsometatarsus with small
but sharp medial and lateral plantar crests, plantar surface
not excavated; metatarsal II much shorter than metatarsal
IV; metatarsal II and IV trochlea plantarly displaced; and
metatarsal II trochlea strongly angled craniomedially.
Holotype. Institute of Vertebrate Paleontology and
Paleoanthropology (IVPP) V20284, a nearly complete
adult individual preserved in dorsal view with gastroliths
and trace impressions of integument around the neck.
Etymology. The species name refers to the elongate
maxilla that distinguishes this taxon from all other Jehol
ornithuromorphs.
Occurrence. Sihedang, Liaoning Province, north-eastern
China; Lower Cretaceous, Yixian Formation, Jehol
Group.
Description. We conducted X-ray analysis of the slab to
extract additional morphological information
2 J. K. O’Connor et al.
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(Supplemental Figs 1, 2). Although the specimen is articu-
lated and appears fairly complete (Figs 1,2), the bone is
poorly preserved in most places, obscuring morphological
details.
Skull. The skull is exposed primarily in left lateral view.
The rostrum forms 6365% of the skull length. This is
greater than the proportion observed in any other Jehol
ornithuromorph with the exception of Xinghaiornis
(Tables 1,2). The premaxillary corpus is preserved in lat-
eral view. As far as can be discerned, the premaxilla is
edentulous. As in enantiornithines with the most elongate
rostra, the premaxillary corpus is low (length is roughly
three to four times the height) and the dorsal and ventral
margins are nearly parallel. The left maxillary process is
not preserved. A crack separates the frontal processes,
which are preserved in dorsal view. Rostrally, a suture is
present between the left and right processes. They become
unfused along their distal halves. Although the processes
do not reach the frontals, the distalmost extremity of both
processes is not preserved. The right premaxillary corpus
is visible in ventral view in articulation with the elongate
right maxilla. The rostral ends of the premaxillae appear
to be unfused (Fig. 3). The maxilla also appears to be
toothless, although small teeth cannot be ruled out due to
the poor preservation. The premaxilla-maxilla contact is
level with the rostral preserved ends of the frontal pro-
cesses. Consistent with the interpretation that this is not a
crack, the premaxilla articulates laterally with the maxilla.
Caudally, the right maxilla is poorly preserved; the blunt
caudal end is approximately level with the lacrimal. Distal
and ventral to the caudal end of the maxilla is a slightly
curved rod-like bone that is probably one of the jugal
bones. The left lacrimal is preserved in articulation with
the frontal. The craniodorsal process is weakly angled ros-
troventrally and the caudodorsal process is angled caudo-
dorsally, as in other basal birds (e.g. Jeholornis,
Sapeornis,Pengornis). The ventral process is laterally
excavated so that the cross section of this process is
L-shaped. This morphology is also observed in some
Figure 1. Dingavis longimaxilla gen. et sp. nov., holotype, IVPP V20284, full slab photograph. Scale bar D20 mm.
New Chinese Cretaceous ornithuromorph bird 3
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enantiornithines (e.g. Parabohaiornis,Pengornis). The
frontals are petal-shaped and strongly domed as in other
Early Cretaceous birds. Preserved in the orbit, two bones
form an expanded articulation (Fig. 3); we suggest this is
the right pterygoid-quadrate articulation.
The mandible is slightly displaced rostral to the cra-
nium so that the mandibular symphysis is located proxi-
mal to the rostral end of the premaxillae (Fig. 3). The left
dentary appears to be preserved primarily in lateral view.
The mandibular symphysis appears to be fully fused and
U-shaped, probably incorporating a predentary bone
(Z.-H. Zhou & Martin 2011). The width of the mandibular
symphysis suggests a very wide lower bill, similar to
some living birds such as ducks, but also observed in Epi-
dendrosaurus. The bone forming the rostral margin is
heavily recrystallized, and we cannot rule out the possibil-
ity that the preserved morphology is exaggerated by taph-
onomic processes. Breaks in the bone separate the
remaining left dentary from the mandibular symphysis.
The dentary is long and straight, contributing to more
Figure 2. Dingavis longimaxilla gen. et sp. nov., holotype, IVPP V20284, interpretative drawing. Anatomical abbreviations: 15, pha-
langes one through five; ca, caudal vertebrae; cc, cnemial crest; cmc, carpometacarpus; co, coracoid; cv, cervical vertebrae; de, dentary;
ep, extensor process; es, extensor sulcus; f, furcula; fe, femur; fi, fibula; fr, frontal; g, gastralia; ga, gastroliths; ha, hallux; hs, horny
sheath; hu, humerus; il, ilium; is, ischium; ma, major digit; mi, minor metacarpal; mtIIV, metatarsals IIV; p, phalanx; pb, pubes; pc,
proximal carpal; pm, premaxilla; py, pygostyle; ra, radius; s, synsacrum; sc, scapula; st, sternal fragments; tc, attachment of the m. tibia-
lis cranialis; tb, tibiotarsus; th, thoracic vertebrae; tm, tarsometatarsus; ul, ulna; l and r represent left and right side, respectively. Scale
bar D20 mm.
4 J. K. O’Connor et al.
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than two-thirds the length of the mandible. Caudally the
dentary is unforked, forming a caudoventrally sloping
articulation with the surangular. The poorly preserved left
angular is visible unfused to the surangular. The mandibu-
lar bones are usually preserved completely unfused in
other basal ornithuromorphs. Two condylar structures pre-
served near the left mandibular joint are interpreted as the
mandibular and otic processes of the left quadrate. A frag-
ment of the left splenial is visible between the two denta-
ries in dorsal view; its preserved portion ends well caudal
to the mandibular symphysis. Both the upper and lower
jaws appear to be edentulous. Although patchy dark min-
eralization between the left dentary and splenial superfi-
cially resembles teeth, this mineralization is observed
throughout the specimen.
Axial skeleton. At least eight cervical vertebrae are pre-
served in near articulation (Figs 1,2). Some poorly pre-
served fragments underlying the proximal vertebra may
represent the axis; the atlas is either not preserved or is
overlain by the skull but could not be identified in the
X-rays due to low resolution (Supplemental Figs 1, 2). The
vertebrae are elongate, with their length more than twice
exceeding their dorsoventral height in lateral view. The
articular surfaces appear to be heterocoelic. A low neural
spine can be observed in a vertebra caudal in the series.
The thoracic vertebrae are mostly obscured by other ele-
ments. The synsacrum is fully fused with the neural spines,
forming a spinal crest along the dorsal surface. Unfortu-
nately, it is so well consolidated that in the absence of
Figure 3. Maxillary elongation in Early Cretaceous ornithothor-
acines. A, B, Dingavis longimaxilla gen. et sp. nov., holotype,
IVPP V20284; A, photograph; B, interpretative drawing. C,
interpretative drawing of the skull of Rapaxavis (Enantiornithes)
for comparison (modified from O’Connor et al. 2011). Anatomi-
cal abbreviations: an, angular; cv, cervical vertebrae; de, den-
tary; fp, frontal process; fr, frontal; jg, jugal; la, lacrimal; ms,
mandibular symphysis; mx, maxilla; na, nasal; pa, parietal; pm,
premaxilla; ptq, pterygoid quadrate articulation?; qd, quad-
rate; sp, splenial; su, surangular; th, teeth; l and r represent left
and right side, respectively. Scale bars D10 mm.
Table 1. Select measurements of the holotype of Dingavis long-
imaxilla gen. et sp. nov. (IVPP V20284) in mm. Parentheses
indicate incomplete measurements.
Right Left
Skull length 58.64
Synsacrum 28.2
Pygostyle 7.8
Humerus 48.9 (51)
Ulna (44.9) (52)
Carpometacarpus 30.4 29.9
Alular metacarpal 4.1 (3.6)
Alular digit phalanx 1 12.4 12.5
Alular digit phalanx 2 4.9 5
Major digit phalanx 1 14 13.2
Major digit phalanx 2 13.2 13.2
Major digit phalanx 3 3.9 4
Minor digit phalanx 1 6.6 7.9
Scapula 38.4 (36.4)
Pubis 42.7
Femur (16) 36.1
Tibiotarsus 55.6 55.4
Tarsometatarsus 37.9 40.6
Table 2. Comparative rostral lengths of Early Cretaceous Jehol
ornithothoracines (referable to Ornithuromorpha unless other-
wise specified). Measurements were taken from the holotype
specimens with the exception of Yanornis martini, and all speci-
mens were studied first hand with the exception of Xinghaiornis
lini and Gansus zheni. Parentheses indicate estimated
measurements.
Skull
length
Rostral
length
Rostral %
of skull
Dingavis 58.64 37 63
Yanornis martini STM9-51 57 32.7 57
Iteravis (4346) 26 57
Gansus zheni 46.3 26.5 57
Xinghaiornis lini 69.6 46.9 68
Longipteryx (Enantiornithes) 55 (35.6) 65
Longirostravis (Enantiornithes) (33) (25)
Rapaxavis (Enantiornithes) 31 18 59
New Chinese Cretaceous ornithuromorph bird 5
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preserved transverse processes it is impossible to estimate
the number of fused vertebrae. However, the synsacrum is
proportionately long, as in other ornithuromorphs. The cau-
dal series is incompletely preserved; the pygostyle is pre-
served in lateral view revealing a slightly upturned,
triangular profile, characteristic of early ornithuromorphs.
Thoracic girdle. Both scapulae are preserved; the left is
in dorsolateral view and the right is dorsomedially exposed
(Figs 1,2). A well-developed acromion was clearly pres-
ent, but its morphology cannot be clearly determined (acro-
mion small in Xinghaiornis). It appears to be straight. The
scapular blade is strongly curved and tapered as in other
ornithuromorphs. The omal end of the right coracoid is vis-
ible near the proximal end of the right scapula. A fragment
identified as the omal end of the right clavicular ramus is
visible between the right scapula and humerus. It is delicate
and tapered. Partially underlying the left ilium is a frag-
ment we identify as the caudal part of the sternum includ-
ing the left intermediate trabecula (Fig. 2). A more robust
fragment preserved lateral to this piece may be part of the
left lateral trabecula. Fragments ventral to the left scapula
are probably also part of the sternum. Many rib fragments
and several isolated gastralia are preserved ventral to these
fragments, proximal to the left ilium.
Thoracic limb. Both humeri are in caudal view. The
humeral shaft is twisted, clearly visible in the right ele-
ment, which is well preserved compared to most other ele-
ments. The proximal articular surface is strongly convex
proximocaudally. The capital incision is wide and very
shallow. The region of the ventral tubercle lacks any signs
of pneumaticity (excavated in some enantiornithines,
pneumatopore in some Late Cretaceous enantiornithines
and living birds). The deltopectoral crest is slightly less
than shaft width (slightly greater than shaft width in Xing-
haiornis) and extends for more than one-third the length
of the humerus. Proximally, it is not continuous with the
humeral head but separated by a slight concavity. This
crest steadily decreases in width distally but ends rather
abruptly. Distally, the olecranon fossa is well developed
but whether muscle grooves were developed cannot be
determined due to abrasion. The left ulna and radius are
poorly preserved and the two elements overlap on the
right. The ulna is proximally bowed as in other Early Cre-
taceous birds; it has a blunt olecranon process. The
straight radius is fairly robust, being more than half the
thickness of the ulna.
A single free carpal is preserved on the left, and two on
the right; these preserve no anatomical information. The
hand (carpometacarpus Cmajor digit) is 25% longer than
the humerus; in other Early Cretaceous ornithuromorphs
the hand is typically subequal to the humerus (e.g. Hon-
gshanornis,Schizooura,Xinghaiornis,Yanornis)or
shorter (e.g. Iteravis,Gansus,Piscivoravis,Zhongjianor-
nis). The humerus is approximately 10% shorter than the
hand in Yixianornis. Proximally the major and minor
metacarpals are fully fused to the distal carpals. The major
metacarpal is straight with an even thickness; the cranial
margin is weakly concave. The minor metacarpal is
slightly less than half (44%) the thickness of the major
metacarpal. The minor metacarpal is completely straight
(as in Yixianornis,Gansus and others), whereas it is dis-
tinctly bowed in some taxa (e.g. Piscivoravis). Distally,
the minor metacarpal ends short of the major metacarpal.
The distal ends of these two metacarpals are unfused. The
alular metacarpal does not appear to be fully fused to the
major metacarpal (fused on the left, slightly separated on
the right). This element is also proportionately short, being
only 13.7% of the total length of the carpometacarpus,
whereas it is typically 20% or greater in other early orni-
thuromorphs (O’Connor & Sullivan 2014). Clearest on the
left, the alular metacarpal has a moderate extensor process,
also present in some Early Cretaceous ornithuromorphs
(e.g. Gansus,Hongshanornis) but absent in others (e.g.
Archaeorhynchus,Piscivoravis,Schizooura). As a conse-
quence of the extensor process, the proximal margin of the
carpal is concave, as in some basal ornithuromorphs and
most living birds. The alular digit is composed of two pha-
langes; the first is slightly bowed, less than half the length
of the carpometacarpus and roughly the same thickness as
the minor metacarpal. The second phalanx is a weakly
recurved ungual. The proximal two phalanges of the major
digit are nearly equal in length, but the caudal margin of
the first phalanx forms a dorsoventrally compressed keel-
like expansion as in other ornithuromorphs. The caudal
expansion is absent at the proximal end of the phalanx but
rapidly expands, reaching maximum thickness by the proxi-
mal third and maintaining this thickness distally (expanded
proximally in Xinghaiornis). The absence of this expansion
proximally accommodates the phalanx of the minor digit,
preserved in articulation on the right. A similar morphology
is observed in Iteravis. The distal ungual phalanx is small
and nearly straight. The minor digit preserves a single
wedge-shaped phalanx that appears to include the second
phalanx fused to it distally (preserved free in Piscivoravis)
so that the distal end tapers sharply (e.g. Iteravis,
Hongshanornis).
Pelvic girdle. The pelvic girdle is fairly complete but
preserved largely in dorsal view with the elements dorso-
ventrally stacked over one and other obscuring some fea-
tures (Figs 1,2). In dorsal view the cranioventral margin
of the ilium forms nearly a 90angle that separates the
convex rostral margin from the deeply concave lateral
margin, as in many other Jehol ornithuromorphs (e.g.
Archaeorhynchus,Piscivoravis,Schizooura,Xinghaior-
nis). Rostrally the preacetabular wing of the ilium is con-
cave and appears to have been very wide, although this is
exaggerated by compression. The postacetabular wing of
the ilium is medially curved and tapered caudally. The
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left ischium is preserved ventral and medial to the left
ilium. A fragment of the distal end of the right is also pre-
served. The left ischium is medially curved so that it is lat-
erally convex and medially concave. Medial curvature is
observed in other ornithuromorphs preserved in partial
dorsal view (e.g. Piscivoravis,Schizooura). It appears to
have a low dorsal process located mid-corpus, as in most
other ornithuromorphs (a distinct, pointed process appears
to be unique to Xinghaiornis). The ventral surface is con-
cave and the distal half is tapered. The pubes are pre-
served only slightly disarticulated, visible in the X-ray
(Supplemental Fig. 1). The medially and dorsally curved
pubes are distally unfused but would have contacted in
vivo, as evidenced from the change in texture visible on
the medial surface of the distal left pubis. The distal ends
are expanded relative to the shaft, as in Iteravis, although
they do not form a distinct boot like that present in some
enantiornithines (e.g. Pengornis,Longipteryx).
Pelvic limb. The femur is short and straight, slightly
shorter than the tarsometatarsus (femur much longer
than tarsometatarsus in Xinghaiornis) and approximately
65% the length of the tibiotarsus (Table 1). The lateral sur-
face of the left femur is smooth proximally, indicating
the absence of a posterior trochanter, present in enantiorni-
thine birds (Chiappe & Walker 2002). A weak fibular con-
dyle appears to be present distally. The tibiotarsus bears a
proximocranially projecting cnemial crest and a short fibu-
lar crest. Distally, in cranial view, a well-developed exten-
sor sulcus is visible on the left. On the right in caudal view
the tibial cartilaginous trochlea is well developed but is dis-
tally limited in its extension up the cranial surface, similar
to other basal ornithuromorphs (e.g. Piscivoravis). The fib-
ula is short, fat and rapidly tapered distally.
The left tarsometatarsus is preserved in dorsal view,
whereas the right is in plantar view. The tarsometatarsus
is fully fused, although the presence of shallow grooves
allows identification of the individual metatarsals; these
grooves may represent a rudimentary flexor sulcus. Meta-
tarsal III is the longest, followed by metatarsal IV; meta-
tarsal II ends short of the metatarsal IV trochlea. A fairly
robust tubercle for the m. tibialis cranialis is present on
the dorsomedial surface of metatarsal III, just below the
proximal articular surface where this metatarsal is plan-
tarly displaced, as in other ornithuromorphs. This tubercle
is well developed in enantiornithines whereas it is typi-
cally more delicate in ornithuromorphs (e.g. Apsaravis,
Hongshanornis) or not developed at all (e.g. Piscivora-
vis); the tubercle in Dingavis is well developed compared
to other ornithuromorphs. As in other basal ornithuro-
morphs, no hypotarsus is present. Very low but distinct
medial and lateral plantar crests are present, as in Gansus
(Y.-M. Wang et al. 2015), but the plantar surface is not
deeply excavated as in Xinghaiornis. The metatarsal III
trochlea is the widest. The trochlea of metatarsals II and
IV are preserved plantarly displaced relative to metatarsal
III. A vascular foramen is present between metatarsals III
and IV, visible on the left. The trochlea of metatarsal II
appears to be strongly angled, similar to Piscivoravis. The
lateral condyle of the metatarsal IV trochlea, excavated
by a deep collateral pit, projects farther plantarly than the
medial condyle, also observed in Apsaravis. The right
metatarsal I is preserved nearly in articulation (Figs 1,2).
It is short (12% of metatarsal II) and articulates with the
plantar surface of metatarsal II so that the hallux was fully
reversed. It is also slightly twisted so that the surface
between the two articulations is concave. The shaft is
sharply tapered proximally; the trochlea is mediolaterally
wide. The pedal phalangeal formula is 2-3-4-5-x. The two
phalanges of the first digit are subequal in length. The
pedal phalanges in the other digits decrease in length dis-
tally. The proximal phalanx of the third digit is the longest
and most robust in the foot. The total length of the third
digit is less than that of the tarsometatarsus, as in Chang-
maornis (longer in Gansus) (Y.-M. Wang et al. 2013).
The pedal unguals are all small, subequal, with very little
curvature. This foot morphology strongly resembles that
of Changmaornis from the Xiagou Formation (Y.-M.
Wang et al. 2013,2015).
Gastroliths. Approximately 40 gastroliths are visible in
the region of the pelvic girdle. Additional stones are scat-
tered about the slab. These stones are fairly large (24
mm), smooth and moderately polished. We interpret these
as gizzard stones underlying the pelvic region. The deli-
cate overlying bone is crushed and broken, revealing the
underlying stones. These gastroliths are similar in size,
morphology and mineralogy to those preserved in speci-
mens of Iteravis and Gansus (S. Zhou et al. 2014; Y.-M.
Wang et al. 2015) but are more numerous in IVPP
V20284, potentially indicating slight dietary differences.
Alternatively, the gastroliths in specimens of Iteravis and
Gansus may represent incomplete aggregates.
Phylogenetic analysis
In order to confirm our morphological inferences, we
placed IVPP V2084 in an expanded version of the
O’Connor & Zhou (2013) Mesozoic bird matrix (see Sup-
plemental material). The data set has been modified to
include only Jeholornis (other taxa considered junior syno-
nyms of this taxon) and exclude the probable scansoriopter-
ygid Zhongornis. Recently described ornithuromorphs were
also included (Archaeornithura,Iteravis,Schizooura).
Although very little information is available we also added
Xinghaiornis, the first analysis to include this important
taxon (X.-R. Wang et al. 2013). The modified matrix con-
sists of 61 taxa, 30 of which are considered ornithuro-
morphs. We analysed the data using the TNT software
New Chinese Cretaceous ornithuromorph bird 7
Downloaded by [Jingmai K. O’Connor] at 06:38 15 January 2016
(Goloboff et al. 2008). We conducted a heuristic search
using tree bisection reconnection (TBR), retaining the sin-
gle shortest tree out of every 1000 replications. This pro-
duced three most parsimonious trees with a length of 889
steps. A second round of TBR produced a total of 860
most parsimonious trees of the same length. In the strict
consensus tree (Fig. 4), Dingavis is part of a basal poly-
tomy of taxa more derived than Archaeorhynchus,which
includes Patagopteryx,Jianchangornis,Zhongjianornis,
Schizooura,Xinghaiornis,Vorona and Chaoyangia. This
tree is only weakly supported, with a consistency index of
0.374 and a retention index of 0.651. Bremer support val-
ues are also very low indicating that the current topology
would largely collapse in trees a single step longer.
Discussion
The new specimen IVPP V20284 can be assigned to the
Ornithuromorpha on the basis of the curved scapula,
plough-shaped pygostyle, globose humeral head, caudally
expanded first phalanx of the major digit, proximally pro-
jecting cnemial crest on the tibiotarsus and well-fused tar-
sometatarsus. IVPP V20284 can be distinguished from
other known taxa by its elongate rostrum and maxilla,
hand that is 25% longer than the humerus and proportion-
ately short alular metacarpal; thus, we erect the new taxon
Dingavis longimaxilla gen. et sp. nov. Previously, all bird
specimens from the newly discovered Sihedang locality
appeared to be referable to a single taxon, Iteravis huch-
zermeyeri (S. Zhou et al. 2014). However, as discoveries
continued, additional ornithuromorph diversity has sur-
faced (Liu et al. 2014). These authors described three new
specimens they assigned to a new species of Gansus,G.
zheni. Although we do not consider these specimens to be
referable to Gansus, previously only known from the Xia-
gou Formation (You et al. 2006), we also recognize minor
differences that suggest they are not referable to Iteravis
huchzermeyeri. The discovery of the edentulous Dingavis
provides evidence of greater trophic diversity in the Sihe-
dang avifauna. Furthermore, similarities in preservation
(bones somewhat three dimensional, colour of the fossil-
ized bone and similar lithology of the slab) suggest that
the holotype of Xinghaiornis lini may also be from Sihe-
dang rather than the Sihetun locality, as reported (Z.-H.
Zhou pers. comm.). A study of the histology in the holo-
type of Iteravis huchzermeyeri has suggested the three-
dimensional preservation of Sihedang specimens is tapho-
nomic, not due to the presence of medullary bone
(O’Connor et al.2015). This increased taxonomic diver-
sity (potentially as many as four ornithuromorph species)
further weakens hypotheses that the Sihedang locality
may represent a breeding site of Iteravis (S. Zhou et al.
2014).
Rostralization in Early Cretaceous birds
In Aves, the plesiomorphic skull is characterized by small
premaxillae and mesorostrine proportions. In neorni-
thines, the premaxilla is expanded and forms a majority of
the rostrum in all taxa, whereas the maxilla is greatly
reduced. Expansion of the premaxilla is a derived feature
within Aves that evolved outside Neornithes, present in
Late Cretaceous ornithurine Hesperornis (Marsh 1880).
Varying degrees of premaxillary expansion also evolved
in parallel in the Early Cretaceous Confuciusornithi-
formes and in at least one lineage of enantiornithines,
present in the Late Cretaceous Gobipteryx (Elzanowski
1977; Chiappe et al. 2001).
In contrast, rostral elongation in Dingavis and the Early
Cretaceous longipterygid enantiornithines was achieved
primarily by lengthening the maxilla (e.g. Rapaxavis,
Longipteryx,Longirostravis)(Fig. 3C) an extinct mor-
photype within Aves. Notably, the premaxillary corpus is
also somewhat elongated in these taxa relative to the
Figure 4. Hypothetical phylogenetic relationships of Mesozoic
birds (trees D860, length D889 steps). Nodes: 1, Aves; 2,
Pygostylia; 3, Confuciusornithiformes; 4, Sapeornithiformes; 5,
Enantiornithes; 6, Longipterygidae; 7, Ornithuromorpha; 8,
Ornithurae; 9, Hesperornithiformes; 10, Neornithes.
8 J. K. O’Connor et al.
Downloaded by [Jingmai K. O’Connor] at 06:38 15 January 2016
plesiomorphic condition (O’Connor & Chiappe 2011). The
upper limit in rostral elongation in both lineages is approxi-
mately equal (Longipteryx 65%; Dingavis 6365%). This
could be merely coincidence or it may suggest that there
are structural limitations to elongating the rostrum through
the maxilla that do not permit truly longirostrine propor-
tions (>70% skull length). This may ultimately have led
this structural organization to be abandoned during avian
evolution. Notably, if limitations existed in the construction
of the avian skull, no such structural limitations are present
in the Pterosauria. This clade includes taxa with rostral
elongation achieved through both the premaxilla (e.g. Pter-
anodon,Tropeognathus) and maxilla (e.g. Gnathosaurus,
Zhenyuanopterus) (Witton 2013) and also reached
extremes of rostralization even greater than observed in
Aves (Marug
an-Lob
on & Buscalioni 2003). We suggest
this may be due to differences in the articulation between
the premaxilla and the maxilla in pterosaurs (extensive
contact between the bones) and birds (short articulation
between fairly delicate processes), the former affording
greater structural stability.
The longest rostrum in an Early Cretaceous bird is
observed in Xinghaiornis (X.-R. Wang et al. 2013). This
taxon shows yet another skull configuration in which the
premaxilla and maxilla contribute equally to the facial
margin. In Xinghaiornis both the premaxilla and the max-
illa are elongated but the premaxilla significantly more so
than the maxilla, which plesiomorphically is much more
elongate than the premaxilla. Although Xinghaiornis is
not truly longirostrine in proportions, the presence of pre-
maxillary elongation probably allowed this lineage to
achieve a greater degree of rostralization than any other in
the Early Cretaceous. Xinghaiornis and Dingavis are both
from the Yixian Formation, probably both from the Sihe-
dang locality, and both fall in the polytomy of basal orni-
thuromorphs only more derived than Archaeorhynchus
(Fig. 4). Differences in the rostral configuration of these
two sympatric taxa highlight the diversity of skull config-
urations present in early birds as they diversified into new
niches and evolved rostral modifications to suit a variety
of trophic habitats. Although parallel diversity evolved in
the Neornithes, this was achieved primarily through modi-
fications to the premaxilla, whereas basal birds show a
greater diversity of configurations but within a more lim-
ited morphospace. Dingavis,Xinghaiornis and the longip-
terygids thus represent early avian experiments in skull
rostralization.
Acknowledgements
We thank Dahan Li for preparing the specimen, and Jie
Zhang for photography. JO’C was supported by the Insti-
tute of Vertebrate Paleontology and Paleontology
[KN215509], and MW by the National Science
Foundation for Fostering Talents in Basic Research of the
National Natural Science Foundation of China
[J1210008]. We also thank two anonymous reviewers for
their comments on an earlier version of this manuscript.
Supplemental data
Supplemental material for this article can be accessed
here: http://dx.doi.org/10.1080/14772019.2015.1129518
ORCID
Jingmai K. O’Connor http://orcid.org/0000-0002-3898-8283
Min Wang http://orcid.org/0000-0001-8506-1213
Han Hu http://orcid.org/0000-0001-5926-7306
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Downloaded by [Jingmai K. O’Connor] at 06:38 15 January 2016
... The frontals are not fused to each other ( Figures 4A,B), which represents the usual condition in non-ornithurine birds, including adult specimens of Archaeorhynchus (Wang et al., 2016;Plateau and Foth, 2020). The right frontal bone is more or less complete and exposed in laterodorsal view. ...
... Consequently, exact identification of particular processes is not possible. Due to the almost pentaradial arrangement of the processes, however, it is clear that the cervicals bear carotid processes, similar to Archaeorhynchus, Schizooura, and other Euornithes Zhou et al., 2013;Wang et al., 2016). The exposed neural canals are enlarged and rounded. ...
... The left coracoid is exposed in anterior view and lies in close association with the anterior end of the left scapula and the proximal end of the left humerus ( Figure 3C). As preserved, the scapula and coracoid are unfused, which is the typical situation for Early Cretaceous ornithothoracine birds (Sereno et al., 2002;Clarke et al., 2006;Zhou and Zhang, 2006;Wang et al., 2016;Chiappe et al., 2020). The coracoid is a strut-like element. ...
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... Jeholornithiformes is an early-diverging bird group from the Early Cretaceous Jehol Biota of China, retaining numerous primitive features, such as a long, bony tail (Zhou & Zhang, 2002;O'Connor et al., 2012;Rauhut et al., 2018). Among Aves, they are resolved by almost all phylogenetic analyses as being the earliest diverging Cretaceous stem bird lineages, crownward only to the Late Jurassic Archaeopteryx Meyer, 1861 from the Solnhofen Limestones in southern Germany (Zhou & Zhang, 2007;Zhou, 2014;O'Connor et al., 2016O'Connor et al., , 2017Wang et al., 2019bWang et al., , 2020bWang et al., 2019a). Jeholornithiformes is the sister lineage of Pygostylia, a clade that includes the edentulous Confuciusornithiformes, Sapeornis Zhou & Zhang, 2002, in addition to the species-rich Enantiornithes and Ornithuromorpha (the lineage that gave rise to modern birds), with the last two of these clades together forming Ornithothoraces. ...
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Jeholornis is a representative of the earliest-diverging bird lineages, providing important evidence of anatomical transitions involved in bird origins. Although ~100 specimens have been reported, its cranial morphology remains poorly documented owing to poor two-dimensional preservation, limiting our understanding of the morphology and ecology of the key avian lineage Jeholornithiformes, in addition to cranial evolution during the origin and early evolution of birds. Here, we provide a detailed description of the cranial osteology of Jeholornis prima, based primarily on high-quality, three-dimensional data of a recently reported specimen. New anatomical information confirms the overall plesiomorphic morphology of the skull, with the exception of the more specialized rostrum. Data from a large sample size of specimens reveal the dental formula of J. prima to be 0–2–3 (premaxillary–maxillary–dentary tooth counts), contrary to previous suggestions that the presence of maxillary teeth is diagnostic of a separate species, Jeholornis palmapenis. We also present evidence of sensory adaptation, including relatively large olfactory bulbs in comparison to other known stem birds, suggesting that olfaction was an important aspect of Jeholornis ecology. The digitally reconstructed scleral ring suggests a strongly diurnal habit, supporting the hypothesis that early-diverging birds were predominantly active during the day.
... Step III occurs in early-diverging Euornithes and involves increased downward curving of caudal end of scapular blade (O'Connor et al., 2016) shifting of glenoid fossa of scapula onto the external surface of bone, causing the fossa to face dorsolaterally (Wellnhofer et al., 2009) appearance of the procoracoid process on the scapular wing of coracoid (Clarke et al., 2006) medial curving and further elongation of the acrocoracoid process (Novas et al., 2021) further reduction in angle between the scapula and coracoid (Wellnhofer et al., 2009) and the complete bony enclosure of triosseal canal. Regarding distinctive pectoral girdle features in particular taxa, Jeholornis has an unusual combination of a prominent procoracoid process and a large supracoracoid foramen (Lefèvre et al., 2014;Turner et al., 2012;Wang et al., 2020a), Sapeornis has a dorsolaterally oriented acrocoracoid process, and Enantiornithes is characterized by an extremely small scapular wing of the coracoid, a single scapula-coracoid articulation, elongation of the hypocleidium, presence of caudal grooves on the furcular rami and a keel on the caudal surface of the hypocleidium, and further solidification of the furcula-scapula articulation. ...
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The morphology of the pectoral girdle, the skeletal structure connecting the wing to the body, is a key determinant of flight capability, but in some respects is poorly known among stem birds. Here, the pectoral girdles of the Early Cretaceous birds Sapeornis and Piscivorenantiornis are reconstructed for the first time based on computed tomography and three-dimensional visualization, revealing key morphological details that are important for our understanding of early flight evolution. Sapeornis exhibits a double articulation system (widely present in non-enantiornithine pennaraptoran theropods including crown birds) which involves, alongside the main scapula-coracoid joint, a small subsidiary joint, though variation exists with respect to the shape and size of the main and subsidiary articular contacts in non-enantiornithine pennaraptorans. This double articulation system contrasts with Piscivorenantiornis in which a spatially restricted scapula-coracoid joint formed by a single set of opposing articular surfaces, a feature also present in other members of Enantiornithines, a major clade of stem birds known only from the Cretaceous. The unique single articulation system may reflect correspondingly unique flight behavior in enantiornithine birds, but this hypothesis requires further investigation from a functional perspective. Our renderings indicate that both Sapeornis and Piscivorenantiornis had a partially closed triosseal canal (a passage for muscle tendon that plays a key role in raising the wing), and our study suggests that this type of triosseal canal occurred in all known non-euornithine birds except Archaeopteryx , representing a transitional stage in flight apparatus evolution before the appearance of a fully closed bony triosseal canal as in modern birds. Our study reveals additional lineage-specific variations in pectoral girdle anatomy, as well as significant modification of the pectoral girdle along the line to crown birds. These modifications produced diverse pectoral girdle morphologies among Mesozoic birds, which allowed a commensurate range of capability levels and styles to emerge during the early evolution of flight.
... In contrast, despite the fact the rostrum is proportionately enlarged relative to other enantiornithines, forming a morphology superficially similar to that in modern toucans (Ramphastidae), the premaxilla remains very small in Falcatakely . In this taxon, as in other enantiornithines and non-neornithine ornithuromorphs, rostral expansion is achieved through an enlarged maxilla (O'Connor et al. 2016). ...
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A new enantiornithine bird is described on the basis of a well preserved partial skeleton from the Upper Cretaceous Qiupa Formation of Henan Province (central China). It provides new evidence about the osteology of Late Cretaceous enantiornithines, which are mainly known from isolated bones; in contrast, Early Cretaceous forms are often represented by complete skeletons. While the postcranial skeleton shows the usual distinctive characters of enantiornithines, the skull displays several features, including confluence of the antorbital fenestra and the orbit and loss of the postorbital, evolved convergently with modern birds. Although some enantiornithines retained primitive cranial morphologies into the latest Cretaceous Period, at least one lineage evolved cranial modifications that parallel those in modern birds.
... Longipteryx chaoyangensis (junior synonyms "Camptodontornis yangi" and "Shengjingornis yangi") is known from the Yixian and Jiufotang formations near Chaoyang and Jinzhou in Liaoning Province, China Li et al., 2012;Wang et al., 2015;Zhang et al., 2000;Zhang et al., 2001). Commonly, Longipteryx is placed together with Boluochia, Rapaxavis, Shanweiniao, and Longirostravis, forming the clade Longipterygidae (O'Connor et al., 2016;Wang et al., 2018;. This clade is characterized by rostra that account for 60% or more of the total skull length ( Figure 1), a dentition that is restricted to the premaxilla and rostral tip of the dentary, and a proportionately large pygostyle (O'Connor et al., 2009;O'Connor et al., 2011a). ...
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While the morphology and evolution of the quadrate among early birds and through the evolutionary origin of birds is not well known, we add to knowledge about that past diversity through description of the morphology of the quadrate in the unusually elongate skull of the Cretaceous enantiornithine bird Longipteryx chaoyangensis. The lateral and caudal surfaces of the quadrate are well exposed in two specimens revealing morphologies typical of early birds and their dinosaurian close relatives like a small otic head and two mandibular condyles. However, both skeletons exhibit quadrates with a unique, enlarged lateral crest that has not been previously described among Mesozoic birds. It is possible that the rostral surface of this lateral expansion served as the origination site for enlarged jaw musculature in a manner similar to the enlarged subcapitular tubercle in extant galloanserine birds. The caudally concave surface of the quadrate likely reflects some aspect of cranial pneumaticity, with its shape and position reminiscent of quadrates found in close non‐avialan maniraptoran relatives. It is possible that this lateral crest has a wider distribution among enantiornithines and other early birds and that the crest has been misidentified as the orbital process in some more damaged specimens. In addition, the enlarged lateral mandibular condyle (relative to the medial condyle) differs from the condition typically reported among enantiornithines and could indicate a difference in jaw function or mechanics in this bird with an elongated rostrum, or simply misinterpretations of morphology. Further examination of the quadrate in temporally early and phylogenetically stemward birds, along with their close outgroups, could greatly impact the study of several different aspects of bird biology including assessment of phylogenetic relationships, interpretation of the function and kinematics of the skull, reconstruction of foraging paleoecology, and evolution of skull morphological diversity among Mesozoic birds. Study of the quadrate of the extinct enantiornithine bird Longipteryx documents new morphologies among birds including an extensive lateral crest and caudolateral fossa that may have been related to evolutionary changes in their bite, and may provide new material for phylogenetic assessment across stemward birds. Our work also highlights an increase in morphological character variability among enantiornithine quadrates, and indicates some potential areas of misinterpretation in previous studies.
... Superficially, gastral mass morphology in Jehol paravians can be roughly divided into three types: 1) a large number of proportionately small gastroliths that are tightly aggregated together, presumably held together by stomach contents due to the tightly packed nature of their association in vivo-this morphology is observed in Caudipteryx (Figure 2A) (Ji et al., 1998;, Jeholornis ( Figure 2B) , and Archaeorhynchus (STM7-11, IVPP V17075, IVPP V17091) Wang et al., 2018); 2) a small number of proportionately larger stones found in loose association-this morphology is observed in Iteravis IVPP V23346 ( Figure 2E), Dingavis IVPP V20284 ( Figure 2G) (O'Connor et al., 2016) and Hongshanornis DNHM D2945 ; and 3) a small number of proportionately larger stones preserved tightly compacted together, protruding from the surface of the slab-this morphology is observed in Bellulornis IVPP V17970 ( Figure 2H) (Wang et al., 2016b). In addition, this gastral mass morphology is also found in Gansus yumenensis from the Early Cretaceous Xiagou Formation in Gansus Province, northwestern China. ...
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Gastroliths, where preserved, can provide indirect evidence regarding diet in extinct avian and non-avian dinosaurs. Masses of gastroliths consistent with the presence of a gastric mill are preserved in many Early Cretaceous Jehol birds mostly belonging to the Ornithuromorpha. Gastroliths are also present in basal birds Sapeornis and Jeholornis in which herbivory is supported by direct evidence these taxa consumed seeds in the form of crop or stomach contents. Although gastroliths have been correlated with herbivory in non-avian dinosaurs, the presence of gastroliths and bone together in Ambopteryx calls this association in to question. Despite being known from greater numbers of specimens than other avian lineages, no unequivocal direct or indirect evidence of diet has been recovered from Jehol deposits for the Enantiornithes. A referred specimen of Bohaiornis guoi IVPP V17963 was described as preserving a small number of gastroliths interpreted as rangle, gastroliths whose function is cleaning the stomach in extant raptorial birds. However, based on comparison with gastroliths in other Jehol birds, it has alternatively been suggested that the identified structures are not ingested stones at all but some unusual mineral precipitate. Considering the limited evidence regarding diet in Enantiornithes and the importance of accurately identifying the traces in Bohaiornis in order to understand the enantiornithine digestive system, we extracted two samples of these purported gastroliths and explored these traces using computerized laminography scanning, scanning electron microscopy, energy dispersive x-ray spectroscopy, ground sections, and body size to gastral mass regressions. Similar analyses were conducted on gastroliths extracted from undisputed gastral masses of two Jehol ornithuromorphs and the non-avian pennaraptoran Caudipteryx. The combined results contradict the hypothesis that these traces are gastroliths and supports the interpretation they are mineral precipitate, most likely authigenic quartz (chalcedony). Although authigenesis is commonly responsible for the preservation of soft tissues, it is unclear if these traces record part of the tissues of this Bohaiornis. This study highlights the importance of a multidisciplinary approach in understanding unusual traces in the fossil record and reveal a previously unidentified taphonomic phenomenon in fossils from Jehol deposits.
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We describe six specimens consisting of cranial remains and associated partial presacral axial series belonging to ornithuromorph birds from the Changma locality of the Lower Cretaceous Xiagou Formation of northwestern Gansu Province, China. Comparison among specimens is limited by the paucity of overlapping elements, their differing exposed views, and, in some specimens, poor preservation. Despite this, three separate taxa are represented, evidenced by differences in their dentary dentitions: one specimen is edentulous, another has sharp, closely spaced, relatively high-crowned and peg-like teeth, and a third preserves blunt, relatively low-crowned teeth placed in a communal groove, a morphology previously reported among adult birds only in Hesperornithiformes. We propose that the high-crowned specimen may be referred to Gansus yumenensis based on shared similarities with the closely related Iteravis huchzermeyeri, including a very similar dentition and an edentulous premaxilla with elongate, unfused frontal processes and no palatal processes. The two other specimens are considered new taxa, for which we erect the names Meemannavis ductrix gen. et sp. nov. and Brevidentavis zhangi gen. et sp. nov. These new specimens confirm that the Changma locality is dominated by ornithuromorph birds and contribute to a better understanding of this important avifauna. The observed variation in dental morphology hints at trophic diversity like that observed in ornithuromorphs from the penecontemporaneous Jehol Group of northeastern China. This article is protected by copyright. All rights reserved.
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Enantiornithes are the most successful group of Mesozoic birds, arguably representing the first global avian radiation,1, 2, 3, 4 and commonly resolved as the sister to the Ornithuromorpha, the clade within which all living birds are nested.1,3 The wealth of fossils makes it feasible to comparatively test evolutionary hypotheses about the pattern and mode of eco-morphological diversity of these sister clades that co-existed for approximately 65 Ma. Here, we report a new Early Cretaceous enantiornithine, Yuanchuavis kompsosoura gen. et. sp. nov., with a rectricial fan combined with an elongate central pair of fully pennaceous rachis-dominated plumes, constituting a new tail plumage previously unknown among nonavialan dinosaurs and Mesozoic birds but which strongly resembles the pintail in many neornithines. The extravagant but aerodynamically costly long central plumes, as an honest signal of quality, likely evolved in enantiornithines through the handicap process of sexual selection. The contrasting tail morphotypes observed between enantiornithines and early ornithuromorphs reflect the complex interplay between sexual and natural selections and indicate that each lineage experienced unique pressures reflecting ecological differences. As in neornithines, early avialans repeatedly evolved extravagant structures highlighting the importance of sexual selection in shaping the plumage of feathered dinosaurs, even early in their evolutionary history.
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Birds are some of the most diverse organisms on Earth, with species inhabiting a wide variety of niches across every major biome. As such, birds are vital to our understanding of modern ecosystems. Unfortunately, our understanding of the evolutionary history of modern ecosystems is hampered by knowledge gaps in the origin of modern bird diversity and ecosystem ecology. A crucial part of addressing these shortcomings is improving our understanding of the earliest birds, the non‐avian avialans (i.e. non‐crown birds), particularly of their diet. The diet of non‐avian avialans has been a matter of debate, in large part because of the ambiguous qualitative approaches that have been used to reconstruct it. Here we review methods for determining diet in modern and fossil avians (i.e. crown birds) as well as non‐avian theropods, and comment on their usefulness when applied to non‐avian avialans. We use this to propose a set of comparable, quantitative approaches to ascertain fossil bird diet and on this basis provide a consensus of what we currently know about fossil bird diet. While no single approach can precisely predict diet in birds, each can exclude some diets and narrow the dietary possibilities. We recommend combining (i) dental microwear, (ii) landmark‐based muscular reconstruction, (iii) stable isotope geochemistry, (iv) body mass estimations, (v) traditional and/or geometric morphometric analysis, (vi) lever modelling, and (vii) finite element analysis to reconstruct fossil bird diet accurately. Our review provides specific methodologies to implement each approach and discusses complications future researchers should keep in mind. We note that current forms of assessment of dental mesowear, skull traditional morphometrics, geometric morphometrics, and certain stable isotope systems have yet to be proven effective at discerning fossil bird diet. On this basis we report the current state of knowledge of non‐avian avialan diet which remains very incomplete. The ancestral dietary condition in non‐avian avialans remains unclear due to scarce data and contradictory evidence in Archaeopteryx. Among early non‐avian pygostylians, Confuciusornis has finite element analysis and mechanical advantage evidence pointing to herbivory, whilst Sapeornis only has mechanical advantage evidence indicating granivory, agreeing with fossilised ingested material known for this taxon. The enantiornithine ornithothoracine Shenqiornis has mechanical advantage and pedal morphometric evidence pointing to carnivory. In the hongshanornithid ornithuromorph Hongshanornis only mechanical advantage evidence indicates granivory, but this agrees with evidence of gastrolith ingestion in this taxon. Mechanical advantage and ingested fish support carnivory in the songlingornithid ornithuromorph Yanornis. Due to the sparsity of robust dietary assignments, no clear trends in non‐avian avialan dietary evolution have yet emerged. Dietary diversity seems to increase through time, but this is a preservational bias associated with a predominance of data from the Early Cretaceous Jehol Lagerstätte. With this new framework and our synthesis of the current knowledge of non‐avian avialan diet, we expect dietary knowledge and evolutionary trends to become much clearer in the coming years, especially as fossils from other locations and climates are found. This will allow for a deeper and more robust understanding of the role birds played in Mesozoic ecosystems and how this developed into their pivotal role in modern ecosystems. Video abstract
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We report on a new species of ornithuromorph bird, Iteravis huchzermeyeri gen. et sp. nov., from the previously unreported Sihedang locality of the Lower Cretaceous Yixian Formation, the oldest ornithuromorph bearing deposit in the world. Unlike most other Cretaceous localities, specimens from this new quarry are largely referable to Ornithuromorpha, similar to the Lower Cretaceous Aptian Xiagou Formation in Gansu Province. Also similar to the Xiagou avifauna, the fauna at Sihedang is largely dominated by a single taxon (described here). Differences in faunal dominance may suggest the Sihedang records a unique ecological habitat. This may also explain the dominance of Gansus in the younger Xiagou Formation locality and suggests that previous hypotheses regarding the shift in dominance between Enantiornithes and Ornithuromorpha need to be reassessed in terms of potential ecological biases due to limited sampling. Furthermore, the recognition of an ornithuromorph dominated locality in the Sihedang significantly weakens the signal of such an inferred trend. Compared to most Jehol birds, the new specimen is relatively better preserved in three dimensions revealing morphological details of the skeleton, as well as preserves feather impressions including a rectricial morphology previously unknown among Mesozoic birds. © 2014, Science China Press and Springer-Verlag Berlin Heidelberg.
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Skulls of Gobipteryx (Aves) from the Upper Cretaceous of Mongolia Andrzej Elzanowski Palaeontologia Polonica 37 (1977), 153-165 Following a preliminary report (Elzanowski 1974), the holotype skull of Gobipteryx minuta is redescribed and another cranial specimen described for the first time. The second specimen confirms the palaeognathous pattern of the palate and (upper) jaw as reconstructed from the poorly preserved palate of the holotype specimen. The avian identity of Gobipteryx is reaffirmed despite claims to the contrary (Brokorb 1976).
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We describe for the first time the histology of an ornithuromorph bird from the Lower Cretaceous Jehol Group, revealing the bone structure of one of the oldest members of this derived clade. The newly discovered Sihedang locality of the Yixian Formation in northeastern China preserves the oldest ornithuromorph dominated avifauna, with all collected birds referable to a single taxon, Iteravis huchzermeyeri. These specimens are all preserved in a relatively greater degree of three-dimensionality compared to Jehol specimens from other localities. We sampled a specimen of Iteravis in order to test the hypothesis that this aggregation of birds may represent a breeding colony. Although medullary bone is known to facilitate three-dimensional preservation, this bone tissue was not present in the histological samples. The specimen is nearly adult with regards to skeletal fusion, and histology indicates medullary expansion had occurred and an inner circumferential layer had already formed. However, lines of arrested growth are absent. Overall the bone histology is comparable to Ichthyornis; this is consistent with the derived phylogenetic placement inferred for this new taxon relative to previously sampled basal ornithuromorphs (Patagopteryx, Hollanda), which all indicate they required more than one year to reach adulthood. This suggests that the modern avian growth strategy evolved in the Early Cretaceous in non-ornithurine birds.
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Although more than half of the evolution of birds occurred during the Mesozoic Era our understanding of this long history focused on the spectacular specimens of the Late Jurassic Archaeopteryx lithographica and the more derived Late Cretaceous hesperornithiforms and ichthyornithiforms for over a century of paleontological research. In the last decade, however, a tremendous burst of new evidence—perhaps unparalleled in the field of vertebrate paleontology—has been uncovered. Indeed, the number of species of early birds described during the 1990s nearly tripled the number of taxa discovered during the previous 130 years elapsed since the discovery of Archaeopteryx in the mid-1800s.
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Ornithuromorpha is the most inclusive clade containing extant birds but not the Mesozoic Enantiornithes. The early evolutionary history of this avian clade has been advanced with recent discoveries from Cretaceous deposits, indicating that Ornithuromorpha and Enantiornithes are the two major avian groups in Mesozoic. Here we report on a new ornithuromorph bird, Archaeornithura meemannae gen. et sp. nov., from the second oldest avian-bearing deposits (130.7[thinsp]Ma) in the world. The new taxon is referable to the Hongshanornithidae and constitutes the oldest record of the Ornithuromorpha. However, A. meemannae shows few primitive features relative to younger hongshanornithids and is deeply nested within the Hongshanornithidae, suggesting that this clade is already well established. The new discovery extends the record of Ornithuromorpha by five to six million years, which in turn pushes back the divergence times of early avian lingeages into the Early Cretaceous.
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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.
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A new species of enantiornithine bird from the Lower Cretaceous Yixian Formation of northeastern China is reported. The new taxon, Shanweiniao cooperorum, possesses several enantiornithine synapomorphies as well as the elongate rostral morphology (rostrum equal to or exceeding 60% the total length of the skull) of the Chinese early Cretaceous enantiornithines, Longipteryx chaoyangensis and Longirostravis hani. The discovery of this new specimen highlights the existence of a diverse clade of trophically specialized enantiornithines, Longipterygidae, for which we present phylogenetic support in a new comprehensive cladistic analysis of Mesozoic birds. Shanweiniao provides new information on the anatomy of longipterygids, and preserves a rectricial morphology previously unknown to enantior-nithines, with at least four tail feathers closely arranged. This supports the hypothesis that enantiornithines were strong fliers and adds to the diversity of known tail morphologies of these Cretaceous birds.
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The midline pattern of sternal ossification characteristic of the Cretaceous enantiornithine birds is unique among the Ornithodira, the group containing birds, non-avian dinosaurs and pterosaurs. This has been suggested to indicate that Enantiornithes is not the sister group of Ornithuromorpha, the clade that includes living birds and their close relatives, which would imply rampant convergence in many non-sternal features between enantiornithines and ornithuromorphs. However, detailed comparisons reveal greater similarity between neornithine (i.e. crown group bird) and enantiornithine modes of sternal ossification than previously recognized. Furthermore, a new subadult enantiornithine specimen demonstrates that sternal ossification followed a more typically ornithodiran pattern in basal members of the clade. This new specimen, referable to the Pengornithidae, indicates that the unique ossification pattern observed in other juvenile enantiornithines is derived within Enantiornithes. A similar but clearly distinct pattern appears to have evolved in parallel in the ornithuromorph lineage. The atypical mode of sternal ossification in some derived enantiornithines should be regarded as an autapomorphic condition rather than an indication that enantiornithines are not close relatives of ornithuromorphs. Based on what is known about molecular mechanisms for morphogenesis and the possible selective advantages, the parallel shifts to midline ossification that took place in derived enantiornithines and living neognathous birds appear to have been related to the development of a large ventral keel, which is only present in ornithuromorphs and enantiornithines. Midline ossification can serve to medially reinforce the sternum at a relatively early ontogenetic stage, which would have been especially beneficial during the protracted development of the super-precocial Cretaceous enantiornithines.This article is protected by copyright. All rights reserved.