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A Nearly Modern Amphibious Bird from the Early Cretaceous of Northwestern China

  • Institute of Vertebrate Paleontology and Paleoanthropology,Chinese Academy of Sciences, Chinese Academy of Sciences

Abstract and Figures

Three-dimensional specimens of the volant fossil bird Gansus yumenensis from the Early Cretaceous Xiagou Formation of northwestern China demonstrate that this taxon possesses advanced anatomical features previously known only in Late Cretaceous and Cenozoic ornithuran birds. Phylogenetic analysis recovers Gansus within the Ornithurae, making it the oldest known member of the clade. The Xiagou Formation preserves the oldest known ornithuromorph-dominated avian assemblage. The anatomy of Gansus, like that of other non-neornithean (nonmodern) ornithuran birds, indicates specialization for an amphibious life-style, supporting the hypothesis that modern birds originated in aquatic or littoral niches.
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to such indirect dissociations, which is indi-
cated as Scheme C in Fig. 4.
The prediction (1) that N(O)–H bond fis-
sion after photoexcitation to the
ps* state
represents an efficient nonradiative decay path-
way for heteroaromatics like imidazole, pyrrole,
and phenol in the gas phase is thus con-
firmed, irrespective of whether the
ps* state
is populated by direct photoexcitation as in
imidazole or pyrrole, or indirectly, by radia-
tionless transfer from a photoprepared
state, as in phenol. The quantum yield for H
atom production after UV excitation of pyrrole
in the wavelength ranges discussed in this work
is estimated to be near unity. Due to the
similarity in the PESs for pyrrole and imid-
azole, we can also assume a high quantum yield
for the H atom production in this case. The
picture is less clear for phenol, but the fast H
atoms formed by the S
coupling at l G
240 nm show anisotropic recoil distributions,
implying fast and efficient fragmentation.
Further, the recent PTS study of phenol photol-
ysis at 248 nm (25) reports no fragmentation
channels other than H þ C
O at that wave-
length. The available evidence thus suggests
that H atom loss is a major process after UV
excitation of these gas phase molecules. Fu-
ture challenges include the following: (i) ex-
tending such high-resolution PTS studies to
larger, less volatile biomolecules like adenine,
histidine, tyrosine, and tryptophan, and (ii)
exploring whether such photoinduced prompt
N(O)–H bond fission processes also operate in
the condensed phase.
References and Notes
1. A. L. Sobolewski, W. Domcke, C. Dedonder-Lardeux,
C. Jouvet, Phys. Chem. Chem. Phys. 4, 1093 (2002).
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3. Imidazole, pyrrole, and phenol were obtained commer-
cially (Aldrich, Gillingham, UK, 98%). Pyrrole, at its room
temperature vapor pressure (È11 torr) and diluted in
700 torr of Ar, was introduced into the photolysis region
in the form of a pulsed, skimmed molecular beam. For
imidazole and phenol, solid samples were packed in the
tube leading to the same pulsed molecular beam source
and heated to È100-C (imidazole) or 60-C (phenol), and
the resulting vapor entrained in 700 torr of Ar before
expansion into the interaction region.
4. L. Schnieder, W. Meier, K. H. Welge, M. N. R. Ashfold,
C. M. Western, J. Chem. Phys. 92, 7027 (1990).
5. B. Cronin, M. G. D. Nix, R. H. Qadiri, M. N. R. Ashfold,
Phys. Chem. Chem. Phys. 6, 5031 (2004).
6. m
and m
in Eq. 1 are the masses of the H atom (m
1.0079 dalton) and of the partner fragments (imid-
azole, pyrrolyl, and phenoxyl, with respective masses
0 67.07 dalton, 66.08 da lton, and 93. 11 dalton),
d 0 0.368 m is the length of the flight p ath, and t is the
measured H atom TOF.
7. The angular variation of the product yield is characterized
by the beta (b) parameter. Photoexcitation preferentially
selects molecules that are aligned so that their transition
moment (m) is parallel to e
. Direct dissociation occurs
on a time scale that is much shorter than a classical
rotational period. The resulting fragments will recoil along
the axis of the breaking bond in the photoexcited
molecule, i.e., they will display a spatial anisotropy that
reflects the original mIe interaction. The photofragment
angular distribution is given by I(q) 0 [1 þ bP
where q is the angle between the fragment recoil velocity
vector v and the TOF axis, and P
(x) 0 (3x
j 1)/2 is the
second-order Legendre polynomial. b takes limiting values
of þ2 in the case of prompt dissociation after excitation
via a parallel transition (i.e., m lies along the breaking
bond) and –1 in the case of a perpendicular transition.
Less anisotropic fragment recoil distributions (i.e., with b
closer to 0) are observed in the case of predissociations
(i.e., where the excited state lifetime is comparable to, or
longer than, the rotational period of the parent molecule).
8. R. N. Zare, Angular Momentum. Understanding Spatial
Aspects in Physics and Chemistry (Wiley, New York,
9. Equilibrium structures and vibrational frequencies
discussed in this work were calculated using Gaussian
03 (Revision B.04, M. J. Frisch et al., Gaussian, Inc.,
Pittsburgh, PA, 2003), B3LYP, with a 6-311G(d,p)
basis set.
10. Convention identifies the N atom involved in the NjH
bond in imidazole as atom 1, and the other heavy atoms in
the ring labeled by counting in a clockwise direction in the
case of the structure depicted in Fig. 1, i.e., C2, N3, etc.
11. A. J. Gianola et al., J. Phys. Chem. A 109, 11504 (2005).
12. Vibronic coupling is an example of a breakdown of the
Born-Oppenheimer separation, which applies when the
vibrational and electronic degrees are coupled sufficiently
strongly that they cannot be factored. In the case of an
electric dipole forbidden transition, inclusion of a
quantum of a nonsymmetric vibration changes the overall
(vibronic) symmetry and permits the transition (with an
intensity that depends on the degree of mixing of the
vibrational and electronic wave functions).
13. B. O. Roos, P.-A. Malmqvist, V. Molina, L. Serrano-Andres,
M. Merchan, J. Chem. Phys. 116, 7526 (2002).
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Spectrosc. 24, 402, 413 (1967).
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Phys. 283, 153 (2002).
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20. R. J. Lipert, S. D. Colson, J. Phys. Chem. 93, 135 (1989).
21. J. Lorentzon, P.-A. Malmqvist, M. Fu
lscher, B. O. Roos,
Theor. Chim. Acta 91, 91 (1995).
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J. Chem. Phys. 122, 224315 (2005).
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26. S. Ishiuchi et al., J. Chem. Phys. 117, 7077 (2002).
27. K. Daigoku, S. Ishiuchi, M. Sakai, M. Fujii, K. Hashimoto,
J. Chem. Phys. 119, 5149 (2003).
28. Two alternative numbering schemes for the normal mode
vibrations of benzene and benzene derivatives are
commonly found in the scientific literature (the so-called
Wilson and Herzberg assignments). We consistently use
the former. To assist readers familiar with the latter, the
Herzberg labels for the modes of phenol discussed in this
work are: n
Y n
, n
Y n
, n
Y n
29. We are grateful to the Engineering and Physical Sciences
Research Council UK for financial support via the
Portfolio Partnership LASER and to K. N. Rosser for his
outstanding practical support of this work.
26 January 2006; accepted 24 April 2006
A Nearly Modern Amphibious Bird
from the Early Cretaceous of
Northwestern China
Hai-lu You,
Matthew C. Lamanna,
Jerald D. Harris,
Luis M. Chiappe,
Jingmai O’Connor,
Shu-an Ji,
Jun-chang Lu¨,
Chong-xi Yuan,
Da-qing Li,
Xing Zhang,
Kenneth J. Lacovara,
Peter Dodson,
Qiang Ji
Three-dimensional specimens of the volant fossil bird Gansus yumenensis from the Early
Cretaceous Xiagou Formation of northwestern China demonstrate that this taxon possesses
advanced anatomical features previously known only in Late Cretaceous and Cenozoic ornithuran
birds. Phylogenetic analysis recovers Gansus within the Ornithurae, making it the oldest known
member of the clade. The Xiagou Formation preserves the oldest known ornithuromorph-dominated
avian assemblage. The anatomy of Gansus, like that of other non-neornithean (nonmodern)
ornithuran birds, indicates specialization for an amphibious life-style, supporting the hypothesis
that modern birds originated in aquatic or littoral niches.
eornithean (modern) birds are the most
diverse extant tetrapods, comprising
È10,000 species (1). Neornitheans, plus
the predominantly Late Cretaceous Hesperornithes
and Ichthyornis dispar, constitute the Ornithurae, a
clade that, along with a few other Cretaceous taxa,
comprises the Ornithuromorpha (2). Previously
reported, alleged Early Cretaceous ornithurans
are either fragmentary (3, 4), of debatable age
(5), or have received only limited examination
(6–8). Furthermore, they are rare compared to
members of the extinct clade Enantiornithes
(9, 10). Consequently, the early evolution of the
Ornithuromorpha and the phylogenetic, tempo-
ral, and paleoecological contexts of ornithuran
(and ultimately neornithean) origins remain ob-
scure. One of the first Early Cretaceous birds
discovered was Gansus yumenensis, based on
an isolated partial left pelvic limb from the
Lower Cretaceous (?Aptian-Albian, È115to105
million years ago; see supporting online material)
Xiagou Formation near Changma, Gansu Prov-
16 JUNE 2006 VOL 312 SCIENCE
ince, northwestern China (11) (Fig. 1). Gansus
was initially recognized as more closely allied
to neornithean birds than is Archaeopteryx; sub-
sequent discoveries have reinforced this hypoth-
esis (2, 12).
Here we describe five new, tern-sized
specimens of G. yumenensis, also from the
Xiagou Formation near Changma, that col-
lectively represent the entire skeleton except
the skull, mandibles, and cranial-middle
cervical vertebrae (Fig. 2 and figs. S1 to 6).
Unlike many compressed or split avian fossils
from the Jehol Group of northeastern China,
most of the new Gansus specimens consist of
three-dimensional, largely uncrushed and
undistorted bones, and many include soft
tissues. Autapomorphies are difficult to
pinpoint in the fragmentary Gansus holotype,
but the most frequently cited feature is pro-
nounced, distally projecting flexor tubercula
separate from, and distal to, the proxi-
moplantar ends of the pedal unguals (10, 11).
One of the new specimens has identical pedal
morphology (Fig. 2J and fig. S5); skeletal
elements of this specimen are indistinguishable
from their counterparts in the remaining four
skeletons, justifying the referral of all to G.
yumenensis. Unless otherwise noted, the phylo-
genetically important characters of Gansus
discussed below represent apomorphies relative
to more basal birds (see also supporting online
The caudal cervical and 10 thoracic vertebrae
of Gansus are plesiomorphically not hetero-
coelous. The thoracics are excavated by deep,
emarginate, craniocaudally elongate, lateral pneu-
matic fossae. The cranialmost three to four tho-
racics possess well-developed ventral processes
(Bhypapophyses[) (Fig. 2G and fig. S4). The
cranialmost three of the 10 to 11 synsacral verte-
brae exhibit dorsally directed costal processes.
The tail comprises six to seven free vertebrae,
all with poorly developed cranial and caudal
zygapophyses, and a pygostyle the length of
three caudals. All specimens lack ossified gastra-
lia and uncinate processes.
A tall carina extends the length of the ster-
num (Fig. 2G and fig. S4). Closely spaced
coracoidal articular sulci embay the cranial
edge of the element. The thin U-shaped
furcula has an È38- intraclavicular angle.
The dorsally convex scapula tapers distally.
The strutlike, plesiomorphically apneumatic
coracoid possesses well-developed procora-
coid and lateral processes (Fig. 2E and fig.
S2), a deep circular scapular cotyle, and a
humeral articular facet situated well ventral to
the acrocoracoid process.
The proximal end of the plesiomorphi-
cally apneumatic humerus exhibits a ventral
tubercle, capital incisure, and domed artic-
ular condyle. The cranially projecting bi-
cipital crest bears a transverse sulcus on its
proximoventral surface and a tiny fovea
caudodistally. A shallow brachial fossa lies
proximal to approximately subequal, crani-
ally developed distal humeral condyles. The
ulna is slightly longer than the humerus and
displays a prominent bicipital tubercle and a
deep narrow brachial impression. The dorsal
trochlear surface of the dorsal condyle is
developed as a semilunate ridge. The carpal
trochlea (semilunate carpal) is completely
co-ossified with, and positioned proximal
to, major and minor metacarpals that may
also be fused distally. The weakly devel-
oped extensor process of the alular meta-
carpal extends cranially just beyond the
shelflike phalangeal articular facet. The
alular metacarpal does not reach the proxi-
mal terminus of the intermetacarpal space.
The craniocaudal diameter of the major
metacarpal is more than twice that of the
minor. The proximal phalanx of the major
digit is strongly dorsoventrally compressed,
flat caudally, and longer than the second
The iliac preacetabular alae extend crani-
ally beyond the synsacrum, overlapping the
caudalmost pair of thoracic ribs. A weak,
subtriangular preacetabular tuberculum (Bpec-
tineal process[) is situated cranioventral to the
acetabulum. A preacetabular (Bcuppedicus[)
fossa is absent. A well-developed antitro-
chanter occupies the caudodorsal corner of
the acetabulum. The pubis and ischium are
seamlessly fused to the ilium at the acetabu-
lum. The pubes are strongly retroverted,
nearly parallel to the ischia; their distalmost
È5 to 6% are in contact but not fused. The
iliac (Bdorsal[) process of the ischium,
situated approximately at midshaft, broadly
contacts, and may be co-ossified with, the
caudoventral surface of the ilium, enclosing a
craniocaudally elongate ilioischiadic fora-
men (Fig. 2B and fig. S1).
The femur exhibits a trochanteric crest
proximolaterally and a patellar sulcus craniodis-
tally. The lateral gastrocnemial (Bectocondylar[)
tubercle and condyle form a single distolateral
trochlear surface. The conjoined cranial and
lateral cnemial crests of the tibiotarsus make
up a single, well-developed, proximocranially
projected rounded crest (Fig. 2C and fig. S1).
A tibiotarsal extensor canal is present as an
emarginate groove that plesiomorphically
lacks a supratendinal pons. The tarso-
metatarsal articular surface of the approxi-
mately subequal distal condyles extends onto
the tibiotarsal caudal surface. The fibula
terminates proximal to the ankle. The hypo-
tarsus lacks crests and sulci (Fig. 2H and fig.
S4). Plantar displacement of the proximal end
of metatarsal III creates a deep dorsal
extensor sulcus that contains a pronounced
tibialis cranialis tuberosity and one vascular
foramen that penetrates to the plantar surface.
Metatarsal I is twisted and distally deflected
so that its plantaromedial surface is concave
proximal to its trochlea. The trochlea of
metatarsal II lies proximal to the proximal-
most extent of those of metatarsals III and IV.
It also exhibits marked plantar offset and
lateral rotation and is compressed mediolat-
erally as compared to those of metatarsals III
and IV. Metatarsals III and IV completely
Institute of Geology, Chinese Academy of Geological Sciences,
26 Baiwanzhuang Road, Beijing 100037, People’s Republic of
Section of Vertebrate Paleontology , Carnegie Museum
of Natural History , 4400 Forbes Avenue, Pittsburgh, PA
15213–4080, USA.
Science Department, Dixie State College,
225 South 700 East, St. George, UT 84770, USA.
Dinosaur Institute, Natural History Museum of Los Angeles
County , 900 Exposition Boulevard, Los Angeles, CA 90007,
Fossil Research and Development Center, Third Geology
and Mineral Resources Exploration Academy of Gansu
Province, 1 Langongping Road, Lanzhou, Gansu 730050,
People’s Republic of China.
Provincial Museum of Gansu
Province, Nature Department, 3 West Xijin Road, Lanzhou,
Gansu 730050, People’s Republic of China.
Geology and
Paleontology Program, Department of Bioscience and
Biotechnology, Drexel University, 409 Stratton Hall, 32nd
and Chestnut, Philadelphia, P A 19104, USA.
Department of
Animal Biology, School of V eterinary Medicine, University of
Pennsylvania, 3800 Spruce Street, Philadelphia, P A 19104,
*To whom correspondence should be addressed. E-mail: (M.C.L);
Fig. 1. Map of China
(white), with Changma lo-
cality in Gansu Province and
fossil bird–producing de-
posits of the Jehol Group in
Liaoning Province (È20 00
km away) marked by bird
silhouettes. SCIENCE VOL 312 16 JUNE 2006
enclose a large, proximodistally elongate,
distal vascular foramen. The first phalanges
of all pedal digits are longer than any of their
respective distal phalanges; all unguals are
small, short, and unrecurved.
Wing feathers preserved with one speci-
men (Fig. 2D and fig. S2) are asymmetrical
and virtually identical to those of volant mod-
ern birds. Semiplumes or down also appear to
be present.
Most Early Cretaceous bird species have been
recovered from northeastern China and Spain
and are primarily non-ornithuromorphs (enan-
tiornitheans plus more basal taxa) (8, 10, 13).
However, most of nearly 50 bird specimens
recovered from Changma appear to pertain
to Gansus. Thus, the XiagouFormationpre-
serves the oldest known avian assemblage
dominated by ornithuromorphs, possibly
indicating the first stages of the rise of
ornithuromorphs to diversity-based domi-
nance over enantiornitheans (supporting on-
line material).
Despite pectoral and alar features that
indicate powered flight, Gansus pelvic limb
elements exhibit specializations that are
characteristic of amphibious (14) birds. Oste-
ologically, these include the prominent, prox-
imally projecting cnemial crests on the
tibiotarsus; proximal position of the trochlea
of metatarsal II; elongate pedal digits EIII and
IV each longer than the tarsometatarsus
(tables S1 and S2)^ with elongate proximal
phalanges (all longer than any penultimate
phalanges); and unrecurved unguals with
large flexor tubercula. Except the last, these
features predominantly occur elsewhere in
undoubted foot-propelled divers such as
Hesperornis, loons (Gaviidae), and grebes
(Podicipedidae) (15); the cnemial crests are
more elongate in Gansus than in the slightly
younger hesperornithean Enaliornis (5). Sim-
ilar flexor tubercula characterize some extant
shorebirds (Charadriiformes) (3), herons (Ar-
deidae), and diving ducks (Anatidae) (16).
Moreover, one new Gansus specimen pre-
serves tubercular skin surrounding the pedal
digits (Fig. 2J and fig. S5) that indicate
interdigital telae (webbing) extending at least
to the proximal ends of the unguals. The
presence of web-footed birds in the Early
Cretaceous is supported by footprints else-
where in Asia (17). Gansus has typically been
considered a sandpiper (Scolopacidae) analog
(3, 11), implying that it was not amphibious
(that is, it lacked fully webbed feet and did
not dive) but instead waded and probed near-
shore sediments for food (1). Its anatomy,
however, demonstrates that it was more
similar to, but not as adept as, foot-propelled
diving birds such as grebes, loons, and diving
In all consensus trees from a phylogenetic
analysis (see supplementary online material
for methods and details), Gansus occurs with-
Fig. 2. New specimens of G. yumenensis (Chinese Academy of Geological Sciences, Institute of
Geology, prefix CAGS-IG-04-). (A) CM-002, articulated caudal cervical, thoracic, synsacral, and
caudal vertebrae, pelvic girdle, and partial pelvic limbs in right dorsolateral view. (B) CM-002,
pelvis and synsacrum. (C) CM-002, proximal right tibiotarsus [indicated by arrowhead in (A)]. (D)
CM-004, nearly complete skeleton in ventral view with feathers (dark brown) on thoracic limbs,
lacking cranium, cranial-midcervical vertebrae, and both pelvic limbs. (E) CM-004, left coracoid in
ventral view [indicated by arrowhead in (D)]. (F) CM-001, partial right and left pelvic limbs. (G)
CM-003, nearly complete skeleton in ventral view, lacking cranium, cervical vertebrae, distal left
thoracic limb, and right and distal left pelvic limbs. (H) CM-003, proximal tarsometatarsus
[indicated by arrowhead in (G)]. (I) CM-008, partial pelvic limbs with soft-tissue preservation. (J)
CM-008, tubercular soft tissue preserved around toes [indicated by arrowhead in (I)]. (K)
Reconstruction of G. yumenensis based on new specimens. Elements shaded gray remain unknown.
Abbreviations in figure are as follows: cc, cnemial crests; ft, flexor tubercula; dp, dorsal process of
ischium; fu, furcula; ht, hypotarsus; pp, procoracoid process; sc, sternal carina; sy, synsacrum; vp,
ventral processes of cranial thoracic vertebrae.
16 JUNE 2006 VOL 312 SCIENCE
in the Ornithurae (Fig. 3). This position is con-
siderably more derived than that of all known
birds from the Jehol Group of northeastern
China. Gansus predates other, later Cretaceous
ornithurans that are considered to exhibit am-
phibious features Esuch as hesperornitheans^
or are thought to have occupied water-based
niches Esuch as Ichthyornis^ (5, 12, 18–23).
Some younger yet more basal ornithuromorphs,
including Apsaravis ukhaana (24)andPata-
gopteryx deferrariisi (25), occupied fully ter-
restrial niches, as did some later purported
neornitheans (12, 20, 24). Ichthyornis and Gansus
are recovered as proximal outgroups to the Ne-
ornithes, consistent with the hypothesis that ne-
ornitheans originated in an aquatic habitat (26).
Thus (Fig. 3), the most basal ornithuromorphs
appear to have evolved in a terrestrial/arboreal
context (25) but rapidly shifted to an aquatic
ecology (8)(Fig.3).
Before the end of the Cretaceous, some non-
ornithuran ornithuromorphs must have reverted
to a terrestrial life-style (24). The Cretaceous
existence of members of basal neornithean
clades EAnseriformes and possibly Gaviiformes
(19, 20, 22)^ implies that representatives of the
neornithean clades Galliformes and more basal
Palaeognathae, all known fossil and extant
members of which are terrestrial, must also have
existed during the Cretaceous (27). Thus, al-
though neornitheans may have originated in
aquatic niches, some basal neornitheans appar-
ently re-radiated into terrestrial niches before
the Cretaceous/Paleogene extinction event.
Consequently, contrary to recent hypotheses,
adaptation to an aquatic ecology appears to
have played little part in the survival of birds
across the K/P boundary (27).
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R. A. Ketcham, Nature 433, 305 (2005).
23. G. J. Dyke et al., Naturwissenschaften 89 ,408
24. J. A. Clarke, M. A. Norell, Am. Mus. Novit. 3387,1
25. L. M. Chiappe, in Mesozoic Birds: Above the Heads of
Dinosaurs, L. M. Chiappe, L. M. Witmer, Eds. (Univ. of
California Press, Berkeley, CA, 2002), pp. 281–316.
26. A. Feduccia, Trends Ecol. Evol. 18, 172 (2003).
27. D. S. Robertson, M. C. McKenna, O. B. Toon, S. Hope,
J. A. Lillegraven, Geol. Soc. Am. Bull. 116, 760 (2004).
28. F. M. Gradstein, J. G. Ogg, A. Smith, A Geologic Time
Scale 2004 (Cambridge Univ. Press, Cambridge, 2004).
29. We thank Z.-c. Bai. and C. Peng and their field crew for
excavation and collection of the specimens; G.-h. Cui and
Y.-q. Zhang for specimen preparation; B. Livezey,
Z.-x. Luo, and R. Mulvihill for discussion; S. Yu for
translating (6); M. Klingler for Fig. 2K; and anonymous
manuscript reviewers. Funding was provided by the
Discovery Quest program for The Science Channel to H.-l.Y.,
M.C.L., and J.D.H.; the Carnegie Museum of Natural History
to M.C.L.; Dixie State College to J.D.H.; the Chinese
Geological Survey of the Ministry of Land and Resources of
China and the Ministry of Science and Tec hnology of China
(973 Project) to H-l.Y. and Q.J.; and the Gansu Bureau of
Geology and Mineral Resources to D.-q.L.
Supporting Online Material
Materials and Methods
SOM Text
Figs. S1 to S6
Tables S1 and S2
17 February 2006; accepted 19 April 2006
Fig. 3. Phylogenetic position of G. yumenensis (50% majority-rule consens us tree) based on
holotype and new referred specimens; time scale is per (28). Thin line segments represent ghost
lineages; thick line segments represent known ranges of terminal taxa. Clades are denoted by
black circles (see supporting online material for clade definitions). The star represents the
temporal position of Enaliornis spp. Colors indicate known or inferred ecologies as follows: brown,
terrestrial/arboreal; b lue, aquatic/amphi bious; black, equivocal. Note the sequence of amphibious
taxa basal to the Neorni thes. Depicted divergence time s are intended as approxi mations only,
base d o n the oldest occurrence of an included species and sub sequent divergences. Mya, millio n
years ago. SCIENCE VOL 312 16 JUNE 2006
... Newly-recognized euornitheans that have been described since the last substantial work on Ichthyornis postcranial morphology include clades such as Hongshanornithidae (Zhou & Zhang, 2005;O'Connor, Gao & Chiappe, 2010;Chiappe et al., 2014;Wang, Zhou & Zhou, 2016), Songlingornithidae (or Yanornithidae; Fig. 1; Zhou & Zhang, 2001;Clarke, Zhou & Zhang, 2006;Zheng et al., 2014;Wang et al., 2013aWang et al., , 2019Wang et al., , 2020cWang et al., , 2021, and Schizoouridae (Zhou, Zhou & O'Connor, 2012;Wang et al. 2020d). Of particular relevance are taxa such as Gansus (You et al., 2006; and Iteravis Wang et al., 2018), which have been recovered in phylogenetic positions close to Ichthyornis along the most crownward portion of the avialan stem lineage. In light of these recent discoveries, renewed investigations into the morphology of Ichthyornis may provide important insights into key morphological transitions immediately preceding the origin and diversification of the avian crown group, as well as the refinement of powered flight capacity among Mesozoic avialans (Pittman et al., 2020c). ...
... A few additional taxa, such as Apsaravis (Clarke & Norell, 2002), Ambiortus (Kurochkin, 1985;O'Connor & Zelenkov, 2013), Hollanda (Bell et al., 2010) and Patagopteryx (Chiappe, 1996(Chiappe, , 2002 have occasionally been recovered within Ornithurae, close to Ichthyornis and Hesperornithes, but these results have not been consistently recovered in most studies (O'Connor & Zelenkov, 2013;Field et al., 2018b;Pittman et al., 2020a;Wang et al., 2020cWang et al., , 2020d. Recent analyses have recovered alternative phylogenetic positions for Ichthyornis with respect to the diving Hesperornithes, which have been recovered in a position either slightly crownward of (O'Connor, Chiappe & Bell, 2011;Wang et al., 2017Wang et al., , 2019Atterholt, Hutchison & O'Connor, 2018;Field et al., 2018b), slightly stemward (Chiappe, 2002;Clarke, 2004;You et al., 2006;Huang et al., 2016;Wang et al., 2020c;Torres, Norell & Clarke, 2021) or in an unresolved polytomy with Ichthyornis (Fig. 1). The relative position of both groups is highly sensitive to both the dataset and the methods used in phylogenetic analyses (Wang et al., 2017;Field et al., 2018b;Pittman et al., 2020a). ...
... Fully heterocoelous thoracic vertebrae are also found in Hesperornithes (Marsh, 1880;Bell & Chiappe, 2020, Apsaravis (Clarke & Norell, 2002), and in Khinganornis , in which they are opisthocoelous, and in Patagopteryx (Chiappe, 2002), in which they are procoelous, but the detailed morphology of the vertebral articular surfaces is difficult to reconstruct for most fossil avialans due to poor preservation. A condition with amphicoelous thoracic vertebrae similar to that of Ichthyornis seems to be widespread among Mesozoic euornitheans, and has been inferred in Yixianornis (Clarke, Zhou & Zhang, 2006), Piscivoravis , Iteravis and Gansus (You et al., 2006;, but reconstructing the extent of this condition across Mesozoic euornitheans remains challenging. ...
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Ichthyornis has long been recognized as a pivotally important fossil taxon for understanding the latest stages of the dinosaur–bird transition, but little significant new postcranial material has been brought to light since initial descriptions of partial skeletons in the 19th Century. Here, we present new information on the postcranial morphology of Ichthyornis from 40 previously undescribed specimens, providing the most complete morphological assessment of the postcranial skeleton of Ichthyornis to date. The new material includes four partially complete skeletons and numerous well-preserved isolated elements, enabling new anatomical observations such as muscle attachments previously undescribed for Mesozoic euornitheans. Among the elements that were previously unknown or poorly represented for Ichthyornis, the new specimens include an almost-complete axial series, a hypocleideum-bearing furcula, radial carpal bones, fibulae, a complete tarsometatarsus bearing a rudimentary hypotarsus, and one of the first-known nearly complete three-dimensional sterna from a Mesozoic avialan. Several pedal phalanges are preserved, revealing a remarkably enlarged pes presumably related to foot-propelled swimming. Although diagnosable as Ichthyornis, the new specimens exhibit a substantial degree of morphological variation, some of which may relate to ontogenetic changes. Phylogenetic analyses incorporating our new data and employing alternative morphological datasets recover Ichthyornis stemward of Hesperornithes and Iaceornis, in line with some recent hypotheses regarding the topology of the crownward-most portion of the avian stem group, and we establish phylogenetically-defined clade names for relevant avialan subclades to help facilitate consistent discourse in future work. The new information provided by these specimens improves our understanding of morphological evolution among the crownward-most non-neornithine avialans immediately preceding the origin of crown group birds.
... In sum, the knowledge of Early Cretaceous ornithuromorphs is almost restricted to Asia and had been, up to now, entirely absent from Gondwanan landmasses. This state of knowledge indicates that we remain largely uninformed about the phylogenetic, temporal, and paleoecological contexts of the early evolutionary history of Ornithuromorpha (You et al., 2006). ...
... Although K. mater is represented by an isolated foot, some anatomical features may be indicative of its habits and ecological adaptations. Kaririavis mater lacks most features often present in many modern aquatic and semiaquatic birds, including elongate and gracile toes, a laterally compressed distal tarsometatarsus and a highly recessed trochlea II (You et al., 2006). ...
... In K. mater the only available ungual phalanx (presumably corresponding to digit II) is proportionally stout and distally hooked, with relatively large flexor tubercles (in Enantiornithes, well-developed flexor tubercles are not present; e.g., Chiappe, 1993;Chiappe and Calvo, 1994;Kurochkin, 1995;Sanz et al., 2002;Carvalho et al., 2015a, b). The ungual morphology of K. mater strongly differs from that of other Early Cretaceous ornithuromorphs (e.g., Archaeorhynchus spathula, Gansus yumenensis, Songlingornithidae, Hongshanornithidae, Schizoouridae; Hou and Liu, 1984;Hou, 1997;You et al., 2006;Zhou and Zhang, 2006;, which show small and dorsoplantarly short ungual phalanges. These features could imply a distinct ecological niche for K. mater contrasting with most Early Cretaceous ornithuromorph birds, which are interpreted as semiaquatic in habit. ...
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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.
... IVPP V15077 (Institute of Vertebrate Paleontology and Paleoanthropology) is a referred specimen of Gansus yumenensis with scales well preserved in situ around the intertarsal joint of the tibiotarsus and the tarsometatarsus 16 . To date, all reported specimens of Gansus yumenensis are from the Early Cretaceous Xiagou Formation, Changma Basin, China 16,20,21 . Stable isotope chemostratigraphy places the age of the fossil quarries in the early Aptian 22 , possibly a crucial time to our understanding of how birds evolved from feathered legs to scaled legs. ...
... Phylogenetic analysis places Gansus in the Ornithuromorpha (Fig. 5), the most inclusive avian clade that contains all taxa close to modern birds than Enantiornithes 31 . The elongated pedal phalanges, unrecurved unguals with large exor tubercula, and webbed-feet indicate that Gansus was adapted to life aquatic environments 16,20,21,32 . Water-based niches have also been suggested for multiple other ornithuromorphs, including Hongshanornis, Yixianornis, Yanornis, Icnthyornis, and Parahesperornis [33][34][35][36] . ...
... Water-based niches have also been suggested for multiple other ornithuromorphs, including Hongshanornis, Yixianornis, Yanornis, Icnthyornis, and Parahesperornis [33][34][35][36] . It has been suggested ornithuromorphs rapidly shifted their niches from a terrestrial/arboreal context to an aquatic ecology during evolution 21,35 . The evolution of scaled tarsometatarsi in ornithuromorphs could be because scaled tarsometatarsi are better suited for an aquatic ecology than feathered tarsometatarsi. ...
Full-text available
Most modern birds have scales covering the foot, while our knowledge of early avian scales is limited, mainly due to the scarcity of fossil record. Here we characterize the morphological details of two types of scales preserved in IVPP V15077, a referred specimen of the Early Cretaceous bird Gansus . The scutellate and interstitial scales, which, in combination with previous discovery of scutate and reticulate scales in other Early Cretaceous birds, indicates that all four types present in modern birds have appeared in the Early Cretaceous. A phylogenetic context of fossilized scales suggests that the evolution of reticulate scales is conservative while that of the other types is more variable. It is consistent with the molecular hypothesis of the scales in modern birds and reptiles that most integumentary structures in amniotes are homologous with modified signaling modules to form various integumentary phenotypes, among which the reticulate scales may use the conserved signaling pathway.
... 11.4;Atterholt et al. 2018: fig. 2H), and Mesozoic taxa of the Ornithuromorpha, such as Apsaravis (Clarke and Norell 2002), Yixianornis (Clarke et al. 2006), Yanornis (Zhou and Zhang 2001), Gansus (You et al. 2006), as well as the Ichthyornithiformes (Clarke 2004: fig. 40) and Hesperornithiformes (Bell and Chiappe 2020). ...
Full-text available
The occurrence of lateral openings and pleurocoels (lateral fossae) in the corpus of the thoracic vertebrae of extant and fossil neornithine birds is reviewed, with both features having been identified as osteological correlates of the avian pulmonary system. Openings mainly occur in larger species with a high overall bone pneumatization but do not seem to serve for the passage of lung or air sac diverticula. Pleurocoels, on the other hand, are not directly related to pneumatic features and constitute a plesiomorphic trait that was widespread in Mesozoic non-neornithine birds. It is noted that an inverse correlation exists between the occurrence of pleurocoels and the pneumatization of the humerus, with pleurocoels being mainly found in extant and fossil taxa, in which the humerus is not pneumatized by diverticula of the clavicular air sac. Here it is hypothesized that pleurocoels primarily serve to increase the structural resistance of the vertebral body and were reduced multiple times in neornithine birds. In some taxa, their reduction may be related to the development of the furcula, which assists ventilation of the clavicular and cervical air sacs and may thereby contribute to the pneumatization of both, the humerus and the thoracic vertebrae. If so, Mesozoic non-neornithine birds, which had a rigid furcula with massive shafts as well as non-pneumatic humeri and pronounced pleurocoels, are likely to have differed in functional aspects of their air sac system from extant birds.
Full-text available
Most modern birds have scales covering feet, but our knowledge of early avian scales is limited, mainly due to their scarcity in the fossil record. Here we describe the morphological details of scutellate and interstitial scales preserved in IVPP V15077, a specimen of the Early Cretaceous bird Gansus from the Changma Basin in northwestern Gansu Province, Northwest China. These results, combined with previous reports of scutate and reticulate scales, show that all four types of scales present in modern birds already appeared in the Early Cretaceous. The phylogenetic distribution of skin appendages of feet, including feathers and scales, shows that non-avian dinosaurs already evolved scales resembling those in modern birds, and that scales can coexist with feathers on feet, suggesting that avian scales may be homologue with scales of non-avian dinosaurs. However, to further test this hypothesis, more research combined with a strengthened focus on detecting specimens with soft tissue preservation is necessary.
Paleosols are useful evidence of paleoclimates and paleoenvironments independent of fossils. Zhangye Danxia National Geopark of Gansu Province (northwestern China) has been protected for its stunning varicolored badlands of Early Cretaceous (Aptian-Albian) claystones. However, the paleoclimates and paleoenvironments forming such unique succession are currently not well understood. The widespread pedogenic features, for example root traces and soil horizons, indicate different paleosols, which provides clues of associated paleoclimates and paleoenvironments. In the present study, combining field work and soil micromorphology, we recognized, classified, and interpreted 155 sequential paleosol profiles of 14 different pedotypes (soil types) in the 755-m-thick section. These pedotypes have modern analogues in South Asia, indicating hotter and more humid paleoclimate than at present in Zhangye. Systematic analysis of soil units based on comparison to their modern analogues allows reconstruction of paleoenvironments in eleven humidity stages. Variation in waterlogging of the paleosols based on the ratio of Hm / Gt agreed well with regional and global paleoclimatic records, confirming its utility in paleoclimate reconstruction during Aptian and Albian. The identification and characterization of the paleosol succession provides a significant base for detailed paleoclimatic reconstruction during this period.
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Secondary aquatic adaptations evolved independently more than 30 times from terrestrial vertebrate ancestors1,2. For decades, non-avian dinosaurs were believed to be an exception to this pattern. Only a few species have been hypothesized to be partly or predominantly aquatic3–11. However, these hypotheses remain controversial12,13, largely owing to the difficulty of identifying unambiguous anatomical adaptations for aquatic habits in extinct animals. Here we demonstrate that the relationship between bone density and aquatic ecologies across extant amniotes provides a reliable inference of aquatic habits in extinct species. We use this approach to evaluate the distribution of aquatic adaptations among non-avian dinosaurs. We find strong support for aquatic habits in spinosaurids, associated with a marked increase in bone density, which precedes the evolution of more conspicuous anatomical modifications, a pattern also observed in other aquatic reptiles and mammals14–16. Spinosaurids are revealed to be aquatic specialists with surprising ecological disparity, including subaqueous foraging behaviour in Spinosaurus and Baryonyx, and non-diving habits in Suchomimus. Adaptation to aquatic environments appeared in spinosaurids during the Early Cretaceous, following their divergence from other tetanuran theropods during the Early Jurassic17. In extinct species including non-avian dinosaurs, bone density is shown to be a reliable indicator of aquatic behavioural adaptations, which emerged in spinosaurids during the Early Cretaceous.
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.
Our understanding of the early evolution of birds has advanced over the past 2 decades, thanks to an ever-improving fossil record. Extraordinary fossils have revealed new details about the evolution of the avian brain, respiratory system, digestive tract, and reproductive system. Many of the traits most strongly associated with birds first arose in nonavian theropod dinosaurs. Theropods evolved pennaceous feathers, incipient wings, and gliding flight long before modern birds appeared. Birds likewise inherited features such as an expanded forebrain, gizzard, dorsally immobile lung, pigmented eggs, and paternal brooding system from their theropod ancestors. Yet, the earliest birds also retained primitive traits such as teeth, clawed hands, long bony tails, partially buried nests, and slower growth. The evolution of birds was profoundly influence by the Cretaceous–Paleogene mass extinction, which wiped out the previously dominant Enantiornithines (“opposite birds”). This sets the stage for modern birds to radiate into the most diverse major clade of tetrapods.
Many studies of the limb bones from birds of the major clades reveal a mosaic evolution in morphological characters. From this, we assume that uninterrupted compact bone evolved independently multiple times outside of the crown group. We hypothesise that there are key intraskeletal changes in the osteohistological features, such as the organisation of the vascular network. To test these hypotheses, we analysed and described the osteohistological features of five different midshaft samples of Gansus yumenensis, a non‐ornithurine Euornithes from China, based on virtual models obtained from synchrotron microtomography scans, a less invasive method that the traditional physical cross section. We performed quantitative analyses with volume, surface area and estimated ratios. The osteohistological features of Gansus yumenensis were compared with those of stem and crown birds. From our analyses, we discuss the pros/cons of using synchrotron microtomography scans compared to traditional physical cross section. Our analyses demonstrate that Gansus yumenensis is the fourth described extinct Euornithes to exhibit uninterrupted bone deposition in all bone samples, providing further support for multiple origins of this feature outside of the bird crown group. Finally, our osteohistological investigation of Gansus yumenensis provides future study avenues regarding the evolution and development of bone tissue in fossil birds.
This paper describes a new fossil from the Early Cretaceous Jiufotang Formation in Yixian County, western Liaoning. This new specimen has been well preserved, and moreover an entire Jinanichthys is hold in its mouth. Further study of Yanornis not only provides direct evidence for studying its living conditions, behaviors and prey styles, but also is of great value for discussing the reasons of the colony unusual death of the vertebrates of the Jehol Biota.
Conference Paper
The tunneling effect is a kind of quantum effect used extensively. The sensor based on tunneling effect has some advantages, such as high sensitivity, rapid response, low power consumption, low driving voltage and so on. In particular, combined with the MEMS technology, tunneling effect has shown a good application foreground in micro sensor fields. According to the quantum mechanics, such as Schordinger's equation, the theory models of tunneling effect are presented in this paper. Also the expressions of the transmission coefficient and tunneling current about the tunneling barriers are obtained. On the basis of these, a kind of MEMS micro magnetometer based on tunneling effect is presented. The mechanics model of the membrane, which is the key component and is subjected to the axial residual stress at both ends, is founded. The membrane's parameters are optimized and simulated. Some key fabrication processes of the micro magnetometer, such as silicon wafer, glass, combined plate process are developed. Further more, the prototype of the MEMS micro magnetometer based on tunneling effect is fabricated.
Ambiortus from the Khurilt beds (Neocomian) of central Mon-golia shows a combination of characters that confirms the assign-ment of this fossil to a separate order, Ambiortiformes. Otogornis genghisi Hou, 1994, of the Yijinhouluo Formation (earliest Creta-ceous or latest Jurassic) of Ordos, China, was first described as Aves incertae sedis. Ambiortus and Otogornis share specialized characters, such as a thickened, three-edged acrocoracoid with an acute top; a flat, wide humeral articular facet of the scapula; ven-tral position of a small, oval humeral articular head; and a thin, long intermediate phalanx of the major wing digit. The generic sta-tus of Otogornis is supported by some other diagnostic characters. Several advanced characters demonstrate the assignment of Ambiortus and Otogornis to the Palaeognathae. These two forms show the occurrence of paleognathous birds in the Early Creta-ceous of Central Asia.
For several hours following the Chicxu- lub impact, the entire Earth was bathed with intense infrared radiation from ballis- tically reentering ejecta. The global heat pulse would have killed unsheltered organ- isms directly and ignited fires at places where adequate fuel was available. Shelter- ing underground, within natural cavities, or in water would have been a necessary but not always sufficient condition for sur- vival. Survival through sheltering from an initial thermal pulse is not adequately con- sidered in literature about Cretaceous- Tertiary nonmarine extinctions. We com- pare predicted intense, short-term, thermal effects with what is known about the fossil record of nonmarine vertebrates and sug- gest that paleontological evidence of surviv- al is compatible with theoretical results from bolide physics.
 We describe the oldest tracks of web-footed birds from the Early Cretaceous in South Korea. The tracks are characterized by a wide divarication angle and a long reversed hallux. The web is semipalmate and restricted to the proximal portion of the three forward digits. The tracks from the Early Cretaceous in South Korea are smaller than those of the Late Cretaceous, therefore confirming the trend of size increasing in the early evolution of birds as shown by skeletal fossils. The discovery of web-footed tracks with abundant non-web-footed tracks indicates that there was a considerable diversification of shore birds as early as the Early Cretaceous.
Photofragment translational spectroscopy was used to study the photodissociation of pyrrole at 193 and 248 nm under collision-free conditions. Five primary dissociation channels were observed at 193 nm. Two channels resulted from cleavage of the NH bond to yield H + pyrrolyl radical with one channel following internal conversion (IC) to the ground state (≈21%) and the other originating from electronically excited pyrrole (≈30%). Two dissociation channels involved elimination of HCN following IC. One channel producing HCN + vinylmethylene (≈25%) following ring opening and hydrogen migration and the other proceeding via a bridged 3H-pyrrole intermediate to form HCN+cyclopropene (≈24%). The last channel at 193 nm involved IC to the ground state followed by ring opening and NC bond cleavage to form NH+CHCCHCH2 (<1%). At 248 nm three dissociation channels were observed, all of which involved the elimination of atomic hydrogen. Analogous to the results at 193 nm, two of these channels resulted from cleavage of the NH bond with one channel following IC (≈42%) and the other dissociating from an excited electronic state (≈47%). The third dissociation channel at 248 nm involved the cleavage of one of the two CH bonds in electronically excited pyrrole (≈11%). Translational energy distributions were determined for all observed dissociation channels. From consideration of the maximum translational energy of the photofragments D0(NH) =88±2 kcal/mol, D0(CH) = 112.5±1 kcal/mol and ΔHr(pyrrolyl radical) = 62±2 kcal/mol were determined.
The early evolution of living birds has been sharply debated, with two disparate interpretations. Molecular-clock studies consistently date the emergence of modern bird orders at ∼100 million years ago or older, coincidental with major continental breakup. This is supported by some biogeographers who use phylogenetics, accept an ancient evolutionary origin and use historical geology to guide their reasoning. The fossil record, however, provides evidence that modern birds represent an explosive Tertiary radiation, following the Cretaceous–Tertiary cataclysm, and their origins are almost 50 million years younger than that predicted by molecular studies. Here, I argue that this explosive, punctuated model conforms to the typical pattern of vertebrate evolution characterized by rapid diversification following a major extinction event.