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Long-standing controversy surrounds the question of whether living bird lineages emerged after non-avian dinosaur extinction at the Cretaceous/Tertiary (K/T) boundary or whether these lineages coexisted with other dinosaurs and passed through this mass extinction event. Inferences from biogeography and molecular sequence data (but see ref. 10) project major avian lineages deep into the Cretaceous period, implying their 'mass survival' at the K/T boundary. By contrast, it has been argued that the fossil record refutes this hypothesis, placing a 'big bang' of avian radiation only after the end of the Cretaceous. However, other fossil data--fragmentary bones referred to extant bird lineages--have been considered inconclusive. These data have never been subjected to phylogenetic analysis. Here we identify a rare, partial skeleton from the Maastrichtian of Antarctica as the first Cretaceous fossil definitively placed within the extant bird radiation. Several phylogenetic analyses supported by independent histological data indicate that a new species, Vegavis iaai, is a part of Anseriformes (waterfowl) and is most closely related to Anatidae, which includes true ducks. A minimum of five divergences within Aves before the K/T boundary are inferred from the placement of Vegavis; at least duck, chicken and ratite bird relatives were coextant with non-avian dinosaurs.
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Acknowledgements The L.S.B. Leakey Foundation provided a major grant for the Gona Project,
and the National Science Foundation (and Researching Hominid Origins Initiative-RHOI), the
Wenner-Gren Foundation and the National Geographic Society funded the research. We thank
N. Toth and K. Schick (co-directors of CRAFT Stone Age Institute, Indiana University) for their
overall assistance. S.S. thanks N. Toth and K. Schick, and Friends of CRAFT for the Research
Associate position at the Institute. The research permission by the Ministry of Youth, Sports and
Culture, the Authority for Research and Conservation of Cultural Heritage and the National
Museum of Ethiopia is greatly appreciated. We thank the Afar Regional Administration and the
Afar colleagues at Eloha and Asayta for their hospitality, and A. Humet for the hard work in the
field. Y. Beyene, C. Howell, B. Lasher and A. Almquist encouraged the research. D. Stout,
L. Harlacker, M. Everett and T. Pickering assisted in the field, and A. Tamburro at CRAFT. The
manuscript has benefited from discussions with B. Asfaw, M. Asnake, R. E. Bernor, J.-R. Boisserie,
M. Brunet, S. Frost, Y. Haile-Selassie, O. Lovejoy, M. Pickford, E. Smith, H. Wesselman and
T. White. M. Sahnouni and B. Smith helped with computer graphics.
Competing interests statement The authors declare that they have no competing financial
Correspondence and requests for materials should be addressed to S.S. (
Definitive fossil evidence for the
extant avian radiation in the
Julia A. Clarke
, Claudia P. Tambussi
, Jorge I. Noriega
Gregory M. Erickson
& Richard A. Ketcham
Department of Marine, Earth and Atmospheric Sciences, North Carolina State
University, Campus Box 8208, Raleigh, North Carolina 27695, USA
North Carolina Museum of Natural Sciences, 11 West Jones Street, Raleigh,
North Carolina 27601-1029, USA
Museo de La Plata-CONICET, Paseo del Bosque s/n. La Plata (1900), Argentina
Centro de Investigaciones Cientı
ficas y TTP- CONICET, Matteri y Espan
3105 Diamante, Entre
os, Argentina
Department of Biological Science, Florida State University, Conradi Building,
Dewey Street and Palmetto Drive, Tallahassee, Florida 32306-1100, USA
Division of Paleontology, American Museum of Natural History, Central Park
West at 79
Street, New York, New York 10024-5192, USA
Department of Geology, The Field Museum, 1400 South Lake Shore Drive,
Chicago, Illinois 60605, USA
High-Resolution X-Ray Computed Tomography Facility, Jackson School of
Geosciences, University of Texas at Austin, 1 University Station, C-1100, Austin,
Texas 78712-0254, USA
Long-standing controversy
surrounds the question of whether
living bird lineages emerged after non-avian dinosaur extinction
at the Cretaceous/Tertiary (K/T) boundary
or whether these
lineages coexisted with other dinosaurs and passed through this
mass extinction event
. Inferences from biogeography
molecular sequence data
(but see ref. 10) project major avian
lineages deep into the Cretaceous period, implying their mass
at the K/T boundary. By contrast, it has been argued
that the fossil record refutes this hypothesis, placing a ‘big bang’
of avian radiation only after the end of the Cretaceous
However, other fossil data
fragmentary bones referred to extant
bird lineages
have been considered inconclusive
. These
data have never been subjected to phylogenetic analysis. Here we
identify a rare, par tial skeleton from the Maastrichtian of
as the first Cretaceous fos sil definitively placed
within the extant bird radiation. Several phylogenetic analyses
supported by independent histological data indicate that a new
species, Vegav is iaai, is a part of Anseriformes (waterfowl) and is
most closely related to Anatidae, which includes true ducks. A
minimum of five divergences within Aves before the K/T bound-
ary are inferred from the placement of Vegavis; at least duck,
chicken and ratite bird relatives were coextant with non-avian
The Vegavis iaai holotype specimen from Vega Island, western
Antarctica, was discovered in 1992 and received rudimentary
preparation that, in fact, degraded delicate bones that were orig-
inally exposed. It was reported
as a possible ‘transitional’ form
close to extant lineages
. For a decade since, the specimen’s exact
systematic position and possible crown clade avian status have
been debated
. Significant new preparation, X-ray computed
tomography (CT)
and recovery of latex peels of the specimen
before its original preparation reveal numerous, previously
unknown bones and anatomical details. These new data, when
included serially in three of the largest cladistic data sets considering
, Aves
and Anseriformes
, establish hierarchically nested
character support for the placement of Vegavis.
Aves Linnaeus, 1758 (sensu Gauthier, 1986)
Neognathae Pycraft, 1900
Anseriformes Wagler, 1831
Anatoidea Leach, 1820 (sensu Livezey, 1997)
Vegavis iaai sp. nov.
Etymology. ‘Vegavis’ is for the holotype specimen’s Vega Island
provenance; avis’ is from the Latin for bird; and ‘iaai’ is for the
Instituto Anta
rtico Argentino (IAA) expedition that collected the
Holotype. MLP 93-I-3-1 (Museo de La Plata, Argentina), a dis-
articulated partial postcranial skeleton preserved in two halves of a
concretion (Figs 1 and 2; see Supplementary Information for
additional CT scan images, photographs, character data and
measurements). Newly uncovered elements include five thoracic
vertebrae, two cervical vertebrae, left scapula, right ulna, all pelvic
bones, right and left fibulae and left? tarsometatarsal shaft. Pre-
viously reported elements
include the complete right humerus,
proximal left humerus, right coracoid, femora, left tibiotarsus, distal
right radius, sacrum, distal left (right of ref. 15) tarsometatarsus,
proximal right (left of ref. 15) tarsometatarsus and more than six
dorsal ribs.
Locality. Cape Lamb, Vega Island, locality VEG9303 of the 1992/
1993 IAA expedition
. Deposits are near-shore marine fine-grain
from the Middle? to Upper Maastrichtian (,66–68
million years ago (Myr)) lithostratigraphic unit K3 of ref. 21 (see
Supplementary Information for locality, horizon and dating
Diagnosis. Vegavis is unique among the surveyed taxa (Fig. 3) in
that it has a low ridge on the medial edge of the proximal tibiotarsus
that is proposed to be an autapomorphy of the new species (Fig. 2).
The additional unique combination of characters from the phylo-
genetic analyses that differentiate Vegavis are given in the Methods.
Description. Vegavis has heterocoelous cervical and thoracic ver-
tebrae and 14–15 fused sacral vertebrae (Fig. 1). The apneumatic
coracoid is penetrated by a supracoracoideus nerve foramen (Fig. 1).
The blade of the scapula is slightly curved and narrow (Fig. 1). Its
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coracoid tubercle is well projected and hemispherical. The humerus
is slightly longer than the sacrum and about the length of a
tibiotarsus (Fig. 2). Its deltopectoral crest is anteriorly deflected,
less than shaft width and extends for approximately one-third of
the shaft length (Fig. 2). A faint scar is developed in the location of
the scapulohumeralis cranialis muscle insertion in Aves
(Fig. 2).
The capital ridge of the humeral shaft is strongly marked and the
pneumotricipitalis fossa is shallow. The brachial scar angles obli-
quely, deepening ventrodistally into a fossa. The dorsodistal radius
preserves one narrow ligamental groove.
The pelvic elements are firmly ankylosed to each other but may
not have been fused to the sacrum. That the ilioischiadic fenestra
was closed posteriorly is inferred from a flat sheet of bone (Fig. 1)
preserved in both parts of the concretion. The postacetabular ilium
is approximately twice the length of the preacetabular portion. A
small pectineal process is present. The obturator foramen is
elongate and posteriorly demarcated. The pubis is robust, straight,
posteriorly directed and subparallel with the ischium (Fig. 1). The
femur has a low trochanteric crest proximally (Fig. 1) and a patellar
groove distally (Fig. 2). The proximal tibiotarsus preserves proximal
portions of anterior and lateral cnemial crests (Fig. 2). The distal
condyles are approximately the same width, and an ossified supra-
tendinal bridge is developed over the extensor groove (Fig. 2). The
diameter of the intercondylar groove is approximately one-third of
the total distal tibiotarsal width. Metatarsals II–IV are fused
throughout their length to enclose the distal vascular foramen
(Fig. 1). Metatarsal II extends distally to approximately the base
of metatarsal IV. There are four crests bounding three distinct
hypotarsal sulci (Fig. 3c, insets). The medial hypotarsal crest is
plantarly projected slightly farther than the other approximately
equally projected crests.
The morphology of the Vegavis hypotarsus, with multiple,
similarly proportioned canals, shares its derived structure with
Anatidae (true ducks, geese and swans; Fig. 3c, insets). This feature,
however, is only one of 20 unambiguously optimized synapomor-
phies preserved in Vegavis that support its placement as part of
the interested clades Ornithurae, Aves, Neognathae, Anseriformes
and Anatoidea, and finally, in an unresolved trichotomy with
Figure 1 The half of the Vegavis iaai concretion that preserves most of MLP 93-I-3-1.
Photograph (left) and volume renderings using CT data, highlighting the bone and
rendering the matrix semi-transparent to elements preserved within the block (right).
ac, acetabulum; c, coracoid; cv, cervical vertebra; df, distal vascular foramen; f, femora;
fb, fibula; fen, ilioischiadic fenestra; h, humerus; il, ilium; ish, ischium; op, obturator
process; p, pubis; r, radius; rb, rib(s); tm, tarsometatarsus; tv, thoracic vertebrae;
s, sacrum; sc, scapula; u, ulna.
Figure 2 Recovered latex peel of the other half of the Vegavis iaai holotype block before
original preparation. The coracoid, humerus and tibia were severely damaged when
prepared out of this block. acc, anterior cnemial crest; c, coracoid; dpc, deltopectoral
crest; f, femur; fc, fibular crest; h, humerus; lcc, lateral cnemial crest; mc, medial crest;
osb, ossified supratendinal bridge; r, radius; t, tibiotarsus; sc, scapula; scs, scar of
m. scapulohumeralis cranialis.
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Presbyornis and Anatidae (Fig. 3). This placement of Vegavis implies
a minimum of five cladogenetic events within Aves by the Upper
Maastrichtian. The anseriform crown clade must be present
(including three anseriform lineages with extant descendants) as
well as parts of minimally stem-lineage neoavian neognaths,
palaeognaths and galliforms.
Histological analysis of the Vegav is radius (using polarized
microscopy) and examination of the humeral and femoral dia-
physes (using dissecting microscopy) revealed most of the cortices
to be composed of a highly vascularized (semi-reticular pattern)
fibrolamellar matrix that grades into an avascular matrix perioste-
. Lines of arrested growth (LAG or growth lines; Fig. 4) are
absent in all specimens. Portions of the medullar cavities are lined by
lamellar endosteal bone (Fig. 4). These characteristics suggest that
the Vegavis holotype specimen was a somatically (skeletally) mature
adult at the time of death
. This suite of features is phylogenetically
inconsistent with more common basal Mesozoic birds such as
enantiornithines but supports placement of Vegav is within
Ornithurae, a clade inclusive of extant bird lineages
(Fig. 3).
This conclusion is consistent with the independent phylogenetic
The placement of Vegavis confirms the origin of Aves and the
presence of several basal lineages by the latest Cretaceous. This result
is compatible with either limited deep avian divergences by this time
and, thus, limited survivorship at the K/T boundary
, or the
presence of most major lineages in the Cretaceous
and ‘mass
at this boundary. It contradicts a proposed early Tertiary
crown clade origin
; basal avian lineages were present with non-
avian dinosaurs. Hypotheses implying a causal relationship between
the extinction of non-avian dinosaurs and diversification of basal
avian lineages
must address these new data. Vegavis is the most
complete Cretaceous specimen to be identified as part of the extant
avian radiation and the first so identified through cladistic analyses;
therefore, it provides the first reliable Cretaceous internal cali-
bration point for ‘molecular clock’ approaches to dating the
emergence of all living birds. It is strikingly close in age to some
(for example, 66 Myr
) estimates of crown anseriform divergences
made using these techniques
. However, these estimates place
most other major avian divergences earlier than or approximately
contemporaneous with the Cretaceous
, a proposal still unsup-
ported by the fossil record in the Cretaceous. Only the lineage
leading to the presently most speciose extant clade of birds,
Neoaves, can be inferred present by the Maastrichtian from Vegavis
Figure 3 Phylogenetic placement of Vegavis in three successive cladistic analyses
progressing from Avialae to Anseriformes (see Methods). a, Placement within Avialae in
the strict consensus cladogram of two most parsimonious trees (MPTs): length, 385;
consistency index (CI), 0.67; retention index (RI), 0.81; rescaled consistency index (RC),
0.54. b, Placement within Aves in the strict consensus of three MPTs: length, 822; CI,
0.33; RI, 0.48; RC, 0.16. c, Placement in Anseriformes in one MPT: length, 148; CI, 0.91;
RI, 0.88; RC, 0.81. Bootstrap support values .50% from 2,000 replicates (10 random
addition sequences/replicate; random start trees; tree bisection reconnection) are
reported below and to the right of corresponding nodes. Insets in c compare the right
hypotarsus (see also character 90:0, ref. 16) of exemplars for Tinamiformes (Eudromia
elegans), Galliformes (Ortalis canicollis), Anhimidae (Chauna torquata) and Anatidae (Anas
platalea). All analyses used PAUP* 4.0b10 (ref. 28) and branches were collapsed if
minimum length was 0. Character scoring of Vegavis in all data sets is given in the
Supplementary Information.
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Although the Vegavis holotype was originally suggested to be
‘Presbyornithidae indeterminate’
, there is no evidence that it is
part of this extinct taxon of predominately Eocene wading birds,
averred by some to be transitional shorebird–duck ‘mosaics’
Presbyornithids were proposed to be bridging taxa to waterfowl,
indicating shorebird-like taxa to be the progenitors of all extant bird
. Vegavis has different proportions from Presbyornis
that are closer to other extant basal anseriform species. Thus, there is
further support
that the wader proportions and the ecology used
to diagnose Presbyorntihidae
are derived for that particular
anseriform lineage and not ancestral avian characteristics. Finally,
because of Vegavis placement and its unknown skull morphology,
advanced filter feeding cannot be assumed to be present in the
anseriform lineage by the Maastrichtian. The Anseriformes that can
be inferred as present by this point are lineages that today include
large-bodied terrestrial browsers and occasional omnivores (that is,
screamers, Anhimidae and magpie geese, Anseranas) as well as the
lineage leading to true ducks and geese. A
Vegavis iaai was placed phylogenetically in three successive cladistic analyses progressing
from Avialae to Anseriformes. Placement within Avialae was evaluated using the ref. 19
data set: 200 characters, 19 ingroup taxa; branch and bound search (Fig. 3a). Placement
within Aves was evaluated using the ref. 20 data set: 148 characters, 46 ingroup taxa,
heuristic search strategies of original publication (Fig. 3b). Placement in Anseriformes was
evaluated using the ref. 16 data set: 123 characters, 8 ingroup taxa, branch and bound
search (Fig. 3c). Extinct taxa Anatalavis and Presbyornis are included as the only other
well-preserved basal anseriforms. Anatalavis is scored in this matrix from ref. 29.
The following unambiguously optimized synapomorphies are preserved in Vegavis and
support its placement (character numbers in parentheses refer to the data sets referenced).
Ornithurae: at least 10 sacrals (61:4, ref. 19), domed humeral head (106:1, ref. 19),
radius shaft with muscular impression (135:1, ref. 19), posterodorsal antitrochanter
(158:1, ref. 19), pubis mediolaterally compressed (166:1, ref. 19), patellar groove present
(172:1, ref. 19), distal tibiotarsal condyles equal in width (182:1, ref. 19) and proximal
metatarsal III plantarly displaced (190:1, ref. 19).
Aves: anteriorly deflected humeral deltopectoral crest (112:1, ref. 19) that is less than
shaft width (113:0, ref. 19), at least 15 ankylosed sacral vertebrae (61:6, ref. 19; 91:3, ref. 20)
and ossified supratendinal bridge on tibiotarsus (100:1, ref. 20).
Neognathae: closed ilioischiadic fenestra (94:1, ref. 20, 154:1, ref. 19) and humeral
m. scapulotriceps groove (127:1, ref. 19; 81:1, ref. 20).
Anseriformes: diminutive pectineal process on pelvis (82:1, ref. 16) and hypotarsus
with well developed cristae and sulci (103:12, ref. 20).
Anatoidea: lack of a sternal pneumatic foramen (70:0, ref. 16; apneumatic coracoid
90:0, ref. 19), ovoid m. scapulohumeralis cranialis scar (78:1, ref. 20) and metatarsal II
shorter than IV (202:2, ref. 19). Lack of a pneumatic foramen on the proximomedial
surface of ribs (59:2, ref. 16) and numerous hypotarsal cristae (90:0, ref. 16) are also
synapomorphies of Vegavis, Presbyornis and Anatidae relative to Anseranas, but are
ambiguously optimized because they are unknown in the Eocene Anatalavis. Loss of the n.
supracoracoideus foramen (65:1, ref. 20) and weak to absent thoracic vertebrae lateral
excavations (58:0, ref. 19) are unambiguously optimized as synapomorphies of Anatidae
relative to Vegavis and Presbyornis, but it is unresolved if Vegavis is the sister taxon of
Anatidae, Presbyornis,orPresbyornis þ Anatidae.
Received 16 July; accepted 19 October 2004; doi:10.1038/nature03150.
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Supplementary Information accompanies the paper on
Acknowledgements We thank Museo de La Plata for permission to CT scan and sample MLP
93-I-3-1 for histological analysis; M. Fox for repreparation of the fossil; M. Reguero, S. Marenssi
and E. Olivero for stratigraphic information; T. Rowe and J. Humphries of UTCT lab for
assistance with CT imaging; R. Edwards for photographs; A. Vin
as for line drawings; B. Creisler
for consultation on species name validity; and M. Norell for comments on the manuscript.
Support for this project from an NSF Office of Polar Programs grant to J.A.C., the AMNH
Division of Paleontology and Yale University is gratefully acknowledged.
Competing interests statement The authors declare that they have no competing financial
Correspondence and requests for materials should be addressed to J.A.C.
Figure 4 Histological section from the MLP 92-I-3-1 radius viewed with polarizing
microscopy. The innermost seven-eighths of the cortex show a moderately vascularized,
semi-reticular pattern, fibrolamellar matrix that is uninterrupted by lines of arrested
growth. These data suggest that the animal showed relatively rapid, uninterrupted growth
as in most living birds, including Anatoidea
. The outermost cortices (top) are avascular
indicating that a slowing of growth occurred, presumably as adulthood was approached.
The presence of endosteal, avascular lamellar bone that partially lines the medullar cavity
supports this developmental status interpretation. The primitive avialan long bone
histological condition consists of moderately vascularized cortices with most vascular
canals oriented longitudinally. The cortices in these birds are interrupted by lines of
arrested growth (LAGs)
. The vascular pattern and absence of LAGs in MLP 92-I-3-1 is
consistent with its placement within Ornithurae
from the independent morphological
character evidence.
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... Dataset 5 is based on Livezey [1,91], consisting of 11 taxa and 123 characters of which 94 are PI and 27 are non-osteological (Supplementary Appendix E1). Datasets 5 and 6 differ from one another only by the addition of Nettapterornis and Vegavis and the exclusion of non-osteological characters in the latter [12,14] (79 PI characters, Supplementary Appendices F1 and F2). Dataset 7 is that of Field et al. 2020, as modified [20,43,92] (Supplementary Appendix G1). ...
... Both phylogenetically unconstrained and constrained [20] total-evidence (i.e., character data with tip-dating) Bayesian analyses were also performed on dataset 7 (Supplementary Appendices G4 and G5, respectively). We modified the Field et al. dataset by adding new character data for Vegavis [92], changing fixed dates to temporal ranges [14,15,30,64,72,73,[93][94][95][96][97][98], relaxing the clock rate prior, deleting one redundant species of Megapodiidae, and correcting the sample probability of neotaxa. Bayesian analyses were performed with MrBayes 3.2 [99] with the following settings: lset rates = gamma, ngammacat = 4, coding = variable, clockratepr = exp(1), mcmcp temp = 0.1, nchain = 4, samplefreq = 4000, printfr = 1000, nruns = 2, mcmc ngen = 60,000,000. ...
... The interorbital septum (12) is nearly complete. The lacrimal bone (13) is small, unfused, and generally triangular in the lateral aspect, with the ventral margin (14) forming a straight horizontal line between the orbital process (15) and the rostral apex; the small, rounded supraorbital process forms an acute angle with the much narrower supraorbital margin of the frontal bone. The ectethmoid (16) is extremely low. ...
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We describe nearly complete skeletons of basal Anseriformes from the Latest Paleocene to the early Eocene of North America and Europe. Collectively, these birds appear to be representative of anseriforms near the divergence of Anhimae and Anseres, but their exact positions relative to these clades remains uncertain. A new family, Anachronornithidae nov. fam., is erected on the basis of one of these, Anachronornis anhimops nov. gen., nov. gen. et sp., to which the others cannot be confidently assigned. The new fossils augment a growing collection of early Pan-Anseriformes, which in their diversity do not paint an unambiguous picture of phylogeny or character state evolution on the path to or within crown-Anseriformes. Anachronornis nov. gen. is similar in some aspects of both cranial and postcranial anatomy to other well-represented early Paleogene Anseriformes and members of Anseres, such as Presbyornis Wetmore, 1926. However, it exhibits a more landfowl-like bill, like that of Anhimae and unlike the spatulate bill of Anseres. Additional specimens of similar basal Anseriformes of uncertain affinities from the early Eocene of North America and Europe further complicate interpretation of character state polarity due to the mosaicism of primitive and derived characters they exhibit.
... Antarctica: Latest Cretaceous deposits in Antarctica have produced some avialan remains, including the ornithurines Vegavis (Noriega and Tambussi 1995;Clarke et al. 2005), Polarornis (Chatterjee, 2002) and Antarcticavis (probable ornithurine; Cordes-Person et al., 2020). Preliminary descriptions have placed Vegavis in the Anatoidea (Clarke et al., 2005) and some cladistic analyses suggest this taxon may be an early stem-group anseriform Worthy et al., 2017). ...
... Antarctica: Latest Cretaceous deposits in Antarctica have produced some avialan remains, including the ornithurines Vegavis (Noriega and Tambussi 1995;Clarke et al. 2005), Polarornis (Chatterjee, 2002) and Antarcticavis (probable ornithurine; Cordes-Person et al., 2020). Preliminary descriptions have placed Vegavis in the Anatoidea (Clarke et al., 2005) and some cladistic analyses suggest this taxon may be an early stem-group anseriform Worthy et al., 2017). However, others have argued that Vegavis falls outside the avian crown clade (Wang et al., 2014b;Mayr et al., 2018), so its status as a crown bird is contentious. ...
... Total-clade loons (Gaviiformes) were long regarded as present in the latest Cretaceous on the basis of Neogaeornis (Olson, 1992) and Polarornis (Chatterjee, 2002), although the status of these taxa as gaviiforms is dubious (Mayr, 2016) and at least Polarornis may be closely related to, if not synonymous with, Vegavis . Until recently, only one comparatively well-supported crown-bird fossil has emerged from the entirety of the Mesozoic and, even then, from within approximately one million years of the end-Cretaceous massextinction event (Noriega and Tambussi, 1995;Clarke et al., 2005). The phylogenetic position of this taxon, Vegavis iaai, is debated Mayr et al., 2018), with recent analyses recovering it as an early stem-group anseriform (Worthy et al., 2017) and others questioning its validity as a crown bird (Mayr et al., 2018). ...
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An unabated surge of new and important discoveries continues to transform knowledge of pen-naraptoran biology and evolution amassed over the last 150+ years. This chapter summarizes progress made thus far in sampling the pennaraptoran fossil record of the Mesozoic and Paleocene and proposes priority areas of attention moving forward. Oviraptorosaurians are bizarre, nonparavian pennaraptorans first discovered in North America and Mongolia within Late Cretaceous rocks in the early 20th century. We now know that oviraptorosaurians also occupied the Early Cretaceous and their unquestionable fossil record is currently limited to Laurasia. Early Cretaceous material from China preserves feathers and other soft tissues and ingested remains including gastroliths and other stomach contents, while brooding specimens and age-structured, single-species accumulations from China and Mongolia provide spectacular behavioral insights. Less specialized early oviraptorosaurians like Incisivosaurus and Microvenator remain rare, and ancestral forms expected in the Late Jurassic are yet to be discovered, although some authors have suggested Epidexipteryx and possibly other scansoriopterygids may represent early-diverging oviraptorosaurians. Long-armed scansoriopterygids from the Middle-Late Jurassic of Laurasia are either early-diverging oviraptorosaurians or paravians, and some have considered them to be early-diverging avialans. Known from five (or possibly six) feathered specimens from China, only two mature individuals exist, representing these taxa. These taxa, Yi and Ambopteryx, preserve stylopod-supported wing membranes that are the only known alternative to the feathered, muscular wings that had been exclusively associated with dinosaurian flight. Thus, scansoriopterygid specimens-particularly those preserving soft tissue-remain a key priority for future specimen collection. Dromaeosaurids and troodontids were first discovered in North America and Mongolia in Late Cretaceous rocks. More recent discoveries show that these animals originated in the Late Jurassic, were strikingly feathered, lived across diverse climes and environments, and at least in the case of dromaeosaurids, attained a global distribution and the potential for aerial locomotion at small size.
... head, unlike in CPAP 5931, though this could be due to deformation in the A. capelambensis specimen (Cordes-Pearson et al., 2020). The best preserved ornithurine from the southern high latitudes is Vegavis iaai (Clarke et al., 2005(Clarke et al., , 2016. The articular portion of the scapula is superficially very similar to that of CPAP 5931. ...
... Cretaceous theropod remains from Antarctica are all found within the James Ross Basin, along the Antarctic Peninsula (Acosta Hospitaleche et al., 2019;Lamanna et al., 2019). Remains from Campanian and Maastrichtian deposits on Seymour, James Ross, and Vega islands include isolated bones of non-avian and avian theropods (Acosta Hospitaleche et al., 2019;Lamanna et al., 2019) and partial skeletons of the paravian Imperobator antarcticus (Case et al., 2007;Ely and Case, 2019) and ornithurines V. iaai (Clarke et al., 2005(Clarke et al., , 2016 and P. gregorii (Chatterjee, 2002;Acosta Hospitaleche et al., 2019). Notably, populations during the latest Cretaceous of the Magallanes-Austral Basin and James Ross Basin would have been the last cross-continental Gondwanan populations to maintain connectivity during the end Cretaceous, as changes in sea level intermittently exposed connections to the Antarctic Peninsula (Poblete et al., 2016;Reguero and Goin, 2021), leading to similarities in the taxa found in both. ...
... Theropods are underrepresented in Maastrichtian deposits at near high-latitudes in the Southern Hemisphere, but it is striking that the most represented clade is ornithurine birds (Alvarenga and Bonaparte, 1988;Olson, 1992;Clarke and Chiappe, 2001;Chatterjee, 2002;Chiappe, 2002;Clarke et al., 2005;Ksepka and Cracraft, 2008;Clarke et al., 2016;Cordes-Pearson et al., 2020; see Fig. 10 and Table S1). At these latitudes, no enantiornithines have been recovered from Maastrichtian deposits (Fig. 10), while they still make up the majority of bird fossils recovered from northern South America (e.g., El Brete, Argentina; Chiappe, 1993;1996;Walker and Dyke, 2010; see Table S1). ...
... Although, here again, the possibility of homoplasy should not be overlooked, further studies on Cretaceous materials may provide new indirect evidence on the presence of Palaeognathae in the Cretaceous. In fact, the presence of Neognathae in the Late Cretaceous was confirmed by body fossils from Maastrichtian (Late Cretaceous) deposits in Antarctica (Clarke et al., 2005) and Europe , indirectly supporting the presence of Palaeognathae in the Late Cretaceous. If some Late Cretaceous rhea-style 'ratite-morphotype' eggshells turn out to be true palaeognath eggshells, our interpretation ( Figure 14) will be further supported with evidence. ...
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The avian palaeognath phylogeny has been recently revised significantly due to the advancement of genome-wide comparative analyses and provides the opportunity to trace the evolution of the microstructure and crystallography of modern dinosaur eggshells. Here, eggshells of all major clades of Palaeognathae (including extinct taxa) and selected eggshells of Neognathae and non-avian dinosaurs are analysed with electron backscatter diffraction. Our results show the detailed microstructures and crystallographies of (previously) loosely categorized ostrich-, rhea-, and tinamou-style morphotypes of palaeognath eggshells. All rhea-style eggshell appears homologous, while respective ostrich-style and tinamou-style morphotypes are best interpreted as homoplastic morphologies (independently acquired). Ancestral state reconstruction and parsimony analysis additionally show that rhea-style eggshell represents the ancestral state of palaeognath eggshells both in microstructure and crystallography. The ornithological and palaeontological implications of the current study are not only helpful for the understanding of evolution of modern and extinct dinosaur eggshells, but also aid other disciplines where palaeognath eggshells provide useful archive for comparative contrasts (e.g. palaeoenvironmental reconstructions, geochronology, and zooarchaeology).
... The origin of the bird crown group is well-established to have occurred during the Cretaceous Period (Jarvis et al., 2014;Prum et al., 2015;Berv & Field, 2018), but the scarcity of Late Cretaceous crown bird material complicates our understanding of the early morphology and evolutionary history of the group (Chatterjee, 1989(Chatterjee, , 2000Clarke et al., 2005Clarke et al., , 2016Longrich, Tokaryk & Field, 2011;Field et al., 2020aField et al., , 2020b. Given this significant gap in the crown bird fossil record, work attempting to understand aspects of the ecology, biology, and morphology of the earliest crown birds must rely on inferences based on extant birds and the most crownward-known stem birds (Zheng et al., , 2018Berv & Field, 2018;Field et al., 2018a;Wang et al., 2018;O'Connor, 2019;Torres, Norell & Clarke, 2021). ...
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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.
... Other fossil birds registered in the Cretaceous period belonged to the Ornithuromorpha, a clade that included the iconic Ichthyornis (Field et al. 2018) and the aquatic Hesperornis (Bell and Chiappe 2016), among others. Modern birds, Neornithes (Aves in the sense of Gauthier 1986), appeared in the Upper Cretaceous (Clarke et al. 2005(Clarke et al. , 2006Ksepka et al. 2017;Field et al. 2020). By the K-Pg extinction event most arboreal-dwelling birds became extinct. ...
Brain morphology has become a key element to predict a wide array of cognitive and behavioral, sensory and motor abilities, and to determine evolutionary rates of phenotypic transformation. Our information on early bird brain morphology comes of natural endocasts or studies of the intracranial cavity. Although the first studies of fossil bird brains were published almost two centuries ago, there is still relatively little known about the avian brain and its evolution compared with other groups such as mammals. This is due primarily to the fact that few three-dimensionally preserved skulls of early birds are recognized. The avian brain occupies the entire intracranial cavity, so that it is possible to reconstruct high-quality 3D virtual endocast models that can be used as excellent proxies for both volume and morphology of the brain. This technique has driven advances in avian paleoneurology from 2000 onwards. In this chapter, we provide a holistic view of the main features of the avian brain and senses, its disparity and potential use in paleobiological inferences, and discuss the main changes across the transition from non-avian theropods to derived Neornithes.
白垩纪-古近纪之间(K/Pg,~66 Ma)发生了显生宙以来的第五次生物大灭绝,其古环境、古气候的反演长期是国内外的研究热点。四川盆地峨眉山地区保存了完整且连续的K/Pg陆相地层,是研究K/Pg界线的理想地区。本文采集了峨眉山地区白垩系灌口组(K2g)顶部、K/Pg界线、古近系名山组(E1-2m)底部的岩石样品,利用元素在剖面上的变化特征进行了古环境、古气候的综合分析。结果表明:与大陆地壳相比,K/Pg界线处的砂岩有明显铂族元素异常,可能与撞击地球的陨石、德干高原火山的喷发都有关系。根据Pb、K2O/Na2O、Rb/Sr、硅铝率、硅铝铁率等共12个指标推断研究区在K/Pg过渡阶段的古气候最可能为:K2g晚期最为温暖湿润、K/Pg界线最为炎热干燥、E1-2m早期气候较为炎热干燥。气候的急剧变化可能与小行星撞击和德干火山喷发等极端因素有关。根据δCe、U/Th、V/Cr、Ni/Co、Sr/Ba共5个指标推断研究区在K/Pg过渡阶段的古环境为:氧化环境、陆相沉积。
Explanations of pantropical distributions are challenging for taxa that diverged during the Cenozoic, after Gondwana broke apart. The ‘boreotropics hypothesis’ suggests that pantropical birds originated in the Laurasian forests. Extant parrots (Psittaciformes) are one the most species‐rich pantropical avian clades, but their known evolutionary history does not fit a boreotropical origin. Most living parrots and the earliest diverging lineages of the Psittaciformes inhabit the remnants of Gondwana, whereas the oldest stem and crown fossils are from the remnants of Laurasia. Our study proposes a biogeographic hypothesis that focuses on the Cenozoic connections between Laurasia and Gondwana to explain extant and fossil geographical distributions. Global. Psittaciformes. We generated a time tree using previously derived data from 32 molecular markers for 312 parrot species and reconstructed their biogeographic history using maximum likelihood. Two scenarios were compared: one with dispersal constrained to adjacent areas, including the connections between the Northern and Southern Hemispheres, and one without this constraint. Our results indicate that the pantropical distribution of parrots was shaped by two major geological events. First, the final breakup of parts of Gondwana may have caused the first splits within crown parrots, establishing two parallel radiations: Psittacidae in the Neotropics and Psittaculidae in Australasia. Second, igneous palaeoprovinces could have connected major biogeographic realms. It seems that Atlantogea and Eurogondwana were important, as they connected South America, Africa and Europe, thus reconciling the Gondwanan crown splits and the early Laurasian fossils. Our time tree allowed more concise biogeographic correlations between parrots and their sister group, the passerines and Earth's tectonic history. The crown lineages of Psittacopasseres appear to have originated in the Southern Hemisphere remnants of Gondwana, but stem lineages appear to have been able to disperse into the Northern Hemisphere through palaeobiogeographic provinces in the Cenozoic.
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Dinosaurs, like other tetrapods, grew more quickly just after hatching than later in life. However, they did not grow like most other non-avian reptiles, which grow slowly and gradually through life. Rather, microscopic analyses of the long-bone tissues show that dinosaurs grew to their adult size relatively quickly, much as large birds and mammals do today. The first birds reduced their adult body size by shortening the phase of rapid growth common to their larger theropod dinosaur relatives. These changes in timing were primarily related not to physiological differences but to differences in growth strategy.
We describe a new large representative of the important fossil anseriform taxon Presbyornithidae from the latest Cretaceous (Maastrichtian) Nemegt Formation of southern Mongolia. This new taxon, Teviornis gobiensis, n. gen. et n. sp., is known from the associated manual portion of a right wing and the distal end of a right humerus, but is clearly diagnosable with respect to all other known representatives of the fossil Presbyornithidae. It is placed within the clades Anseriformes and Presbyornithidae, respectively, on the basis of a number of derived characters of the carpometacarpus and digits. Importantly, description of Teviornis confirms the presence of members of the neornithine clade Anseriformes (“waterfowl”) in the Late Cretaceous, as has been suggested previously on the basis of much less diagnostic fossil material as well as from clade divergence estimates founded on molecular sequence data. The extinct Presbyornithidae thus has a worldwide distribution and ranged in age from at least the Maastrichtian through to the uppermost Eocene.
Consensus is elusive regarding the phylogenetic relationships among neornithine (crown clade) birds. The ongoing debate over their deep divergences is despite recent increases in available molecular sequence data and the publication of several larger morphological data sets. In the present study, the phylogenetic relationships among 43 neornithine higher taxa are addressed using a data set of 148 osteological and soft tissue characters, which is one of the largest to date. The Mesozoic non-neornithine birds Apsaravis, Hesperornis, and Ichthyornis are used as outgroup taxa for this analysis. Thus, for the first time, a broad array of morphological characters (including both cranial and postcranial characters) are analyzed for an ingroup densely sampling Ne-ornithes, with crown clade outgroups used to polarize these characters. The strict consensus cladogram of two most parsimonious trees resultant from 1000 replicate heuristic searches (random stepwise addition, tree-bisection-reconnection) recovered several previously identified clades; the at-one-time contentious clades Galloanseres (waterfowl, fowl, and allies) and Palaeognathae were supported. Most notably, our analysis recovered monophyly of Neoaves, i.e., all neognathous birds to the exclusion of the Galloanseres, although this clade was weakly supported. The recently proposed sister taxon relationship between Steatornithidae (oilbird) and Trogonidae (trogons) was recovered. The traditional taxon "Falconiformes" (Cathartidae, Sagittariidae, Accipitridae, and Falconidae) was not found to be monophyletic, as Strigiformes (owls) are placed as the sister taxon of (Falconidae + Accipitridae). Monophyly of the traditional "Gruiformes" (cranes and allies) and "Ciconiiformes" (storks and allies) was also not recovered. The primary analysis resulted in support for a sister group relationship between Gaviidae (loons) and Podicipedidae (grebes)-foot-propelled diving birds that share many features of the pelvis and hind limb. Exclusion of Gaviidae and reanalysis of the data set, however, recovered the sister group relationship between Phoenicopteridae (flamingos) and grebes recently proposed from molecular sequence data.
— We studied sequence variation in 16S rDNA in 204 individuals from 37 populations of the land snail Candidula unifasciata (Poiret 1801) across the core species range in France, Switzerland, and Germany. Phylogeographic, nested clade, and coalescence analyses were used to elucidate the species evolutionary history. The study revealed the presence of two major evolutionary lineages that evolved in separate refuges in southeast France as result of previous fragmentation during the Pleistocene. Applying a recent extension of the nested clade analysis (Templeton 2001), we inferred that range expansions along river valleys in independent corridors to the north led eventually to a secondary contact zone of the major clades around the Geneva Basin. There is evidence supporting the idea that the formation of the secondary contact zone and the colonization of Germany might be postglacial events. The phylogeographic history inferred for C. unifasciata differs from general biogeographic patterns of postglacial colonization previously identified for other taxa, and it might represent a common model for species with restricted dispersal.
All associated partial skeleton, including the skull but lacking legs, from the lower Eocene London Clay of Essex, England, pos-sesses derived characters of the coracoid and furcula that show it to belong to the Anseranatidae, which previously had no fossil record. Except for its much larger size, the humerus of this speci-men is identical to that of Anatalavis rex (Shufeldt) from the late Cretaceous or early Paleocene of New Jersey. The Eocene speci-men is described as a new species, Anatalavis oxfordi, and the genus Anatalavis is transferred from the form-family Graculavidae to a new subfamily, Anatalavinae, of the Anseranatidae. Anatala-vis is characterized by a very broad duck-like bill, a proportion-ately very short and robust humerus, and an anterior portion of the pelvis resembling that of ibises and other wading birds more than that of any known anseriform. Other features of its osteology are unique within the order.
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