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18. Ahmad, N. in Pedogenesis and Soil Taxonomy II. The Soil Orders. Developments in Soil Science 11B
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Ethiopia. Nature 371, 330–333 (1994).
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Supplementary Information accompanies the paper on www.nature.com/nature.
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
interests.
Correspondence and requests for materials should be addressed to S.S. (ssemaw@indiana.edu).
..............................................................
Definitive fossil evidence for the
extant avian radiation in the
Cretaceous
Julia A. Clarke
1,2
, Claudia P. Tambussi
3
, Jorge I. Noriega
4
,
Gregory M. Erickson
5,6,7
& Richard A. Ketcham
8
1
Department of Marine, Earth and Atmospheric Sciences, North Carolina State
University, Campus Box 8208, Raleigh, North Carolina 27695, USA
2
North Carolina Museum of Natural Sciences, 11 West Jones Street, Raleigh,
North Carolina 27601-1029, USA
3
Museo de La Plata-CONICET, Paseo del Bosque s/n. La Plata (1900), Argentina
4
Centro de Investigaciones Cientı
´
ficas y TTP- CONICET, Matteri y Espan
˜
a,
3105 Diamante, Entre Rı
´
os, Argentina
5
Department of Biological Science, Florida State University, Conradi Building,
Dewey Street and Palmetto Drive, Tallahassee, Florida 32306-1100, USA
6
Division of Paleontology, American Museum of Natural History, Central Park
West at 79
th
Street, New York, New York 10024-5192, USA
7
Department of Geology, The Field Museum, 1400 South Lake Shore Drive,
Chicago, Illinois 60605, USA
8
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
1–9
surrounds the question of whether
living bird lineages emerged after non-avian dinosaur extinction
at the Cretaceous/Tertiary (K/T) boundary
1,6
or whether these
lineages coexisted with other dinosaurs and passed through this
mass extinction event
2–5,7–9
. Inferences from biogeography
4,8
and
molecular sequence data
2,3,5,9
(but see ref. 10) project major avian
lineages deep into the Cretaceous period, implying their ‘mass
survival’
3
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
1,6
.
However, other fossil data
—
fragmentary bones referred to extant
bird lineages
11–13
—
have been considered inconclusive
1,6,14
. These
data have never been subjected to phylogenetic analysis. Here we
identify a rare, par tial skeleton from the Maastrichtian of
Antarctica
15
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
dinosaurs.
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
15
as a possible ‘transitional’ form
close to extant lineages
15
. For a decade since, the specimen’s exact
systematic position and possible crown clade avian status have
been debated
6,14,16,17
. Significant new preparation, X-ray computed
tomography (CT)
18
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
Avialae
19
, Aves
20
and Anseriformes
16
, 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
specimen.
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
15
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
15
. Deposits are near-shore marine fine-grain
sandstones
21
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
details).
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
15,22
(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-
ally
23
. 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
23
. 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
24,25
(Fig. 3).
This conclusion is consistent with the independent phylogenetic
results.
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
9,10
, or the
presence of most major lineages in the Cretaceous
2–5,8
and ‘mass
survival’
3
at this boundary. It contradicts a proposed early Tertiary
crown clade origin
1,6
; 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
9,26
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
9
) estimates of crown anseriform divergences
made using these techniques
9,10
. However, these estimates place
most other major avian divergences earlier than or approximately
contemporaneous with the Cretaceous
2–5,9
, 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’
placement.
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’
15
, 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’
1,6,22,27
.
Presbyornithids were proposed to be bridging taxa to waterfowl,
indicating shorebird-like taxa to be the progenitors of all extant bird
lineages
1,6,22,27
. Vegavis has different proportions from Presbyornis
that are closer to other extant basal anseriform species. Thus, there is
further support
16
that the wader proportions and the ecology used
to diagnose Presbyorntihidae
17,22,27
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
Methods
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 www.nature.com/nature.
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
interests.
Correspondence and requests for materials should be addressed to J.A.C.
(Julia_Clarke@NCSU.edu).
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
24,25
. 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)
24,25
. The vascular pattern and absence of LAGs in MLP 92-I-3-1 is
consistent with its placement within Ornithurae
25
from the independent morphological
character evidence.
letters to nature
NATURE | VOL 433 | 20 JANUARY 2005 | www.nature.com/nature308
© 2005 Nature Publishing Group
