saurornitholestes robustus, n. sp. - Robert M. Sullivan

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robustus based on geographic and stratigraphic parsimony.
Two species of Saurornitholestes are now known: S. langstoni and
S. robustus. Currie (2005) cited three undescribed partial skeletons, two
from the Dinosaur Park Formation of Alberta and one from the Two Medicine
Formation of Montana.
Although Saurornitholestes is considered to be similar to the Asian
dromaeosaurid Velociraptor, recognition of two separate genera has been
the consensus of most workers (Currie, 2005). Differences in the postcranial
skeleton have already been documented by Norell and Makovicky
(1997), and the deeper pedal ungual in Saurornitholestes robustus, if properly
referred, further reinforces the argument for generic and specific distinction.
Although the frontals are not preserved in the holotype of
Velociraptor mongoliensis (AMNH 6515) (Osborn, 1924; Sues, 1977),
frontals are known from referred material (GIN 1000/24, 100/25) described
in detail by Barsbold and Osmólska (1999). Comparison of the frontal material
to that seen in a cast of skull of Velociraptor mongoliensis from a
private collection, also verify the taxonomic distinction between the genera
Velociraptor and Sauronitholestes.
All specimens of Saurornitholestes robustus come from the De-nazin
Member of the Kirtland Formation, which is Kirtlandian age. The duration
of the Kirtlandian is approximately 2 million years (74.8 to 72.8 Ma)
based on recent correlations (see Sullivan and Lucas, 2006). The fossils
from the De-na-zin Member can be more precisely dated at 73 Ma based
on the 40 Ar/ 39 Ar dates of 73.04 Ma (Ash J) and 73.37 Ma (Ash H), pub-
Barsbold, R. and Osmólska, H., 1999, The skull of Velociraptor (Theropoda) from
the Late Cretaceous of Mongolia: Acta Palaeontologica Polonica, v. 44, p.189-
219.
Baszio, S., 1997a, Palaeoecology of dinosaur assemblages throughout the Late Cretaceous
of South Alberta, Canada: Courier Forschungsinstitut Senckenberg, v.
196, p. 1-31.
Baszio, S., 1997b, Systematic Palaeontology isolated dinosaur teeth from the latest
Cretaceous of south Alberta, Canada: Courier Forschungsinstitut Senckenberg,
v. 196, p. 33-77.
Brinkman, D., 2005, An illustrated guide to the vertebrate microfossils from the
Dinosaur Park Formation: Unpublished guide, prepared for the Alberta Paleontological
Society, Workshop on vertebrate microfossils (Jan. 26, 2002); revised
April 3, 2005, 141 p.
Currie, P.J., 1987, Theropods of the Judith River Formation of Dinosaur Provincial
Park, Alberta, Canada; in Currie, P.J. and Koster, E.H., eds., Fourth Symposium
on Mesozoic Terrestrial Ecosystems, Short Papers, v. 3: Drumheller, Tyrrell
Museum of Palaeontology, p. 52-60.
Currie, P.J., 2005, Theropoda, including birds; in Currie, P.J. and Koppelhus, E.B.,
eds., Dinosaur Provincial Park: Bloomington and Indianapolis, Indiana University
Press, p. 367-397.
Currie, P.J., Rigby, J.K., Jr., and Sloan, R.E., 1990, Theropod teeth from the Judith
River Formation of southern Alberta, Canada; in Carpenter, K. and Currie, P.J.,
eds., Dinosaur systematics: Perspectives and approaches: Cambridge, Cambridge
University Press, p.107-125.
Currie, P.J., and Varricchio, D.J., 2004, A new dromaeosaurid from the Horseshoe
Canyon Formation (Upper Cretaceous) of Alberta, Canada; in Currie, P.J.,
Koppelhus, E.B., Shugar, M.A., and Wright, J.L., eds., 2004, Feathered Dragons.
Studies on theTransition from Dinosaurs to Birds. Bloomington, Indiana
University Press, p. 112-132.
Eberth, D.A., 2005, The geology; in Currie, P.J. and Koppelhus, E.B., eds., Dinosaur
Provincial Park: Bloomington and Indianapolis, Indiana University Press,
p. 367-397.
Fassett, J.E. and Steiner, M.B., 1997, Precise age of C33N-C32R magnetic-polarity
reversal, San Juan Basin, New Mexico and Colorado: New Mexico Geological
Society, Guidebook 48: 239-247.
Kirkland, J.I., Gaston, R., and Burge, D., 1993, A large dromaeosaur (Theropoda)
from the Lower Cretaceous of Eastern Utah: Hunteria, v. 2, 1-16.
Norell, M.A. and Makovicky, P.J., 1999, Important features of the dromaeosaurid
skeleton II: Information from newly collected specimens of Velociraptor
REFERENCES
lished by Fassett and Steiner (1999), which bracket the upper and lower
portions of the De-na-zin Member. By contrast, specimens of
Saurornitholestes (S. langstoni) from the Dinosaur Park and Two Medicine
formations are considerably older, 75 Ma at the very least (Eberth,
2005). It is not unreasonable to conclude that given the age difference, that
the morphological differences between the species of Saurornitholestes
are significant. Despite ongoing claims of endemic faunas and provincialism
of Western Interior dinosaurs during the Late Cretaceous (see Sullivan
and Lucas, 2006, for citations), these differences are mostly due to temporal
differences, not biogeographic ones. The cosmopolitan nature of the
dinosaur faunas during the Late Cretaceous is borne out by the generic
similarities of faunas from the north to the south. The coastal plain along
the western margin of the Western Interior seaway provided a barrier free
corridor for dinosaur dispersal.
ACKNOWLEDGMENTS
I thank James Gardner (Royal Tyrrell Museum of Palaeontology,
Drumheller) and Phil J. Currie (University of Alberta, Edmonton) for access
to comparative material; and Phil J. Currie and Don Brinkman (Royal
Tyrrell Museum of Palaeontology, Drumheller) for discussions concerning
Saurornitholestes. Don Brinkman and Spencer G. Lucas reviewed this
contribution and I thank them for the comments and suggestions.
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for the Late Cretaceous of Western North America: New Mexico Geological
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faunal composition, temporal position and biostratigraphic correlation in the
nonmarine Upper Cretaceous of western North America: New Mexico Museum
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