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Sauroposeidon in the Cloverly!
D'Emic, M.D., & B.Z. Foreman. 2012. The beginning of the sauropod dinosaur
hiatus in North America: insights from the Lower
Cretaceous Cloverly Formation of Wyoming. Journal of Vertebrate Paleontology
32(4):883-902
DOI: 10.1080/02724634.2012.671204
ABSTRACT
We redescribe and present newly excavated sauropod material from the Lower
Cretaceous Cloverly Formation of Wyoming that we refer to
the titanosauriform Sauroposeidon proteles. In contrast to previous hypotheses
that it was a brachiosaurid, we assert that
Sauroposeidon is a member of the Somphospondyli on the basis of numerous
features. Thus, the mid-Cretaceous disappearance of
sauropods from the North American fossil record concerned both brachiosaurids
and somphospondylans. We find claims for titanosaurs
in the Early Cretaceous of North America to be unsubstantiated. The latest
register of Sauroposeidon and other Early Cretaceous
North American sauropods (before the 'sauropod hiatus') occurs in or below the
coastal units marking transgression of the Western
Interior Seaway, whereas many ecologically disparate dinosaur groups are
present both below and above this boundary in the same
geologic units that sauropods are found in. The presence of these
through-ranging groups with sauropods before and after sauropod
absence suggests that appropriate sauropod-bearing environments were present
into the Late Cretaceous, implying that the
disappearance of sauropods is not attributable to taphonomic or sampling bias.
Furthermore, field observations of the Cloverly
Formation indicate that Cretaceous pre-hiatus sauropods inhabited near-coastal
environments, which were abundant in the western
United States well after the start of the hiatus. The start of the sauropod
hiatus is interpreted as the result of a genuine
continent-wide extinction, coincident with the appearance of (and perhaps
attributable to competition with) advanced ornithischian
herbivores, decrease in habitat due to the incursion of the Western Interior
Seaway, or both.
Thomas R. Holtz, Jr.
Email: tholtz@umd.edu Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661
Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843
Mailing Address: Thomas R. Holtz, Jr.
Department of Geology
Building 237, Room 1117
University of Maryland
College Park, MD 20742 USA