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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 
DOI: 10.1080/02724634.2012.671204

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
Fax: 301-314-9661               

Faculty Director, Science & Global Change Program, College Park Scholars
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