New specimens of a titanosaur sauropod from the Maastrichtian of Big Bend National Park, Texas

ABSTRACT

New specimens of a titanosaur sauropod from Maastrichtian strata in Big Bend National Park, Texas, include well-preserved dorsal vertebrae in association with pelvic elements. Anterior dorsal vertebrae are characterized by postspinal and centroprezygapophyseal laminae, with spinodiapophyseal laminae convergent on the anterior base of the neural spine. Posterior dorsal vertebrae are characterized by postzygodiapophyseal laminae and divided spinodiapophyseal laminae, with spinoprezygapophyseal laminae contributing to the prespinal lamina. The ilium and pubis differ from specimens previously collected, indicating a greater morphological disparity among titanosaurs in the Maastrichtian of West Texas than previously recognized. This disparity may be attributable to intraspecific variation or to the presence of multiple taxa. The new material is compatible with the only presently known North American titanosaur, Alamosaurus sanjuanensis, but is not formally referred due to lack of overlap with the hypodigm of that species. Comparison with other derived titanosaurs finds the closest affinities to Trigonosaurus pricei, Uberabatitan riberoi, and Baurutitan britoi of the Upper Cretaceous Brazilian Bauru Group, consistent with a South American immigration event at the end of the North American sauropod hiatus.

ACKNOWLEDGMENTS

The authors thank S. Wick, J. Browning, and D. Evans for assistance in specimen collection, A. Brink, N. Coint, K. Hoch, T. Schiller, J. Schubert, C. Schulte, G. Tembe, and R. Westerfield for field and laboratory assistance, and J. Wilson for advice and critical review of the original drafts. M. D’Emic and P. Upchurch contributed valuable insight and recommendations in their reviews of the manuscript. T. Rowe and L. Murray provided access to specimens at the Texas Memorial Museum, University of Texas, Austin. Translation of Salgado et al. (2006) was made by M. D’Emic and A. Schepers and obtained through the Polyglot Paleontologist Web site (http://www.paleoglot.org). The support of the Texas Tech Department of Geosciences and the staff of Big Bend National Park was essential to the success of this project.

Handling editor: Matt Friedman