A sauropod dinosaur pes from the latest Cretaceous of North America and the validity of Alamosaurus sanjuanensis (Sauropoda, Titanosauria)

Abstract

ABSTRACT Complete sauropod pedes are rare in the fossil record, which has limited their use in systematics. We describe a nearly complete, large sauropod pes from the Maastrichtian-age Naashoibito Member of the Kirtland Formation of New Mexico, U.S.A., that bears synapomorphies of some eusauropod clades, such as the presence of metatarsal I with a wide shaft and laterally deflected pedal unguals. Novel pedal characters presented herein, such as the presence of an embayment on the proximomedial corner of metatarsal IV, suggest that the Naashoibito specimen likely belongs to a titanosauriform. Based on its provenance, the Naashoibito specimen likely belongs to the derived titanosaur Alamosaurus sanjuanensis, which is the only recognized Late Cretaceous titanosaur in North America. However, formal referral to Alamosaurus awaits discovery of overlapping materials with the holotype or definitively referred remains. The holotypic scapula of Alamosaurus sanjuanensis is diagnostic, providing a basis for referral of some other Maastrichtian North American titanosaur specimens to the genus. Confirmation of these referrals and the description of the pes presented herein augment the data relevant to the systematic problems that have historically surrounded Alamosaurus.