On a Sequence of Sacrocaudal Theropod Dinosaur Vertebrae from the Lower Cretaceous Santana Formation, Northeastern Brazil

Abstract

Besides being rare, most theropod remains from fossil deposits of Brazil are incomplete. Up to date the Romualdo Member (Aptian/Albian) of the Santana Formation yielded six theropod specimens. To those we add the description of a sequence of three posterior sacral and six anterior caudal vertebrae with three chevrons (MN 4743-V). Differences between MN 4743-V and members of the major theropod clades such as Ceratosauria, Allosauroidea and Coelorusauria do not allow its assignment to one of those groups. Instead, MN 4743-V is referred to the Spinosauroidea (Spinosauridae plus Torvosauridae), based on the presence of three robust laminae below the transverse process of the anterior caudals, which delimit three fossae. The lack of paired processes on the chevrons suggest that within Spinosauroidea MN 4743-V is a member of the Spinosauridae. This is congruent with previous findings of spinosaurids in the Romualdo Member. MN 4743-V differs from the remaining specimens that present sacrocaudal elements indicating the co-existence of at least five theropod species in this deposit.