Evidence of a derived titanosaurian (Dinosauria, Sauropoda) in the “Kem Kem beds” of Morocco, with comments on sauropod paleoecology in the Cretaceous of Africa

Abstract

A well preserved middle caudal vertebra from middle Cretaceous (Albian–lower Cenomanian) deposits informally known as the “Kem Kem beds” exposed in the Gara Sbaa region of Morocco is attributed to a large-bodied titanosaurian sauropod dinosaur. It represents one of the best-preserved and most complete skeletal elements reported for this sauropod group from the Kem Kem sequence. The vertebra is generally similar to middle caudals of the lithostrotian titanosaur Baurutitan britoi from the Upper Cretaceous Bauru Group of Brazil, but differs in several respects, such as: (1) a transversely compressed (as opposed to more square in posterior view) centrum; (2) a taller, anteroposteriorly longer, and more anteriorly positioned neural spine; and (3) prezygapophyses that are subtriangular in lateral view. It represents an animal that likely attained a very large body size (possibly over 25 m in total length), considerably larger than the diplodocoid Rebbachisaurus garasbae, the only named sauropod from the Kem Kem assemblage. Additional, selected specimens from the Kem Kem beds are described, with some probably referable to Titanosauria. In the Kem Kem sequence, sauropod fossils are far less common than those of predatory dinosaurs, which include several coeval, multi-ton taxa. This was likely due to an abundance of potential aquatic prey as well as complex niche partitioning among sympatric theropods, pterosaurs, and crocodyliforms. Nevertheless, some predators, such as the giant theropod Carcharodontosaurus saharicus, likely preyed on sauropods. The taxon represented by the new vertebra (and possibly other isolated remains from the Kem Kem region) and the giant Egyptian titanosaurian Paralititan stromeri rank among the largest known sauropods. Most other North African Cretaceous sauropods appear to have reached only modest adult body sizes; this could, however, be an artifact of the limited number of fossils and uncertainty in the ontogenetic stages represented by most specimens. The morphology of the Kem Kem vertebra suggests that the taxon it represents may have been more closely related to South American and/or European titanosaurians than to other members of this clade from sub-Saharan Africa.