Unraveling sauropod diversity in the Portezuelo Formation of Patagonia through a comprehensive analysis of new and existing material

Abstract

The Portezuelo Formation preserves an outstanding record of the upper Turonian - lower Coniacian of Gondwana. Despite the discovery of a significant amount of sauropod fossil material from the Formation, only two species have been formally described to date: Malarguesaurus florenciae and Futalognkosaurus dukei. Here we present new sauropod material mostly composed of non-articulated caudal vertebrae that belong to at least two different titanosauriforms on the basis of following features: anterior caudal vertebrae with procoelous-opistoplatyan articulations, transverse processes that reach the posterior articular face of the centrum and neural spines with a lateromedial width of ~ 50% of its anteroposterior length; anterior and middle caudal vertebra with the neural arch restricted to the anterior half of the centrum; middle caudal centrum with circular cross-section. Phylogenetic analysis recovers the new material in close relation to Malarguesaurus within a monophyletic clade sister to Somphospondily. This clade shares large pedicel height with a vertical anterior border on the middle caudal vertebrae, a vertical orientation of the neural spines on the distalmost middle caudal vertebrae and proximalmost posterior caudal vertebrae, and subequal relative lengths of the proximal ulnar condylar processes. The specimens presented here are distinct not only from Malarguesaurus and Futalognkosaurus, but also from other indeterminate titanosaur remains from the same formation. Whilst we err on the side of caution in not naming new taxa here, the two specimens significantly expand what we know about sauropods in the Turonian-Coniacian ecosystems of Patagonia, which will continue to do so as more material is discovered.