Redescription of the key specimen MACN-Pv-N 35: Laminar anatomy and hyposphene–hypantrum in an early rebbachisaurid (Dinosauria, Sauropoda) from Patagonia, Argentina

Abstract

The purported basal rebbachisaurid MACN PV 35 specimen from the La Amarga Formation (Lower Cretaceous) is re-described. It is represented by a single mid to posterior dorsal neural arch and it was considered as a basal rebbachisaurid based on the well-developed hyposphene. Here I provided a re-description and a phylogenetic analysis including a new combination of morphological characters. The peculiar ovoidal hollow hyposphene, particularly recognizable in this specimen, is completely different from the massive and rhomboidal hyposphene present in Diplodocidae or Histriasaurus. The presence of a laterodiapophyseal fenestra on the transverse process recover the specimen MACN PV 35 as a Rebbachisaurinae closely related to Katepensaurus. The reassessment of the specimen MACN PV 35 as a Rebbachisaurinae improves our knowledge about the evolutionary history of Rebbachisauridae, opening the field for future investigations into how hyposphene evolved within the group.