New basal synapsid discovery at the Permian outcrop of Torre del Porticciolo (Alghero, Italy)

Abstract

The Torre del Porticciolo fossil locality is notable for producing the first osteological material of a basal (i.e., non-mammalian) synapsid in Italy, the giant herbivore Alierasaurus ronchii, which although known from fragmentary remains, likely represents the largest known late early to early middle Permian synapsid (6–7 m total length). Recently, a new productive site was discovered about 100 m from the Alierasaurus type locality, but roughly at the same stratigraphic level. The fragmentary nature of most of the recovered bones prompted a taphonomical analysis in order to define the type of find, the kind of burial, and the mode of preservation. The vertebrate remains allowed us to infer a complex taphonomical process involving a multiphase entombment. The recovered bones were subjected to both re-exhumation and reworking. The last short and violent transportation phase before final entombment occurred as a high-energy flow, probably caused by a river flood that carried sediment and bones together to be emplaced in a semi-perennial pond in a crevasse splay deposit. Preliminary analysis of recovered material indicates the presence of a large carnivorous basal synapsid referable to the family Sphenacodontidae. This discovery represents the first carnivorous non-therapsid synapsid from the Permian of Italy and one of only very few known from Europe.