New characters of the giant caseid Alierasaurus ronchii are described here based
on material recovered from the type locality in the Permian deposits of Cala del Vino
Formation (Sardinia NW) and additional preparation of the previously collected material.
All new described osteological elements are characterized by the same state of
preservation and, given the absence of double elements and the total compatibility in
absolute size, the new material can be attributed without doubt to the holotypic individual
of A. ronchii. Highly diagnostic material includes a caudal neural spine with a broad
bifid distal termination. This represents a synapomorphy characterizing the more
derived caseids, thus fully confirming the attribution of the Sardinian specimen to
Caseidae. Also the other vertebral material and newly collected ribs show a typical
caseid structure, fully consistent with the previously published material. Despite the
highly partial nature of Alierasaurus, the taxon was included in a recent phylogenetic
analysis of caseids to investigate its phylogenetic position within the monophyletic
Caseasauria. Alierasaurus falls as the sister taxon of Cotylorhynchus, and is autapomorphic
in the general construction of MT-IV and proximal phalanx IV-I. The absolute
size of the newly recovered material confirms a gigantic body size for Alierasaurus,
comparable, if not greater, to that of the huge North American species Cotylorhynchus
hancocki (up to 6 m in length). Such gigantic adult body size, closely correlated to its
herbivorous lifestyle, must have been selected during evolution of caseids, leading to
substantial advantages in terms of fitness
