New information on the lower jaw of Aetosauroides scagliai Casamiquela, 1960 (Aetosauria: Pseudosuchia).

PAES NETO, V.; BRUST,A.; SOARES, M. B.; CESAR LEANDRO SCHULTZ; J.B. DESOJO

CABA

Jornada; XXX Jornadas Argentinas de Paleontología de Vertebrados; 2018

Aetosauria is a monophyletic group of heavily armored Late Triassic pseudosuchian archosaurs with a cosmopolitan distribution during the Carnian-Norian. The oldest members of this group are found in the Ischigualasto (Argentina) and the Santa Maria (Brazil) Formations, where Aetosauroides scagliai is recorded. In Brazil, two more derived taxa, close related to Desmatosuchus lineage, also occur, Aetobarbakinoides brasiliensis and Polesinesuchus aurelioi, each of them represented only by a single individual. We report a new specimen UFRGS-PV-1246-T from the Piveta Site, on the São João do Polesine city, RS, Brazil. It consists of several small disarticulated postcranial elements including: the left femur (total length of 30 mm), five amphicoelous spool-shaped centra (one cervical and four dorsal), eight dorsal paramedian osteoderms (TDPO), three caudal paramedian osteoderms, one lateral osteoderm and many fragments. TDPO present the characteristic pattern of all basal aetosaurs, but tinier in size, with the length of less than 4 mm and 12 mm of width. No prominent lateral fossa was observed on the centra, a shared condition with Polesinesuchus and Aetobarbakinoides but distinct to Aetosauroides. It is observed the presence of a ventral keel on the cervical vertebra, like in Polesinesuchus and Aetosauroides. All centra were found isolated or with a non-fused neurocentral suture which is suggested of an early ontogenetic stage. Further description and a phylogenetic analysis will test the relationships of UFRGS-PV-1246-T with Polesinesuchus. This specimen may represent the smallest individual ever found and, its study will contributes to improve the knowledge on aetosaurian ontogeny and evolution.