Descrição e Taxonomia de um Aetossauro Juvenil da Formação Santa Maria (triassico, Carniano Da Bacia do Paraná)

Abstract

Aetosaurs (Archosauria: Pseudosuchia) are armored tetrapods virtually cosmopolitan and restricted to the Upper Triassic. Their fossils are found in all continents, excepting Antarctica and Australia). In Brazil, their fossil record come from the Santa Maria Formation (Middle/Upper Triassic of Paraná Basin) which outcrops in the state of Rio Grande do Sul. To the present, two species are described in this unit (Hyperdapedon acme zone), Aetosauroides scagliai and recently described Aetobarbakinoides brasiliensis. The aim of this study is the description of the new material, which belongs to a new genus of a probable juvenile individual. The new material consists of a partial parietal and a well preserved basioccipital and disarticulated postcranial elements: partial axial skeleton (cervical, dorsal, sacral and caudal elements); an incomplete shoulder girdle (partial scapulas, coracoids and interclavicle); two partial forelimbs (a single incomplete humerus and both ulnae); a right pelvic girdle (ilium, ischium and pubis); parts of both hindlimbs, comprising femora, tibiae and fibulae, tarsal elements (both astragalus and left calcaneum), and pes (metatarsal III, Pedal phalanx V, unidentifiable phalanges and a two claws), and ten dorsal and ventral appendicular osteoderms. . The presence of an unique combination of characters allowed the recognition of a new species named Polesinesuchus aurelioi. The filogenetic analysis shows that Polesinesuchus is the sister taxon of Aetobarbakinoides and both form a clade that is the sister-group of a large monophyletic clade that comprises the subfamilies Desmatosuchinae and Typothoracisinae. Due to the low representativeness of the previous aetosaurid record in Brazil, the results of this study contribute to a better understanding of the Aetosauria.