A new aetosaur from the Upper Triassic of the Santa Maria Formation, southern Brazil

DA-SILVA, L.R.; DESOJO, J.B.; CABREIRA, S.F; AIRES, A.S.,; MÜLLER, R.T. ; PACHECO, C.P.; DIAS- DA-SILVA, S

ZOOTAXA

MAGNOLIA PRESS

Lugar: Auckland; Año: 2014

1175-5326

Aetosaurs are armored pseudosuchian archosaurs widespread in Upper Triassic Units. In the last years, their known diversity significantly increased in South America, where four species are known: Aetosauroides scagliai, Neoaetosauroides engaeus, Aetobarbakinoides brasiliensis and Chilenosuchus forttae. This contribution presents and describes a new Late Triassic juvenile aetosaur from the Santa Maria Formation of southern Brazil, Polesinesuchus aurelioi gen. et sp. nov. Its juvenile ontogenetic stage is suggested by its small size and neurocentral suture opened in all vertebrae. However, future paleohistological investigation is necessary to fully corroborate this assumption. This new taxon is distinguished from all other aetosaurs by the presence of a unique combination of character states (not controlled by ontogeny) such as: cervical vertebrae with prezygapophyses widely extending laterally through most of the anterior edge of the diapophysis; absence of hyposphene articulation in both cervical and mid-dorsal vertebrae; presence of ventral keel in cervical vertebrae; anterior and mid-dorsal vertebrae without a lateral fossa in their centrum; proximal end of scapula expanded; medial portion of scapular blade anteroposteriorly expanded; a short humerus with a robust shaft; and the iliac blade dorsoventrally very low with a long anterior process slightly exceeding the pubic peduncle. Regarding its phylogenetic relationships, the present analysis placed Polesinesuchus as the sister taxon of Aetobarbakinoides and both as sister taxa of the monophyletic clade composed of Desmatosuchinae and Typothoracisinae. However, the data-matrix used in this study lacks information about appendicular skeleton. So, the results should be considered with caution. Therefore, this analysis had pointed out the necessity of a phylogenetic reassessment of Aetosauria with the inclusion of as many postcranial characters as possible. As Polesinesuchus aurelioi is (when compared to other aetosaurs) quite complete regarding its postcranial anatomy, it adds significant anatomical information regarding this interesting group of pseudosuchians.