A new specimen provides insights into the anatomy of Irajatherium hernandezi, a poorly known probainognathian cynodont from the Late Triassic of southern Brazil

• Published in: Anatomical record (Hoboken, N.J. : 2007) N.J. : 2007), 2022-11, Vol.305 (11), p.3113-3132
• Main Authors: Kerber, Leonardo, Martinelli, Agustín G., Müller, Rodrigo T., Pretto, Flávio A.
• Format: Article
• Language: English
• Subjects: Anatomy; Candelária Sequence; Caturrita Formation; Cerebral hemispheres; Humerus; Ictidosauria; Maxilla; micro CT‐scan; Norian; Palate; Phylogeny; Probainognathia; Rostrum; Scapula; Triassic; Tritheledontidae; Zygomatic arch
• ISSN: 1932-8486; 1932-8494
• DOI: 10.1002/ar.24830

Irajatherium hernandezi is a poorly known non‐mammaliaform cynodont from the Late Triassic of southern Brazil. A new specimen of this cynodont was found in recent fieldwork to the type‐locality, Sesmaria do Pinhal (Candelária), providing new insights into the anatomy of this mammalian forerunner. This specimen comprises a partial skull preserving the left canine, two left and three right postcanines, and an isolated exoccipital; the left dentary with the canine and postcanines; a fragment of the right dentary; the proximal portion of the left partial humerus; the right scapula; and indeterminate fragments. Based on new material, it is here suggested that I. hernandezi presents: a rostrum broad and short, possibly long as the temporal region; three foramina on the lateral surface of the maxilla, that could correspond to the external openings of the rostral alveolar, infraorbital, and zygomaticofacial canals; a slender zygomatic arch and an absent postorbital bar; a posteriorly wide temporal fossa; a long secondary palate, slightly surpassing the level of the last postcanine tooth; the cerebral hemispheres of the cranial endocast divided by a median sulcus; the scapular blade long and straight, and the postscapular fossa absent in lateral aspect. Finally, I. hernandezi and other tritheledontids were included in a phylogenetic analysis of Eucynodontia. The analysis recovered unresolved relationships for ictidosaurs/tritheledontids, nested within a polytomy with Tritylodontidae and a clade composed by Pseudotherium argentinus, Botucaraitherium belarminoi, Brasilodon quadrangularis, and Mammaliaformes.