New material of Irajatherium hernandezi Martinelli, Bonaparte, Schultz & Rubert 2005 (Eucynodontia, Tritheledontidae) from the Upper Triassic (Caturrita Formation, Paraná Basin) of Brazil

TEO OLIVEIRA; AGUSTIN MARTINELLI; MARINA BENTO SOARES

PALAEONTOLOGISCHE ZEITSCHRIFT

SPRINGER HEIDELBERG

Lugar: HEIDELBERG; Año: 2011 vol. 85 p. 67 - 82

0031-0220

In this contribution, new specimens of the tritheledontid eucynodont Irajatherium hernandezi, from the Late Triassic (Caturrita Formation) of southern Brazil, are analyzed. The new material provides significant information on incisor count, canine size and shape, basicranial morphology, and other aspects of skull and dentition. A cladistic analysis with the inclusion of the new data supports the assignment of Irajatherium to Tritheledontidae, basal to Chalimininae and Pachygenelinae. Previously unknown characters of Irajatherium revealed by the new material include the presence of three lower incisors, the first incisor is enlarged; the presence of large upper and lower canines with deep paracanine fossa on the maxilla; almost complete upper and lower postcanine tooth row with a similar pattern of other tritheledontids (e.g. Pachygenelus and Chaliminia); a conspicuous crest in the inner surface of the maxilla for the attachment of the inferred maxillary nasal turbinates; partially confluent jugular foramen and fenestra rotunda within the jugular fossa, separated by a finger-like projection of the posterolateral wall of the opisthotic; and hypoglossal foramina located outside the jugular fossa. Irajatherium is a key taxon to understand the early evolution of ictidosaurs, a group of cynodonts close related to mammaliaforms during the cynodont-mammal transition from the Late Triassic to Early Jurassic.