ON THE PREMAXILLARY DENTITION OF MASSETOGNATHUS PASCUALI (CYNODONTIA, TRAVERSODONTIDAE) FROM THE LATE MIDDLE−EARLY LATE TRIASSIC OF ARGENTINA

MARTINELLI, A.; EZCURRA, M. D.; SOARES, M. B.; FIORELLI, L. E.; GAETANO, L. C.; DESOJO, J. B.

Zapala/Villa el Chocon

Jornada; XVIII Jornadas Argentinas de Paleontología de Vertebrados; 2014

The medium-sized traversodontid cynodont Massetognathus pascuali is one of the most commonly recovered vertebrates of the late Ladinian-earliest Carnian Chañares Formation (Villa Unión-Ischigualasto Basin, Argentina). This genus is also known from the Dinodontosaurus Assemblage Zone of the Santa María Sequence 1 (Paraná Basin, Brazil). Recent fieldwork in the Chañares Formation resulted in the finding of an association of Archosauriformes and several well-preserved specimens of Massetognathus with complete dentition, some of them representing very young individuals. Although this taxon has been subject of several contributions, some details of its dentition are still poorly understood and/or documented. Therefore, we revisit the premaxillary dentition of M. pascuali. This species has four upper and three lower incisors. They are strongly compressed labio-lingually and leaf-shaped, with crenulated mesial and distal margins. Adjacent to the main cusp, there are up to five cuspules mesially and up to six distally. Upper incisors are close, but not in contact with each other, forming a semi-circular cutting edge.There are wear facets on mesial and distal edges in most incisors and on the labial and lingual surfaces of I3. Incisor morphology is rather variable in traversodontids, being that of M. pascuali one of the most bizarre among traversodontids. This tooth morphology is shared with its close relative Santacruzodon hopsoni (early Carnian, Brazil) and Arctotraversodon pelmmyridon (Carnian, Nova Scotia). In Dadadon isaloi (Carnian, Madagascar) the I4 has an accessory distal cusp and lowers incisor have partially crenulated distal margin but its condition is rather different from that of the aforementioned traversodontids.