The sister group of mammals: small cynodonts from the Late Triassic of Southern Brazil.

JOSE BONAPARTE; AGUSTIN MARTINELLI; CESAR SCHULTZ; ROGERIO RUBERT

REVISTA BRASILEIRA DE PALEONTOLOGIA

SOC BRASILEIRA PALEONTOLOGIA

Lugar: Porto Alegre; Año: 2003 vol. 5 p. 5 - 27

1519-7530

Two new derived cynodonts from the Late Triassic of southern Brazil demonstrate the unexpected variety and distribution of the very small, presumably insectivorous probainognathians, from which morganucodontid mammals eventually originated. Brasilodon quadrangularis n.g.n.sp., is characterized by quadrangular upper and lower postcanines with a symmetrical distribution of cusps and little morphological variation along the tooth row. Brasilitherium riograndensis n.g.n.sp. has quadrangular upper postcanines as in Brasilodon but asymmetrical lower postcanines, some of them similar to those in Megazostrodon. The different proportions of the preorbital and orbitotemporal region and the different structure of the lower postcanines recorded in Brasilodon and Brasilitherium support the distiction of both genera. Several derived characters of the skull in Brasilodon and Brasilitherium and a morganucodontid-like lower dentition in Brasilitherium, suggest closer relationships to the morganucodontid mammals than for either tritheledontids or tritylodontids.