REDESCRIPTION OF PLATYCRANIELLUS ELEGANS (THERAPSIDA, CYNODONTIA) FROM THE LOWER TRIASSIC OF SOUTH AFRICA, AND THE CLADISTIC RELATIONSHIPS OF EUTHERIODONTS

ABDALA, F.

PALAEONTOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2007 vol. 50 p. 591 - 618

0031-0239

Platycraniellus elegans is an enigmatic Triassic cynodont from South Africa that has only been briefly described previously. New preparation of the holotype and additional unpublished material allows a detailed redescription and comparison with different cynodonts. Platycraniellus elegans is recognized as a valid species of basal cynodont. The distinct suborbital angulation of the zygomatic process, previously considered as a diagnostic character in chiniquodontid cynodonts, and more recently observed in some galesaurids, is also present in P. elegans. A larger, second specimen was initially referred to P. elegans, but most recently considered to belong to Galesaurus planiceps. Close comparison of this specimen with the holotype of P. elegans and with galesaurid specimens allows a tentative allocation to G. planiceps. A cladistic analysis of 32 taxa (two gorgonopsians, seven therocephalians and 23 cynodonts) and 96 craniodental characters places P. elegans as sister taxon of Eucynodontia. Results from the analysis favour a dichotomy between (1) Cynognathia, including the sectorial-toothed cynodonts Ecteninion, Cynognathus and the gomphodont cynodonts, and (2) Probainognathia, including most sectorial-toothed eucynodonts (e.g. Lumkuia, Probainognathus, Chiniquodon), tritheledontids, tritylodontids and mammaliaforms. The Late Triassic sectorial-toothedEcteninion is the most basal member of Cynognathia, whereas the Middle Triassic Lumkuia is the basal representative of Probainognathia. Tritylodontids (Oligokyphus and Kayentatherium) are placed among Probainognathia, forming a monophyletic group with the tritheledontid Pachygenelus, whereas Brasilitherium is the sister taxon of  Mammaliaformes. The cladistic analysis also indicates paraphyly for Therocephalia, with the whaitsiid Theriognathus identified as sister taxon of Cynodontia.