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

2007; Wiley; Volume: 50; Issue: 3 Linguagem: Inglês

10.1111/j.1475-4983.2007.00646.x

1475-4983

Fernando Abdala,

Ichthyology and Marine Biology

Abstract: 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 New preparation of the holotype and additional unpublished material allows a detailed redescription and comparison with different cynodonts.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‐toothed Ecteninion 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.