The presence of the Triassic dicynodont Kannemeyeria (Therapsida, Dicynodontia) in western Gondwana

DOMNANOVICH, NADIA; MARSICANO, CLAUDIA

Neuquen

Conferencia; III Congreso Latinoamericano de Paleontología de Vertebrados; 2008

The Triassic genus Kannemeyeria corresponds to large size dicynodonts restricted to western Gondwana (South Africa, Zambia, Namibia, and Argentina). The genus was erected by Seeley in 1908 and since then many specimens have been described and several species recognized. This genus has an important biostratigraphic significance in Gondwana as it constitutes an index fossil of the Cynognathus Assemblage Zone of South Africa. At present the general consensus is that only four species are recognized: K. simocephalus, K. wilsoni, K. cristarhynchus, and K. argentinensis (King 1988). However, Lucas and Wild (1995) have postulated that Kannemeyeria argentinensis (Bonaparte, 1966) was not valid and synonymized it to K. cristarhynchus (Keyser and Cruickshank, 1979) from Zambia. More recently, Renaut and Hancox (2001) in a re-evaluation of the Argentinean material have proposed that it inclusion in Kannemeyeria can not be supported because the putative diagnostic characters present in the holotype are the result of the lateral compression of the skull. Furthermore, they emphasized that several characters present in “K. argentinensis” specimens are identical to the Argentinean shansiodontiid Vinceria, thus suggesting that this two taxa may be cogeneric. Therefore, Kannemeyeria might be not represented in South America and thus, restricted to the African continent. “K. argentinensis” was described by Bonaparte (1966) based only on a skull and some postcranial elements from the Early-Middle Triassic Puesto Viejo Group of central-western Argentina (southern Mendoza). Subsequently, this author mentioned the presence of two additional specimens from the same levels, but they were never figured and/or described (Bonaparte, 1971). A currently undegoing revision of the Argentinian dicynodonts allowed to corroborate that the characters present in “K. argentinensis” are not related to the distortion of the holotype material, and that the specimens assigned might represent a valid taxon closely related to Kannemeyeria. Nevertheless, several characters, as those of the palate, in the holotype and part of the referred material (PVL 3471) relate them to the shansiodontiids, a basal Triassic group of dicynodonts, and to some Permian taxa. The remaining inedit material, MACN 18.871, once referred to “K. argentinensis” is now considerate a representative of the shansiodontiid taxon Vinceria. According to the present discussion, the conventionally recognized close relationship, based on the common presence of Kannemeyeria, between the Early-Middle Triassic tetrapod faunas in South America and southern Africa is not longer sustain.