Jean-Sébastien Steyer

Permian and Triassic Dicynodont (Therapsida: Anomodontia) Faunas of the Luangwa Basin, Zambia: Taxonomic Update and Implications for Dicynodont Biogeography and Biostratigraphy

Dicynodont fossils were first collected in the Luangwa Basin, Zambia, in the 1920s, but limited detailed study and taxonomic uncertainty have obscured their biostratigraphic utility and their implications for topics such as dicynodont biogeography and the effects of the end-Permian extinction. Here we present a comprehensive taxonomic revision of the dicynodonts of the Luangwa Basin, taking into account specimens in all major museum collections and new material collected by our team in 2009. We recognize 14 dicynodont species from the Upper Permian Upper Madumabisa Mudstone: Pristerodon mackayi, Endothiodon sp., Diictodon feliceps, Compsodon helmoedi, Emydops sp., Dicynodontoides cf. D. nowacki, a new tusked cistecephalid, cf. Katumbia parringtoni, Kitchinganomodon crassus, Oudenodon bainii, Odontocyclops whaitsi, Dicynodon huenei, Syops vanhoepeni, and a new lystrosaurid. Previous reports of Lystrosaurus in the basin appear to be in error. In addition, we found no significant partitioning of dicynodont taxa in the northern and southern parts of the basin, despite substantial differences in preservation, indicating the presence of a single faunal assemblage in the Upper Permian. The Madumabisa dicynodont assemblage is best correlated with the Cistecephalus Assemblage Zone of South Africa. The shared presence of Dicynodon huenei and possibly Katumbia in the Luangwa Basin and the Ruhuhu Basin of Tanzania suggests that the Tanzanian Usili Formation also can be correlated with the Cistecephalus zone. Interestingly, the Madumabisa assemblage from Zambia is more similar to the coeval assemblage from South Africa, despite its closer geographic proximity to Tanzania. The Karoo and Ruhuhu basins also include more endemic species in the Permian than the Luangwa Basin. The Middle Triassic Ntawere Formation preserves four dicynodont species (Kannemeyeria lophorhinus, “Kannemeyeria” latirostris, Zambiasaurus submersus, Sangusaurus edentatus), which occur at two stratigraphic levels. The lower Ntawere assemblage resembles that of the Omingonde Formation of Namibia in the presence of Kannemeyeria lophorhinus and potentially Dolichuranus (if “K.” latirostris represents this taxon). The upper Ntawere assemblage shares the genus Sangusaurus with that of the Manda beds of Tanzania and includes the endemic Zambiasaurus. Comparisons of these assemblages to the Omingonde and Manda suggest that both are best correlated with the Cynognathus C subzone. When combined with data on other tetrapod taxa, our revised dicynodont assemblages contribute to an emerging picture of broad faunal similarity in southern and eastern Africa during the Late Permian, and increasing differentiation between the South African and other Karoo basins following the end-Permian extinction.

New dicynodonts (Therapsida, Anomodontia) and updated tetrapod stratigraphy of the Permian Ruhuhu Formation (Songea Group, Ruhuhu Basin) of southern Tanzania

ABSTRACT Permian tetrapod fossils were discovered in the Tanzanian Ruhuhu Formation in 1963, but they have received far less attention than the tetrapods of the overlying Usili (formerly Kawinga) Formation. Here, we describe two dicynodonts collected in the Ruhuhu Formation in 2008. Abajudon kaayai, gen. et sp. nov., is represented by a partial skull and mandible and is characterized by autapomorphic upper teeth that are triangular in cross-section, have procurved tips, and bear a deep groove on the mesial surface. Although it shows similarities to taxa such as Endothiodon and Chelydontops, the exact relationships between A. kaayai and other dicynodonts are uncertain. The second specimen also consists of a partial skull and mandible. We refer it to cf. Endothiodontia based on the medial placement of the long maxillary tooth rows, the presence of depressions on the palatine pad, a long posterior dentary sulcus, and similarities of the mandibular dentition. Tetrapods occur in three fossiliferous horizons in the Ruhuhu Formation. The likely Middle Permian lower horizon includes dinocephalians, temnospondyls, and the dicynodonts described here. The middle horizon includes a new, tusked species of Endothiodon and at least one other dicynodont. The upper horizon appears to sample an assemblage similar to that of the Usili Formation and therefore may be of Late Permian age. The discovery of Middle Permian fossils in Tanzania and Zambia provides the opportunity to test whether southern Gondwana was characterized by a cosmopolitan tetrapod fauna for an extended period of time before the biogeographic restructuring caused by the end-Permian mass extinction.