PERMIAN AND TRIASSIC TETRAPOD FAUNAS AND PALEOENVIRONMENTS OF TANZANIA AND ZAMBIA: IMPLICATIONS FOR THE PERMO-TRIASSIC TRANSITION

The end-Permian extinction had profound and lasting consequences in the marine realm. The causes and effects of the extinction in the terrestrial realm, especially its effects on tetrapod communities, are less certain because most available data come from either the Karoo Basin (South Africa) or the fore-Ural region (Russia). Over the past three years, we conducted fieldwork in the Ruhuhu Basin (Tanzania) and the Luangwa Basin (Zambia) to gain insight into environmental and faunal changes in these regions during the Permo-Triassic transition. The Upper Permian Usili Formation (Tanzania) and Madumabisa Mudstone (Zambia) represent an interplay between humid floodplain and lacustrine environments within basins where sedimentation was mainly controlled by subsidence during early phases of rifting. At the same time, the Karoo Basin was dominated by wide alluvial plains with drainage sourced in the southern Gondwanide mountains flowing into a wide semi-arid foreland sag basin depositing large, low-angled alluvial packages in response to differential subsidence in the basin rather than source area uplift. The Permian tetrapod assemblages of the basins show many similarities, with abundant dicynodont therapsids and rarer carnivorous therapsids, pareiasaurs, and temnospondyls. Some endemic species exist in each, but many low-level taxa are shared between the three areas. The Early and Middle Triassic are represented by the Kingori Sandstone and Lifua Member in Tanzania, and the Escarpment Grit and Ntawere Formation in Zambia. These units document a trend towards increasingly arid Permo-Triassic environments similar to that recorded in the Karoo Basin. Associated tetrapod assemblages, particularly those of the Anisian Lifua Member, Ntawere Fomation, and Cynognathus Assemblage Zone (South Africa), show greater degrees of differentiation. For example, crown-group archosaurs are diverse and abundant in the Lifua Member but are absent from the Cynognathus zone. Taken together with new data suggesting that Antarctica served as a refugium for tetrapods in the immediate aftermath of the extinction, these observations imply that recovery proceeded in a strongly regionalized fashion in southern Gondwana, despite similar environmental changes occurring in each place.