The early history of tetrapods in the Southern Hemisphere: the spatial and temporal distribution of Paleozoic basal tetrapods in western Gondwana.

MARSICANO, CLAUDIA; ABDALA, FERNANDO; SMITH, ROGER; RUBIDGE, B.

Las Vegas

Congreso; 70th Annual Meeting SVP; 2011

The history of early tetrapod diversification in Gondwana has remained elusive, particularly in the southern part of the supercontinent. The earliest record of non-amniotes include Pennsylvanian temnospondyl footprints from northern Chile followed by a gap of more than 40 My that separates it from the diversified Middle Permian faunas known from both southern Africa and South America. The only exception is the Early Permian temnospondyl remains reported from western Namibia (Gai-as Formation). Recent work in the area evidenced they are fairly abundant in nearly the whole succession and just above the Mesosaurus bearing-levels. They represent the only evidence of non-amniotes in western Gondwana during the early-middle Permian and the earliest body-fossil remains of the group. Comparatively, the Gondwanan early amniote record is better represented. The oldest record of amniotes in Gondwana are the mesosaurids, a group of endemic aquatic parareptiles known only from Artinskian (Early Permian) levels of Namibia, South Africa, Uruguay, and Brazil. It was not until the Guadalupian (Middle Permian) that more diverse amniote faunas comprising only synapsids are represented in southern Africa and Brazil. Nevertheless, several tetrapod footprints and trackways from Permian levels of western Argentina have recently been re-evaluated and the host sequences dated. They reveal diverse amniote faunas, including small-to-medium sized animals, all recorded in interdune deposits, which have been dated as Artinskian, the same age as the mesosaurid-bearing strata. This would imply that amniotes were already widespread in south-western Gondwana by the beginning of the Permian, with both fully terrestrial and specialized aquatic forms. This early diversification was probably related to a climatic shift linked to the withdrawal of Gondwanan glaciations, an event recently dated in western Argentina as late Pennsylvanian, significantly earlier than was previously thought.