Giant stem tetrapod was apex predator in Gondwanan late Palaeozoic ice age

Abstract

Current hypotheses of early tetrapod evolution posit close ecological andbiogeographic ties to the extensive coal-producing wetlands of the Carboniferouspalaeoequator with rapid replacement of archaic tetrapod groups by relatives ofmodern amniotes and lissamphibians in the late Carboniferous (about 307 millionyears ago). These hypotheses draw on a tetrapod fossil record that is almost entirelyrestricted to palaeoequatorial Pangea (Laurussia)1,2. Here we describe a new giantstem tetrapod, Gaiasia jennyae, from high-palaeolatitude (about 55° S) earlyPermian-aged (about 280 million years ago) deposits in Namibia that challenges thisscenario. Gaiasia is represented by several large, semi-articulated skeletonscharacterized by a weakly ossified skull with a loosely articulated palate dominated bya broad diamond-shaped parasphenoid, a posteriorly projecting occiput, andenlarged, interlocking dentary and coronoid fangs. Phylogenetic analysis resolvesGaiasia within the tetrapod stem group as the sister taxon of the CarboniferousColosteidae from Euramerica. Gaiasia is larger than all previously described digitedstem tetrapods and provides evidence that continental tetrapods were wellestablished in the cold-temperate latitudes of Gondwana during the final phases ofthe Carboniferous–Permian deglaciation. This points to a more global distribution ofcontinental tetrapods during the Carboniferous–Permian transition and indicatesthat previous hypotheses of global tetrapod faunal turnover and dispersal at thistime2,3 must be reconsidered.