Chapter 3 - Evolution of Ancient and Modern Amphibians and Reptiles

Abstract

This chapter introduces some extinct amphibian and reptilian taxa and discusses the history of the clades that compose the modern herpetofauna. The origin of terrestriality was quickly followed by an eruption of new species with new lifestyles and body forms. Although amphibian (anamniote) diversification began earlier, amniotes were the dominant group by the mid-Permian in terms of number of species and individuals, based on the fossil record. Tetrapods largely disappeared from the fossil record at the end of the Devonian. They next appeared en masse in the Upper Mississippian and Lower Pennsylvanian when fossils representing lowland lake and swamp assemblages reappeared. More than a dozen clades are recognized, and they include several groups of anthracosaurs, at least three amphibian groups, and the enigmatic Crassigyrinus. Unlike subsequent tetrapods, all known early tetrapods had more than five digits; Acanthostega had eight digits on its forefeet. In the Pennsylvanian, many new tetrapod groups appeared: geophyrostegid and limnoscelid anthracosaurs, eryopoid amphibians, and nectrideans and three groups of microsaurs. This fauna lived predominantly in the lowlands.