Basal Reptilians, Marine Diapsids, and Turtles: The Flowering of Reptile Diversity

Abstract

Reptiles form the most diverse clade of living land vertebrates. They include lizards, snakes, crocodiles, birds, and turtles, as well as many fossil groups. In this chapter we revise the otic anatomy of early reptilians, including some aquatic groups and turtles. Basal members possessed a stout stapes that still retained its ancestral bracing function, and they lacked a tympanic membrane. The acquisition of tympanic hearing did not happen until later in the evolution of the clade and occurred independently in both parareptiles and diapsids. Parareptiles also show additional otic modifications that are convergent with much later reptilians, which are potentially related to the evolution of more terrestrial habits. In contrast, in aquatic reptiles, such as ichthyosaurs, thalattosaurs, and sauropterygians, the otic anatomy and hearing capacities are adapted to an aquatic medium, resulting in many convergences in their otic anatomy. In turtles, however, there are differences in the configuration and morphology among Triassic and modern taxa.