The amphibians were the earliest developed four-legged animals and are
represented by such living forms as the toads, frogs, and salamanders.
Amphibians are cold-blooded animals that primarily breathe by lungs and
spend most of their life on land, but during their early stages of
development they live in the water where they breathe by means of gills.
The amphibians apparently developed from the crossopterygian fishes
during late Devonian time and were relatively abundant in the
Pennsylvanian, Permian, and Triassic.
Amphibian remains in Texas are confined largely to lower Paleozoic and
upper Mesozoic rocks. Numerous interesting and important discoveries of
fossil amphibians have been made in north and west Texas where their
remains (Pl. 40) have been collected in association with early types of
reptiles. The areas where Permian red beds are exposed in Archer and
Baylor counties and where Triassic red beds are exposed from Big Spring
north along the edge of the High Plains have furnished most of these
specimens.