Fossils occur mainly in the river channel and floodplain deposits of the Beaumont Formation and in the terrace deposits cut into the Beaumont Formation. Rancholabrean fossils from South Texas were first described by E. D. Cope over 100 years ago. The majority of fossil mammals from South Texas are grazers, such as horses and mammoths. Grazers live in savannas and grasslands and feed mainly on grasses. They often have high-crowned cheek teeth, in which the enamel extends below the gum line and the roots are frequently open.
Browsers are less common.
Browsers are typically forest-dwelling animals that feed mainly on stems, twigs, and leaves. Browsers can be recognized by their low-crowned cheek teeth in which the enamel extends to the gum line and the roots are closed. During the Pleistocene, South Texas was a mosaic of grassland and woodland environments which supported a much greater diversity of mammals than at present. There were probably extensive woodlands along the rivers. Time travelers to the Pleistocene of this region might at first glance think they were on the Serengeti Plain of Africa.