The Families of Perissodactyls
Three families of perissodactyls have survived into recent time, Rhinocerotidae (rhinos), Tapiridae (tapirs) and Equidae (horses). The modern members of these three perissodactyl families are instantly recognizable. Rhinos have large tremendously powerful looking bodies with a large nasal horn; horses are long-limbed gracile runners, while tapirs have a rather primitive-looking body with a retracted nasal bone and short proboscis (trunk). Although the number of species alive within each of these families is very few, each of these families has a long history with many extinct species. There are also a number of perissodactyl families known only from fossils, including the Chalicotheriidae, Brontotheriidae, Palaeotheriidae, Amynodontidae, and Hyracodontidae. Each of these families includes members that are as easily recognizable as modern perissodactyls. For instance, chalicotheres possessed very specialized limbs with claws rather than hooves. Brontotheres evolved tremendous body sizes, elongate saddle-shaped skulls with elaborate bony horns on their noses. Because perissodactyls stemmed from a common ancestor, the earlier representatives of these families look very similar to each other and many lack highly specialized features (such as horns) that characterize more advanced members of each family. Because paleontologists are interested in tracing the origins of these families and understanding their interrelationships, they must trace their lineages to a time that precedes the evolution of many of these more specialized characters. For this reason, many of the perissodactyl families are defined by less obvious, and seemingly insignificant characters, such as minor variations in the shape of their teeth, that are useful for tracing the group back to the most primitive members.
Click on the skulls or the names in this phylogeny to explore some of the different groups of perissodactyl families.