have a diverse fossil record although there are only 6 modern genera of
horses, tapirs, and rhinos. Perissodactyls
are easily recognized by their odd number of toes, unlike the artiodactyls
which possess an even number of toes.
The primitive arctocyonids evolved into
the condylarth family Phenacodontidae
that included Early Eocene forms like Loxolophus which had a short diastema
behind the first premolar and Karagalax, a tapiroid. In Phenacodus, digits I and V are reduced on both hands and feet.
Tetraclaenodon was closer to horse
ancestry. Homogalax was the ancestor of tapirs,
including basal species of tapir such as Heptodon, Helates (Eocene), and Prototapir (Oligocene) (
Tapirs possess five digits on their front legs (although the thumb is vestigial) and three digits on their hind legs. They are nocturnal animals which inhabit areas near water. Jaguars and humans are their primary predators. They are herbivores.
The skull of a modern tapir is depicted below.