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PERISSODACTYLS

     Perissodactyls 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) (Maas, 2001).  North American tapirs and reached sizes slightly larger than their modern South American descendants (Kurten, 1988).

The skull of a modern tapir is depicted below.

tapir skull TAPIR
     Hyracodon of the Eocene was ancestral to the various groups of rhinos.  They were common and diverse in the Northern Hemisphere during the Oligocene and Miocene but became extinct in North America after the Pliocene.  Teloceras (below) is an American hornless rhinocerous.  Paraceratherium (also known as Balucitherium and Indricotherium) was the largest terrestrial mammal that ever lived, standing 18 feet at the shoulder and weighing 44,000 pounds. Fossils of wooly rhinos indicate that the flattened horns were often worn in a manner which suggests that they could be used to clear snow (Kurten, 1988).
teloceras wooly rhino
elasmotherium indricotherium

brontotherium

brontotherium
rhino
moropus

    The brontotheres were an extinct group of rhinos that had reached dog-sized species by the Oligocene and rhino-sized species by the Miocene. 

Moropus was horse sized.

chalicothere
     The Chalcotheroids had very large claws which they protected by walking on their knuckles. 
chalicothere