An odd-toed ungulate (or perissodactyl) is a mammal with hooves that feature an odd number of toes on the rear feet. Odd-toed ungulates comprise the order Perissodactyla (Greek: περισσός, perissós, "uneven", and δάκτυλος, dáktylos, "finger/toe").
The middle toe on each hind hoof is usually larger than its neighbors. Odd-toed ungulates are relatively large grazers and, unlike the ruminant even-toed ungulates (artiodactyls), they have relatively simple stomachs because they are hindgut fermenters, digesting plant cellulose in their intestines rather than in one or more stomach chambers. Odd-toed ungulates include horses, tapirs, and rhinoceroses.
This episode featured Propalaeotherium, one of the relatives of the early horse. It was a small, cat-sized animal that was prey for Gastornis: the Eocene was a time when birds ate horses. Propalaeotherium did not have any specializations of the later odd-toed ungulate species, and still had toes, rather than hooves, and was a browser, not a grazer, unlike the later animals. It died out when the great jungles of the early Eocene began to vanish.
This episode featured Embolotherium, one of the last brontothere species.
The brontotheres appeared in early Eocene and at first were small, but the last species, like Embolotherium, were huge and had delicate bony crests on their snouts. These crests were used to intimidate rivals and frighten away carnivores such as Andrewsarchus. All brontotheres were primarily browsers, and vanished by the time of the Miocene, when the scrublands in which they lived vanished, to be replaced by steppes, deserts, and savannas.
Also known as Paraceratherium and Baluchitherium, this cousin of rhinoceroses could rival some of the dinosaurs in sheer size and power. It fed only on leaves and the adult animals were virtually invulnerable, but the youngsters were more vulnerable to carnivores like Hyaenodon.
This episode also featured Chalicotherium, a strange mammal that was related to horses, but ate like pandas and looked like a gorilla. It walked on the knuckles of its front legs and used its claws to grasp branches and fight-off predators - but it still was prey to Hyaenodon and Entelodon.
This episode featured a cousin of Chalicotherium - Ancylotherium. Although the two animals were related, Ancylotherium walked as most other mammals do: on the soles of its feet, not its knuckles. It was one of the last members of the chalicothere family and died out during the Pliocene - most of its relatives, including the knuckle-walkers, died out back in the Miocene. Zebras were common during the Pliocene and survived into the Pleistocene and Holocene.
This episode featured the woolly rhinoceros, a cousin to the modern species, especially the Sumatran rhinoceros.
Unlike the modern species, the woolly rhinoceros was covered in a dense coat of fur, especially during the winter (it shed during spring and summer, remaining in a lighter underwool), but otherwise it was just as bad-tempered and territorial as the modern species are, relying on its keen senses of smell and hearing to detect females, rivals and enemies.
