Taxonomy of the Modern Horse




Living beings, different from plants in capacity for movement and rapid motor response to stimulation



Bilaterally symmetric animals with notochord, dorsal hollow neutral tube, and gill clefts in the pharynx



Animals with a backbone of vertebrae, definite head, ventrally-located heart, and well-developed sense organs



Warm-blooded animals with hair covering; females with mammary glands that secrete milk for nourishing young



Odd-toed hoofed mammals,

Including living horses, rhinoceroses and tapirs, and including extinct titanotheres and chalicotheres



Horses, Zebras, Wild Ass




All modern equines: rigid spine; long neck, nose and legs; fused leg bones with no rotation; flexible muzzle; deep jawed



True Horse



[specific breed]

[Arabian, TB, QH; not color breeds]




Evolution of the Horse:


1.      Eohippus


a         Eohippus (meaning "dawn horse") was the earliest-known horse - it was the size of a tiny dog. Another name for this genus is Hyracotherium (meaning "mole beast").

b        Anatomy: Eohippus (Hyracotherium) was only 2 feet (60 cm) long and 8 to 9 inches (20 cm) high at the shoulder.

This primitive horse had 4 hoofed toes on the front feet and 3 hoofed toes on each hind foot. It had a long skull with 44 long-crowned teeth.

c         Diet: Eohippus was a grazing herbivore that ate soft leaves and plant shoots.

d        When Eohippus lived: Eohippus lived during the early Eocene Epoch, about 50 million years ago. It lived in the Northern hemisphere (in Asia, Europe, and North America). The first fossils of this tiny horse were found in England by the famous paleontologist Richard Owen in 1841 and named Hyracotherium.


2.      Mesohippus


a         The "middle horse" earned its name.  Mesohippus is intermediate between the eohippus-like horses of the Eocene, (which don't look much like our familiar "horse") and more "modern" horses.


b        Where & When?  Fossils of Mesohippus are found at many Oligocene localities in Colorado and the Great Plains of the US (like Nebraska and the Dakotas) and Canada.  This genus lived about 37-32 million years ago


3.      Pliohippus


a         Grandfather" to the modern horse, Pliohippus appears to be the source of the latest radiation in the horse family.  It is believed to have given rise to Hippidion and Onohippidion, genera that thrived for a time in South American, and to Dinohippus which in turn led to Equus.


b        Where & When?  Fossils of Pliohippus are found at many late Miocene localities in Colorado, the Great Plains of the US (Nebraska and the Dakotas) and Canada.  Species in this genus lived from 12-6 million years ago.