Evolution Of Horse

Eocene and Oligocene: early equids

Hyracotherium
Orohippus
 Epihippus
 Mesohippus
 Miohippus


Miocene and Pliocene: true equines

 Kalobatippus
 Parahippus
 Merychippus
 Hipparion
 Pliohippus
 Dinohippus
 Plesippus


 Modern horses

 Equus
 Pleistocene extinctions
 Return to the Americas


Toes
The ancestors of the horse came to walk only on the end of the third toe and both side toes. Skeletal remnants show obvious wear on the back of both sides of metacarpal and metatarsal bones, commonly called the “splint bones”. They are the remnants of the second and the fourth toe. Modern horses retain the splint bones; they are often believed to be useless attachments, but they in fact play an important role in supporting the carpal joints (front knees) and even the tarsal joints (hocks).

Teeth
Throughout the phylogenetic development, the teeth of the horse underwent significant changes. The type of the original omnivorous teeth with short, "bumpy" molars, with which the prime members of the evolutionary line distinguished themselves, gradually changed into the teeth common to herbivorous mammals. They became long (as much as 100 mm), roughly cubical molars equipped with flat grinding surfaces. In conjunction with the teeth, during the horse’s evolution, the elongation of the facial part of the skull is apparent, and can also be observed in the backward-set eyeholes. In addition, the relatively short neck of the equine ancestors became longer, with equal elongation of the legs. Finally, the size of the body grew as well.