Family Equidae

   The Class Ungulata encompasses hoofed mammals and includes the Order of odd-toed Perissodactyla and the Order of the even-toed Artiodactyla.  Equines have a single digit on each foot (their hoof) which makes them a part of the Order Perissodactyla.  Other ungulates such as the Tapir and Rhinoceros are also a part of this order as they also have an odd number of digits on their feet.  Tapirs do have 4 toes on their front feet, however, their hind feet (like all feet on a Rhino) have 3.  The determination of which Order the Ungulate belongs to depends on the number of toes on the hind feet of the animal.

Some examples of ungulates and the difference between the two Orders:

(Perissodactyla and Artiodactyla)

  Equines also have vestigial toes, with the chestnut (thought of as a vestigial digit, however, it is not associated with the metacarpus or metatarsus so this is up for debate) and the ergot.  The chestnut is associated with the area just above the knee on the front legs and below the hock on the back.  The ergot is located just under the fetlock joint.

  The Family Equidae includes many extinct Genera that are all related to the modern day horse.  The only Genus that has made it to the modern day (Extant), is the Genus "Equus".  Extinct Equids were browsing herbivores that ate the leaves off of trees, but as the forests in Africa and Asia dwindled and prairie and savannah grass ecozones expanded, their diets had to change to grazing on grasses.


  The Equus Genus includes the 3 Zebra species, the Kiang, the domesticated Horse, various species of the wild Ass (Donkey), and the Onager.

http://earthsky.org/earth/how-zebras-got-their-stripes

Zebras.  If you want to learn more about them, check out my Zebra post.

 

https://www.gettyimages.com/detail/photo/kiang-mother-and-foal-running-native-to-high-res-stock-photography/537009377

Kiang

https://www.marwell.org.uk/zoo/explore/animals/17/african-wild-ass

Wild Ass

https://www.gettyimages.co.uk/detail/photo/onager-or-asiatic-wild-ass-endangered-high-res-stock-photography/533818930

Onager