The Family of Horses
| Taxonomy | |
| Class: | Mammalia, mammals |
| Order: | Perissodactyla, odd-toed ungulates |
| Family: | Equidae, horses |
The family of Equidae comprises 6 species
| Equus ferus | Wild Horse |
| Equus hemionus | Asian Wild Ass |
| Equus africanus | African Wild Ass |
| Equus zebra | Mountain Zebra |
| Equus grevyi | Grevy’s Zebras |
| Equus burchelli | Plain Zebras |
They all share common features:
Equids have a strong and muscular body structure. During evolution they have developed a skeleton which enables an extended stride length and thus efficient running. The clavicula (collar bone) is absent. Radius and ulna of the foreleg, and tibia and fibula of the hind leg are fused. Ulna and fibula are reduced. Therefore radius and tibia support the weight. The third metapodal is elongated. The metatarsus is longer than the metacarpus. All digits are reduced with exception of the third, which is encased in a hoof. Since equids walk on the tips of their toes, they are named unguligrade. Asian Wild Asses are the most efficient runners, achieving top speeds of about 80 km / h and thus outrun the fastest racing horses (record 69 km / h). In addition they are able of keeping up pace of approximately 40 km / h over one hour, even at high temperatures.
Equids have high crowned cheek teeth (premolars and molars) with complex enamel grinding surfaces. They therefore show a certain resistance to wear when grinding tough silicified grass tissues
| Dental formula : | ICPM | mare: | 30(3-4)3 | stallion: | 31(3-4)3 |
| ICPM | 30(3-4)3 | 31(3-4)3 |
Canines appear between four and five years of age in stallions. They do not occur in mares. The gap between incisors and premolars is named diastema.
Their eyes are large and situated at the sides of the skull. Each eye covers a visual angle of nearly 180 degrees. This offers an unlimited view which is most important to flight animals. Predators can be recognized early without requiring head turning. The only blind spot is directly in front and behind the individual. In addition the visual system of equids makes it impossible to see the ground and objects right in front at the same time. Therefore roaming horses move their heads up and down in order to check the environment.
The eyes of equids show a phototopic system, e. i. they are capable of colour vision. Cones located on the retina absorb light of short wavelength (hues of blue) and of middle to long wavelength (shades of green and yellow-green). Like most vertebrates horses experience their environment by dichromatic colour vision. Humans and some primates have trichromatic colour vision, including hues of red.
Digestion of cellulose is carried out in the well developed caecum.
Similar to humans perspiratory glands are distributed over the skin as adaptation to arid latitudes.
Equids inhabit arid landscapes and those dominated by grass vegetation. They can be found on every continent with exception of Antarctica.
Social Systems
| A | Harem: One stallion defends approximately three to five mares and their progeny (Wild Horses Equus ferus przewalskii, Plain and Mountain Zebras E. burchellii and E. zebra). |
| B | Territory: Stallions defend territories which are visited by mares (African Wild Asses E. africanus, Asian Wild Asses E. hemionus and Grévy Zebra E. grevyi). |
Gravidity between 11 and 12 months. A few days after birth mares are ready to mate again.
Progeny leaves the group at the age of one or three years and joins bachelor groups.
Maximum age in captivity is about 36 years. In general, Przewalski’s horses do not exceed 20 years of age.
