Everything about Equidae totally explained
Equidae is the family of horse-like animals, which belong to the order
Perissodactyla. It is sometimes known as the
horse family. Apart from the
horse, other extant equids include assorted subspecies of
donkey or ass, and the
zebras. All of these are in the
genus Equus.
Characteristics
Equids are medium to large
mammals, with long heads, and necks with a
mane. Their legs are slender and end in a single,
unguligrade toe, protected by a horny
hoof. They have long, slender, tails, either ending in a tuft, or entirely covered in flowing hair. They are adapted to generally open terrain, from
plains and
savannas, to mountains or
deserts.
The
pinnae ("ears") of equids are mobile, enabling them to easily localise the origin of sounds. They have two-color, or
dichromatic vision. Their eyes are set back far on the head, giving them a wide angle of view, without entirely losing
binocular vision. Equids also have a
vomeronasal organ, that allows males to use the
flehmen, or 'lip-curling' response to assess the sexual state of potential mates.
Equids are
herbivores, and feed predominantly on tough, fibrous food, such as
grasses and sedges. When in need, that'll also eat other vegetable matter, such as leaves, fruits, or bark, but are normally
grazers, not browsers. Unlike
ruminants, with their complex stomachs, equids break down
cellulose in the "hindgut" or
cecum, a part of the
colon. Their dentition is almost complete, with cutting
incisors to crop food, and grinding
molars set well back behind a
diastema. The dental formula for equids is:
Equids are social animals, living in herds or bands. Horses, along with Plains and Mountain Zebras, have permanent herds generally consisting of a single male and a band of females, with the remaining males forming small "bachelor" herds. The remaining species have temporary herds, lasting only a few months, which may be either single-sexed or mixed. In either case, there are clear hierarchies established amongst the individuals, usually with a dominant female controlling access to food and water resources and the lead male controlling mating opportunities.
Females, usually called
mares in horses and zebras, or, in the case of asses and donkeys, jennys, usually bear a single
foal, after a gestation period of approximately 11 months. Young equids are able to walk within an hour of birth, and are
weaned after four to thirteen months (animals living in the wild naturally wean foals at a later date than those under
domestication). Depending on species, living conditions and other factors, females in the wild may give birth every year or every other year.
Equids who are not in foal generally have a seasonal
estrous cycle, from early spring into autumn. Most females enter an
anestrus period during the winter and thus don't cycle in this period. The reproductive cycle is controlled by the photoperiod (length of the day), with estrus triggered when the days begin to lengthen. Anestrus prevents the female from conceiving in the winter months, as that would result in her foaling during the harshest part of the year, a time when it would be more difficult for the foal to survive. However, equids who live near the
equator, where there's less change in length of day from season to season, have no anestrus period, at least in theory. Further, for reasons that are not clear, about twenty percent of domestic mares in the Northern Hemisphere will cycle the year round.
Evolution
The oldest known equid
fossils date from the early
Eocene, 54 million years ago. This species,
Hyracotherium (formerly known as
Eohippus), was a fox-sized animal with three toes on its hind feet, and four on the front feet. It was herbivorous browser on relatively soft plants, and already adapted for running. The complexity of its brain suggests that it was already an alert and intelligent animal. Later species reduced the number of toes, and developed teeth more suited for grinding up grasses and other tough plant food.
The group became relatively large during the
Miocene, with many new species appearing. By this time, equids were more truly horse-like, having developed the typical body shape of the modern animals. Many of these species bore the main weight of their bodies on their central, third, toe, with the others becoming reduced, and barely touching the ground, if at all. The surviving modern genus,
Equus, had evolved by the early
Pleistocene, and spread rapidly though the world.
Classification
Order Perissodactyla (In addition to Equidae, Perissodactyla includes four species of tapir in a single genus, as well as five living species (belonging to four genera) of rhinoceros.) † indicates extinct species.
Any equid with partial zebra ancestry is also called a zebroid.
Further Information
Get more info on 'Equidae'.
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