Equus (genus)

The Equus genus includes animals like horses, asses, and zebras. They are special kinds of mammals called perissodactyls, which means they have an odd number of toes on each foot. Today, there are seven living species in this genus. Many more existed long ago and are known only from fossils.

These animals have slender legs, long heads, and necks. Most have manes and tails. They eat plants, mostly grass and other soft vegetation. They have simpler stomachs but can still live on foods that are not very nutritious.

Today, domestic horses and donkeys live all around the world. Wild horses and their relatives mainly live in Africa and Asia. In the wild, these animals live in groups led by a male, or in areas where males protect resources. Females usually take care of the babies, but males sometimes help too. They talk to each other using sounds and body language. Sadly, human activities have made it harder for wild equine populations to survive.

Etymology

The word equus comes from Latin. It means "horse". It is related to the Greek word hippos, which also means "horse".

Taxonomic and evolutionary history

Further information: Evolution of the horse

The genus Equus was first described by Carl Linnaeus. It is the only living group in the family Equidae. The earliest equids were small, about the size of a dog, and lived a very long time ago. They had three toes on their back legs and four on their front legs, with small hooves.

Over millions of years, these animals grew larger and their side toes got smaller. By the time the genus Equus appeared, they had just one main toe on each foot. Equus includes all living equines today. The oldest known species, Equus simplicidens, looked a bit like a zebra but had a head shape similar to a donkey. Fossils have been found in places like Idaho, the USA, and also in Europe and Russia.

Today, Equus includes seven living species. Scientists think the common ancestor of all modern equines lived a very long time ago. Studies of old horse bones suggest this ancestor may have lived a bit later than first thought. The species in Equus split into two main groups: the noncaballoids, which include zebras and asses, and the caballoids, or “true horses,” which include the common horse E. caballus and the wild horse E. ferus przewalskii. Zebras evolved in Africa, while asses and true horses spread into other parts of the world.

Extant species

Prehistoric species

Many extinct species of Equus have been found in fossils. Some of these may actually be the same species, just with different names. DNA studies of old horse remains suggest that many of these “different” species were actually one highly-variable widespread species.

• American species

  • Equus alaskae – Alaskan horse
  • Equus conversidens – Mexican horse
  • Equus fraternus
  • Equus francisi – now placed in a separate genus, Haringtonhippus
  • Equus giganteus – Giant horse
  • Equus lambei – Yukon horse
  • Equus neogeus – often placed in a separate genus, Amerhippus
  • Equus niobrarensis – Niobrara horse
  • Equus occidentalis – Western horse
  • Equus scotti – Scott's horse
  • Equus semiplicatus
  • Equus simplicidens – Hagerman horse

• Eurasian species

  • Equus altidens^{[citation needed]}
  • Equus major
  • Equus suessenbornensis
  • Equus livenzovensis
  • Equus senezensis
  • Equus dalianensis^{[citation needed]}
  • Equus lenensis – Siberian horse
  • Equus latipes^{[citation needed]}
  • Equus hydruntinus – European wild ass
  • Equus namadicus
  • Equus ovodovi
  • Equus yunnanensis
  • Equus stenonis – Stenon zebra
  • Equus sivalensis

• African species

  • Equus algericus^{[citation needed]}
  • Equus capensis – Giant zebra
  • Equus mauritanicus – Saharan zebra

Domestic species

• Equus caballus – Domestic horse
• Equus asinus – Domestic donkey

Hybrids

Main article: Equid hybrid

Equine species can crossbreed with each other. The most common hybrid is the mule, a cross between a male donkey and a female horse. Another hybrid is a hinny, made from a male horse and a female donkey. Other mixes include the zorse, a mix of a zebra and a horse, and a zonkey or zedonk, a mix of a zebra and a donkey. In places where Grévy's zebras live near plains zebras, they can have babies together.

Biology

Further information: Equine anatomy and Horse behavior

Equines include horses, asses, and zebras. They come in many sizes but all have long heads and necks with slender legs that end in a single toe. Grévy's zebra is the largest wild type, standing up to 13.2 hands tall and weighing up to 405 kg. Domesticated horses can be much bigger, with some draft horses reaching 18 hands tall and weighing over 1,000 kg, while miniature horses may be as small as 30 inches tall.

These animals are built for running long distances. Their teeth are designed for grazing, with strong molars for grinding grass. Males often have special canine teeth they can use in fights. Equines have good eyesight and can move their ears to locate sounds. Their coats may change with the seasons, and zebras have distinctive black-and-white stripes.

Human relations

The earliest proof that people began to tame horses comes from places in Ukraine and Kazakhstan around 4000–3500 BCE. By 3000 BCE, horses were fully tamed, and by 2000 BCE, many more horse bones appeared in places across northwestern Europe. This shows that tamed horses were spreading. The best proof of taming comes from graves where horse remains were buried with chariots from the Sintashta and Petrovka cultures around 2100 BCE.

Przewalski's horse is not an ancestor of tamed horses, but the two can have babies together. Donkeys were first tamed by people moving with animals in North Africa more than 5,000 years ago. Scientists think donkeys were tamed twice from one wild ancestor. Trying to tame zebras did not work well.