Evolution and Domestication of the Horse

Practice flashcards covering the taxonomic classification of horses, their evolutionary ancestors, and environmental changes across geologic epochs.

Perissodactyla

An order of ungulates that walk on the terminal bones of the toes and have enlarged toenails forming hooves; horses, rhinoceroses, and tapirs belong to this order.

Plantigrade

A type of foot posture in mammals, such as humans and bears, where the surface of the whole foot touches the ground.

Digitigrade

A type of foot posture in mammals, such as dogs and cats, where only the phalanges touch the ground.

Unguligrade

A type of foot posture in mammals, such as horses and deer, where the tip of one or two digits touch the ground.

Equidae

The family within the Perissodactyla order that includes horses, zebras, donkeys, and asses.

Equus

The only recognized surviving genus within the Equidae family, with species living from $5\,MYA$ to the present.

ITIS

The Integrated Taxonomic Information System; an easily accessible database reviewed periodically to provide reliable information on species names and hierarchical classification.

Hyracotherium

Also known as Eohippus, this represents the oldest known horse, living from $55\,MYA$ to $45\,MYA$, characterized by 4 toes on the front foot and 3 on the hind foot.

Orohippus

A genus known as the mountain horse that lived during the Eocene epoch ($52\,MYA - 45\,MYA$); it was slightly larger than Eohippus and had unfused radius and ulna bones.

Mesohippus

A horse genus from the Oligocene epoch ($37\,MYA - 32\,MYA$) that stood about two feet at the shoulders and had three toes on both front and hind feet.

Homeothermic

Warm-blooded animals that can control their metabolic temperatures; the rise of these animals was favored during the changing seasons of the Oligocene epoch.

Merychippus

A horse genus living from $17\,MYA$ to $11\,MYA$ that is considered the ancestor of all later grazing horses and possessed high-crowned check teeth.

Pliohippus

A genus living $12\,MYA - 5\,MYA$ that stood about $1.25\,meters$ tall; it is thought to have given rise to the Hippidion genus in South America.

Hippidion

A horse genus that lived in South America from $2\,MYA$ to $10,000\,YA$, speculated to have a flexible snout and reaching about $4.6\,feet$ at the shoulder.

Dinohippus

A genus living from $13\,MYA$ to $5\,MYA$ that is the closest relative to the Equus genus and was the most common horse in North America.

Stenoids

A molecular division of extant Equus that includes zebras and asses.

Caballoids

A molecular division of extant Equus comprising true horses, which diverged from the stenoids approximately $4\,MYA$.

Beringia

A land bridge roughly $1,000\,miles$ wide that connected Asia with North America during the Pleistocene epoch.