Horses

By | September 9, 2016

The earliest horses were small, leaf-eating mammals that lived in forests. Around 20 million years ago, Earth’s climate changed and grasslands began to replace forests. Horses moved to the open plains and adapted to a diet of grass. They grew larger and their legs became longer, making them swifter on their feet. Hundreds of different prehistoric horse species have been found all over the world. They show that the evolution of the horse was like a tree, with many dead ends.

FAMILY FACT FILE

Key features
■ Long, narrow heads
■ Long necks
■ Slender legs
■ Large teeth
■ Hoofed feet, with odd numbers of toes (some had one toe, others three)

When
Horses first appeared in the Paleogene Period, 54 million years ago.

Hipparion (hip-AH-ree-on)

hipparion


When: 23–2 million years ago (Neogene)

Fossil location: N. America, Europe, Asia, Africa

Habitat: Grasslands, plains

Length: 5 ft (2 m)

Diet: Leaves and grass

With its long muzzle and slender legs, the lightly built Hipparion resembled a modern pony. Unlike horses today, which have only one toe on each foot, it had three. Its full weight was borne on its large middle toe, which ended in a hoof. The other toes did not touch the ground, so the feet sprung off the ground quickly, helping the animal to run faster.

GRASS-EATER

Hipparion lived on grassy plains. Horses never fully evolved the ability to digest grass. As a result, their manure is full of undigested stalks.

Merychippus (MEH-ree-KIP-us)

merychippus


When: 17–10 million years ago (Neogene)

Fossil location: USA, Mexico

Habitat: Plains

Length: 3 ft (1 m)

Diet: Grass

Merychippus was the first horse thought to have fed only on grass, unlike its leaf-eating ancestors. It was also the first to have a head similar to a modern horse’s, with a long muzzle, deep jaws, and eyes set on either side of its head. Its neck was long, so it was able to graze on grass comfortably. Merychippus lived in large herds, traveling long distances to feed. It could run fast on its long legs, even breaking into a gallop when chased by predators.

Pliohippus (PLY-oh-HIP-us)

pliohippus


When: 12–2 million years ago (Neogene)

Fossil location: USA

Habitat: Plains

Length: 3 ft (1 m)

Diet: Plants

Until recently, scientists thought Pliohippus was the ancestor of modern horses, partly because it walked on single-toed feet. However, it had curved teeth (other horses had straight teeth) and strange depressions on its face. With its long, slender limbs, Pliohippus was built for speed.

Equus (ECK-wuss)

equus-1


When: 4 million years ago to now (Neogene)

Fossil location: Worldwide

Habitat: Plains and grasslands

Length: 9 ft (3 m)

Diet: Grass

The name Equus includes all modern horses, from racehorses and domestic donkeys to wild zebras. Outside Africa, wild horses are now rare. Equus horses clearly show the much bigger brains that are typical of later mammals. Medium to large in size, they have long heads and long, maned necks. They can run fast, especially when threatened, and live in herds.

Protorohippus (PRO-tore-oh-HIP-us)

protorohippus


When: 52–45 million years ago (Paleogene)

Fossil location: USA

Habitat: Woodlands

Length: 1 ft (0.3 m)

Diet: Plants

One of the earliest known horses, tiny Protorohippus was a forest-dwelling animal that perhaps lived on its own or in pairs, mostly eating leaves rather than grass. It had very short limbs, with hind legs slightly longer than its fore legs, which suggests that it was a good jumper. Of its three toes, the middle one was enlarged and carried the weight of the animal.

Mesohippus (MEE-zoe-HIP-us)

mesohippus


When: 40–30 million years ago (Paleogene)

Fossil location: USA

Habitat: Woodlands

Length: 2 ft (0.5 m)

Diet: Plants

Mesohippus (“middle horse”) had features of both early and later horses. Like modern horses, it had a long snout with a gap between its front and back teeth. A fast runner, its long, slender legs resembled those of today’s horses, except that Mesohippus’s feet had three toes. It probably fed on bushes and trees, chewing the leaves with teeth smaller than those of grass-eating horses.

LIVING RELATIVE

horses-modern

Palomino horses

Modern horses are large, fast-running mammals with slender legs ending in single-toed, hoofed feet. They have long heads, long tails, and manes of hair on the neck. Today, there are more than 400 breeds of domestic horse but only seven wild species, including zebras and onagers.

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