Hoofed Mammals

By | September 9, 2016

Hooves are simply enlarged toenails that support an animal’s weight and help it walk on hard ground. All hoofed mammals evolved from ancestors with five toes, but over time some toes withered away, leaving just one, two, or three main hooves per foot. Early hoofed mammals were as small as cats, but later species grew to a huge size on a diet of grass or leaves.

FAMILY FACT FILE

Key features
■ Most were plant eaters
■ Walked and ran on four legs
■ Toes with hooves
■ Large teeth to grind vegetation; some also had tusks
■ Some had horns

When
Hoofed mammals first appeared in the Paleogene Period (about 65 million years ago). Most lived in forests or grasslands.

Megacerops (MEG-a-SEH-rops)

megacerops


When: 38–30 million years ago (Paleogene)

Fossil location: N. America, Asia

Habitat: Plains

Length: 10 ft (3 m)

Diet: Plants

When Native Americans of the Sioux tribe in the United States found the huge fossilized bones of Megacerops in the ground, they thought they were the remains of mythical creatures that galloped across the clouds causing storms, and so named them “thunder horses.” Megacerops was indeed a relative of the horse, but in build and size it was more like a modern rhinoceros and was probably covered in thick hide.
The bones above its shoulders bore long spines to support its huge neck muscles and heavy head.

Feeding habits

megacerops-teeth

Megacerops’s teeth suggest it ate soft plants rather than rough vegetation. It may have had a long tongue and flexible lips to choose plants with care.

Uintatherium (WIN-tah-THEE-ree-um)

uintatherium


When: 45–40 million years ago (Paleogene)

Fossil location: N. America, Asia

Habitat: Plains

Length: 10 ft (3 m)

Diet: Plants

Uintatherium was another rhinoceros-like mammal, with a large, barrel-shaped body. Its skull was large and flat, but its brain was very small. On its head were three pairs of horns covered in skin, with the biggest horns at the back. Male Uintatheriums had larger horns than females, which suggests that they used them for display or for fighting other males. The animal’s great weight and short legs suggest it usually moved slowly, although it may have been capable of short bursts of speed.

Phenacodus (fen-ACK-oh-duss)

phenacodus


When: 55–45 million years ago (Paleogene)

Fossil location: N. America, Europe

Habitat: Grasslands, open woodlands

Length: 3 ft (1 m)

Diet: Grass

Like horses, Phenacodus had a skeleton well suited to running. In fact, experts once thought it was an ancestor of the horse. It had longer, more flexible legs than other primitive hoofed mammals and carried most of its weight on its three middle toes.
Its large, squarish teeth were ideal for grinding up tough vegetation. Phenacodus may have had a striped or spotted coat to blend in with woodland undergrowth and help it hide from predators.

Mesoreodon (ME-zoe-REE-oh-don)

mesoreodon


When: 23 million years ago (Paleogene)

Fossil location: USA

Habitat: Deserts, prairies

Length: 3 ft (1 m)

Diet: Plants

Mesoreodon was a sheep-sized hoofed mammal with big eyes. One fossil was found with its voicebox preserved. Studies of the voicebox reveal that Mesoreodon could make loud, hooting sounds like modern howler monkeys—perhaps to frighten predators and warn members of its herd. It had sharp canine teeth that were probably used to defend against attacks, or for display. The teeth at the back of the mouth had crescent-shaped edges, suitable for chewing low-growing plants.

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