Category Archives: Mammals


This family of mostly carnivorous mammals includes dogs, bears, foxes, raccoons, weasels, and perhaps surprisingly—seals, sea lions, and walruses, which evolved from bearlike ancestors. Caniform means “dog-shaped,” but early caniforms were tree-climbing animals that resembled pine martens. As they colonized the ground they evolved into more dog- and then bearlike forms. FAMILY FACT FILE Key… Read More »

A Sticky End

Thirty-eight thousand years ago, a pack of saber-toothed cats were pursuing a weak mammoth. The mammoth stumbled into what it thought was a shallow pool, and found itself trapped in sticky tar. The cats were soon trapped, too. Hunted and hunters died. They had fallen into a massive tar pit. LA BREA Thousands of fossilized… Read More »

Rabbits and Rodents

Rodents—which include rats, mice, and squirrels—were as plentiful in prehistoric times as they are today. Rabbits, too, hopped and jumped across the landscape in much the same way as their modern descendants. Although most were small herbivores, some species grew to a scarily large size. FAMILY FACT FILE Key features ■ Rodents have four special… Read More »

Hoofed Mammals

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… Read More »


Herds of tiny, deerlike mammals known as Leptomeryx fed in the forests and grasslands of North America for more than 13 million years. Leptomeryx was not much bigger than a hare and probably just as nimble, darting around on its tiny hooves in the undergrowth. This little planteater flourished in huge numbers and was probably… Read More »


Seven million years ago, this odd-looking herbivore was common on the plains of South America. It looked like a mixture of different animals, with a body like a horse’s, a long neck like a camel’s, and perhaps even a short trunk. Macrauchenia belonged to an extinct family of hoofed mammals that existed only in South… Read More »


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… Read More »


Chalicotherium was a bizarre hoofed mammal that looked like a cross between a horse and a gorilla. Its front hooves had evolved into massive, hooklike claws, which it probably used to pull branches down from trees so it could reach the leaves. When not on the move, Chalicotherium sat on its haunches feeding. It may… Read More »


Today there are only five or six species of rhinoceros, all fairly similar. In prehistoric times the rhino family was much more varied, its members ranging from dog-sized animals to giants as tall as trees and heavier than any other land mammals. Some prehistoric rhinos were long-legged hornless animals built like horses for speed; others… Read More »

Elephants and Relatives

The three living species of elephant are the largest land animals today. But elephants weren’t always so huge. The earliest known species was just 2 ft (60 cm) tall—the size of a cat. Over time they grew larger and their trunks and tusks grew longer, giving rise to an extraordinary range of giant mammals. FAMILY… Read More »