The Cenozoic Era, which is often described as the “Age of Mammals,” began 65 million years ago. Following the disappearance of the dinosaurs, mammals proliferated in number, size, and diversity. The Los Angeles County Natural History Museum has a gallery devoted to The Age of Mammals.
Rhinos, horses and camels all originally evolved in North America and then migrated to other parts of the world. Rhinos became extinct in North America prior to the last Ice Age. Shown below are some of the ancestors of rhinos, horses and camels.
Hyracotherium granger
This is an early ancestor of the horse, formerly called Eohippus (“dawn horse”). These animals were small forest dwellers that ate soft vegetation. These small animals had four-toed front feet, three-toed hind feet, and were designed for running. About 50 million years ago, these small ancestors of the horse became extinct in Europe, but continued to evolve in North America. According to Ian Lange, in his book Ice Age Mammals of North America: A Guide to the Big, the Hairy, and the Bizarre:
“These animals had a curved back and a long, low skull. The cheek teeth had low crowns—what paleontologists call brachyodont teeth. This style of teeth allows animals to crush leaves, which makes them effective browsers.”
With regard to size, these small animals were about 1 foot tall and weighed up to 45 pounds.
Miohippus annectens
This three-toed browsing horse was found through central and western North America from 37 million to 19 million years ago.
Neohipparion leptode
This three-toed grazing horse was about the size of today’s zebra, but with a smaller head. While it had three toes, the side toes did not touch the ground.
Equus simplicidens
This is the ancestor of the modern horse. Sometimes called the American zebra, its skull, skeleton, and teeth are similar to those of Grevy’s zebra of eastern Africa. Hundreds of specimens of this species were found at the Hagerman Fossil Beds National Monument in Idaho and the species is also known as the Hagerman horse.
Equus accidentalis
Throughout California, Arizona, and Nevada, Equus accidentalis, the western horse, was widespread during the last part of the Ice Age. Along with other megafauna in North America, the western horse became extinct about 11,000 years ago. According to the Museum display:
“Its high-crowned teeth were adapted for grazing, but food particles from the teeth of La Brea horses indicate they were also eating leaves and shrubs.”
Poebrotherium wilsoni
This is an early camel that lived in open forests. It first appears in the Oligocene (37-24 million years ago). According to the Museum display:
“Camels differ from other cud-chewing mammals (such as deer and cattle) because they have incisors and canine teeth in their upper jaw. Camels evolved in North America, where they became adapted to a wide variety of habitats. They subsequently migrated to Eurasia, Africa, and South America.”
Stenomylus hitchcocki
This was a gazelle-like camel that was built for speed. According to the Museum display:
“Unlike living camels, the feet of Stenomylus ended in hoofed toes rather than soft pads. Stenomylus had very tall teeth which, like those of pronghorns and gazelles, were used for processing a mixed diet of grass and leaves.”
Oxydactylus campestris
This was a giraffe-like camel which was widely distributed in North America from 26 million to 16 million years ago.
Titanotylopus nebraskensis
This giant camel is found only in western North America from 5 million to 1 million years ago. Camels originated in North America and later migrated to Eurasia (about 8 million years ago) and to South America (about 3 million years ago). With regard to size, it had a shoulder height of about 12 feet and weighed about a ton. In comparison, the modern one-humped camel (Camelus dromedaries) stands only 6-7 feet at the shoulder and weighs 1,320 to 2,200 pounds.
Teleoceras fossiger
This is a hippo-like rhinoceros. According to the Museum display:
“This aquatic rhino has body proportions similar to a hippo, and it probably lived part of the time in water. It was not highly adapted for life in the water as hippos are, because its nose, eyes, and ears were not located as high on its head.”
This was the last rhino to inhabit North America. Ian Lange reports:
“This large rhinoceros evidently thrived during Miocene and early Pliocene time before becoming extinct.”
More Paleontology
Paleontology 101: Ancient Cats (Photo Diary)
Paleontology 101: Dinosaur Hall (Photo Diary)
Paleontology 101: Wolves, Dogs, Cats, and Bears (Photo Diary)
Paleontology 101: The Mesozoic--The Age of Dinosaurs (Photo Diary)