Part 24

The earliest proboscideans, the elephants and their relatives, first appeared in the late Eocene of Africa and were about the size of a small modern elephant but had larger heads and shorter trunks. Proboscidean development is marked by an increase in size, change in skull and tooth structure, and elongation of the trunk. Two well-known fossil proboscideans are the mammoth and the mastodon, both of which inhabited Texas during Pleistocene time. The mastodons resembled the elephants, but the structure of their teeth was quite different (fig. 25). Moreover, the mastodon skull was lower than that of the elephant and the tusks were exceptionally large—some reaching a length of 9 feet.

DINOBASTIS × ¹/₂₀ CANIS DIRUS × ¹/₁₅ HYRACOTHERIUM × ¹/₁₀ PLIOHIPPUS × ¹/₂₀

There were several types of mammoths, and the woolly mammoth is probably the best known. This animal lived until the end of the Pleistocene and, like the woolly rhinoceros discussed below, is known from ancient cave paintings and frozen remains. Information gathered from these sources indicates that this great beast had a long coat of black hair with a woolly undercoat (Pl. 49).

During the Pleistocene, mammoths were widespread over the United States, and their remains are abundant in many stream deposits of this age. Proboscidean bones have been reported from Pleistocene rocks in many parts of Texas, where they are commonly found in sand and gravel pits.

Order Perissodactyla.—

The perissodactyls, or odd-toed animals, are mammals in which the central toe on each limb is greatly enlarged. Modern representatives include the horses, rhinoceroses, and tapirs. Extinct members of the Perissodactyla include the titanotheres, chalicotheres, and baluchitheres, all of which grew to tremendous size and took on many unusual body forms.

HORSES.—

One of the first perissodactyls was Hyracotherium (also called Eohippus), which is the earliest known horse (Pl. 47). This small animal, whose remains have been found in Big Bend National Park, was about 1 foot high and his teeth indicate a diet of soft food. Following the first horse, there is a long series of fossil horses which provide much valuable information on the history of this important group of animals.

The record of the development of the horse is well represented in Texas, and the bones and teeth of fossil horses are common in certain parts of the State. Fossils of this type have been reported from the Tertiary of the Trans-Pecos, Gulf Coastal Plain, and High Plains regions of Texas, and the teeth of Pleistocene horses have been found in sand and gravel pits in many parts of the State. Horse teeth (fig. 26) are particularly useful fossils as they may be accurately identified and used to determine the age of the rocks in which they are found.

TITANOTHERES.—

This group of odd-toed mammals appeared first in the Eocene, at which time they were about the size of a sheep. By Middle Oligocene time they had increased to gigantic proportions but still had a small and primitive brain. Brontotherium (Pl. 48) was slightly rhinoceros-like in appearance and is believed to be the largest land animal that ever inhabited the North American continent. This animal was about 8 feet tall at the shoulders; a large bony growth protruded from the skull and this was extended into a flattened horn, which was divided at the top.

UINTATHERIUM × ¹/₄₅ BRONTOTHERIUM × ¹/₃₅

Although the titanotheres underwent rapid development during the early Tertiary, these huge beasts became extinct during the middle of the Oligocene epoch. Titanothere remains have been reported from the Trans-Pecos region of Texas.

CHALICOTHERES.—

The chalicotheres were in some ways like the titanotheres, but they also exhibited many peculiarities of their own. The head and neck of Moropus, a typical chalicothere, were much like that of a horse, but the front legs were longer than the hind legs, and the feet resembled those of a rhinoceros except that they bore long claws instead of hoofs. The chalicotheres lived in North America from Miocene until Pleistocene time but were probably never very numerous, and their remains have not yet been discovered in Texas.

RHINOCEROSES.—

The rhinoceroses are also odd-toed animals, and there are many interesting and well-known fossils in this group. The woolly rhinoceros (Pl. 49) was a Pleistocene two-horned form that ranged from southern France to northeastern Siberia. The woolly rhinoceros is well known from complete carcasses recovered from the frozen tundra of Siberia and from remains that were found preserved in an oil seep in Poland. These unusual specimens plus cave paintings made by early man have given a complete and accurate record of this creature. Although the woolly rhinoceros has not been reported from Texas, other fossil rhinoceroses have been found in the High Plains and Gulf Coastal Plain of Texas. These fossils have been found in rocks ranging from Middle Oligocene to late Pliocene in age.

Baluchitherium, the largest land mammal known to science, was a hornless rhinoceros that lived in late Oligocene and early Miocene time. This immense creature measured approximately 25 feet from head to tail, stood almost 18 feet high at the shoulder, and must have weighed many tons. Remains of these creatures have not been discovered in North America, and they appear to have been restricted to Central Asia.

Order Artiodactyla.—

The artiodactyls are the even-toed hoofed mammals and include such familiar forms as pigs, camels, deer, goats, sheep, and hippopotamuses. This is a large and varied group of animals, but the basic anatomical structure of the limbs and teeth show well the relationship between the different forms. Artiodactyls are abundant fossils in rocks ranging from Eocene to Pleistocene in age and are common in rocks of this age in Texas.

ENTELODONTS.—

These giant pig-like artiodactyls lived during Oligocene and early Miocene time and were distinguished by a long heavy skull that held a relatively small brain. The face was marked by large knobs which were located beneath the eyes and on the underside of the lower jaw, and although these knob-like structures were blunt they had the appearance of short horns. Certain of these giant swine attained a height of 6 feet at the shoulders and had skulls that measured 3 feet in length (Pl. 46). Entelodont remains have been found in the Miocene of the Texas Coastal Plain.

CAMELS.—

The first known camels have been reported from rocks of upper Eocene age, and these small forms underwent considerable specialization of teeth and limbs as they developed in size. Many of the camels that lived during the middle Cenozoic had long legs which were well adapted to running and long necks which would have allowed the animals to browse on the leaves of tall trees.

The earliest known Texas camels were found in rocks of Oligocene age, and camels, like horses, must have been abundant in Texas during the Pleistocene for their fossilized remains are common in many parts of the State.

WOOLLY RHINOCEROS × ¹/₂₀ WOOLLY MAMMOTH × ¹/₄₀

BOOKS ABOUT FOSSILS

The following books are recommended for the reader who wants to know more about fossils and fossil collecting. The publications listed below cover various phases of historical geology and paleontology and range from children’s books to the more technical publications of the professional paleontologist. This list, however, is by no means all-inclusive and many other interesting and useful publications are available.