The Brontotheres/Titanotheres

One of the animals featured in the recent BBC programme Walking with Prehistoric Beasts is a brontothere. Also known as the titanotheres, they were some of the largest mammals to have ever walked the earth.

The brontotheres are members of the Family Brontotheriidae, meaning the "thunder beasts." They first appeared during the Early Eocene Epoch (55 to 36 million years ago) in North America and eastern Asia (remember that these continents were still joined in the northern regions) as very small animals, similar in size and appearance to the early horses, such as Hyracotherium. They became extinct during the Mid-Oligocene Epoch (36 to 22.5 million years ago).

Although they existed for only about 15 million years, over 40 different genera of brontotheres have been described.

Perhaps the most noticeable feature of the brontotheres, aside from their large size, are their large nasal "horns." These are not true horns, in that they were not covered in a horny sheath composed of keratin as seen in cattle, but were actually covered by a layer of thick skin, like the ossicones seen on the heads of giraffes. Because of the bony nature of these outgrowths, it would have been extremely painful for the animals to fight with them, especially if they were broken or damaged.

In the earlier, smaller genera these outgrowths were about the same size in both males and females, but in later, larger genera the males tend to have larger "horns," indicating that they were probably used for attracting mates.

Brontotheres had large, squarish teeth that were low-crowned with a thick enamel covering. Their teeth were unspecialized, and they probably fed on soft forest vegetation. Brontotheres probably occupied an ecological niche similar to that of our modern rhinoceroses, browsing in the open plains, although there would not have been any grassy savannas at the time. Remember that the grasses did not develop until the Late Paleocene Epoch (65 to 55 million years ago).

Grasses were rare until the Oligocene Epoch, when the cooler and drier global climate allowed them to spread into the open spaces not occupied by temperate forests as the tropical forests retreated to the equatorial regions, forming grasslands. Grasses really did not become common until the Late Miocene Epoch (22.5 to 5 million years ago). Be sure to read my article "Grasses and Grazers" for more information.

Eotitanops is the earliest known brontothere. Eotitanops did not look very much like the later brontotheres; it actually bore a close resemblance to its distant relative Hyracotherium. Both were small browsing animals with four toes on their front feet and three toes on their hind feet. The descendents of Hyracotherium would reduce the number of toes and become fast runners, while the descendents of Eotitanops would keep this ancestral number of toes.

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