Brontotherium

Order: Perissodactyla

Family: Brontotheriidae

Brontotherium, also known as Brontops, belonged to a group of large plant eating mammals collectively know as the Bronotheres or Titnaotheres. The Brontotherium were abundant herbivores in the early Tertiary period and throughout most of the Oligocene. They fed on the soft vegetation of trees and bushes that made up the forests that covered much of North America and eastern Asia. Standing as much as eight feet at the shoulder, the Brontotherium would have superficially resembled a large rhinoceros in appearance.

Fossils of the Brontotherium were first discovered in 1892 in White River, South Dakota. Henry Fairfield Osborn, curator of vertebrate Paleontology at the American Museum of Natural History, became so fascinated by the unique new discovery that he jealously guarded the museum's specimens and wouldn't allow other paleontologist to study and describe them. Due to a lack of shared knowledge, new Brontothere fossils were sometimes unnecessarily classified as new species or subfamilies. It wasn't until a decade or so after the death of Osborn in 1945 that many of the different classifications were determined to be different sexes of the same species or individuals with subtle differences.

Brontotheres, among the largest mega-fauna of their time, were massive animals weighing several tons. Their most distinguishable feature was a set of forked horns that grew near the end of the snout on both males and females. The Brontotheres also sported massive shoulder and neck muscles attesting to a powerful wrestling and butting ability. Brontothere horns, although lacking in primitive genera, were very prominent in the later species. These structures were an outgrowth of the nasal bone and were probably covered with skin or a horn sheath and are not to be confused with the horns of rhinos which are composed of compacted hair. The forked nose horns were often large and ornate, larger in the males than the females. They were probably used in much the same way as seen in modern rhino species. Males would have used them for courtship and rivalry displays when competing for prospective females or for intraspecies battle for dominance of the herd or family group. The horns would have also been an effective tool for defense. Although nearly invulnerable to predators as an adult, Brontothere mothers would have been able to ferociously wield their nose horns in defense of their calves.

The lifestyle of the Brontotherium can only be surmised. Based on modern large herbivores, the brontotheres probably lived in small or large herds and spent most of their time browsing on the leaves of trees and bushes. Brontothere herds may have been lead by a dominant male and consisted of mostly females and their calves. Young bulls may have left the herd until the time in which they were large enough and experienced enough to start their own herd or compete with bulls of existing herds. In contrast, Brontothere herds may have been matriarchal, led by dominant females similar to modern day elephant herds, and would have only come together with males of their species for breeding purposes. Such theories can only be based on conjecture. Fossil evidence leaves little clues to indicate their lifestyle or behavioral patterns.

The Brontotherium and related species are believed to have gone extinct in the late Oligocene as a result of changing habit. As the forests started to diminish, vast, dry grasslands grew in their place. The Brontotherium were used to a diet of soft forest vegetation and ill suited to digest the tough grasses that were spreading across their habitat. All Brontothere species eventually became extinct, their closest living relatives include horses, rhinoceroses and tapirs.