Embolotherium


Embolotherium is an extinct genus of brontothere that lived in Mongolia during the late Eocene epoch. It is most easily recognized by a large bony protuberance emanating from the anterior of the skull. This resembles a battering ram, hence the name Embolotherium. The animal is known from about 12 skulls, several jaws, and a variety of other skeletal elements from the Ulan Gochu formation of Inner Mongolia as well as the Ergilin Dzo Formation of Outer Mongolia.

Taxonomy

Several species of Embolotherium have been named, including Embolotherium andrewsi, Embolotherium grangeri, Embolotherium louksi, Embolotherium ultimum, Embolotherium ergilensi, and Embolotherium efremovi. However, only two species, Embolotherium andrewsi and Embolotherium grangeri, appear to be valid. Other supposed species of Embolotherium are probably synonymous with these two species and were originally based on juvenile skulls, poorly preserved fossil material, or specimens that are not significantly different from either E. andrewsi or E. grangeri.
Another genus of brontothere, Titanodectes, which was named for several lower jaws found in the same sedimentary deposits as Embolotherium, probably represents the same beast as Embolotherium grangeri. Protembolotherium is another closely related genus from the Middle Eocene, which is distinguished by a noticeably smaller ram.

Description

The skull reaches a condylobasal length of 920 mm. Complete skeletons of Embolotherium have not yet been recovered, although many postcranial elements referable to it have been collected. The postcranial skeleton of Embolotherium suggests a powerful, graviportal animal with a close resemblance to the late Eocene North American brontothere Megacerops, which it rivaled or somewhat exceeded in size, making Embolotherium one of the largest brontotheres, if not the largest. Unlike many of the other Late Eocene brontotheres, there is no clear evidence that Embolotherium was sexually dimorphic. All known specimens have large rams. Therefore, coupled with the fact that the rams were hollow and fragile in comparison to the solid and sturdy horns of the North American brontotheres, such as Megacerops, it does not seem likely that the ram served as a weapon for contests between males. Rather, it might have had a non-sexual function, such as signaling to each other. The ram may have served as a specialized resonator for sound production. This hypothesis is suggested by the fact that the bony nasal cavity extends to the peak of the ram, thus implying that the nasal chamber was greatly elevated, possibly creating a resonating chamber.