The first major study of brontotheres was undertaken by Henry Fairfield Osborn in the 1920s, and he produced almost a thousand pages of material regarding these animals that is now known to be largely inaccurate. However, the two volumes he published were so immense that no one was willing to tackle the subject again until the late 20th century.
It is now known that much of Osborn’s ideas were incorrect, and that he greatly exaggerated the amount of diversity within the family. The genera Brontotherium, Titanotherium, Brontops, Allops, Menops, Menodus, Symborodon, and Diploclonus are now all believed to belong to a single genus, Megacerops. Osborn’s ideas regarding the evolution of brontotheres is also not correct. He believed their evolutionary path was a direct straight line from one species to the next; thanks to research undertaken by Bryn Mader (1989) and Matthew Mihlbachler (2008) it is now known that the brontothere family tree was not linear at all but had many branches and offshoots.