About fifteen years after the American Museum of Natural History opened, the trustees realized that the Museum was falling behind other institutions in developing a collection of dinosaurs and other fossil vertebrates. In 1891, they hired Henry Fairfield Osborn as the first curator of the new Department of Vertebrate Paleontology. Within a decade, Osborn assembled a talented staff of curators and collectors, and fossils were soon streaming into the Museum from all over the world.

One of Osborn's favorite groups for study was the brontotheres, and he was the first to carry out comprehensive research on them. Fascinated in particular by the horns on later brontotheres, he used variations in their shape to describe numerous new species. Analyses made in the 1990s tended to group many of Osborn's finely divided species together, thereby reducing their total number.