[5] Osborn was one of the most well known scientists in the United States during his own lifetime, “second only to Albert Einstein", and was a prominent public advocate for the existence of evolution.

In 1891, Osborn was hired by Columbia University as a professor of zoology; simultaneously, he accepted a position at the American Museum of Natural History, New York, where he served as the curator of a newly formed Department of Vertebrate Paleontology.

As a curator, he assembled a remarkable team of fossil hunters and preparators, including William King Gregory, Roy Chapman Andrews, Barnum Brown, and Charles R. Knight.

[14] (Modern researchers use computed tomography scans and 3D reconstruction software to visualize the interior of dinosaur endocrania without damaging valuable specimens.

)[15] On November 23, 1897, he was elected member of the Boone and Crockett Club, a wildlife conservation organization founded by Theodore Roosevelt and George Bird Grinnell.

[16] Thanks to his considerable family wealth and personal connections, he succeeded Morris K. Jesup as the president of the AMNH's Board of Trustees in 1908, serving until 1933, during which time he accumulated one of the finest fossil collections in the world.

[22] But his decision to invest heavily in exhibition also alienated certain members of the scientific community and angered curators hoping to spend more time on their own research.

[23] Additionally, his efforts to imbue the museum's exhibits and educational programs with his own racist and eugenist beliefs disturbed many of his contemporaries and have marred his legacy.

[24] Osborn was a supporter of the "tritubercular (or tri-tubercular) theory" of the evolution of mammalian teeth, originally proposed by Edward Drinker Cope based on fossil tooth morphology, and a rival to the "concrescence theory" proposed by German dentist and physician Carl Röse based on analysis of the development of modern mammal teeth.

It later turned out to be a junior synonym of Prosthennops a peccary (a group closely related to and resembling pigs), to Osborn's considerable embarassment.

[4] While the monograph has been regarded as being a monumental and significant work, later researchers have criticised Osborn for overestimating the number of proboscidean species.

Osborn largely failed to take into account the effect of tooth wear on the shape of mammoth teeth, which was a partial cause of the confusion.

[29] Osborn was one of the most well known scientists in the United States during his own lifetime, “second only to Albert Einstein",[5] and was the author of a number of books aimed at popular audiences.

Writing before Piltdown was exposed as a hoax, the Eoanthropus or "Dawn Man" Osborn maintained sprang from a common ancestor with the ape during the Oligocene period which he believed developed entirely separately during the Miocene (16 million years ago).

Therefore, Osborn argued that all apes (Simia, following the pre-Darwinian classification of Linnaeus) had evolved entirely parallel to the ancestors of man (homo).

[citation needed] Due to this, he endorsed Madison Grant's The Passing of the Great Race, writing both the second and fourth prefaces of the book, which argued for such views.