While they may not attract as much public attention as the Museum’s dinosaurs, fossil mammals have always been a key component of vertebrate paleontology at the AMNH. Henry Fairfield Osborn, who arrived in 1891, was himself a mammal paleontologist and was responsible for hiring several outstanding vertebrate paleontologists with interests in fossil mammals: these included William Diller Matthew, William K. Gregory, Walter Granger, and Jacob Wortman. In 1895, the Museum purchased E. D. Cope's collection of c. 10,000 North American fossil mammals; the Cope collections, containing many important type specimens, became the kernel of the paleontological collection.

The fossil mammal collection grew under the guardianship of Osborn, who became Museum President in 1908. Important expeditions were made to the Fayum Basin, Egypt (1901); the Bridger Basin of Wyoming (1903, 1904), the White River Badlands of South Dakota (1906), and the Miocene Agate Springs site of western Nebraska (1919). The Central Asiatic Expeditions of the 1920s, under the direction of Roy Chapman Andrews, although best known for their dinosaur discoveries, made extensive collections of Cenozoic mammals.

In 1916, the Department of Paleontology began a long association with Childs Frick, the son of steel magnate Henry Clay Frick and a longtime American Museum trustee. Using his personal fortune to employ a small army of collectorsand researchers including Morris Skinner, Theodore Galusha and Beryl Taylor, Frick accumulated a collection of over 200,000 fossil mammals, which formed the basis of a series of monographic studies on mammal evolution. The collection was donated to the Museum after Frick’s death in 1965.

After Osborn's death, in 1933, the fossil mammal collection continued to grow through the activities of a succession of outstanding curators, including George Gaylord Simpson (South America, New Mexico, Wyoming), Malcolm McKenna (Wyoming, Montana, Colorado), and Richard Tedford (Australia, New Mexico). The financial assets of the Childs Frick Corporation, which were donated to the Museum along with Frick’s fossil collections in 1968, assisted in the construction of a new, 10-story collection and office building, which opened in 1973.

In recent years AMNH Provost and Senior Vice President Michael Novacek and Curator Malcolm McKenna reestablished the long standing ties between the Museum and Central Asia, making a remarkable series of discoveries in Mongolia that are providing new insights into the evolution of mammals. Similar close field research and training collaborations in paleomammalogy are underway in China (Jin Meng) and South America (John Flynn).