Bobb Schaeffer, a specialist in fossil fishes, came to the American Museum of Natural History in 1936 as a student of the curator William King Gregory. At the Museum during the 1930s and 1940s, Schaeffer, who maintained Gregory's high standard of anatomical analysis, helped develop the "new systematics," an integration of population genetics and paleontology.

Bobb Schaeffer's most permanent contribution will be his careful descriptions and objective analyses of fish fossils, studies that will form the basis of future work. He also tried to relate embryonic development to evolution in vertebrates, and was the first to propose that jawed vertebrates evolved as a result of altered developmental patterns in the head region of their common ancestor.