Recently, environmental concerns have stimulated increased interest and activity in the study of North Dakota mammals. Based on field work carried out mainly from 1912 to 1914, Bailey includes a considerable amount on the natural history of the mammals native to the state but no keys. Keys to North American mammals are available in several works but few are available for specific regions or states. Some of these keys, or parts of them, are difficult to use. I have often had to consult several of them before I could key out a specimen.
Most keys use a combination of skin and skull features for separation of species.
Frequently, a skin or a skull is all that is available. Thus, one is often frustrated in an attempt to identify a specimen. With the publication of this skull key I hope to fill a gap and facilitate the further study of mammals in the state. I have attempted to write as uncomplicated a key as I could so that students, amateur naturalists, and professionals can use it. The illustrations were done by J. Frank Cassel.