Since its introduction, many people have used this manual as both a reference and tool for working in and teaching mammalogy. However, it has not been available in recent years, having gone out of print. Copies of the second edition are increasingly difficult to locate and those in existence now contain out-of-date information. These facts point to the desirability of a third edition, a possibility suggested on a number of occasions by colleagues and past users of the book. Our intention, with the development of this edition, is to provide a comprehensive treatment of all mammal genera, both native and introduced, occurring in North America north of Mexico, inclusive of marine mammals found in coastal waters.

Primary changes to this edition include a reorganization and update of taxonomy following D. E. Wilson and D. M. Reeder’s “Mammal species of the world: A taxonomic and geographic reference” and additional works following its publication in 1993. Several additional exotic genera known to (or potentially) occur in the wild have also been incorporated. As an aid to the user, exotic genera are identified by asterisks in the text and on figure captions. It should also be noted that several of these genera (i.e. Mus and Rattus) are widespread in distribution and locally abundant whereas others, such as Erinaceus, Meriones, Cricetus, and Mesocricetus, may not actually exist in the wild. Old figures have been replaced with line drawings, each including dorsal, ventral, and lateral views of all genera included in the key. As with previous editions, many sources have been drawn upon for both factual and illustrative purposes. Although far from comprehensive, the Selected References section has also been updated to include material used in updating this key, as well as additional books and sources of interest to both the professional and amateur.

Primary changes to the third edition include:

Order Didelphimorphia - renaming of Order Marsupialia
Order Insectivora - addition of the exotic genus Erinaceus; reduction of Microsorex to a subgenus of Sorex
Order Chiroptera - addition of Molossus; Nyctinomops split from Tadarida; Idionycteris split from Corynorhynus, which has been renamed from Plecotus
Order Carnivora - merging of Orders Carnivora and Pinnipedia into single Order Carnivora; division of felid genera Felis and Lynx into Puma, Panthera, Lynx, Herpailurus, Leopardus, and Felis; addition of the domestic cat in genus Felis; Thalarctos reduced to a subgenus of Ursus; Lutra renamed Lontra
Order Cetacea - Lagenorhynchus renamed as Peponocephala
Order Artiodactyla - addition of Camelus and Lama in Family Camelidae; change of Tayassu to Pecari; Bison synonomized with Bos
Order Rodentia - Eutamias reduced to a subgenus of Tamias; Chaetodipus elevated as separate genus from Perognathus; Family Cricetidae combined into Muridae; addition of exotic genera Meriones, Cricetus, and Mesocricetus; Podomys elevated to a separate genus from Peromyscus
Order Lagomorpha - addition of domestic rabbit, genus Oryctolagus; Brachylagus elevated to a distinct genus from Sylvilagus