Mammal Classification
To classify all Earth's known plants and animals, scientists have traditionally used a hierarchical system of classification that was based on overall similarity among organisms. The system, which was introduced by the 18th century Swedish botanist Carolus Linnaeus, separates animals from plants and places each at the head of its own kingdom. The two kingdoms are broken down into successively smaller, less inclusive groups, including phylums, subphylums, classes, orders, families, genera, and species. The class Mammalia, for example, is one of nine classes in the kingdom Animalia, phylum Chordata, subphylum Vertebrata.
From the start, Linnaeus employed Latin for his binomial nomenclature, both because Latin was commonly used by scientists at the time and because it would avoid the confusion different languages would bring. Each species is identified by a genus name and a specific epithet. For example, the domestic cat is called Felis domesticus.
Taxonomists—today more commonly referred to as systematists —are attempting more and more to classify mammals in a way that reflects their evolutionary history. And as information is acquired from newly discovered fossils or molecular genetics, they rearrange the current classification scheme, adding new species and moving species from one genus to another.
More than 500 new species of mammals have been identified in the last 20 years; 10 to 12 are named each year. By the classification system used in this guide, there are currently 4,629 known species grouped in 1,135 genera, in turn grouped in 136 families in 26 orders. These orders are then organized according to whether they belong to subclass Prototheria, which includes all monotremes , or subclass Theria. Theria includes two subgroups, known as infraclasses: Metatheria for marsupials and Eutheria for placental mammals. On the following pages, all current extant families are listed according to their order.
Next >>Monotremes
