Mammalogy in the context of "Homeothermy"

A mammal (from Latin mamma 'breast') is a vertebrate animal of the class Mammalia (/məˈmeɪli.ə/). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles and birds, from which their ancestors diverged in the Carboniferous Period over 300 million years ago. Around 6,640 extant species of mammals have been described and divided into 27 orders. The study of mammals is called mammalogy.

The largest orders of mammals, by number of species, are the rodents, bats, and eulipotyphlans (including hedgehogs, moles and shrews). The next three are the primates (including humans, monkeys and lemurs), the even-toed ungulates (including pigs, bovids and whales), and the Carnivora (including cats, dogs, and seals).

Mammal Species of the World: A Taxonomic and Geographic Reference (MSW) is a standard reference work in mammalogy giving descriptions and bibliographic data for the known species of mammals. It is now in its third edition, published in late 2005, which was edited by Don E. Wilson and DeeAnn M. Reeder. An online version is hosted by Bucknell University (see "External links" below).

The Checklist Committee of the American Society of Mammalogists was charged with compiling and updating MSW. In its Annual Report for 2015, the Committee noted that it is under contract with Johns Hopkins Press for the 4th edition of MSW, which will be edited by DeeAnn M. Reeder and Kristofer M. Helgen. The database was made editable for the authors, with the intention of more frequent website updates. The 4th edition was initially expected to be published in 2017, and then deferred until 2019, but it has yet to be published as of 2025. The Checklist Committee has since been repurposed into the Biodiversity Committee, which in 2018 released and now maintains the Mammal Diversity Database.