nonmammal

Nonmammal is a term used to describe any animal that is not a mammal. It is not a formal taxonomic group, but a broad, informal category used in biology, ecology, and everyday language to distinguish mammals from all other animals.

The nonmammal category encompasses a vast diversity of life, including birds, reptiles, amphibians, and fish, as well as invertebrates such as insects, mollusks, crustaceans, echinoderms, and cnidarians. Because mammals possess distinctive features such as mammary glands, hair, and three middle ear bones, nonmammals do not share those traits. However, nonmammals exhibit wide variation in physiology, reproduction, and ecology. For example, many lay eggs (birds, most reptiles, fish, amphibians), while some nonmammals bear live young (like certain sharks and some lizards) though without mammary glands. Temperature regulation also varies; nonmammals are often ectothermic, but birds are endothermic, and some fish and reptiles have complex thermoregulation. The category is thus descriptive rather than phylogenetically precise.

In practice, "nonmammal" is used in discussions of ecology, paleontology, or education to contrast with mammals. It is often preferred to avoid lengthier phrases such as "non-mammalian species" but can be ambiguous and is less precise than explicit taxonomic grouping.