The '''mammals''' are the [[Class (biology)|class]] of [[vertebrate]] [[animal]]s characterized by the presence of [[memorymammary gland]]s, which in [[female|females]] produce [[milk]] for the nourishment of young; the presence of [[hair]] or [[fur]]; and which have endothermic or "[[warm-blooded]]" bodies. The brain regulates endothermic and circulatory systems, including a four-chambered [[heart]]. Mammals encompass some 5500 [[species]], distributed in about 1200 [[genus|genera]], 152 [[Family (biology)|families]] and up to 46 [[Order (biology)|order]]s, though this varies depending on the [[scientific classification|classification scheme]] adopted.
[[Phylogenetics|Phylogenetically]], '''Mammalia''' is defined as all of the descendants of the last common ancestor of [[monotreme]]s (e.g., [[echidna]]s) and [[therian]] mammals ([[marsupial]]s and [[placental]]s), including [[human]]s.
