<skos:note xml:lang="en">Large and varied class of vertebrate animals characterized by being warm-blooded, having mammary glands that secrete milk to feed the young, bearing live young (with few exceptins), hair (although it has largely disappeared in some adult animals, such as whales), a lower jaw that is hinged directly to the skull instead of through a separate bone (the quadrate) as in all other vertebrates, three tiny bones that transmit sound waves across the middle ear, a muscular diaphragm separating the heart and the lungs from the abdominal cavity, a left aortic arch, and mature red blood cells lacking a nucleus.</skos:note>