Are dolphins considered mammals, and what determines if an animal is a mammal or not?
Yes, dolphins are mammals; specifically, they belong to order Cetacea. Neither warm-bloodedness nor air-breathing are characteristics that define mammals, since they’re shared with other animal groups. Basically, a mammal has 4 major traits: 1) Hair 2) Mammary glands that produce milk to feed the young 3) Lower jaw formed by a single bone, the dentary, and 4) Middle ear with three ossicles: hammer, anvil and stirrup Only mammals have these four diagnostic characteristics. Many people confuse them, and mention other traits that are not diagnostic. Examples: — live-bearing: the platypus and the echidnas are mammals and lay eggs — warm-blooded: so are birds, as well as some fish and marine turtles — air-breathing: all terrestrial vertebrates have lungs. Hair is very reduced in dolphins, but they possess hairs when they’re embryos, and they retain hair-associated structures after they’re born, especially as sensitive areas on their head.
