Marine Reptiles, Birds & Mammals

All vertebrates evolved from bony fishes. They adapted to land, but some species, like whales for instance, reinvaded the ocean. Reptiles are cold-blooded (poikilotherms & ectotherms) like most fish, but they still lay eggs on land. Seabirds are warm-blooded (homeotherms & endotherms) and they have watertight feathers that help keep their body temperature constant. Marine mammals are warm-blooded, they have fur instead of feathers, most of them are viviparous, & as embryos most have a placenta.