Mammals are a warm-blooded vertebrate class, Mammalia, and are found on every continent and in the oceans. Mammals are distinguished by the female mammary glands used to feed their young, having hair or fur, three middle ear bones, and a hinged jaw. Mammals diverged from reptiles and birds in the late Triassic, a fact which is known from studying the bones and skulls of Mammalian ancestors to see that the jaws of prehistoric reptiles became the ear bones of mammals today. One of the most adaptable animal classes on the planet, mammals utilize every possible form of transportation (walk, crawl, burrow, swim, climb, etc.) and may live solitarily or in groups for protection depending on the species.