 The integumentary structure contains some typical characteristics common to terrestrial vertebrates , such as the presence of highly cornified outer layers , renewed periodically through a moulting process controlled by the pituitary and thyroid glands . Local thickenings ( often called warts ) are common , such as those found on toads . The outside of the skin is shed periodically more or less in one piece , in contrast to mammals and birds where it is shed in flakes . Amphibians often eat the sloughed skin . Caecilians are unique among amphibians in having mineralized dermal scales embedded in the dermis between the furrows in the skin . The similarity of these to the scales of bony fish is largely superficial . Lizards and some frogs have somewhat similar osteoderms forming bony deposits in the dermis , but this is an example of convergent evolution with similar structures having arisen independently in diverse vertebrate lineages . 
