· The internal or external hardened tissue lodges to form the skeleton. · Organism will remain small and slow-moving if there had been no skeletal support and to serve as levers on which muscles act. · Skeleton of invertebrates is most often rated on the surface, forming a lifeless or dead whereas the skeleton of vertebrates develops often underneath the surface forming a living or growing endoskeleton. Types of the Vertebrate Skeleton · There are three types of skeletons developed in vertebrates. 1. Epidermal horny exoskeleton · These are hard and horny or keratinized derivatives of one layer of skin, such as claws of reptiles, feathers of birds, and hairs, horns and hoofs of mammals etc. · All living amphibians lack an exoskeleton. 2. Dermal bony skeleton The dermal bony skeleton is derived from the dermis of the skin. · It includes bony scales and plates or scutes of reptiles, fin-rays of fishes and antlers of mammals. 3. Endosk...