*The order Chelonia includes tortoises, terrapins and turtles. *They are described as ‘reptiles in boxes’ as their body is enclosed in box like dorsal carapace and ventral plastron. *Chelonians are believed to be the direct descendants of primitive cotylosaurs. *They are ectothermic, which implies that their body temperature remains close to the temperature of their environment, and they are rely completely on external sources of heat. *They have relatively low metabolic rates. *All turtles have a bony shell consisting of (i) a carapace formed from costal bones with fused ribs, neural bones with fused thoracic vertebrae, and peripheral bones; (ii) a plastron consisting of interclavicle, clavicle, and three to five additional pairs of dermal bones sutured together. *The carapace and plastron are firmly united along their edges, but have apertures for the head, tail, and fore and hind limbs. *The limbs and tail can almost always be withdrawn at will under the shelter of the thoracico-abdominal case …show more content…
*The limbs and tail can almost always be withdrawn at will under the shelter of the thoracico-abdominal case formed in this way by the carapace and plastron, and the head is also generally