Living Archosaurs: Turtles, Crocodilians, and BirdsA. Turtles have bodies encased in a bony shell.1. The turtle body plan, largely defined by a bony, boxlike shell, has changed little since the group first appeared during the Triassic period2. The 250 living species of turtles occupy terrestrial, freshwater, and marine habitats.B.Crocodilians are semi-aquatic, predatory archosaurs.C. Birds have key adaptations that reduce body______ and power_____1. Birds (Aves) appeared in the Jurassic period as descendants of carnivorous, bipedal dinosaurs. They are members of the archosaurs. Powered flight gave birds access to new adaptive zones, setting the stage for their astounding evolutionary success2. The skeletons of birds are both lightweight and strong. Most birds have adaptations, such as hollow limb bones with small supporting struts.3. The bones associated with are generally large. The forelimb and forefoot are elongated, forming the structural support for the wing. Not all birds are strong fliers, like ostriches.4. Like the skeleton, soft internal organs are modified in ways that reduce weight. Most birds lack a urinary bladder; uric acid paste is eliminated with digestive wastes.5. All birds also possess which are sturdy, lightweight structuresderived from scales in the skin of their ancestors.6. Other adaptations allow birds to harness the energy needed to power their flight muscles. Their metabolic rates are eight to ten times higher than those of reptiles. They have an efficient respiratory system and four-chambered heart to distribute oxygen.