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Reptilia • Reptiles are the evolutionary base for the rest of the tetrapods. • Early divergence of mammals from reptilian ancestor. • Early reptiles arose from amphibian ancestor and were small, lizard-like insectivores. Characteristics • Scales • Amniotic egg • Ectothermic – Must live in favorable conditions or hibernate. – Being ectothermic enables an organism to survive on much less food than an endothermic organism. • Three chambered heart – Alligators have 4 • Claws Characteristics • Positioning of legs more directly under animal (more support). • Paired limbs with five toes. –Adapted for running, climbing, swimming. –Absent in snakes. Characteristics • Body covered with horny epidermal scales made from protein keratin. – Scales serve to reduce water loss and provide protection. – Reptiles molt as they grow. • Brain = first cerebral cortex (capable of reasoning, planning, perception) Respiration • All reptiles breathe using lungs. • Aquatic turtles have developed more permeable skin. • Some species have modified their cloaca to increase the area for gas exchange. Circulation • Most reptiles have a 3-chambered heart with a partially divided ventricle. – No mixing of blood from lungs with deoxygenated blood. – Crocodiles have 4 chambers and a unique feature: cog teeth. Cog Teeth Digestion/Excretion • Excretory waste = uric acid • Lack structures in nephrons to reabsorb water, so water absorption happens in the colon. Reproduction • Internal fertilization: gametes not subject to desiccation (drying out). • Amniote egg = significant evolutionary breakthrough. – Egg covered by tough, water-resistant, leathery or calcerous shell. – Extra embryonic membranes compartmentalize the interior for several functions – keep fetal homeostasis http://www.youtube.com/watch?v=t1kFiehGh9s Amniotic Egg • Chorion = hard covering permeable to respiratory gases but not water. • Allantois = functions in gas exchange and a storage reservoir for metabolic waste. • Amnion = fluid-filled sac acts as cushion for embryo and prevents desiccation. • Yolk sac = food for embryo; eliminates need for larval stage. Orders • Crocodilia = crocodiles, alligators • Testudines = turtles and tortoises • Sphenodonta = tuatara • Squamata = lizards, snakes (largest group) Order Crocodilia • • • • • 23 species of crocodiles, alligators, & caimans Largest of the living reptiles Amphibious carnivores Live in tropics/subtropics Lizard-like body with short legs, clawed/webbed toes, massive tail • Flat head with nostrils at tip • Powerful jaws • Dorsal side armored with dermal plates Order Testudines • • • • • • • 260 species of turtles/tortoises Oldest group of reptiles (225 mya) Only reptile with shell Only reptile WITHOUT TEETH All lay eggs on land. Third eyelid = nictitating membrane. Longest living vertebrates (100+years in wild)! Order Testudines • Protective body shell – Encases vital organs – Provides some protection to head/limbs – Composed of bony plates covered by horny epidermal scales – 2 parts: upper carapace, lower plastron – Loss of body-wall muscles – Ribs/trunk vertebrae fused to carapace Order Squamata • 4675+ species of lizard • 2700+ species of snakes • 140 species of amphisbaenians – Limbless, burrowing animals – Vestigial eyes under skin • Most successful, diversified of living reptiles. • Occur in most habitats of world amphisbaenians Snakes • Elongated derivative of lizard (increased vertebrae, not lengthening of segments) • Lack limbs, eyelids, ear openings • Jaw bones are loosely united to allow swallowing of large prey • Throat and windpipe are at separate ends of mouth to allow breathing while eating • Can be venomous (hemotoxin/neurotoxin) • Tongue to smell, some have heat pits to sense body heat Snakes • No legs • No external ears • Jacobson’s organ – Sense smell with aid of tongue • Cornea of eye protected with a spectacle – transparent membrane • Skull bones loose – Swallow large prey 17 Snakes • An extrasensory organ in the roof of a snake's mouth • Sharpens its sense of smell. • Two hollow, highly sensitive saclike structures • Allows it to track both prey and potential mates Snakes • “Pit" organ located between the eye and the nostril on each side of the head. • Detects heat given off by warm-blooded prey Lizards • • • • • • • Legs, eyelids, ear openings Halves of lower jaw united Small lizards - Adhesive toe pads Color is variable Slender body Small scales Self amputation to escape predators – Can’t regrow – Costly; lose muscle/stored fat http://www.youtube.com/watch?v=GgB4u6Mgy2M Chameleon • How are chameleons able to change color? – Special cells called CROMATOPHORES http://science.howstuffworks.com/zoology/28369fooled-by-nature-chameleon-colors-video.htm Insane in the Chromatophore: