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 worldamphisbaenians

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

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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

Insane in the Chromatophore:http://www.youtube.com/watch?v=G-OVrI9x8Zs

http://science.howstuffworks.com/zoology/28369-fooled-by-nature-chameleon-colors-video.htm