KINGDOM ANIMALIAPhylum Chordata

Subphylum VertebrataClass Reptilia

Vertebrate Classes

History

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.

Common FeaturesPositioning of legs

more directly under animal (more support).Paired limbs with

five toes. – Adapted for running,

climbing, swimming.– Absent in snakes.

Common FeaturesBody covered with

horny epidermal scales made from protein keratin. – Scales serve to reduce

water loss and provide protection.

– Reptiles molt as they grow.

Jaws adapted to biting/tearing.

Common featuresRespiration through

internally protected and moistened (a moist cloacal surface in some turtles).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.

Story About the Crocodile Heart

Common featuresExcretory waste = uric

acid (doesn’t waste water)Brain = first cerebral

cortex (capable of reasoning, planning, perception)

Still ectothermic– Must live in favorable

conditions or hibernate.– Being ectothermic enables an

organism to survive on much less food than an endothermic organism.

ReproductionInternal fertilization: gametes not subject

to desiccation. Amniote egg = significant evolutionary

breakthrough.– Egg covered by tough, water-resistant, leathery

or calcerous shell.– Extraembryonic membranes compartmentalize

the interior for several functions.

Amniote Egg

Amniote EggChorion = 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.

Reptile SkullsExcept for turtles, all reptiles

have two temporal openings in the skull.

These openings have allowed for attachment and expansion of the jaw muscles.

Subclass AnapsidaOrder Testudines

260 species of turtles/tortoisesOldest group of reptiles (225

mya)Protective body shell

– Encases vital organs– Provdes some protection to

head/limbs– Composed of bony plates covered by

horny epidermal scales– 2 parts: upper carapace, lower

plastronPrimitve features:

– Loss of body-wall muscles– Ribs/trunk vertebrae fused to

carapace– Lack teeth/horny beak grab and tear

food

Subclass AnapsidaOrder Testudines

All lay eggs on land.

Third eyelid = nictitating membrane.

Longest living vertebrates (100+years in wild)!

Subclass DiapsidaSuperorder Lepidosauria

– Order Squamata• 4675+ species of lizard• 2700+ species of snakes• 140 species of amphisbaenians

– Limbless, burrowing animals– Vestigial eyes under skin

– Order Rhynchocephalia• 2 species of Tuatara• Solitary, nocturnal, burrowing

animal

Most successful/diversified of living reptiles.

Occur in most habitats of world.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 heatLizards:

– Legs, eyelids, ear openings– Halves of lower jaw united

Order Squamata

Superorder ArchosauriaIncludes extinct

dinosaurs/pterosaurs and birds

23 species of crocodiles, alligators, & caimans

Largest of the living reptiles

Amphibious carnivoresLive in tropics/subtropicsLizard-like body with short

legs, clawed/webbed toes, massive tail

Flat head with nostrils at tip

Powerful jawsDorsal side armored with

dermal plates