Chapter 18

Reptiles and Amphibians

Cold-blooded Animals

• Reptiles are considered cold-blooded animals.

• Their body temperature fluctuates with the temperature of their surroundings.

• Scientifically this is known as poikilotherms.

Similarities among Reptiles

• All true reptiles are vertebrates• All are cold-blooded• All have tough, dry skin which is covered in

scales.• Most molt several times a year• All (except snakes) are tetrapods• Each has claws• Most are oviparous• Some are ovoviviparous – eggs are kept inside

the female and then the babies hatch and are “born” alive.

Lizards: The most numerous Reptiles

• Lizards are a “squamate”

• Lizards have eyelids (snakes do not)

Lizards: The most numerous Reptiles

• Various habitats – lizards are most numerous in tropical habitats

• Varying sizes – majority are less than a foot long

• Poisonous lizards – only two species in North and Central America are poisonous – the Gila monster and the Mexican beaded lizard.

Lizards: The most numerous Reptiles

• Some lizards have tails that detach that enables them to escape from predators.

• Other defense mechanisms: - chuckwallas inflate their bodies in crevices.

- some can glide from tree to tree - frilled lizards make themselves look scary to

predators - horned lizards (we have these) have prickly

“horns” on them…they also squirt blood out of their eyes.

Lizards:Eating Habits

• Most lizards are insectivores…

• Some lizards are herbivores – ex: the chuckwalla

Snakes:the most widespread reptiles

• Snakes are legless vertebrates

• Snakes are not found in artic regions – because they cannot survive freezing temperatures.

• To survive cold temperatures elsewhere, they “hibernate” by burrowing into the ground.

Snakes

• Snakes come in varying sizes:

the blind snake is only 5 to 6 inches

the python and anaconda are the largest, growing to 30 feet and 300 pounds

the longest snake in North America is the indigo snake that can grow to 9 feet in length

Snakes:Methods of Locomotion

1. Lateral undulation: a majority of snakes move by this – the snake bends into a series of curves as it keeps its body flat on the ground.

2. Reticular movement: thick bodies snakes – move in a straight line – some use this to climb trees

3. Concertina movement – the front part of the body moves forward and the then pulls the back portion up to it.

4. Sidewinding movement – the snake move sideways – they lift their body off the ground as they move.

Snakes

• Snakes have a scaly skin

• As the dead cells reach the surface, they form a tough layer.

• When the outer skin becomes worn or thin or too small, it is shed

Snakes:Sense organs

• Scale covered eyes – most snakes are nearsighted – they can see movement, but cannot differentiate between objects.

• Hearing without ears – they have no external ear opening – they do have an inner ear- they cannot hear high pitched sounds

they use their lower jaw (attached to a quadrate bone) to transmit sounds to their ear membrane (much like birds)

Snakes:Sense organs

• Sense of smell – the snake has nostrils, but its primary sense of smell is its tongue

• The snake flicks out its tongue and picks up smell particles that it sends to the Jacobson’s organ where nerve endings decipher the smell.

Snakes:Design for Feeding

Double hinged jaw:

The snakes jaw comes undone and the snake is able to consume large prey.

Engulfing a Meal:

Snakes eat their prey whole.

Snakes

Groups of snakes:Blind snakes – smallest snake – often

mistaken for wormsConstrictors – kill their prey by

“constricting” their prey – includes pythons, boas, and anaconda

Colubrids – 2/3 of all snakes – they can be terrestrial, aquatic, or arboreal – includes garter snakes, water snakes, king snakes, and racers.

Majority are harmless – but, a group of them do have fangs, but the fangs are in the back of the mouth – so they rarely bite a human.

Snakes

Groups of snakes:Elapids – all are poisonous – fangs

in the front of the mouth – over half of all elapids live in Australia – also includes cobras

the king cobra is the largest venomous snake

also includes mambas – highly aggressive snake

in the us, we have the coral snake

sea snakes are also elapids

Snakes

Groups of snakes: Vipers – Most are viperids,

which means they have fangs that retract beck into a fold of skin.

pit vipers – have heat sensor that allows them to “see” an object

examples in the us: cottonmouth (highly aggressive), copperheads, and rattlesnakes.

Snake Venom

Of the 2700 species of snakes, only 250 are venomous…

There are two types of toxins in snake venom:

1. neurotoxin: nerve poison – affects the nervous system, shutting down the heart lungs and muscles.

2. hemotoxin: blood poison – damages blood vessels and destroys red blood cells.

Snakebite Treatment

Only 8-12 snakes bites are fatal in the U.S. each year…

Use of antitoxin (antivenin) has decreased the death rate worldwide…

Keep the person calm and the limb lower than the heart to slow the motion of the poison…

NEVER attempt to “suck” the venom out with your mouth…you may infect yourself!

Turtles

• Turtles: the only reptile with a shell…

• The upper shell is called a carapace.

• The lower shell is the plastron.

Characteristics of Turtles

• 50 species live in the U.S. of the 240 species worldwide..

• Turtles hibernate in the cold winters.

• Some use estivation to survive dry periods.

• They are toothless.

Freshwater Turtles

• Includes the box turtle, which is no longer sold as a pet due to the salmonella that it carries.

• Snapping turtle

Salt Water Turtles

• The largest living turtles…

• They lay their eggs on the sand of beaches, but do not care for the young…

Tortoises

• Land turtles• The longest living

animal – the giant turtle on the Galapagos island – 150 years old

Our Mojave Desert tortoise…

Crocodilians

• The largest living reptiles.

Characteristics of Crocodilians

• Have partially webbed feet for moving through water

• Powerful tails• All crocodilians are carnivorous• They include salt water crocodiles, alligators,

caimans • Oviparous – but they tend the nest unlike other

reptiles• Nile crocodiles (the largest) can grow to 20 feet

long• There are fossils of extinct crocs that were 40

feet long

Tuataras:Spiny-crested Reptiles

• Inhabits New Zealand

• It has a third “eye” – called a parietal eye – situated on top of its brain

• The “eye” senses radiation

• It is insectivorous

Amphibians

• Live in both the land and water

• Includes frogs and toads

Characteristics of Amphibians

• Most are oviparous – eggs can attach anywhere

• Usually pass through an aquatic, gilled larval stage

• All have a three chambered heart

• Some estivate by burrowing into the soil to avoid drying out and heat

Frogs and Toads:Leaping Amphibians

• Frogs have smooth skin

• Toads have rough “warty” skin

• Protective covering

• Toxic skin secretions – one ounce of the arrow-poison frog can kill 3 million people

• External fertilization – female lays the eggs and then the male fertilizes them

Anatomy of an Amphibian

• Features of the head- Protruding eyes- nictitating membranes – transparent

inner eyelids• Features of the oral cavity

- tongue is attached in front- maxillary teeth – project from upper jaw – are called vomerine teeth because they

extend from bones of the skull- Frog swallows by pushing food with its

eyeballs

Anatomy of an Amphibian

• Digestive system - swallow prey whole- “fat bodies”, above the kidneys keep frog alive during periods of estivation and

hibernation• Respiratory system

- frog can breath through tiny capillaries in mouth- under water the frog can “breath” in the water through its skin

Anatomy of an Amphibian

• The circulatory system

- three chambered heart

Other Amphibians

Salamanders – amphibians with tails

- some salamanders have no lungs or gills – they use buccal respiration

Caecilians – limbless amphibians

- most live underground

- 7 to 52 inches long