Chapter 17 and 18 Notes, Reptiles and Amphibians

Chapter 17 and 18 Notes, Reptiles and Amphibians

Characteristics of Class Amphibia

Most amphibians are tetrapods, meaning they have four limbs, but some are limbless.

Amphibians have smooth, moist skin. Amphibians respire by lungs, skin, and gills;

either separately or in combinations. Amphibians have a 3-chambered heart, with

two atria and one ventricle. Amphibians are ectotherms, meaning they

require an external source of heat.

Caecilians: Order Gymnophiona (Apoda)

Snakelike, slender, elongate body that is limbless and they live in burrows.

Caecilians live in tropical regions. Caecilian's eyes are small and the adults are

usually completely blind. Caecilians are carnivores that eat mostly worms

and invertebrates. Fertilization is internal, and eggs are usually

deposited in moist ground near the water.

Caecilian

Salamanders: Order Urodela (Caudata)

Salamanders are tetrapod amphibians with tails. Most of the common salamanders of North

America are less than 15 cm (6”) long. Some are much larger, like the giant Japanese

salamander that can exceed 1.5 m (4-5 ft). Most salamanders have four equal sized limbs set

at right angles to their body. Carnivorous larvae and adults that typically prey

on worms, arthropods, and molluscs.

Salamander

Giant Japanese Salamander

Frogs and Toads: Order Anura (Salientia)

Frogs and Toads lack tails as adults. All frogs and toads bear a tail in the larva stage. Frogs and Toads are adapted for jumping. The name Anura means “without a tail” and

Salientia means “jumping or leaping”. Eggs of frogs and toads hatch into a tadpole,

having a long, finned tail, internal and external gills, no legs, and herbivorous teeth.

Frogs and Toads


Adults are much different than the larval form. After tadpoles go through metamorphosis, frogs

and toads lose their tail and gills, develop legs, and become carnivores.

Frogs and Toads vary in size from the West African Goliath frog (30 cm from nose to anus), to some that are less than 1 cm in length.

The Goliath frog can consume rats and ducks.

Goliath Frog


Frogs are found all over the world, but the majority of them are found in tropical regions.

Those that live in colder climates, hibernate in the winter. Some frogs hibernate in the soft mud of pools and streams.

Terrestrial frogs, such as tree frogs, hibernate in the humus of the forest floor.

Some can even withstand freezing temperatures by accumulating glucose and glycogen which prevents ice-crystal formation.

Class Reptilia

Body is covered in scales made of keratin. Most are tetrapods, some are limbless. Respiration is mostly by lungs. 3-chambered heart in most, with the exception

of the crocodilians which are 4-chambered. Ectothermic; body temperature is modified by

behavior thermoregulation. Sexes separate; fertilization is internal Eggs covered with calcareous or leathery shells

with internal embryonic membranes.

Characteristics of Reptiles

Reptile scales are different than scales on a fish. The scales on a reptile are made of keratin and are similar in material to mammal skin, with an epidermis and dermis. Fish scales are more similar to bone or teeth material.

Reptile eggs are amniotic, meaning they have internal membranes, like the chorion and allantois, which help exchange gases and metabolic waste products. The tough leathery shell also allows them to be laid in dry terrestrial environments, unlike fish and amphibian eggs.

Reptile Scales

Amniotic Egg of a Reptile

Characteristics of Reptiles

Reptiles have a double pump circulation with a systemic (deoxygenated) and pulmonary (oxygenated) circulation similar to mammals.

Reptiles do not have completely separated ventricles, which causes partial mixing of deoxygenated and oxygenated blood.

Reptilian lungs are more efficient than amphibian lungs because their rib cage can expand and contract, although they lack a muscular diaphragm like mammals.

Circulatory System of Amphibians

Circulatory System of Reptiles

Circulatory System in other Vertebrates as a Comparison

Turtles: Order Testudinata

The body of a turtle is enclosed in two shells; the dorsal shell called the carapace and the ventral shell called the plastron. The carapace is fused with the ribs and the vertebrae.

The shell provides protection for the head, arms, and legs, which can be retracted into the shell.

The turtle cannot expand its chest to breath so it uses its abdominal and pectoral muscles to draw air into the lungs.

Turtle Skeleton


Turtles lack teeth, but have beak-like jaws lined with tough plates made of keratin.

Turtles are almost completely deaf and mute, but they have a good sense of smell and vision.

Turtles are oviparous, with internal fertilization. All turtles, including marine forms bury their

amniotic eggs in the ground. Nest temperatures determine the sex of the

turtles; low temps males, high temps females.


Leatherback marine turtles can reach 2 meters in length and weigh up to 725 kg (about as heavy as a large moose at 1600 lbs)

Some land tortoises like the Galapagos Island tortoises can weigh several hundred kilograms.

Most tortoises are slow moving, moving only a few hundred meters per hour.

Their low metabolism may explain their longevity. Some living over 150 years.

Leatherback Sea Turtle

Galapagos Island Tortoise

Order Squamata: Lizards and Snakes

About 95% of all known living reptiles One feature of the squamates that has made

them some of the most successful of all the reptiles is the kinetic skull.

The kinetic skull is an adaptation of the squamates that allows the snout to be tilted upward, in order to capture and manipulate their prey and increase the force of the jaws.

The Kinetic Skull

Lizards: Suborder Sauria

Includes geckos, iguanas, skinks, and chameleons

Most lizards are tetrapods, except the glass lizards which are limbless

Lizards have movable eyelids, snakes do not. Lizards have rods and cones in their eyelids

which give them keen daytime vision, except some nocturnal geckos that have only rods.

Most lizards have external ears, snakes do not.

Gecko Feet, The Wall Climbers

Iguanas

Skinks

Chameleons

Glass Lizards

Lizards: Suborder Sauria

Lizards are well adapted to living in hot, arid climates like the desert.

Lipids in their skin minimize water loss. Concentrated urine (uric acid) saves water. Some lizards, like the Gila monster of the

southwestern U.S., store fat in their tails, which they use for an energy and water reservoir.

Ectotherms do not require as much energy to live as do endotherms.

Gila Monster

Snakes: Suborder Serpentes

Snakes are limbless and usually they lack pelvic and pectoral girdles.

Numberous vertebrae and ribs which provide support, protection, and more leverage for the muscles to increase efficiency in locomotion.

Highly kinetic skull enables snakes to swallow prey several times their size whole.

Snakes have no movable eyelids, although they have permanently covered transparent eyelids.

Snake Skeleton


Snakes have no external ears. Most snakes have relatively poor vision. Some arboreal (tree-dwelling) snakes have

excellent binocular vision, that is useful for tracking prey through branches.

Snakes do have internal ears that can detect limited low frequency sounds

Snakes are sensitive to vibrations conducted through the ground.


Probably the most advanced sensory organs used by the snakes to detect prey is the detection of chemicals from a pair of pitlike organs found in the roof of their mouth called the Jacobson's organs.

Jacobson's organs are lined with olfactory epithelial cells that are connected to a rich network of sensory neurons.

Their forked tongue, flicks the air and picks up scent molecules, which are carried to the Jacobson's organs.

Jacobson's Organ


Most snakes kill their prey by grabbing it and swallowing it whole, but it is dangerous.

Constrictor snakes, kill their prey first by constriction, then swallow the prey whole.

Some constrictors can swallow prey as large as deer, leopards, and even crocodiles.

The muscles of constrictors are quite large, and they slow them down. So most constrictors tend to ambush rather than seek out prey.

Constrictors


Other snakes kill their prey with venom before swallowing it whole.

Vipers (Viperidae family) have large, movable fangs at the front of their mouths.

Cobras, mambas, and coral snakes (Elapidae family) have permanently erect fangs.

Some of the vipers are called pit vipers because they possess special heat-senstive pit organs on their heads that detect infrared heat produced by endotherms.

Vipers

Cobra and Coral Snake

Viper (Rattlesnake Teeth)

Cobra (Elapidae Teeth)

Pit Vipers


Many of the North American venomous snakes are pit vipers, like the rattlesnakes, water moccasins, and the copperheads.

Approximately 8,000 bites are reported in the United States each year, but only 5-10 of those 8,000 reported result in death.

There are two types of snake venom; the neurotoxic kind that attacks the optic nerves causing blindnes, and the phrenic nerve of the diaphragm causing paralysis of respiration.


The other type of snake venom is a hemorrhagin that destroys red blood cells, blood vessels, and causes internal hemorhaging of internal tissues.

It is estimated that worldwide, 50,000-60,000 people die each year from snakebites.

Most are in third world tropical countries where people are not properly fit with good shoes, and medical facilities are lacking.

Order Sphenodonta: Tuataras

Only two living species in New Zealand. Strange lizard like reptile, although the skull is

very different than that of snakes and lizards. Skull is not movable like the kinetic skull of the

order Squamata (snakes and lizards), plus there are some other structural differences.

They also have a median “third eye” with a retina and lens and is sensitive to light, but it is unusual because it is covered with scales.

Tuatara

Order Crocodilia: Crocodiles and Alligators

Long, massive skull and jaw that is adapted to provide a wide gape and a rapid, powerful bite.

Teeth are set in sockets, which is a feature similar to some of the dinosaurs.

Crocodilians have a secondary palate, which is similar to mammals and allows them to breath when the mouth is full of water and/or food.

In crocodiles, some of the lower jaw teeth overlap the upper jaw that is more narrow, alligators lack this feature.

Crocodilian Palate Covering the Back of the Throat

Crocodiles and Alligators

Crocodiles and Alligators


Crocodiles are known to attack large prey like cattle, deer, and even people. Alligators are less aggressive and seldom attack people.


Crocodilians lay their eggs in dead vegetation or in the sand and guard the nest. When the eggs hatch, the babies cry out to the mother and she digs them out.

After she digs them out she delicately places them in her mouth and carries them safely to the water to be released.

Incubation soil temp. determines the gender of the young the same way as the turtles, except in crocodilians, low soil temp. produces females and high soil temp. produces males.

Crocodilian Parental Care

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Chapter 17 and 18 Notes, Reptiles and Amphibians