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) Caecilians have a long slender body that is limbless and they live in burrows. Caecilians live in tropical regions. Caecilian's eyes are small and they are almost completely blind. Caecilians are carnivores that eat mostly worms and other invertebrates. Fertilization is internal, but eggs are usually deposited in moist ground near the water.

Caecilians

Salamanders: Order Urodela (Caudata) Salamanders are tetrapod amphibians with tails. Most of the salamanders in North America are less than 6 inches (15 cm) long. Some are much larger, like the giant Japanese salamander that can exceed 4-5 feet (1.5 meters). Most salamanders have four equal-sized limbs set at right angles to their body. Salamanders are typically carnivores that prey on worms, arthropods, and mollusks.

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 finned tail, internal and external gills, no legs, and tadpoles are herbivores.

Frogs and Toads

Frogs and Toads: Order Anura (Salientia) 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 long or 1 ft.), to some that are less than 1 cm in length. The Goliath frog can consume rats and ducks.

Goliath Frog

Frogs and Toads: Order Anura (Salientia) 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 ponds and streams. Terrestrial frogs, such as tree frogs, hibernate in the humus (leaf litter) of the forest floor. Some can even withstand freezing temperatures by accumulating glucose and glycogen which prevents ice-crystal formation.

Frozen Alaskan Wood Frog

Class Reptilia Body is covered in scales made of keratin. Most are tetrapods, some are limbless. Respiration is by lungs, not by skin or gills. 3-chambered heart in most, with the exception of the crocodilians which have a 4-chambered heart. Ectothermic; body temperature is modified by behavioral thermoregulation. Fertilization is internal Amniotic eggs covered with leathery shells with internal embryonic membranes.

Characteristics of Reptiles Reptile scales are different than fish scales. The scales on a reptile are made of keratin and are similar in material to mammal skin. Reptile eggs are amniotic, meaning they have internal membranes, (chorion and allantois) which help exchange gases and metabolic waste. The tough leathery shell also allows the eggs to be laid in dry terrestrial environments.

Reptile Scales

Amniotic Egg of a Reptile

Characteristics of Reptiles Reptiles have a double pump circulation with systemic (deoxygenated) and pulmonary (oxygenated) circulation. 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. Shell provides protection for the head, arms, and legs, which can be retracted into the shell. The turtle cannot expand the chest to breath so they use abdominal and pectoral muscles to draw air into the lungs.

Turtle Skeleton

Turtles: Order Testudinata Turtles lack teeth, but they have beak-like jaws lined with tough plates made of keratin. Turtles are almost completely deaf, 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 temperatures males, high temperatures females.

Turtles: Order Testudinata Leatherback marine turtles can reach 2 meters in length and weigh up to 725 kg (about as heavy as a large moose at 1500 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 order squamata that has made them some of the most successful and diverse of all the reptiles is the kinetic skull. The kinetic skull is an adaptation of order squamata 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 eyes which give them excellent 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 (fats) 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. Numerous vertebrae and ribs which provide support, protection, and more leverage for the muscles to increase efficiency in locomotion. The kinetic skull enables snakes to swallow prey several times their size. Snakes do not have movable eyelids, but they do have permanently covered transparent eyelids.

Snake Skeleton

Snakes: Suborder Serpentes Snakes have no external ears. Snakes do have internal ears that can detect limited low frequency sounds. Snakes are sensitive to ground vibrations. Most snakes have relatively poor vision. Some arboreal (tree-dwelling) snakes have excellent binocular vision, that is useful for tracking prey through branches.

Snakes: Suborder Serpentes Probably the most advanced sensory organs used by the snakes to detect prey is the detection of chemicals from a pair of pit-like organs found in the roof of their mouth called the Jacobson's organ. Jacobson's organs are lined with olfactory sensory neurons. Their forked tongue, flicks the air and picks up scent molecules, which are carried to the Jacobson's organ.

Jacobson's Organ

Snakes: Suborder Serpentes Most snakes kill their prey by grabbing it and swallowing it whole, but this 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 their prey rather than seek out their prey.

Constrictors

Snakes: Suborder Serpentes 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-sensitive 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

Snakes: Suborder Serpentes 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 US each year, but only 5-10 of those reported bites result in death. There are two types of snake venom; the neurotoxic kind that attacks the optic nerves causing blindness, and the phrenic nerve of the diaphragm causing suffocation.

Snakes: Suborder Serpentes The other type of snake venom is a hemorrhagin that destroys red blood cells, blood vessels, and causes internal hemorrhaging 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 reptiles, although the skull is different than that of snakes and lizards. Skull is not movable like the kinetic skull of the order Squamata (snakes and lizards). 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 that allows them to breath when the mouth is full of water and/or food. In crocodiles, some of the lower jaw teeth overlap the narrow upper jaw. Alligators lack this feature.

Crocodilian Palate Covering the Back of the Throat

Crocodiles and Alligators

Crocodiles and Alligators

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

Order Crocodilia: Crocodiles and Alligators 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. Soil temperatures determine the gender of the young the same way as turtles, except in crocodilians, low soil temperatures produces females and high soil temperatures produces males.

Crocodilian Parental Care