Class: Reptilia

Types of Reptiles

Common Garter Snake

Monitor

Glass Snake

Characteristics Class: Reptilia----to creep

• 7,000 species only 300 of which in the US and Canada

• Fossils date back to 300 million years

Origin and Evolution• From the studies of fossils and

comparative anatomy, biologists infer that reptiles arose from a group of ancestral reptiles called cotylosaurs, which lived about 310 million years ago.

- Fossils indicate that these four-legged, sprawling vertebrates resembled small lizards and had teeth used for eating insects

-The abundance of insects at the time may have been one reason the cotylosaurs flourished.

Origin and Evolution• During the Permian period these reptiles

began to adapt to other available environments, giving rise to new forms of reptiles.

- These groups included flying reptiles called pterosaurs

• - Two groups of marine reptiles: the ichthyosaurs and plesiosaurs

• - And the thecodonts

• - The dominant land reptiles came from the thecodonts.

- The small lizard-like carnivores, many of which walked on their hind legs.

• The thecodonts were the first archosaurs ( “ruling reptiles”), a group that later included the early crocodiles, the dinosaurs, and the reptiles that evolved into birds.

• The Mesozoic era is known as the Age of Reptiles.

- During this time reptiles , esp. the dinosaurs, dominated all other forms of life.

Origin and Evolution - Dinosaur means “terrible lizard” however

many of the dinosaurs were small.• Yet the incredible size of some dinosaurs

distinguish the group from all other forms of life.

-One of the largest dinosaurs was the brachiosaurus, 77,000 kg.

• It was as long as a tennis court, as tall as a four-story building, and heavier than elephants.

Characteristics of Reptiles

1. Strong, bony skeletons and feet with claws2. Ectothermic (cold-blooded)3. Dry scaly skin4. Amniote eggs5. Respiration with lungs6. Ventricle partially divided7. Internal fertilization

Body Plan• Bilateral symmetry

• Endoskeleton made of bone

• Striated and smooth muscles

• Limbs paired with five toes for walking on land

• Jaws have powerful crushing ability

Skin• Body covered with horny epidermal

scales made of keratin

• Epidermis and dermis

• No glands

Respiration• By lungs, cloaca used by some

• Suck air in by enlarging the thoracic cavity

• No diaphragm

Circulation• Closed with both pulmonary and

systemic systems

• Two separate circulations within the heart– Either a complete partition separates the

atria/ventricles or blood flow in such a way that oxygenated blood never mixes with unoxygenated blood

Nutrition• Carnivores

• Various methods of getting food– Poison or bacteria

– Sticky tongue

– constrictors

Digestion• Complete digestion mouth—anus

• Intracellular/extracellular digestion

• Adaptations to excrete bones and hair

Excretion• One metanephric kidney

– Allows efficient water conservation

• Salt glands located near nose to aid in conservation of water during excretion by making body fluids hyperosmotic

• Elimination of nitrogenous wastes as uric acid

Nervous System• Small brain with large cerebrum• Well developed sense organs (except

hearing)

• Jacob’s Organ is a specialized olfactory organ. Scents are carried here by the tongue

-eye sight

-touch/feel

-taste

-smell

Reproduction• Sexual reproduction with internal fertilization• oviparous• Egg covered by a hard porous shell, contains

– amnionic fluid with yolk for food

– allantois and chorion to remove metabolic waste

• Eggs are laid in sheltered locations on land

Allantois

• Helps the embryo exchange gases and handle liquid waste.

• The allantois, along with the amnion and chorion (other embryonic membranes), identify humans as amniotes, along with reptiles, dinosaurs, birds, and other mammals.

• Of the vertebrates, only Ichthyopsidas (fish and amphibians) lack this structure.

Chorion

• Also called the Serosa, the outermost membrane around the embryo. It develops from an outer fold on the surface of the yolk sac.

• In reptiles and birds it fuses with the allantois. In direct contact with the eggshell of reptiles and birds, this chorioallantoic membrane absorbs oxygen through the porous shell from the atmosphere for nourishment of the embryo; it also discharges waste carbon dioxide through the shell.

Development• Development begins in the egg

• Young hatch as lung-breathing juveniles

Environmental Interactions

• No developmental stages

• Predators, herbivores, scavengers

• Can be poisonous

• Temperature can dictate the sex of the animal – low=male/high=female

Types of Reptiles

4 Main Groups (ORDERS) Sphenodonta = tuatara

Testudines = turtles and tortoises

Crocodilia = crocodiles, alligators Squamata = lizards, snakes (largest group)

Order Sphenodonta

•Taurtaras•Only found in New Zealand; they have no external ears and a 3rd eye

Order Testudines

Tortoises usually live on the land, turtles in the water

What's this famous turtle's name?

Snapping turtles can be very aggressive

The top of a turtle's shell is the carapace, the bottom is the plastron.

Is this a turtle or a tortoise?

Order Crocodilia

Alligators are found mainly in North and South America and only live in freshwater

Alligators only show their upper teeth when their mouth is closed, and their snouts are rounder (u-shaped)

Crocodiles can live in fresh or salt water; most are found in Africa, India, and Asia

Crocs have a pointed snout and show both rows of teeth when their mouths are closed.

The Nile Crocodile takes care of its young, a unique trait among reptiles

The gavial is a crocodilian with a long, slender snout

Caimen

Order Squamata

Snakes and Lizards will be discussed in the next presentation......