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Fundamentals of Biology
Lesson 23

Reptiles


I. General Characteristics.

    A. Scaly skin.
    B. Lungs from birth.
    C. Reproduce on land.
    D. Eggs encased in shells.
    E. Internal fertilization.
    F. 3-chambered heart (most) with a partly divided ventricle.
    G. Claws on toes.
    H. Ectothermic.

II. Orders.

    A. Squamata – snakes, lizards, and tuatara.
    B. Testudinata – turtles and tortoises.
    C. Crocodilia – alligators and crocodiles.

III. Skin.

    A. Scales are part of the skin, not separate as in fish.
    B. Skin is thick and dry to prevent heat and water loss.
        1. Skin contains keratin (a protein) and lipids which seal in moisture.
        (2. Keratin is also a component of feathers, horns, and hair.)
    C. Scales are replaced in tortoises and crocodiles as they wear away, but in snakes and lizards are shed several times a year in a molt.

IV. Eggs.

    A. Fertilized internally.
    B. Encased in a shell.
        – Shell is porous, allowing gas exchange but preventing water loss.
    C. Four membranes
        1. Amnion.
            a. Encloses the embryo.
            b. Amniotic fluid cushions and protects the embryo.
        2. Yolk sac  – contains the yolk -- food for the embryo.
        3. Allantois – stores embryonic wastes.
        4. Chorion.
            a. Surrounds all the other membranes.
            b. Regulates exchange of O2 and CO2.

V. The Tuatara.

    A. Formerly classed as order Rhynchocephalia, now part of order Squamata.
    B. Only found on a few islands near New Zealand.
    C. A non-functional eye on top of its head.

VI. Snakes

    A. Methods of Locomotion.
        1. Serpentine.
            a. S-shaped motion.
            b. Used in both crawling and swimming.
        2. Concertina.
            a. Drawing into a tight S shape, then extending forward.
            b. Used when between two structures.
        3. Rectilinear.
            a. Wavelike muscular action on ventral surface.
            b. Scutes (broad scales) grip the earth.
        4. Sidewinding.
            a. Continual looping motion – only touches the ground at 2 or 3 points.
            b. Used where traction is poor; e.g. deserts.

    B. Feeding.
        1. Carnivorous: rodents, insects, lizards, eggs, other snakes.
        2. Locating the prey.
            a. Eyes are weak.
            b. Nostrils lead to nasal cavities.
            c. Jacobson’s organs enhance the sense of smell.
                i. Tongue gathers traces of chemicals and deposits them on the Jacobson’s organs.
                ii. They detect very slight traces of odors.
            d. Heat sensing pits.
                i. Present in pit vipers.
                ii. Located between nostrils and eyes.
                iii. Can sense warm-blooded animals even in total darkness.
            e.    No ears, but can sense vibrations in the ground.
        3. Killing the prey.
            a. Swallow alive.
            b. Suffocate by constriction.
            c. Poison.
                i. Supplied by glands in its head.
                ii. Flows through the fangs.
        4. Ingesting the prey.
            a. Swallow whole.
            b. Quadrate bone enables the jaws to spread far apart.
            c. Lower jaw bones connected in the front by an elastic ligament – they can move independently to pull in prey.
            d. Inward pointing teeth make escape impossible.
            e. Skin of mouth and neck is extremely elastic – can stretch over very large animals.
            f. Ribs may even dislocate temporarily to accommodate prey.

    C. Types of venom.
        1. Neurotoxin.
            a. Attacks the nervous system.
            b. Quickly paralyzes prey.
        2. Hemotoxin.
            a. Slower working, but more deadly for large animals.
            b. Destroys blood vessels and red blood cells.

    D. Short, fixed-fang poisonous snakes.
        1. Venom is usually neurotoxin.
        2. Venom is delivered as the snake “chews” its prey.
        3. Cobras.
            a. Native to Asia.
            b. King Cobra is the largest poisonous snake – 18 feet.
        4. Coral snakes.
            a. Southern U.S. and the tropics.
            b. Brilliant red, yellow, and black bands.
        5. Sea snakes.
            a. Large lung enables them to remain submerged for hours.
            b. Venom is 2 - 50 times more deadly than the King Cobra.

    E. Long, retractable-fang poisonous snakes.
        1. Venom is usually hemotoxin.
        2. Vipers – not in U.S.
        3. Pit vipers.
            a. Water moccasin – southern lakes and swamps.
            b. Copperhead. – eastern woodlands.
            c. Rattlesnake.
                i. Most dangerous in the U.S.
                ii. The rattle is a series of loose, horny segments.

VII. Lizards.

    A. General Characteristics.
        1. 2 pair of limbs.
        2. Ears.
        3. Closable eyelids.
        4. Ventral scales are similar to the rest of the body.

    B. Types.
        1. Chameleons.
            a. Native to Africa, Madagascar, India.
            b. Tree dwellers.
            c. Toes and tail can grasp branches.
            d. Keen eyes can act in unison or independently.
            e. Grabs insects with its long sticky tongue.
            f. Change color in response to light temperature, excitement.
        2. Anole – American lizard capable of color change.
        3. Two poisonous lizards.
            a. Gila Monster of the SW U.S.
            b. Mexican beaded lizard.
            c. Have venom in lower jaws.
        4. Monitor lizards.
            a. Komodo dragon is the largest – 10 feet.
            b. Found on the island of Komodo in the East Indies.

VIII. Turtles and Tortoises.

    A. Tortoises – land dwellers; turtles – water dwellers.

    B. Shell.
        1. Dorsal carapace.
        2. Ventral plastron.

    C. Eyes.
        1. Upper and lower eyelids.
        2. Nictitating membrane.
        3. Horny beaks, but no teeth.

    D. Females bury eggs and then leave.
    E. Giant tortoises of the Galapagos Islands can weigh 350 lbs.
    F. Leatherback sea turtles may reach 1500 lbs.

IX. Alligators and Crocodiles.

    A. Alligators.
        1. Blunt, wide snout.
        2. Teeth fit within the jaws.

    B. Crocodiles.
        1. Thinner, pointed snout.
        2. Some teeth protrude.

    C. Common Characteristics.
        1. 4-chambered heart.
        2. Stealthy carnivores.
            a. Eyes and nostrils on top of head.
            b. Glide silently under the surface of the water.
            c. Kills its prey by thrashing and tearing with its teeth.
            d. Can close its nostrils, ears, and windpipe.
        3. Lay eggs in rotting vegetation to keep warm.

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