Chapter 43: Reptiles

43-1 Origin and Evolution of Reptiles

43-2 Characteristics of Reptiles

43-3 Modern Reptiles

I. History of Reptiles (~ 360 m.y.a. divergent population of amphibians)• Earliest were small, lunged, 4-legged vertebrates (resembling lizards) with TEETH modified for eating INSECTS.

43-1 Origin and Evolution of Reptiles

(A) Age of Reptiles (Mesozoic era, from 245 to 65 m.y.a.)• Period of TIME on Earth when nearly ALL of LARGEST vertebrates were reptiles. (rapid DIVERSIFICATION led to this evolutionary success)

(1) Dinosaurs (including pterosaurs, plesiosaurs, and ichthyosaurs)• Extinctions at end of Cretaceous period (65 m.y.a.) eliminated about 60% of ALL species, including ALL DINOSAURS.

(B) Extinction of Dinosaurs (a PORTION of a MASS extinction)• Coincided with extinction of numerous OTHER terrestrial and aquatic species; Questions remain as to WHAT triggered this MASS extinction?

(1) Asteroid-Impact Hypothesis (suggests a RAPID die-off)• Huge asteroid hit Earth, sending DUST into atmosphere REDUCED the SUNLIGHT (i.e., climate/temperature shifts, PLANTS died)

(1) Luis and Walter Alvarez first proposed the asteroid-impact hypothesis after the discovery of abnormally HIGH levels of IRIDIUM in sediments from the end of the Cretaceous Period. According to the Alvarez team, what was the proposed source of iridium? High iridium levels were then initially discovered at ONE site in Italy. Since then, high levels have been found at MORE than 100 sites around the world, ALL dating back from the end of the Cretaceous Period. Explain HOW the worldwide distribution of iridium may be important EVIDENCE for the asteroid-impact hypothesis.

Critical Thinking

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II. Success of Reptiles (Class Reptilia)• SURVIVING the extinction were FOUR modern reptilian orders that diversified into 6,000 + species today.

(2) Describe the costs versus the benefits that are associated with autotomy for a lizard.

Critical Thinking

(3) When a female leatherback turtle comes up on a beach to lay eggs, she first digs a deep hole, lays her eggs, and covers them up with sand. Next, she crawls about 100 m and digs another hole. This time she lays no eggs but just covers the hole with sand. Suggest a possible explanation for this behavior.

Critical Thinking

(4) Examine this photo of the inside of a turtle’s carapace. In cartoons, turtles are often depicted as crawling out of their shell. What can you use as evidence that would either support or refute this reptilian behavior?

Critical Thinking

(A) The Amniotic Egg (reptiles, BIRDS, MAMMALS—paved way for land)• Encases EMBRYO in secure, self-contained environment with MORE protection for development than a gelatinous AMPHIBIAN egg:

FOUR membranes are PRESENT in the amniotic egg:

(1) Amnion, (2) Yolk Sac, (3) Allantois (4) Chorion

(1) Amnion (surrounds embryo)• Thin membrane enclosing FLUID in which embryo FLOATS.

(2) Yolk Sac (surrounds yolk)• Encloses yolk, a fat-rich FOOD supply for developing embryo.

(3) Allantois (WASTE depot, GAS-exchanger membrane)• Vascular membrane STORES wastes and acts as embryo’s LUNG, exchanging GASES with environment.

(4) Chorion (overall protective membrane)• Surrounds ALL other membranes and helps to PROTECT developing embryo.

(5) Albumen (water/protein depot with yolk)• Mixture of proteins and water contained in egg.

(B) Watertight Skin (keratinized epidermis)• Dry, thick SCALY skin evolved to PREVENT water loss from body, while adding PROTECTION from predators.

(1) Keratin• DURABLE protein found in SCALE EXTENSIONS of epidermis that HOLDS IN water and protects against ABRASIVE injuries.

(C) Respiration and Excretion (adaptations for terrestrial life)• IMPROVED lungs for gas exchange; Excretion of URIC ACID (LESS toxic than ammonia or urea), thus requires LESS water for dilution (only small amounts of water are LOST in reptile urine).

I. Circulatory System• DOUBLE-Loop system with 3-chambered heart (partially divided single VENTRICLE and two ATRIA).

43-2 Characteristics of Reptiles

(A) Heart and Circulatory System (crocodile ~ CLOSEST to 4 chambers)• Heart has FLEXIBILITY that hearts of birds and mammals do not possess (well suited adaptation for reptile ECTOTHERMY).

NOTE: Reptiles REDIRECT blood away from LUNGS towards BODY while:

(1) Remaining Inactive

(2) Underwater

(3) Basking (attempting to RAISE its body temperature QUICKLY)

(1) Septum• A WALL OF TISSUE evolved to PREVENT mixing of oxygenated and deoxygenated blood in heart.

II. Respiration (many snakes have only ONE lung)• INHALATION by expanding rib cage, reducing pressure within thorax and DRAWING AIR into the lungs.

(1) Alveoli• Air sacs lining interior of lungs—site of gas exchange/increase surface area.

III. Nervous System• Larger cerebrum and optic lobe, hearing (COLUMELLA), smell (J.O.), and HEAT detection (PITS).

(1) Jacobson’s Organ (e.g., developed in snakes and lizards)• Located in roof of mouth (SMELL) [NOTE: Works with heat-sensitive PITS (below eyes) and JAW BONES that detect VIBRATIONS]

(5) Why may it be advantageous for a snake to kill its prey, either through constriction or venom, before trying to consume it?

Critical Thinking

IV. Thermoregulation • Metabolic activity OR environment can be used to adjust BODY temperature to suit metabolic needs. (basking, sitting in shade)

(6) The skin of a basking lizard is usually heavily pigmented (dark); however, as a lizard warms, the skin lightens. Suggest a function explanation for this temporarily morphological change.

Critical Thinking

(1) Ectotherm (SLOW metabolism—generates LITTLE heat)• Body is warmed by ABSORBING heat from surroundings

(e.g., fish, amphibians, and reptiles).

(2) Endotherm (RAPID metabolism—generates MUCH heat)• Most have insulation (fur, feathers, fat, etc…) to RETAIN heat resulting from METABOLIC ACTIVITY (e.g., birds and mammals).

(A) Advantages and Limitations of Ectothermy (NARROW temp. range)• Require ~90% LESS food than endotherm (same size); BUT ectothermic metabolism CANNOT provide energy for sustained physical exertion.

V. Reproduction and Parental Care• THREE patterns of reproduction involving eggs and nutrition for the offspring: (1) Oviparity, (2) Ovoviviparity, (3) Viviparity

(1) Oviparity (adj. Oviparous)• Eggs hatch OUTSIDE body of mother (e.g., MOST reptile species, ALL bird species, and THREE species of mammals).

(2) Ovoviviparity (adj. Ovoviviparous)• Eggs may hatch INSIDE body (BUT are born alive); in a FEW cases, egg WILL be laid RIGHT BEFORE hatching.

(3) Viviparity (adj. viviparous, MOST mammals, few COLDER temp reptiles)• Offspring carried and nourished INSIDE body BEFORE birth (NOTE: A shell does NOT form around egg, instead exchange occurs via a “placenta”)

(7) Numerous species of viviparous snakes and lizards inhabit colder climate habitats. Suggest a reason as to why viviparity may be advantageous in such environments?

Critical Thinking

(4) Placenta (EXCHANGE organ between mother AND offspring)• Forms from MEMBRANES within egg, bringing blood vessels from embryo NEAR the vessels of mother.

(8) Describe which of the three patterns of reproduction in reptiles BEST serves to protect the eggs from predators. Explain your selection.

Critical Thinking

I. Order Chelonia (~250 species of tortoises and turtles)• Aquatic and terrestrial, sharp BEAK, and FUSED bony plates (shell) with GIRDLES located WITHIN ribs (instead of OUTSIDE ribs like others).

43-3 Modern Reptiles

(1) Carapace• TOP, dorsal portion of SHELL fused to vertebrae and ribs of skeleton.

(2) Plastron• LOWER, ventral portion of shell facing ground or water.

(A) Reproduction• Chelonians are EGG-layers (oviparous) AND nests are build on LAND with little care for hatchlings.

II. Order Crocodilia (~21 species of crocodiles, alligators, caimans, gavials)• Large, aquatic predators found in tropical habitats rich in fish and small mammals.

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III. Order Squamata (~ 5,500 species of lizards and snakes)• Most DIVERSE; upper and lower JAWS are LOOSELY hinged to skull for SWALLOWING prey.

(A) Lizards (~3,000 species)• Rely on SPEED, and STEALTH to catch prey and avoid predators; (from small Jacksonian Chameleons to massive Komodo Dragons).

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(1) Autotomy (a DEFENSIVE adaptation)• Tail detaches and continues to squirm drawing predator’s attention, allowing the lizard to escape. (regeneration varies from weeks to months)

(B) Snakes (~2,500 limbless species ranging between 100-400 vertebrae)• Evolution? Ancestors of snakes were terrestrial BUT inhabited thick vegetation, where legs MAY have been a HINDRANCE to rapid movement.

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(C) Capturing and Consuming Prey• Seize and swallow its prey; TWO methods for predation have proved successful:

(1) Constriction

(2) Venom

(1) Constrictors (e.g., boas, pythons, anacondas, king snakes)• Suffocate prey by GRADUALLY increasing tension in its coils, squeezing a little tighter EACH time prey EXHALES.

(2) Elapids (e.g., cobras, mambas, coral snakes)• Inject venom through two SMALL, FIXED hollow fangs in FRONT of mouth

(NOTE: Bite prey and use GROOVED teeth to guide venom into puncture wound; e.g., boomslang and twig snakes)

(3) Vipers (e.g., rattlesnakes, copperheads, and water moccasins)• Inject venom through hollowed LARGE, MOBILE fangs.

(NOTE: When a viper strikes, hinged fangs SWING FORWARD from mouth and inject venom MORE deeply than elapid fangs can)

IV. Order Rhynchocephalia (~ only 2 species remaining)• Tuataras (“spiny lizard”) have a SPINY CREST running down back; inhabit islands of New Zealand, BUT since human development, their numbers have decreased from INTRODUCED predators (i.e., rats and cats)

Extra Slides AND Answers for Critical Thinking Questions

(1) The Alvarezes proposed that iridium came from an asteroid that struck Earth. If iridium was found in only one location, it might indicate a local event. Discoveries of iridium in sites worldwide indicate that the debris from the asteroid’s impact spread over the globe, suggesting a very large catastrophe.

(2) Dark objects absorb more heat. The lizard is dark when it first begins basking so that it can absorb as much heat as possible. As the lizard warms, it lightens, lessening its heat absorption.

(3) Ovoviviparity reduces the time the eggs spend outside the mother’s body and reduces the amount of time they are exposed to predators.(4) Killing the prey prevents it from escaping and ensures that the snake won’t be injured by its struggles.

(5) Viviparity reduces exposure to cold and allows eggs to incubate inside the mother’s body.

(6) Replacing the tail requires energy and materials, such as muscle, skin, and blood.

(7) The turtle is digging a decoy hole that may distract the attention of predators from the nest containing the eggs.

(8) Turtles’ ribs and other skeletal structures are attached to their shells, so turtles cannot crawl out of their shells.