Chapter 43: Reptiles 43-1 Origin and Evolution of Reptiles 43-2 Characteristics of Reptiles 43-3 Modern Reptiles
43-1 Origin and Evolution of 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.
(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)
Critical Thinking (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.
II. Success of Reptiles (Class Reptilia) • SURVIVING the extinction were FOUR modern reptilian orders that diversified into 6,000 + species today.
Critical Thinking (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?
(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).