Evolution of Reptiles

Evolution of Reptiles: Reptiles were 1st vertebrates to make a complete transition to life on land (more food & space) Arose from ancestral reptile group called cotylosaurs (small, lizard like reptile) Cotylosaurs adapted to other environments in Permian period 1. Pterosaurs – flying reptiles 2. Ichthyosaurs & plesiosaurs – marine reptiles 3. Thecodonts – small, land reptiles that walked on back legs Mesozoic Era called “age of reptiles” Dinosaurs dominated life on land for 160 million years Brachiosaurs were largest dinosaurs Herbivores included Brontosaurus & Diplodocus, while Tyrannosaurus were carnivores Dinosaurs became extinct at end of Cretaceous period Mass extinction of many animal species possibly due to impact of huge asteroid with earth; Asteroid Impact Theory Amniote (shelled) egg allowed reptiles to live & reproduce on land Amniote Egg: Egg had protective membranes & porous shell enclosing the embryo Has 4 specialized membranes — amnion, yolk sac, allantois, & chorion Amnion is a thin membrane surrounding a salty fluid in which the embryo “floats” Yolk sac encloses the yolk or protein-rich food supply for embryo Allantois stores nitrogenous wastes made by embryo until egg hatches Chorion lines the inside of the shell & regulates oxygen & carbon dioxide exchange Shell leathery & waterproof Internal fertilization occurs in female before shell is formed Terrestrial Adaptations: Dry, watertight skin covered by scales made of a protein called keratin to prevent desiccation (water loss) Toes with claws to dig & climb Geckos have toes modified into suction cups to aid climbing Snakes use scales & well developed muscular & skeletal systems to move Lungs for respiration Double circulation of blood through heart to increase oxygen to cells Partial separation in ventricle to separate oxygenated & deoxygenated blood Ectothermic – body temperature controlled by environment May bask or lie in sun to raise body temperature or seek shade to lower body temperature; known as thermoregulation Water conserved as nitrogen wastes excreted in dry, paste like form of uric acid crystals EXTINCT REPTILES Ever since the dinosaurs died off 65 million years ago, reptiles have had it relatively easy in the extinction department, not nearly as susceptible to environmental changes as birds, mammals, and amphibians. Regardless, there have been snakes, turtles, lizards, and crocodiles that have gone extinct in historical times. Jamaican Giant Galliwasp It sounds like something from a story, but the Jamaican giant galliwasp was a species of anguid lizard known as Celestus occiduus. Galliwasps (mostly belonging to a related genus, Diploglossus) can be found all over the Caribbean—there are variants native to Cuba, Puerto Rico, and Costa Rica—but the Jamaican giant galliwasp never quite came to terms with civilization and was last seen alive in the 1840s. Galliwasps are mysterious, secretive creatures that mainly hunt at night, so there's still a lot we don't know about their resiliency to ecological pressure. Round Island Burrowing Boa The Round Island burrowing boa is a bit of a misnomer: In fact, this 3- foot-long snake used to be native to the Indian Ocean island of Mauritius (where the dodo had gone extinct a few centuries before) and was only pushed out to the much smaller Round Island thanks to the depredations of human settlers and their pets. The last known sighting of the shy, gentle, euphoniously named Round Island burrowing boa was in 1996; by then, erosion of this snake's natural habitat by invasive goats and rabbits had spelled its doom. Cape Verde Giant Skink Skinks—not to be confused with skunks—are the world's most diverse lizards, flourishing in deserts, mountains, and polar regions. Still, individual skink species are every bit as vulnerable to destruction as any other type of animal, as evidenced by the early 20th-century disappearance of the Cape Verde giant skink, Chioninia cocteri. This species was unable to adapt either to the resident humans of the Cape Verde Islands, who prized this reptile for its valuable "skink oil," or to the relentless desertification of its natural habitat. Kawekaweau The largest gecko that ever lived, the 2-foot-long kawekaweau (you may find it easier to refer to it by an alternate name, Delcourt's giant gecko) was native to New Zealand, but human settlers drove it to extinction in the late 19th century. The last known kawekaweau was killed by a Maori chieftain around 1873. He didn't bring the body back with him as evidence, but his detailed description of the reptile was enough to convince naturalists that he had made a genuine sighting. (The name kawekaweau, by the way, refers to a mythical Maori forest lizard.) Rodrigues Giant Tortoise Rodrigues giant tortoises came in two varieties, both of which disappeared around the turn of the 19th century: the domed tortoise Cylindraspis peltastes, which only weighed about 25 pounds and barely meriting the adjective "giant" and the saddle-backed tortoise, Cylindraspis vosmaeri, which was substantially bigger. Both of these testudines lived on the island of Rodrigues, located about 350 miles east of Mauritius in the Indian Ocean, and both were hunted to extinction by human settlers, who must have been amused by these turtles' social behavior (slow-moving herds of the saddle-backed tortoises numbered in the thousands. Martinique Giant Ameiva The Martinique giant ameiva, Pholidoscelis major, was a slender, 18- inch-long lizard characterized by its pointy head and forked snakelike tongue. Ameivas can be found all over South and Central America as well as the Caribbean, but not on the island of Martinique, where the resident species has long been extinct. There's speculation that the Martinique giant ameiva may have been doomed not by human settlers but by a hurricane that literally tore apart its natural habitat. The Horned Turtle The horned turtle, genus Meiolania, was a large testudine that roamed Australia, New Caledonia, and Vanuatu. The youngest bones discovered are about 2,800 years old and are from the South Pacific island country of Vanuatu, where it was presumably hunted to extinction by aboriginal settlers. (This seems rather odd, considering that Meiolania came equipped with two horns over its eyes and a spiked tail reminiscent of Ankylosaurus.) Meiolania, by the way, came by its Greek name "little wanderer" by reference to another extinct reptile of Pleistocene Australia, the giant monitor lizard. Wonambi One of the few prehistoric snakes to be discovered in Australia, Wonambi naracoorthsis, was an 18-foot-long, 100-pound predator capable of taking down (though perhaps not swallowing) a full- grown giant wombat. A related species, W. barriei, was described in 2000. Even at the height of its powers, though, the Wonambi snakes were an evolutionary last gasp: The family of snakes from which it descended, the "madtsoiids," had a global distribution for tens of millions of years but were restricted to Australia on the cusp of the modern era. The Wonambi went extinct about 40,000 years ago, slightly before (or coincident with) the arrival of the first Aboriginal Australians. Giant Monitor Lizard Megalania, the "giant wanderer"—not to be confused with Meiolania, the "little wanderer," described above—was a 25-foot-long, 2-ton monitor lizard that would have given theropod dinosaurs a run for their money. Megalania was probably the apex predator of late Pleistocene Australia, preying on resident megafauna like the giant short-faced kangaroo and capable of giving Thylacoleo (the marsupial lion) a run for its money. Why did the giant monitor lizard go extinct 40,000 years ago? No one knows for sure, but suspects include climate change or the disappearance of this reptile's usual prey. Quinkana Quinkana was far from the biggest crocodile that ever lived, but it made up for its relative lack of heft with its unusually long legs and sharp, curved, tyrannosaur-like teeth, which must have made it a true menace to the mammalian megafauna of late Pleistocene Australia. Like its fellow reptiles from Down Under, Wonambi and the giant monitor lizard, Quinkana went extinct about 40,000 years ago, either because of hunting by Aboriginal settlers or the disappearance of its customary prey. .

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