Reptiles and Birds - Field Natural History - Lecture Notes, Study notes of History

Download Reptiles and Birds - Field Natural History - Lecture Notes and more Study notes History in PDF only on Docsity! Field Natural History Reptiles and Birds – Kissing Cousins? I. Careers in home heating and cooling – endotherms and ectotherms. A. How animals heat their bodies. 1. Endotherms - animals that use metabolic heat to raise their body temperature. (“Warm- blooded”) 2. Ectotherms - animals that obtain energy from their surroundings. (“Cold-blooded”) a. Warmth from sunlight. b. The ground in their burrows. c. The water in which they live. 3. Homeothermic animals that have a constant body temperature. 4. Poikilothermic animals have a body temperature that fluctuates with that of the surrounding environment. 5. Only birds and mammals are considered to be endothermic. a. Endothermy is relatively rare because it is expensive metabolically. b. The heat that they generate comes from the food that they eat. 6. Because endothermy is expensive, animals try to conserve the heat that they generate. a. Heat is conserved by insulating layers- fat or fur. 7. However, endotherms cannot completely turn of the furnace. a. Heat is lost by dilating the blood vessels near the surface of the skin so that it radiates. b. Cooling of the body is also facilitated by evaporative cooling –sweat. c. Panting is another way that some animals cool themselves. 8. In general, endothermic animals are homeothermic. a. However, some ectothermic animals maybe homeothermic. A deep sea fish may be an ectothermic homeotherm. b. Its heat comes from the surrounding sea water, but because the temperature of the sea water in its environment is constant, so is the body temperature of the fish. 9. All living reptiles are ectothermic and most of them are also poikilothermic. a. They regulate their temperature by basking in the sun, or seek shade to avoid overheating. II. The family tree – extinct dinosaur groups. A. Four major extinct groups: Pelycosaurs, Therapsids, Thecodonts and Dinosaurs. 1. Pelycosaurs – early dinosaurs that were more successful than amphibians because of their watertight eggs. Probably ectothermic a. More powerful jaws than amphibians, with long, sharp teeth allowed them to be the first land vertebrates to attack prey their own size. 2. Therapsids – were endothermic, and ate 10 times more than their pelycosaur predecessors. a. As a result, they were more active, particularly under colder conditions or during the winter. Before they went extinct, they gave rise to their descendants, the mammals. 3. Thecodonts – 230 million years ago, the world’s climate began to warm. a. Endothermy was no longer advantageous in a warmer climate, therefore, thecodonts were ectotherms. b. They were the first land vertebrates to be bipedal – they stood and walked on two feet. Major consequence -. They could run faster. Docsity.com Field Natural History 4. Dinosaurs -We used to think they were sluggish - we now believe that some, at least the predators, could move fast. a. Not necessarily stupid either. Evidence of sociality (herd prints with juveniles inside), and nesting behavior. 5. Some scientists contend that dinosaurs did not go extinct, but that one group evolved into Class Aves, the birds. a. Why? Because; 1) They lay an amniotic egg (which is hard, rather than leathery) and 2) reptilian scales are present on the feet and lower legs. 6. However, birds are classified separately because of the evolutionary novelties of birds: feathers, hollow bones and more efficient lungs for flight. III. Birds. 1. The success of flight in birds also relies on a unique morphological development – the feather. a. Considered by some to be adapted from reptile scales. b. Feathers also serve another function useful to an endotherm; they serve as insulators. 2. Feathers -Each feather is comprised of a shaft with lateral branches called barbs. a. Projecting off of the barbs are barbules, which have microscopic hooks. These hooked barbules cross-link, forming a light, but sturdy surface between the barbs. b. Feathers are like scales. If lost, they can be replaced. c. Feathers are considered unique. No other animal on earth, besides birds, has them. 3. Skeletal structure – the bones of birds are thin and hollow. a. Many bones are fused together to make the skeleton even more rigid so larger, stronger muscles may be attached. E.g. breast bone. b. The flight muscles also connect to the fused collarbone, called the “wishbone”. No other living vertebrates have a fused collarbone or a keeled breastbone. IV. Look! It’s a bird, no it’s a reptile, no it’s…..we’re not sure yet. A. Origin of birds. 1. The origin of birds is actually greatly debated. Part of the problem is the preservation of fossilized remains. 2. Archaeopteryx – a fossilized bird is discovered. The skeletal features of this fossil have many similarities to that of a theropod dinosaur (such as velocoraptors). a. Archaeopteryx is about the size of a crow. b. Its skull has teeth, and very few of its bones are fused. c. Its bones are solid, not hollow like a birds. d. It also had a long reptilian tail. e. It had no large breast bone for the attachment of strong flight muscles. f. Finally, it had the forelimbs of a dinosaur. g. These are dinosaurian features – not those of a bird. h. Originally classified as another small dinosaur of similar size – a coelurosaur called Compsognathus -until feathers were discovered on the fossils. 3. What makes Archaeopteryx distinctly avian is that it has feathers on its wings and tail. a. It also has some other bird like features, most notably a wishbone. Dinosaurs did not have wishbones. However, the predecessors of dinosaurs, the thecodonts, did have wishbones. Docsity.com