Ears 31 - Final Paper - Draft 1

Ears 31 - Final Paper - Draft 1 - 1. Introduction 2....

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1. Introduction 2. History of bird-dino debate 3. Flesh out birds…dinosaurs a. Archaeopteryx 4. Bird features 5. Argument for Birds a. Birds are reptiles b. Flight c. Feathers d. Bones / Lungs 6. Argument against birds a. TW 149 – Response to flight b. 7. Choose one and discuss Figures: Chiappe 393, 451 Taking Wing 15, 16, 21, 71, 75, 109, 115, 126, 252 Evolution and Extinction 269, 272, 300, 302, 317, 327 Intro I One of the most intriguing questions of science is the relationship between birds and dinosaurs and more importantly, whether birds evolved from dinosaurs. It appears that all paleontologists agree on the evolutionary relationships between birds and dinosaurs. However, the dispute arises over how they are related. There are many paleontologists who believe that birds are dinosaurs. The birds represent a branch of the dinosaur lineage that survived the Cretaceous crisis and radiated into the forms we know today. However, there are those who would refute this claim and propose instead that birds and dinosaurs had a common ancestor that gave rise to both groups. Birds were never dinosaurs and are merely the closest living group to those extinct reptiles. The evidence for and against these two controversial hypotheses concerns: anatomy, developmental biology and physiology. I will be discussing each of these components at length and relating how they back up the hypothesis posed by paleontologists. Intro II: Beginnings of debate In 1860, shortly after Charles Darwin’s Origin of the Species was published, a German quarry worker spotted an unusual fossil in the limestone of the Solnhofen Formation (late Jurassic Period). This fossil is now referred to as the ‘London specimen’ of Archaeopteryx litographica – a transitional form between two vertebrate groups (reptiles and birds). In most circles the Archaeopteryx is accepted as the oldest known bird and is an important link between birds and other coelosaurs that has helped to illuminate the phylogeny of the group. However, the archaeopteryx is not held as the ancestor of all living birds. 1
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The root of the Birds-Dinosaur argument itself can be traced back to Thomas Henry Huxley, a staunch supporter of Charles Darwin. Huxley saw incredible similarities between birds and the therapod dinosaurs, especially the coelurosaurs . However, Huxley’s theory was not well-accepted when a new theory that birds evolved from a pre- dinosaurian reptile. A. Walker’s ‘crocodylomorph’ and Gerhard Heilmann’s ‘thecodont’ held sway for most of the 19 th and 20 th centuries, or else birds were dismissed as originating from some unknown reptilian ancestor. Heilmann’s thecondont hypothesis was opposite to the dinosaurian origin of birds, and it emphasized on thecondonts, or crocodiles, which are close relatives to dinosaurs (Oliver 3). For Heilmann and other thecondonts it was mainly motivated by the supposed loss of the clavicles in dinosaurs. Today, we can see that no group of thecondonts show specific affinities with birds,
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This note was uploaded on 04/25/2008 for the course ECON 031 taught by Professor Rotating during the Winter '07 term at Dartmouth.

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Ears 31 - Final Paper - Draft 1 - 1. Introduction 2....

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