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Dinosaurs And Birds

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Dinosaurs and Birds

Nat 305

Christopher Meadows

11-2-00

Are birds really dinosaurs or are they simply related? That is a question that has gained new life in recent years due to the overwhelming facts the are pouring in from newly found fossils and studies from fossils that have been found in the past. Two groups have formed in the study of this question: those who believe birds are a direct result of dinosaurs and those who feel dinosaurs and birds must have had a common ancestor. Determining which view is correct is a matter of opinion based on fact. The main problem involves the use of cladistics or phylogenetic systematics to group organisms according to characteristics they share. When one looks at dinosaur fossils, he or she may feel that certain characteristics are used for something entirely different than someone else who has looked at the same fossil.

One cannot talk about dinosaur and bird lineage without mentioning Archaeopteryx. Most paleontologists agree that Archaeopteryx was the first bird. Archaeopteryx thus represents what paleontologists would call a "transitional form" between two major groups of animals, the reptiles (dinosaurs) and birds. The main difference between the theropods and Archaeopteryx were the long arms of the Archaeopteryx, adapted as wings, the feathers, and the presence of a wishbone that the theropods did not have. All of these features tie it to birds and its other characteristics tie it to theropods. One might say it was the "missing link" between the two. Opponents of this idea say that the similarities between Archaeopteryx and theropods were due to convergence, with the birdlike dinosaurs appearing in the Cretaceous some 75 million years after Archaeopteryx. Also, support is gaining that Archaeopteryx was not in fact the first bird, but instead a descendent of an earlier bird ancestor that had developed along a different pathway and actually represents an evolutionary dead end.

Two opponents of the "birds are dinosaurs theory" are Alan Feduccia of the University of North Carolina and Larry Martin of the University of Kansas. They believe that birds evolved from some unknown reptile from a time before dinosaurs came to be. One point they make is that flight must have begun from tree climbing or an arboreal ancestor but that all the proposed dinosaurian ancestors were ground dwellers or cursorial On the other side, supporters for the "birds are dinosaurs theory" feel there

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