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PHYS 0106 (Spring, 2001) Earth History Timeline |
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| Phanerozoic Eon: Mesozoic Era: Jurassic Period | |||
Timeline Links Phanerozoic Neoproterozoic Mesoproterozoic Paleoproterozoic Archean Other Links Historical Geology Page Physical Geology Page Mike's Home Page |
Writer/Researcher: Kristine Langlois Editor: Nancy Sacchetti Web Page Builder: Kristine Langlois The origin of birds has eluded scientists for years. Scientists have debated whose decendents they were. Did they evolve from dinosaurs or, from the reptilian ancestiors of dinsaurs, the Archosaurs? Or did they evolve convergently? Birds and reptiles have some common chatacteristics. Modern birds have scales on their feet and lay eggs. Reptiles are covered by scales and lay eggs also. Fossils of early birds show to have a furcula. The fused furcula (wishbone) was a key that opened the door. Given that a T. rex does not have a furcula, where could early birds have inherited it? It is the therory that birds and dinosaurs descended from Archisaurs. Though modern birds and early birds have similar bone structure, there are differences. Most scientists feel that the early birds could not fly. Their joints did not allow for a lot of movement for flight like modern birds. Scientists feel that early birds glided close to the ground instead of flying. In the 70's, Robert Bakker had arguments that supported endothermy. This showed there were similarities between dinsaurs and modern warm-blooded mammals. There has been a juvenile theroppod fossil found that supports the theory that birds evolved frome dinsaurs. In China's Liaoning Province this fossil which was, 150 million years ago, covered in feathers. The feathers scientists believe were for warmth not for flight. Larger dinosaurs like the T. rex grew rapidly they were believed to be warm-blooded. Scientists now speculate that when dinosaurs hatched they were covered with feathers.
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Though this is speculative many fossils that are bird-like have been found throughout the years. Modern Birds have similar bone structure. Archaeopteryx, Sinornis, and Rahonavis are what scientist believe to be birds. In 1861 Thomas Huxley, an English scientist, hypothesized that a fossil, which had been foun in a limestone in Germany, could be that of a bird. He named it Archaeopteryx. It appeared reptilian with a long tail and teeth in its jaw, but also showed impressions of feathers. Its features were that of part modern bird and part reptilian. This was considered the first fossil of a "bird" found. Only seven fossils of Archaeopteryx have been founs and all have been found in the limestone quarries. There are other early birds that came after
Archaropteryx. 15 million years after Archaeopteryx lived Sinornis evolved. Sinornis, a sparrow like-bird found in China, had features that are closely related to a modern bird. There were no teeth on the beak, and its body and tailbone were shorter than that of Archaeopteryx. Cathy Forster, a paleontologist, uncovered a fossil in Madagascar that had a unique feature. It had a sickel claw on one foot. This fossil had chracteristics of both Archaeopteryx and reptilian theropods. It had bumps on the wings, which she speculated as evidence that the animal was once covered with feathers. She named it Rahonavis. All of the early birds left traces behind that give us a peek into the past. These fossils can be used as a guide for the path of evolution of modern birds.