Word: archaeopteryx
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Dates: during 1990-1999
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...fossil of a pigeon-size creature. Its bone structure and teeth were similar to those of dinosaurs. Yet along with the bones, the 150 million-year-old limestone in which it was trapped had also preserved the unmistakable impressions of feathers and wings. It was ultimately decided that Archaeopteryx, as it was named, was a transitional animal, related to dinosaurs but well along the evolutionary pathway to modern birds...
...happens so often in paleontology, though, the story has become much more muddled. The confusion began in 1964 with the discovery of a 13-ft.-long theropod called Deinonychus that was remarkably similar to Archaeopteryx, perhaps 50 million years more recent, but lacked wings and feathers. Apparently, the evolution from theropod to bird took many turns and detours...
Mononychus may be the discovery of a lifetime. The turkey-size predator, ! with its mouthful of sharp teeth and long tail, looked quite similar to the theropods. Even so, says paleontologist Mark Norell, it shares a number of features with modern birds. "In Archaeopteryx, for example," he explains, "the fibula ((the thin bone in the leg)) touches the ankle. In birds that doesn't happen, and the same is true of Mononychus. Birds have a keeled sternum ((or breastbone)), where the flight muscles attach. Mononychus also had a keeled sternum." Some of Mononychus' wristbones were fused together, which is another...