Rare fossil tells about early evolution of Dinosaur

A rare primitive theropod, or a bipedal, primarily carnivorous dinosaur, is bringing clarity to the early evolution of the group that includes more recent relatives like T. rex and birds. Tawa hallae, uncovered in New Mexican sediments from the Upper Triassic, has evidence of an air sack system surrounding the neck and braincase found in birds today, making this characteristic a much more primitive trait than previously thought. But even more enlightening is that a comparison of T. hallae with other early theropods finds that there is a curious mix of early North and South American forms at the …