Evolution may occassionally undo itself, according to scientists studying the wrist bones of birds. When two-legged dinosaurs evolved into today's birds 230 million years ago, they shed heavy, weight-baring bones for lighter ones. One of the disappeared bones, the pisiform, reappears in the embryos of chickens, pigeons, and parakeets. The pisiform was thought to be an altogether new bone but it's not. “While the physical expression of a gene may be suppressed, it doesn’t mean the possibility of generating that structure has disappeared,” said Luis Chiappe, director of the Dinosaur Institute at the Natural History Museum of Los Angeles. “The gene is still there, it’s just dormant.” Jurassic Park sequel anyone?