Gone does not necessarily mean forgotten, especially in biology. A recent finding by researchers at the University of Manchester and the University of Wisconsin, Madison have found new evidence that the ability to form previously lost organs — in this case, teeth — can be maintained millions of years after the last known ancestor possessed them. Despite the fact that birds last possessed teeth about 70-80 million years ago, the researchers found that modern birds retain the ability to make teeth. The scientists showed that the talpid2 strain of chicken harbours a genetic change that permits tooth formation in both the upper and lower jaw of embryonic birds. These teeth show similar developmental position as mammalian teeth and are associated with similar molecular instructions. When comparing the initial development of the structures, the researchers realised that the teeth forming in the chicken did not look like mammalian teeth, but resembled those of the alligator, the closest living relative of modern birds. The findings strongly suggest that the birds were initiating developmental programmes similar to those of their reptilian ancestors. In addition, the authors found that the ability to form teeth still resides in normal chickens and can be triggered experimentally by molecular signals. Perhaps it is time to revise the saying: 'as rare as hen's teeth'.