Studies of the 113-million-year-old Scipionyx samniticus fossil’s interior structure and unique metabolism has led some scientists to say that none of the known groups of dinosaurs could have been the ancestors of birds. This is because birds have an entirely different lung structure than the Scipionyx samniticus (a small coelurosaurid theropod), and a much different metabolism. However, this is based on the findings from one fossil, one of very few to have internal parts preserved (parts of the windpipe, intestines, muscles, and liver). These results will have to be carefully integrated with other findings, such as the presence of feathers and common skeletal features, to come to any useful conclusions.