Living birds have a more crouched leg posture compared to their dinosaurian ancestors, which generally are thought to have moved with straighter limbs (similar to the postures of humans). This joint study by researchers from the UK and China illuminates how birds shifted toward this more crouched posture. The lower leg of the early Cretaceous (about 125 million years old) bird Confuciusornis that had been fossilized in volcanic ash and lake sediments in China was studied using a variety of techniques which found that this fossil had amazingly well preserved soft tissues around the ankle joint, including cartilages and ligaments. These soft tissues were not just preserved as an ashen replacement of the former tissue, as sometimes happens. Rather, the cellular and fibrous structure of the tissues was preserved at a microscopic level.
\nResearchers from the University of Manchester, with their collaborators from London, Bristol, Nanjing and Beijing used X-ray synchrotron and multiple spectroscopic imaging methods to show that the detailed anatomical preservation extended to the molecular level, with some of the original chemistry of the bird\u2019s tissues remaining. In particular, the team found evidence of fragments of the collagen proteins that made up the leg ligaments, which matched the preservation at the microscopic tissue level of detail. These findings concur with an expanding body of evidence that, under special conditions, some biological molecules including even amino acids or partial proteins, can persist over millions of years in the fossil record. The researchers then reconsidered this evidence in light of the whole anatomy of the Confuciusornis leg, and that of its cousins from earlier dinosaurs to extinct and even modern birds.
\nThe new information gained about the anatomy of the cartilages and tendons show that this early bird had an ankle whose form fit an intermediate function between that of early dinosaurs and modern birds. Overall this reinforced other lines of evidence that the more crouched, zigzag limb posture of birds evolved from early dinosaurs to birds. The research shows that early birds had limbs that were built and worked differently from those of living birds, but were already approaching the modern condition.<\/p>\n