A 145-million-year-old fossil discovered in China has helped scientists discover for the first time the evolution of bird legs.
A report published Wednesday by the University of Manchester has reinforced evidence of how birds evolved gradually from early dinosaurs.
Researchers from Manchester, the Royal Veterinary College and China's Nanjing University, carried out a study of the lower leg of a Confuciusornis bird, which was fossilized in volcanic ash and lake sediments in China 125-145 million years ago.
They found that living birds have a more crouched leg posture than their ancestors, who are generally thought to have moved with straighter limbs similar to those of humans.
Professor John R. Hutchinson from the Royal Veterinary College, who led the study, said: "The new information we 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 gradually from early dinosaurs to birds, with even these early birds having limbs that were built and worked differently from those of living birds, but were approaching the modern condition."
Professor Jiang Baoyu, a co-author of the study from Nanjing University, said: "It was found that the fossil had amazingly well-preserved soft tissues around the ankle joint, including cartilage and ligaments.
"These soft tissues were not just preserved as an ashen replacement of the former tissue, as sometimes happens -- rather, the structure of the tissues was preserved at a microscopic level."
Professor Roy Wogelius from the University of Manchester, one of the collaborators on the project, said: "The preservation in this fossil was exceptional, and allowed us to resolve subtle but important chemical and structural details within this critical early species of bird."
Imaging methods showed that the detailed anatomical preservation extended to the molecular level, with some of the original chemistry of the bird's tissues remaining.
The research 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.
The findings are in line with an expanding body of evidence that, under special conditions, some biological molecules, including even amino acids or partial proteins, can survive over millions of years in the fossil record.
The research was funded by the National Science Foundation of China, Leverhulme Trust, and the British Natural Environment Research Council. The study has been published in the journal Nature Communications.
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