Professor Jiang Baoyu Makes Breakthrough in Studying Evolution of Birds' Ankles

Fossilized Tissue Reveals the Gradual Evolution of Crouched Legs in birds

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). A joint study by researchers from China and the UK, published in the online journal Nature Communications, illuminates how birds shifted toward this more crouched posture. The research team was led by Professor Jiang Baoyu at Nanjing University and Professor John R. Hutchinson at the Royal Veterinary College in UK.

The team studied 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. Professor Jiang said, “We 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.”

Going beyond microscopic analysis, X-ray synchrotron and multiple spectroscopic 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. 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. Their 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. Professor Roy Wogelius from the University of Manchester, one of the collaborators on the project, commented that “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.”

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. This many-layered study was enabled by international collaboration between many scientists from fields as diverse as palaeontology and ornithology, biomechanics, geology and geochemistry, medical imaging and physics. Professor Michael Benton at the University of Bristol added, “Our study exemplifies how a combination of sophisticated technologies with fast-paced discoveries of spectacular fossils is revealing new insights into how major changes in anatomy, physiology and behaviour evolved in animals.”

The research was funded by the National Science Foundation of China, Leverhulme Trust and Natural Environment Research Council (UK).

Baoyu Jiang is a professor in paleontology at the School of Earth Sciences and Engineering, Nanjing University. He acquired his Ph.D. at the Nanjing Institute of Geology and Palaeontology, Academia Sinica in 2003. He did his post-doctoral research at the School of Earth Sciences and Engineering, Nanjing University during 2004 to 2006, and joined the faculty since then and got his professorship there in 2015.  

Professor Jiang’s research interests cover terrestrial Mesozoic stratigraphy, systematics of bivalves, integration of paleontology, stratigraphy and sedimentology in reconstructing past environmental changes. He is currently working on the exceptionally preserved terrestrial fossils from the Middle to early Late Jurassic Yanliao (Daohugou) Biota and the Early Cretaceous Jehol Biota in western Liaoning, NE China. By integrated taphonomic, petrological, sedimentary, and geochemical analyses on the terrestrial fossils and the strata in which they are preserved, his study aims to understand the cause of the mass mortality events and the subsequent process of transport, burial and fossilization of the animal remains.

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