Cellular structure of dinosaur scales reveals retention of reptile-type skin during the evolutionary transition to feathers
by: Zixiao Yang, Baoyu Jiang, Jiaxin Xu, & Maria E. McNamara
Summarized by: Shirley Wang, an undergraduate student at Binghamton University majoring in computer science and minoring in biology. She is interested in learning more about technology and how it can potentially better our relationship with the environment. In her free time, she likes to hike, play video games, and read.
What data were used? The scientists used a preserved juvenile Psittacosaurus specimen from the Early Cretaceous Jehol Biota (approximately 135–120 million years ago) of Nanjing, China to analyze the composition of the preserved skin and skeletal material; fossils are typically only preserved as hard parts (like bones), so soft tissue like skin is rare. The scientists found that the skin seemed to be preserved naturally with silica. What made this data even more significant was the fact that it was preserved three-dimensionally, meaning the silica also preserved the internal cellular structures as well as the epidermal layers (i.e. outermost layers of skin).
What was the hypothesis being tested? The Psittacosaurus was a dinosaur species from the Early Cretaceous Jehol Biota of China that despite not being a bird, had feathers. We currently have little information concerning the soft tissues of organisms in the past, making the silicified Psittacosaurus fossil which preserved these components a rare discovery. Scientists sought to analyze the well-preserved Psittacosaurus fossil to better understand the evolutionary transition from scales to feathers.
Methods: The scientists used three different analytical methods to collect data: a stereomicroscope with UV light (to easily identify the soft tissue remains from other materials, such as bones and sediment), a Scanning Electron Microscopy (SEM) (to take detailed images of skin samples), and a Micro-attenuated Total Reflection Fourier-Transform Infrared (µATR-FTIR) spectroscopy (to analyze the molecular composition of the skin). In Figure 1, the Psittacosaurus fossil can be seen in both normal and UV light to better examine areas of difference between bones and soft tissues in the specimen.
Results: The soft tissue that the scientists analyzed from the Psittacosaurus fossil had the presence of melanosomes (the cell organelles in charge of color patterns) and corneous beta proteins (proteins that make up the epidermal skin layer in modern birds and reptiles). These features and the morphology of the skin appeared to be closely resembling fossilized archosaurian scales, a common ancestor of today’s crocodilians and avians. Samples from the upper epidermis (outermost layer of skin) of the fossil showed a similar structure to the upper epidermis of modern reptiles. Furthermore, the thickness of the upper epidermis’ structures was compared to those of crocodiles and chickens and was found to be of similar sizes.
Why is this study important? This study is important because it is rare to find fossils of soft tissues as a result of the soft tissue of organisms, such as skin and feathers, decaying too quickly for fossilization to occur. Because of this, the knowledge we currently have about extinct organisms is mainly limited to hard tissues, such as bones and teeth. By studying the Psittacosaurus fossil, we can expand our knowledge of how traits in organisms millions of years ago changed to understand how organisms look now.
Broader Implications beyond this study: By better understanding the data gathered from the Psittacosaurus fossil, we can in turn better visualize what early relatives of reptiles and birds looked like and could potentially reshape how we view the evolution of feathers.
Citation: Yang, Z., Jiang, B., Xu, J. et al. Cellular structure of dinosaur scales reveals retention of reptile-type skin during the evolutionary transition to feathers. Nat Commun 15, 4063 (2024). https://doi.org/10.1038/s41467-024-48400-3