The evolution of feathers is associated with novel skin ultrastructures, but the fossil record of these changes is poor and thus the critical transition from scaled to feathered skin is poorly understood. New research led by University College Cork paleontologists sheds light on this issue using preserved skin in Psittacosaurus, a non-avian feathered dinosaur from the Early Cretaceous epoch (135-120 million years ago) — a time when dinosaurs were evolving into birds. The fossil evidence supports partitioning of skin development in Psittacosaurus: a reptile-type condition in non-feathered regions and an avian-like condition in feathered regions.
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The studied Psittacosaurus specimen under natural (upper half) and UV light (lower half) showing the orange-yellow fluorescence of the fossilized skin. Image credit: Zixiao Yang.
Feathers are associated with complex skin adaptations to facilitate feather growth, flight, and heat regulation, making feathered skin distinct from scaly, reptilian skin.
However, the details of the transition between these two skin types in early, feathered animals are unclear.
University College Cork paleontologist Zixiao Yang and colleagues investigated skin evolution using samples from a fossilized Psittacosaurus from the Early Cretaceous Jehol Biota of China, a feathered dinosaur that lived about 130 million years ago and preserves feathers only on the tail.
The researchers were then able to explore the structure of the skin cells using ultraviolet (UV) fluorescence and electron microscopy.
“The fossil truly is a hidden gem,” Dr. Yang said.
“The fossil skin is not visible to the naked eye, and it remained hidden when the specimen was donated to Nanjing University in 2021.”
“Only under UV light is the skin visible, in a striking orange-yellow glow.”
“What is really surprising is the chemistry of the fossil skin. It is composed of silica — the same as glass.”
“This type of preservation has never been found in vertebrate fossils. There are potentially many more fossils with hidden soft tissues awaiting discovery.”
The most exciting aspect of the discovery, however, is what it tells us about the evolution of feathers in dinosaurs.
“The evolution of feathers from reptilian scales is one of the most profound yet poorly understood events in vertebrate evolution,” Professor McNamara said.
“While numerous fossils of feathers have been studied, fossil skin is much more rare.”
“Our discovery suggests that soft, bird-like skin initially developed only in feathered regions of the body, while the rest of the skin was still scaly, like in modern reptiles,”
“This zoned development would have maintained essential skin functions, such as protection against abrasion, dehydration and parasites.”
“The first dinosaur to experiment with feathers could therefore survive and pass down the genes for feathers to their offspring.”
The study appears today in the journal Nature Communications.
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Z. Yang et al. 2024. Cellular structure of dinosaur scales reveals retention of reptile-type skin during the evolutionary transition to feathers. Nat Commun 15, 4063; doi: 10.1038/s41467-024-48400-3
