An analysis of well-preserved dinosaur cells gives us the first clues about how dinosaurs shed their skin. It also shows that 125 million years ago, these fearsome creatures also had dandruff.
Dandruff affects about half of all humans, with the underlying mechanism involving the overgrowth of skin cells -- as the skin continues to grow, and skin cells are pushed outward where they flake off. This happens for everyone, but for most individuals, these flakes of skin are simply too small to be visible. However, under certain conditions, the cell turnover may be unusually rapid, especially in the scalp. This results in what we commonly called dandruff.
Just like with humans, dinosaur dandruff is made of tough cells called corneocytes that, in life, are dry and full of the protein keratin. Researchers were able to assess this:
"The fossil cells are preserved with incredible detail – right down to the level of nanoscale keratin fibrils. What's remarkable is that the fossil dandruff is almost identical to that in modern birds – even the spiral twisting of individual fibres is still visible," said Dr. Maria McNamara, from the University College Cork (UCC), who along with her colleagues, made the discovery.
They found the dandruff amongst preserved 125 million-year-old plumage of feathered dinosaurs and early birds. This is remarkable for several reasons. First of all, it's the first indication of how dinosaurs shed their skin. Secondly, it shows that this modern skin feature evolved at least in the Middle Jurassic, if not earlier.
There was a burst of evolution of feathered dinosaurs and birds at this time, and it's exciting to see evidence that the skin of early birds and dinosaurs was evolving rapidly in response to bearing feathers," McNamara added.
Lastly, this new study adds to the already large body of evidence that these ancient feathered creatures were very different in one key aspect -- flying. The researchers say that modern birds have very fatty dandruff cells because this helps them shed heat when they are flying. The older creatures weren't able to fly at all or were only able to get off the ground for short periods. Feathers are remarkable evolutionary innovations that are associated with complex adaptations of the skin in modern birds, researchers write. However, many dinosaurs also had feathers or proto-feathers, though there were some differences.
"In these fossil birds, their cells are packed full of keratin and there's no evidence they had any fats in these cells at all," said McNamara. "So that suggests they had lower body temperatures than modern birds, almost like a transitional metabolism between a cold blooded reptile and a warm blooded bird."
Ancient feathered dinosaurs and birds probably didn't likely need the advanced cooling system, probably because they couldn't fly, or flew for very limited periods.
Journal Reference: McNamara et al. "Fossilized skin reveals coevolution with feathers and metabolism in feathered dinosaurs and early birds". Nature Communications, doi:10.1038/s41467-018-04443-x