Dinosaur skin fossil ‘Hidden gem’ reveals surprises about feather evolution: ScienceAlert

Strong yet light, beautiful and precisely structured, feathers are the most complex skin appendage ever to evolve in vertebrates.

Despite the fact that people have been playing with feathers since prehistoric times, there is still a lot we don’t understand about them.

Our new study found that some of the first feathered animals also had scaly skin like reptiles.

After the debut of the first feathered dinosaur, Sinosauropteryx primain 1996, a wave of discoveries painted an increasingly interesting picture of feather evolution.

We now know that many dinosaurs and their flying cousins, the pterosaurs, had feathers. In the past, feathers took more forms – for example, banded feathers with flared tips were found in dinosaurs and extinct birds, but not in modern birds. Only some ancient types of feathers have been inherited by birds today.

Paleobiologists have also learned that early feathers were not made for flying. Early feather fossils had simple structures and a sparse body distribution, so they may have been for display or tactile sensation.

Pterosaur fossils suggest that they may have played a role in thermoregulation and color patterning.

As fascinating as these fossils are, the ancient plumage tells only part of the story
evolution of feathers. The remaining action occurred in the skin.

Bird skin today is soft and evolved to maintain, control, grow and pigment feathers, unlike the scaly skin of reptiles.

Dinosaur skin fossils are more common than you think. To date, however, only a few dinosaur skin fossils have been examined at the microscopic level.

These studies, such as a 2018 study of four fossils with preserved skin, showed that the skin of early birds and their close dinosaur relatives (coelurosaurs) was already very similar to the skin of today’s birds. Bird-like skin evolved before the appearance of bird-like dinosaurs.

So to understand how bird skin evolved, we need to study the dinosaurs that branched off earlier in the evolutionary tree.

Our study shows that at least some feathered dinosaurs still had scaly skin, like reptiles do today. This evidence comes from a new specimen of Psittacosaurusa horned dinosaur with bristle-like tail feathers.

Psittacosaurus lived in the early Cretaceous period (about 130 million years ago), but its clan, the ornithischian dinosaurs, separated from other dinosaurs much earlier, in the Triassic period (about 240 million years ago).

In the new specimen, the soft tissues are hidden from the naked eye. Under ultraviolet light, however, the scaly skin reveals an orange-yellow glow. Skin is preserved on the torso and limbs, which are parts of the body that did not have feathers.

These glowing colors are from the silicon minerals that are responsible for preserving fossil skin. During fossilization, silica-rich fluids seep into the skin before it disintegrates, reproducing the skin’s structure in incredible detail. Fine anatomical features are preserved, including the epidermis, skin cells, and skin pigments called melanosomes.

Fossil skin cells have much in common with modern reptilian skin cells. They
share similar cell size and shape and both have fused cell borders – a
a feature known only in modern reptiles.

The distribution of fossil skin pigment is identical to that in modern crocodilian scales. However, the fossil’s skin appears relatively thin by reptilian standards. This suggests the presence of fossils Psittacosaurus were also similar in composition to reptilian scales.

Layers of fossilized skin cells. (Zixiao Yang/credited author)

Reptile scales are hard and tough because they are rich in a type of skin-building protein, healthy horn beta proteins. In contrast, the soft skin of birds is made of a different type of protein, the keratins, which are the key structural material in our hair, claws, nails, hooves and outer skin.

To provide physical protection, the thin, bare skin of Psittacosaurus it must have been composed of robust reptilian-style horn beta proteins. Softer skin like a bird would be too fragile without feathers for protection.

Taken together, the new fossil evidence suggests that Psittacosaurus it had reptilian skin in the areas where there were no feathers. The tail, which retains feathers in some specimens, unfortunately did not preserve any feathers or skin in our specimen.

However, the tail feathers of other specimens indicate that some bird-like skin features must have already evolved to hold the feathers in place. So our finding suggests that early feathered animals had a mixture of skin types, with bird-like skin only on the feathered areas of the body, and the rest of the skin still scaly, as in modern reptiles.

This zoned development would ensure that the skin protects the animal from abrasion, dehydration and pathogens.

What next?

The next gap in knowledge that scientists need to explore is the evolutionary transition from reptile skin Psittacosaurus to the skin of other more heavily feathered dinosaurs and early birds.

We also need more experiments studying the fossilization process itself. There’s a lot we don’t understand about how soft tissue fossilizes, which means it’s hard to tell which skin features in a fossil are true biological features and which are just fossil artefacts.

For the past 30 years, fossils have surprised scientists regarding the evolution of feathers. Future discoveries of fossil feathers may help us understand how dinosaurs and their relatives developed flight, warm-blooded metabolism, and how they communicated with each other.The conversation

Zixiao Yang, Postdoctoral Researcher, University College Cork and Maria McNamara, Professor, Palaeobiology, University College Cork

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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