Strong yet light, beautiful and precisely structured, feathers are the most complex skin appendage ever developed 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 has found that some of the first feathered animals also had scaly skin like reptiles.
After the debut of the first feathered dinosaur, Sinosauropteryx receivesIn 1996, a wave of discoveries painted an even more interesting picture of feather evolution.
We now know that many dinosaurs and their flying cousins, the pterosaurs, had feathers. In the past, feathers came in many forms – for example, ribbon-like feathers with expanded tips were found in dinosaurs and extinct birds, but not in modern birds. Today, birds have inherited only some ancient types of feathers.
Paleobiologists have also learned that early feathers were not designed for flight. Fossils of early feathers had a simple structure and sparse distribution on the body, so they may have been for display or tactile sense.
Pterosaur fossils suggest that they may have played a role in thermoregulation and color formation.
As fascinating as these fossils are, ancient feathers only tell part of the story
evolution of feathers. The rest of the action took place in the skin.
The skin of birds today is soft and developed for the support, control, growth and pigmentation of feathers, unlike the scaly skin of reptiles.
Dinosaur skin fossils are more common than you think. However, to date only a few dinosaur skin fossils have been examined at the microscopic level.
These studies, for example a study of four fossils with preserved skin from 2018, showed that the skin of early birds and their close dinosaur relatives (celurosaurs) was already very similar to the skin of today’s birds. Bird-like skin evolved before bird-like dinosaurs appeared.
So, to understand how bird skin evolved, we need to study the dinosaurs that branched earlier in the evolutionary tree.
Our study shows that at least some feathered dinosaurs still had scaly skin, like today’s reptiles. This evidence comes from a new specimen Psittacosaurusa horned dinosaur with bristle feathers on its tail.
Psittacosaurus they lived in the early Cretaceous (about 130 million years ago), but their clan, the ornithischian dinosaurs, separated from the other dinosaurs much earlier, in the Triassic period (about 240 million years ago).
In the new pattern, the soft tissues are hidden to the naked eye. However, under ultraviolet light, the scaly skin is revealed in an orange-yellow glow. The skin is preserved on the trunk and limbs, which are parts of the body that did not have feathers.
These brilliant colors come from the silicon minerals that are responsible for preserving fossil skin. During fossilization, silica-rich fluids permeated the skin before it disintegrated, replicating 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 pigment distribution of the fossil skin is identical to that of modern crocodile scales. However, fossil skin appears relatively thin by reptilian standards. This suggests fossil scales Psittacosaurus they were also similar in composition to reptile scales.
Reptile scales are hard and rigid because they are rich in a type of skin-building protein, tough corneum beta proteins. In contrast, the soft skin of birds is composed of another type of protein, keratin, which is the key structural material in hair, nails, claws, hooves and our outer skin.
To provide physical protection, thin, bare skin Psittacosaurus it must be composed of solid horned beta proteins like reptiles. A softer bird’s skin would be too fragile without feathers for protection.
Together, the new fossil evidence shows that Psittacosaurus had reptile-like skin in areas where it had no feathers. The tail, which in some specimens preserved its feathers, unfortunately did not preserve its feathers or skin in our specimen.
However, the tail feathers on other specimens show that some features of the bird-like skin had already evolved to hold the feathers in place. So our finding suggests that early feathered animals had a mixture of skin types, with bird skin only in the feathered parts of the body, and the rest of the skin still scaly, like modern reptiles.
This zonal 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-style skin Psittacosaurus on the skin of other more heavily feathered dinosaurs and early birds.
We also need more experiments that study the fossilization process itself. There is much we do not understand about how soft tissues fossilize, which means that it is difficult to tell which features of skin in a fossil are actual biological features and which are simply artifacts of fossilization.
Over the past 30 years, the fossil record has surprised scientists about the evolution of feathers. Future discoveries of fossil feathers could help us understand how dinosaurs and their relatives developed flight, warm-blooded metabolism and how they communicated with each other.
Zixiao Yang, Postdoctoral Fellow, University College Cork and Maria McNamara, Professor of Paleobiology, University College Cork
This article is republished from The Conversation under a Creative Commons license. Read the original article.