By Will Dunham
(Reuters) – A new fossil of the Cretaceous dinosaur Psittacosaurus, a dog-sized herbivore with a parrot-like beak, that was donated to a Chinese university brought a surprise – revealed only after scientists observed it under ultraviolet light .
It retained large patches of beautifully preserved skin, down to its cellular structure, providing new insight into the evolution of skin in feathered dinosaurs. The fossil points to “zoned development” in the skin of these dinosaurs, the researchers said, with Psittacosaurus and probably other feathered dinosaurs having scaly, reptile-like skin on the featherless body regions, with soft, skin-like skin. of a bird, in the areas with feathers.
“Initially we didn’t have much hope of finding soft tissue because, to the naked eye, our specimen appears to preserve only the bones. But we didn’t give up, because we knew that during fossilization soft tissue can be replaced by minerals, which can mix with the sediments” , said Zixiao Yang, a postdoctoral researcher in paleontology at University College Cork in Ireland and lead author of the study published Tuesday in the journal Nature Communications.
“When I turned on the ultraviolet light, I felt my heart almost stop beating. Large patches of scaly skin, covering the chest and belly, glowed a stunning golden yellow color under the ultraviolet light. The fossil skin looked really exquisite, covered in tiny rounded scales about a millimeter wide,” Yang said.
Fossils of any soft tissue are rare. Skin fossils of this quality are even rarer.
Unearthed in northeastern China, the nearly complete fossil, dated to about 130 million years ago, is of a juvenile Psittacosaurus (pronounced SIT-ak-oh-sawr-us), about 66 cm long and approximately 3 years when he died. It was donated in 2021 to Nanjing University from a private collection.
Psittacosaurus is an early member of the lineage of horned dinosaurs called ceratopsians, which later produced large animals like Triceratops. Psittacosaurus itself had no horns. Its name means “parrot lizard” due to its protruding beak, adapted for eating plants.
Many dinosaurs had feathers. In fact, birds evolved from small feathered dinosaurs. The first rudimentary feathers are believed to have evolved from reptilian scales nearly 250 million years ago in animals ancestral to dinosaurs and flying reptiles called pterosaurs.
Psittacosaurus had simple, bristle-like feathers on top of its tail. The rest of the body was covered in scaly skin. The fossil was missing skin from the dinosaur’s feathered regions, but researchers think these areas had bird-like skin.
“This discovery adds nuance to our understanding of the evolution of feathers. The acquisition of modern, bird-like skin occurred only locally on the body. Tough, reptile-like skin remained essential in regions of the body not protected by feathers ” said University College Cork paleontology. professor and study co-author Maria McNamara.
Bird skin has multiple adaptations to feathers.
Birds have a dermal network of microscopic muscles that surrounds each feather and acts as a hydraulic system, including muscles that pull the feathers in different directions. There is also a network of smooth muscles under the skin that keeps the feathers separated, as well as deposits of fatty tissue anchored at the base of the skin that create an even skin surface and feather orientation. Furthermore, the feathers are connected by a system of sensory nerve fibers.
“Until now, we didn’t know whether the skin of dinosaurs and their relatives developed these skin adaptations first and feathers later, or whether they evolved at the same time, and on which parts of the body,” McNamara said.
The Psittacosaurus fossil “strongly suggests that the evolution of feathers — and the new skin adaptations — happened at the same time,” McNamara said.
The dinosaur’s scaly skin closely resembled the skin of modern-day reptiles.
“They are similar in many ways, including the shape, size, arrangement and composition of skin cells, and the way the skin produces color patterns,” Yang said.
(Reporting by Will Dunham in Washington; Editing by Daniel Wallis)
