Science | September 20, 2024

Dinosaurs Evolved Feathers for Far More Than Flight

Fluff and fuzz helped the creatures keep warm, blend in and communicate

Dinosaurs of all shapes and sizes sported feathers. Illustration by Emily Lankiewicz / Full Credit at Bottom of Article

Science Correspondent

The more paleontologists dig, the more feathered dinosaurs they find. Almost three decades have passed since the scientific debut of the first non-avian dinosaur with feathers, Sinosauropteryx, and in that time experts have discovered dozens more. Bird-like raptors, tyrannosaurs, and even horned dinosaurs have been found with feathers and feather-like body coverings, revealing that fluff and fuzz were widespread among dinosaurs.

Most famously, feathers allowed early birds and related dinosaurs like Microraptor to take to the air. But paleontologists have also found feathers and related structures on many other dinosaurs that never would have flapped into the air, like the 30-foot-long Yutyrannus. Among these flightless dinosaurs, plumage had a variety of other functions—from keeping warm to camouflage. Here’s a list of select feathery dinosaurs and what their feathers can tell us about their lives.

Sinosauropteryx

First described in 1996, Sinosauropteryx was a revelation to paleontologists. Experts had long expected that birds shared a close relationship with theropod dinosaurs based on their hollow bones and other anatomical similarities. The earliest bird, Archaeopteryx, had a striking resemblance to dinosaurs like the “terrible claw” Deinonychus. What experts lacked, but hoped for, was a non-bird theropod with preserved feathers to cinch the connection. Sinosauropteryx fulfilled what paleontologists had been looking for—fossilized feathers along the neck, back and tail of the dinosaur left no doubt that birds had evolved from feathery dinosaur ancestors.

But Sinosauropteryx was not a bird. The 124-million-year-old dinosaur belonged to a group of small carnivores called compsognathids, and its feathers were more of a wispy fuzz. When paleontologists researched what color the feathers might be, they found that Sinosauropteryx was rust red with a red and white-striped tail, not unlike today’s red pandas. The overall color pattern would have helped the dinosaur blend into the undergrowth, paleontologists hypothesize, while the banded tail could have been a striking visual signal. Just as cats lash, twitch or shake their tails to communicate with each other, Sinosauropteryx may have done the same. The red and white bands likely drew the attention of other Sinosauropteryx, whether to warn them off, attract them closer or express other dinosaurian intentions.

Psittacosaurus

Paleontologists expected to find feathers and their forerunners around the skeletons of bird-like dinosaurs. What they did not anticipate is that feathery body coverings would be found among dinosaurs with no close relationship to birds at all. In 2002, experts announced that long, bristle-like structures had been found along the tail of an exceptional fossil of the small horned dinosaur Psittacosaurus.

The dinosaur’s bristles are similar in structure to other protofeathers, and they only covered a portion of the dinosaur’s tail. How the bristles related to the dinosaur’s behavior is still a puzzle, but the fact that they are only present on part of the dinosaur’s body and are extravagantly long suggest that they evolved to help Psittacosaurus identify and communicate with each other.

Struthiomimus

From the time Struthiomimus was first described in 1917, paleontologists have been struck by the dinosaur’s similarities to flightless birds like emus. At a glance, the dinosaur looks like an ostrich with a long tail and clawed hands. But it wasn’t until 2012 that paleontologists announced that they’d finally found the dinosaur’s feathers.

Experts had previously missed the feather fossils because plumage was thought to have been too delicate to be preserved in the same sandstone wrapped around the dinosaur’s bones. After the discovery of Sinosauropteryx, however, paleontologists started looking for evidence of fossil feathers that previously might have been overlooked or even destroyed as fossils were freed from their encasing rock. In this case, paleontologists spotted fossil feathers among the remains of three Ornithomimus skeletons, omnivorous theropods that lived about 75 million years ago, two of which were collected in the 21st century and another that had been excavated in 1995 but was not recognized as being feathery until experts had another look.

Oddly enough, paleontologists found that the feathers on the arms of Struthiomimus looked roughly similar to those ostriches have on their arms in another case of unexpected convergence. Ostriches use their long, elaborate feathers in courtship displays, and Struthiomimus may have used its feathery arms in the same way.

Yutyrannus

One of the largest feathery dinosaurs yet found is Yutyrannus, a large carnivore that lived in prehistoric China about 125 million years ago. Its fossils underscore the possibility that other tyrannosaurs, such as T. rex itself, may have had fuzzy feathers, too.

Yutyrannus was not the first member of the tyrannosaur family to be found with fuzzy feathers. The small carnivore Dilong, also an early tyrannosaur, was found with remnants of fluff. But Yutyrannus was about five times as long as Dilong and still covered with wispy feathers from head to tail. Such extensive plumage would have acted as insulation, perhaps indicating that Yutyrannus lived in a colder environment, or one more affected by colder winters, than tyrannosaurs from warmer times and places.

Caihong

Caihong was such a colorful dinosaur that its name is a Chinese word for “rainbow.”

At 161 million years old, Caihong is one of the oldest feathered dinosaurs yet uncovered. The living animal would have been about the size of a crow, covered in long feathers from the back of its head to the tip of its tail and toes. When paleontologists assessed the dinosaur’s feathers, they found that the plumage was iridescent and would have appeared as a rainbow sheen seen in some modern avians like hummingbirds.

Caihong was a predatory dinosaur, likely feeding on lizards, insects, small mammals and other Jurassic morsels that lived in the same forests. And even though Caihong was not a bird, it was probably able to get into the air. Some of the feathers on the dinosaur’s arms are asymmetrical, with a shorter front edge than the back edge. Such feathers are specialized for flapping and movement in the air, hinting that Caihong was aerodynamically adept. Altogether, Caihong indicates that the close relatives of the first birds had already evolved elaborate feathers and gorgeous colors by the middle of the Jurassic.

Microraptor

For most of paleontology’s history, experts thought that birds were the only flying dinosaurs. Microraptor is among the fossils that have changed the story. After it was named in 2000, a stunning fossil of the feathery dinosaur described in 2003 revealed that Microraptor had long, specialized feathers growing from its hind legs as well as its arms. The reptile quickly became known as the “four-winged dinosaur,” and experts wondered what the arrangement might mean for the evolution of flight.

Microraptor lived about 125 million years ago, long after the origin of the earliest birds in the Jurassic. Nevertheless, the dinosaur’s anatomy is marked by a suite of aerodynamic traits. Exactly how Microraptor flew isn’t entirely clear, but the non-avian dinosaur represents a different pathway for getting into the air and indicates that more than one feathery dinosaur lineage evolved to become airborne.

Juravenator

Many feathery dinosaur fossils found so far are from small animals, and Juravenator is among the tiniest of all. The carnivorous Jurassic dinosaur would have been able to easily stand in the palm of your hand, a nipper that had fuzzy feathers as well as scales.

Paleontologists aren’t exactly sure what group of dinosaurs Juravenator belongs to. Some experts think it’s related to other fuzzy dinosaurs like Sinosauropteryx, while others think it is a hatchling from a larger species related to Megalosaurus, large and carnivorous dinosaurs that were the apex predators in their ancient habitats. Either way, the preserved soft tissues of the 151-million-year-old dinosaur show both scales and feathers. The combination hints that fuzzy feathers started as partial body coverings, retained in some feathery dinosaurs and expanded over the body in others.

Caudipteryx

Some non-avian dinosaurs were so bird-like that it can get a little confusing where to draw the line. The parrot-like dinosaur Caudipteryx is one of these cases, not a bird but a different form of dinosaur that evolved to bear some of the same traits. The dinosaur was undoubtedly unable to fly, and so its feathery coat must have been essential to the dinosaur’s life on the ground.

Like many other fuzzy dinosaurs, the 124-million-year-old Caudipteryx had feathers along its arms and body. What makes the dinosaur stand out, however, is that it had a fan of long feathers at the tip of its tail. Studies of the dinosaur’s skeleton indicate that the reptile’s short tail was very flexible, perhaps allowing Caudipteryx to shake its tail feathers to impress or warn off other members of its species.

Concavenator

One of the most confounding cases in the history of feathered dinosaurs is the large carnivore Concavenator. The dinosaur lived about 125 million years ago, around the same time as Sinosauropteryx and Yutyrannus, and stalked what’s now Spain. No feathers were found with the skeleton itself, but anatomical clues on the dinosaur’s arms indicate that the reptile had at least a partial coating of feathers.

One of the lower arm bones of Concavenator, the ulna, shows a line of little raised bumps. In birds, as well as other dinosaurs like Velociraptor, the bumps have been classified as quill knobs where ligaments help anchor feathers. Not all experts agree with this interpretation. Some have questioned whether the bumps might be from tendon attachments or some other tissue. To date, though, the feather interpretation has not been ruled out. Concavenator may have had long feathers along its arms, at the very least. More than that, Concavenator was more closely related to dinosaurs like Allosaurus than fuzzy theropod species, so the dinosaur’s feathers would indicate that the features were more ancient and widespread among predatory dinosaurs than previously thought.

Tianyulong

If the herbivorous dinosaur Tianyulong is any indication, paleontologists have many more feathery dinosaurs left to find. At 158 million years old, the fluffy Tianyulong is older than the oldest bird, Archaeopteryx, which lived roughly 150 million years ago. But like Psittacosaurus, the two-foot-long dinosaur wasn’t closely related to birds at all. Tianyulong was on the entirely opposite side of the dinosaur family tree, hinting that feathers were either a common feature going back to the earliest dinosaurs or had evolved multiple times independently.

So far as paleontologists have found so far, Tianyulong had a mane of simple feathers along the dinosaur’s back. The feathers could have helped the dinosaur thermoregulate, insulating it from the sun’s ultraviolet light. Paleontologists have yet to assess the color of these feathers, but it’s likely that their shades were influenced by the need to both hide from predators and communicate with other Tianyulong.

And possibly more …

When paleontologists first started to uncover feathered dinosaurs, it made sense that the first finds belonged to the broad group that birds belong to—the coelurosaurs. In the three decades since the announcement of Sinosauropteryx, however, experts have found feathers on dinosaurs no one would have expected to wear plumage. Whether fuzz was an early, common dinosaur trait or appeared multiple times, certainly many more feathered dinosaur species are left to be uncovered. Even familiar species might be altered with the discovery of fossil feathers, as Struthiomimus was. With every season that paleontologists return to the world’s Mesozoic rocks, the menagerie of feathery dinosaurs is only set to grow.

Main Image Caption: Illustration by Emily Lankiewicz / Public Domain / Nobu Tamura via Wikipedia under CC By-SA 3.0 / Lucas Attwell via Wikipedia under CC By-SA 4.0 / Fred Wierum via Wikipedia under CC By-SA 4.0 / UnexpectedDinoLesson via Wikipedia under CC By-SA 4.0

Riley Black | | READ MORE

Riley Black is the author of The Last Days of the Dinosaurs and many other books. She is a science correspondent for Smithsonian magazine covering fossils and natural history, and she writes about the prehistoric past for a variety of publications.