A fossilized impression of the skin of a Corythosaurus dinosaur, a hadrosaurid.
As paleontologists increasingly unearth evidence of feathers in prehistoric fossils, our conceptions of what dinosaurs looked like when they roamed the earth has gradually evolved.
Instead of the reptilian appearance we all recognize from childhood toys and films like Jurassic Park, many dinosaurs in fact more closely resembled birds, kind of like this recently discovered little guy, Eosinopteryx brevipenna, a flightless theropod dinosaur that roamed China during the Middle/Late Jurassic period.
Archaeopteryx, also known as Urvogel, the German word for "original bird" or "first bird," was first discovered in 1860 and later fossils of this species presented some of the earliest evidence of flight in these prehistoric animals.
An intermediate creature that was not quite dinosaur but not exactly a bird either when it lived 150 million years ago, Archaeopteryx had teeth, a long tail, and wings capable of flight with claws at the end for grabbing prey.
A century after the discovery of Archaeopteryx, paleobiologists increasingly found anatomical connections between birds and dinosaurs. In the 1970s, artists began to portray dinosaurs with feathers based on accumulating evidence.
Megapnosaurus, shown here, was another species with whom researchers began early to identify with feathers. A lightweight animal that could reach up to 10 feet in length and roamed Jurassic Zimbabwe, Megapnosaurus, also known as Syntarsus, traveled in packs and preyed on small reptiles and fish.
Many of the fossils unearthed that provided evidence of feathers had deteriotated over the eons they remained buried. It wasn't until 2010 that researchers identified color pigments in feathers from dinosaurs and early birds.
Sinosauropteryx, illustrated here, was a theropod dinosaur that had "simple bristles -- precursors of feathers -- in alternate orange and white rings down its tail," according to a description of the study's findings.
Given that so many feathered dinosaurs were in fact flightless, the purpose of the feathers has been a subject of debate. Some dinosaurs may have evolved feathers for social signaling; others had plumage to provide insulation.
In the cases of some dinosaurs, such as the two oviraptors, herbivores related to T. rex that lived during the Cretaceous period, researchers believe the feathers were used for mating displays, similar to modern-day peacocks and turkeys.
Jason Brougham/University of Texas
You might be fooled into thinking the animals in this illustration are something between a murder of crows and a band of blue jays. In fact they are Microraptors that lives more than 130 million years ago.
These four-winged, plumed dinosaurs were no larger than modern-day pigeons and sported iridescent tail feathers.
Researchers believe the shimmering plumage was likely used in mating and other social interactions.
Like the diversity among birds today, not all feathered dinosaurs were lightweight, agile animals. A massive tyrannosaur that lived in China until about 65 million years ago, Yutyrannus huali, meaning "beautiful feathered tyrant," grew up to 30 feet long and could weigh more than 3,000 pounds.
This titanic tyrannosaur, as it was described, significantly increases the size range for feathered dinosaurs.
In a stunning find published in the journal Science in 2011, paleontologists uncovered dinosaur feather preserved in amber that dated back some 79 million years ago.
This discovery provided scientists a new window into the evolution of feathers in terms of structure in the evolutionary timeline from dinosaurs to birds. Even shades of color remained well preserved in the amber.
Some days, it must not have been easy to be a hadrosaur. You're a dinosaur, sure, but it's hard to feel like a badass when your head resembles a duck. On the plus side, these herbivores outlasted more fashionable dinos such as the T-Rex in one respect: They had longer-lasting skin.
Indeed a preponderance of dinosaur skin samples (not actual skin, of course, but fossilized impressions) belong to hadrosaurs. Matt Davis, a fifth-year graduate student in paleontology at Yale University, has suggested a new reason why that might be the case. He proposes in a paper that hadrosaur skin endured because it must have been tougher texturally -- built to last long enough to write itself into the fossil record.
First, some backstory. Typical explanations for all of the hadrosaur skin left behind center around population and habitat. Hadrosaurs were all over the place in dinosaur times, and therefore, the idea goes, they simply left behind more skin for 21st-century paleontologists to ponder. Furthermore, hadrosaurs usually lived along rivers, where they could die in flash floods, their skin preserved in soil sediment unreachable by scavengers.
“If you are a hadrosaur versus another dinosaur, you’re 31 times more likely to preserve skin,” said Davis in a press release. He would know: To firm up the notion of hadrosaur skin prevalence, Davis reviewed published reports about dinosaur skin all the way back to 1841, to get a fix on how often skin samples were those of hadrosaurs as opposed to other dinosaurs.
Across 180 reports, Davis found that 46 percent of body fossils that had skin (not just trace fossil skin from something like footprints) belonged to hadrosaurs.
Next Davis looked at data from 343 dinosaurs found in the Hell Creek Formation in the Dakotas and Montana and at similar dino-rich formations in the United States and Canada. There, the hadrosaur skin fossil prevalence was overwhelming. Of the 22 Hell Creek dinosaurs that were kind enough to deposit traces of skin for future study, 20 came from hadrosaurs -- a whopping 91 percent.
“We’ve always assumed hadrosaur fossils preserved more skin," said Davis. "Now we’ve got the data to prove just how much more.”
As for the population density and habitat arguments for why hadrosaur skin was so abundant, Davis counters that dinosaurs such as ceratopsians were even more common than hadrosaurs, yet far less skin from those creatures has been found, and hadrosaur skin has been discovered in environments other than just river valleys that could preserve skin fossils.
Davis said more more research needs to be done now, to figure out just how hadrosaur skin was tougher and thicker -- which exact characteristics made it so.
Why all the fuss about skin in the first place? While most dinosaur evidence comes in the form of fossilized bones, skin excels as a means for distinguishing among species and can help scientists work out the location and size of muscles as well as tell them more about how dinosaurs moved, where they lived, and how they looked.
Davis's research appears in the September 10 issue of the journal Acta Paleontologica Polonica.