More than a quarter-billion years ago, before dinosaurs were even a gleam in the eye of whatever force created the universe, there were archosaurs, from which dinosaurs, pterosaurs, and crocodilians, among other creatures, descended. They had teeth like crocodiles – and probably a similar attitude – and four-chambered hearts, a revolutionary ankle structure, and, it seems, fluff.
Ever since the discovery of plumed dinosaurs, paleontologists have been arguing over what came first, the ancestor of the chicken or the feather. The conclusion taking shape is astonishing, particularly for those who assumed that what made birds unique and great was their ability to soar through the sky thanks to the innovation of the feather.
Feathers evolved not only 100 million years before birds, but before dinosaurs themselves. That’s the argument made in a new paper by Prof. Mike Benton, a paleontologist at the University of Bristol, and published in the journal Trends in Ecology & Evolution. It was written with Danielle Dhouailly of Grenoble University, Baoyu Jiang of Nanjing University and Maria McNamara of University College Cork.
Their evidence is two-pronged. Prehistoric flying reptiles called pterosaurs had four kinds of feathers that seem akin to the feathers dinosaurs had, indicating that they had a common ancestor and it was plumed. And the second argument is genetics.
The bottom line is that feathers may have originated over 250 million years ago, in the early Triassic period. Nary a dinosaur was treading the planet yet, it seems, though their time was nigh.
Not only were pterosaurs feathered. One that was studied by the team was a ginger, according to inferences based on microscopic examination of the long-dead beast’s feathers, which were found in fossil melanosomes, tiny cell structures that store pigment molecules.
This specimen, obtained by Yuan Zhang, featured melanosome structures typical of orange-reddish brown. There is no evidence as to whether the creature was derided by other pterosaurs for his hue.
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It was the revelation that certain tiny microfossils weren’t bacteria at all, but mineralized melanosomes, that led to papers such as the 2010 article in Nature, “Fossil feathers reveal dinosaurs’ true colors,” in which Benton and others reported on fossil melanosomes in pint-sized theropod dinosaurs who lived over 100 million years ago. Each pigment, such as black, brown, white and ginger, has a typically shaped melanosome.
It bears elaborating that the melanosomes in long-extinct species seem the same as melanosomes in today’s birds and animals. Purple mohawks on a T-rex, however, would be a pure flight of the imagination.
In any event, it prompts the question: Since this new paper describes feathering on pterosaurs – which they used for warmth, not flight – isn’t the case regarding feather evolution closed, especially as the list of non-avian dinosaurs sporting some sort of plumage has grown to dozens?
“I think it isn’t agreed that feathers are primitive to [meaning predate] the origin of dinosaurs. Quite a number of paleontologists would strongly argue against that,” Prof. Benton explains to Haaretz. “They have suggested for instance that the feather-like structures seen in a wide variety of dinosaurs distant from the origin of birds were not feathers at all, and arose independently.”
For example, it has long been evident that flying reptiles known as pterosaurs had “some kind of hair,” Benton says. “But we looked at specimens from China and were able to show that the pterosaurs, which were not dinosaurs but relatives of dinosaurs, actually had feathers too.”
Downy babies with fangs
Fossil evidence of plumage in dinosaurs and early birds (which coexisted) has been piling up. Today’s birds have seven types of feathers, which have all been detected (in fossil form) in dinosaurs. Also, dinosaurs had some types of feathers that today’s birds don’t have. The ginger pterosaur had four feather types, by the way.
There’s no proof that all dinosaurs were feathered, but Benton points out that some fossil feathers feature branching, which is typical of feathers but not of hair, which has a single structure.
Branching was demonstrated for instance in feathers from the famed Ornithischian (non-avian) dinosaur Kulindadromeus, which had both feathers, and scales on its legs that may or may not have been a secondary derivation of feathering.
The first feathers were probably monofilaments, which evolved to keep the archosaurian ancestors of birds and dinosaurs warm during the Early Triassic period. There is even speculation for instance at the American Museum of Natural History that the fearsome featherless giants – T-rex comes to mind – had “adorable” downy babies with fangs. That has not been proven.
The genetic argument suggesting that feathers predate the origin of birds and even of dinosaurs was deduced by Daniella Dhouailly of Grenoble, who has spent her career working on the genetics of hair, scales and feathers, based on existing animals, Benton relates. Shark denticles (their “toothy” skin), scales in bony fish, scales in reptiles, hair in mammals and feathers in birds turn out to share very similar developmental genetic pathways, she explains.
Other work has shown that reptile scales, avian feathers and mammalian hair are the default dermal condition, which gets genetically suppressed on the eyeballs, for instance. Large animals such as elephants and whales have been postulated to have lost most of their body hair because it would be just a metabolic pain.
So feathers could be the default condition of dinosaurs, having arisen in the predecessor to dinosaurs; later feather growth could have been suppressed in massive or armored dinosaurs that would have been impeded, not advanced, by being externally warmed. While quill-like structures or filaments are found in avian skin, don’t start teaching the kids to draw stegosaurs with fuzz just yet. There’s just no evidence for that.