Which came first, the feathers or the birds? Feathers first, scientists now say definitively. Yet this feathery revelation doesn't arise from discoveries of ancient birds, but of birds' ancestors—dinosaurs.
At a recent Berlin conference, scientists celebrated continuing revelations from the most famous feathered dinosaur, Archaeopteryx, in the city where the most complete specimen resides. Long considered the "first bird," it lived 150 million years ago and sparked the notion that birds are the living remnants of the dinosaur line, intriguing even Darwin.
But new finds have confirmed that feathers started long before Archaeopteryx first flapped its wings. (Related: "Archaeopteryx's Evolutionary Humiliation Continues.")
"I think that the common ancestor of dinosaurs probably had feathers and that all dinosaurs had some type of feather, just like all mammals have some type of hair," says paleontologist Jakob Vinther of the United Kingdom's University of Bristol. (See "Evolution of Feathers" in National Geographic magazine.)
A series of revolutionary discoveries backs Vinther's idea and vanquishes the Jurassic Park vision of dinosaurs as leathery brutes. Instead, these fossils paint a plumage-packed picture of the age of dinosaurs. (Related: "Jurassic World Stuck in the 1980s, Experts Grumble.")
The revisions began in the 1990s when a trove of feathered dinosaurs, fleet-footed runners with surprising variety, emerged from fossil beds in China and confirmed those suspicions.
Now, more dinosaur discoveries reveal how deep the roots of feathered dinosaurs really go:
—A "two-tailed" feathered dinosaur called Jeholornis flaunted a jutting frond of feathers on a trailing fan some 120 million years ago. Unrelated to modern-day birds, the find points to a wide diversity in feathered features in dinosaurs.
—A gorgeously preserved Archaeopteryx was unveiled in July, sporting feathers from its head to its feet, rather than just on its wings and tail as had long been thought. Those feathers also suggest that Archaeopteryx wasn't much of a flyer.
—A running dinosaur, Kulindadromeus, lived in Siberia about 160 million years ago, covered in thin, downy, ribboned tufts of feathers. Unlike most previous feathered finds, it belonged to a different group than the theropod dinosaurs, kin to Tyrannosaurus rex and modern-day birds.
That a feathered Kulindadromeus belonged to a group unrelated to birds demonstrates that "of course, evolution is not directed to a final outcome that we see as a bird," says Vinther. That find also adds support to the 2009 discovery of the bristled Tianyulong, a running dinosaur unrelated to bird ancestors that also lived in China around the same time. Its discoverers had suggested the filaments along its back resembled feathers, and at the time, the idea met with some controversy.
"We can now be very confident that feathers weren't just an invention of birds and their closest relatives but evolved much deeper in dinosaur history," says Steve Brusatte of Scotland's University of Edinburgh.
Vinther now thinks that dinosaur skins likely sported all sorts of complex bristles and feathers, "all the way back to the common ancestor of dinosaurs." Perhaps this even includes the flying reptiles that lived as far back as 228 million years ago called pterosaurs, "which also have fluffy skin."
Altogether, the recent finds not only point to the startling antiquity of feathered critters, says paleontologist Martin Sander of Germany's University of Bonn, but they also help explain their evolutionary emergence. (Enjoy a fun look at the diversity of modern feathers.)
Feathers supercharged dinosaur evolution. Recent surveys of fossil sizes show that the ancestors of birds shrank rapidly over the tens of million of years before Archaeopteryx appeared.
In August, for example, a team headed by paleontologist Michael Lee of the South Australian Museum in Adelaide reported in Science magazine that the dinosaur ancestors of birds decreased in weight from about 359 pounds (163 kilograms) to 1.8 pounds (0.8 kilograms) over 50 million years to reach the size of Archaeopteryx. That rate of change in body size happened much more quickly in this line of dinosaurs than in others. (For more on what happened later, see: "Birds Evolved Slowly From Dinosaurs—Then Took Off.")
In a commentary accompanying that report, Michael Benton of the United Kingdom's University of Bristol wrote that miniaturization is "what makes a bird a bird and not a flying dinosaur."
What drove that miniaturization? Feathers. Feathers provided the evolutionary advantages—warmth, display, and for some, flight—that allowed these dinosaurs to outcompete their unfeathered peers and reptiles.
In a review of the recently reported discoveries published last month in the journal Science, Sander and colleagues sketched out the evolutionary pathway for feathers, starting with primitive dinosaurs flaunting a bit of fluff to birds soaring through the skies.
The first downy protofeathers probably evolved as insulation in early dinosaurs. Yale's Richard Prum has shown that manipulating the two genes responsible for growing lizards' scales can produce feathers, which were an improvement over reptile skin for keeping warm-blooded dinosaurs warm.
Better insulation allowed smaller, faster dinosaurs—ones with quicker metabolisms, such as the turkey-size Compsognathus longipes—to evolve over time.
Success led to success, with feathered dinosaur species proliferating after 180 million years ago with the breakup of the supercontinent Gondwana, Sander says. The splitting apart of the supercontinent suddenly provided a diversity of habitats and species for these varied species.
Between the emergence of the earliest dinosaurs about 230 million years ago and the era of Archaeopteryx, 150 million years ago, "dinosaurs got smaller and smaller," Sander says, "but [then] they ran into a new problem."
The problem? All those new species needed some way to distinguish among themselves in order to find mates, while at the same time camouflaging themselves from rivals and hiding out from predators. Early protofeathers were terrific for insulation, which explains today's down-filled coats. But puffy tufts were lousy at displaying colors.
Dull tufts came at a price, because dinosaurs had inherited color vision from their reptilian predecessors, Sander says. He argues they likely possessed the "tetrachromacy" acuity of modern birds, he argues. Superior to human color vision, tetrachromacy allows for fine discrimination of hues into the ultraviolet spectrum of light.
So to the evolutionary rescue came pennate, or planar, feathers, with strong central quills and ridge-lined sides, structures that allowed brighter colors to flourish. Lustrous blues, greens, and the glowing sheen called iridescence—famously seen today on the throat of many hummingbirds—rely on tightly arranged filaments in these feathers. Lanes of color molecules called melanosomes interspersed with supporting keratin (the stuff in your hair and fingernails) supply the brightest hues of these structurally generated colors.
Seen in running dinosaurs such as Oviraptor philoceratops, which lived about 70 million years ago, pennate feathers adorned many dinosaurs, not just the flyers that followed Archaeopteryx. In July, paleontologists reported that 125 million years ago, a four-winged microraptor dinosaur seems to have sported a long, feathered tail that served as an air brake, allowing it to glide onto prey.
A cottage industry in recreating dinosaur feather colors has sprouted over the last decade to deal with these discoveries. Brown University's Ryan Carney, a National Geographic Society Waitt grantee, reported in a 2012 study of fossilized melanosomes that Archaeopteryx sported matte black feathers with dark tips. (See: "Feathered Dinosaur Had Black Wings?")
At the recent Society for Vertebrate Paleontology meeting in Berlin, Carney fended off suggestions that Archaeopteryx feathers lacked melanosomes, meaning they were white, or that his team's study had actually described fossilized bacteria, not melanosomes.
"If they were bacteria, it would throw into question the whole notion of looking for color," Carney said. But new chemical spectroscopy observations presented at the meeting, he says, show "these are melanosomes, and not bacteria."
Equipped with bright plumage and color vision, dinosaurs then benefited from an evolutionary "feedback loop" leading to feathers all over their hides, suggests biologist Marie-Claire Koschowitz of Germany's University of Bonn, the lead author of the recent review with Sander. In this view, flight almost looks like an afterthought in dinosaur evolution, just one more way of moving for the lumbering, running, gliding, and soaring dinosaurs that ruled the world long ago.
But dinosaurs didn't rule everywhere. They conquered the sky but mostly skipped swimming, Sander says, and feathers might also help explain this hole in their dominion. The largest carnivorous dinosaur, Spinosaurus, seems to have been one of the only aquatic ones. (See "Mister Big" in National Geographic magazine.)
Penguins aside, he notes that you don't see a lot of birds that outdo fish or sharks as swimmers. Feathers may have made for evolutionary success on land for dinosaurs, but they offered little advantage at sea.
Regardless, feathered flight allowed early birds to survive in diverse habitats, which seems the key to their survival when their relatives went extinct about 66 million years ago. Flying and tweeting among us are the descendants of the onetime overlords of the planet.
"Most dinosaur enthusiasts would give a leg to see a dinosaur, but I am always astonished how few people are aware that birds are in fact dinosaurs." says Koschowitz. "Real life dinosaurs, everywhere in our cities, bopping around on their little clawed feet and being detested for spreading their little dinosaur germs."
Jamie Shreeve contributed reporting for this story from the Society for Vertebrate Paleontology meeting in Berlin in November.
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