Feathers aren't just for flight. It can be easy to forget that.
The resilient, unique biological structures are what allowed dinosaurs to take to the air, after all, and drawing backwards from a chickadee to Archaeopteryx and deeper still, it would be only be natural to highlight the evolution of feathers' aerodynamic capabilities. Yet even from our living avian dinosaurs we know that feathers provide insulation, help birds to put on garishly colorful displays, and, with some flapping, allow their owners to better run up inclines, among other things. On top of all that, a newly-discovered dinosaur offers another reminder that there's more to feathers than flight.
Described by paleontologist Ulysee Lefèvre and colleagues, the fluffy fossil is among the latest to come out of the roughly 160 million year old Chinese deposits that have already yielded dozens of exquisitely-preserved dinosaurs. They've named it Serikornis - the silk bird - even though it's not technically a bird but one of the flightless feathered dinosaurs that clusters near the origin of avians in the bigger evolutionary tree. It's that position, in conjunction with the dinosaur's plumage, that makes it stand out.
Serikornis didn't just have one feather type. The feathers of the neck, for example, are similar to the wispy bundles found in other dinosaurs like Sinornithosaurus, while the arms have a mess of "short, slender, symmetrical, and poorly differentiated feathers" similar to those of Anchiornis. And on its hindlimbs, Serikornis has both fuzz and long pennaceous feathers like those of Microraptor. That's what makes this new dinosaur particularly significant.
Serikornis wasn't a flier. Its bones, as well as its feathers, indicate a terrestrial mode of life. Yet it has leg feathers that are often associated with the evolution of flight - a hypothesis that one line of feathered dinosaurs went through a four-winged gliding phase on the way to powered flight, embodied by Microraptor and its relatives. For a more archaic and grounded dinosaur to have leg feathers, then, indicates that long leg feathers evolved in a terrestrial context - perhaps for displays, Lefèvre and coauthors suggest - before being inherited by increasingly arboreal and aerodynamic dinosaurs. Life on the ground opened the possibility flight.

Fossil Facts
Name: Serikornis sungei
Meaning: Serikornis means "silk bird", while sungei honors paleontologist Sun Ge.
Age: Jurassic, around 160 million years ago.
Where in the world?: Linglongta, China.
What sort of organism?: A paravian dinosaur.
How much of the organism’s is known?: A single, articulated skeleton with feathers.
Reference:
Lefèvre, U., Cau, A., Cincotta, A., Hu, D., Chinsamy, A., Escuillie, F., Godefroit, P. 2017. A new Jurassic theropod from China documents a transitional step in the macrostructure of feathers. The Science of Nature. doi: 10.1007/s00114-017-1496-y
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