Exquisitely well-preserved feathered dinosaurs from the Late Jurassic and Early Cretaceous of north-eastern China have considerably helped paleontologists to better understand how birds evolved from dinosaurs. It has been previously postulated that the emergence of feathers was driven by their aerodynamic properties but a new species, named Serikornis sungei “the silk bird”, provides new clues about how dinosaurs feathers evolved.
The little pheasant-sized dinosaur, which bears four wings (that is, two forewings and two hindwings) is mainly covered with simple feathers similar to the wispy bundles found in other dinosaurs like Sinornithosaurus. The first four-winged dinosaur, as known as Microraptor, was reported from the Tiaojishan Formation in Liaoning Province in 2000.
This Middle-Late Jurassic Formation has already provided other four-winged species such as Aurornis and Anchiornis, another basal dinosaur close to the transition between dinosaurs and birds. The plumage of Serikornis is well-preserved and the limbs bear short, slender, symmetrical, and poorly differentiated feathers similar to those of Anchiornis. In other words, the limb feathers attached to the arms and the legs of Serikornis are totally different from the flight feathers of modern birds.
Serikornis wasn’t a flier and its anatomy coupled to the macrostructure of the feathers indicate a terrestrial mode of life. Although the hindlimbs bear feathers, a feature often associated with the evolution of flight, they are not suited to sustain a flight. So the presence of leg feathers on a more archaic and grounded dinosaur imply that long leg feathers evolved in a terrestrial context. The structure of the pennaceous feathers also goes in that direction because of barbules, a structure that hook barbs together and which is essential to resist air pressure during the wing beat, are absent in Serikornis. This absence is corroborated by optical and electronic microscopy.
What does the plumage of Serikornis serve? It is postulated that the feathering of this little dinosaur may have primitively been used as a thermoregulatory system or as a social display even if it could not be ruled out that Serikornis was able to scramble up tree trunks with its sharp and recurved claws and parachute to the ground, using its plumage to slow down its descent.
The next step of the research will bring new information about how the terrestrial context has driven the emergence of flight among basalmost Jurassic paravians and how this emergence has played a major role on the diversification of ecological niches necessary to develop a modern-like type of flight.
These findings are described in the article entitled A new Jurassic theropod from China documents transitional step in the macrostructure of feathers, published in the journal The Science of Nature. This work was led by Ulysse Lefèvre at the Royal Belgian Institute of Natural Sciences.