Dinosaur 'Silky' Is A Key Fossil in Feather Evolution

The perfectly preserved fossil of Serikornis sungei. (Photo: Thierry Hubin, RBINS)
25/08/2017
Dinosaur 'Silky' Is A Key Fossil in Feather Evolution
post by
Reinout Verbeke

Belgian palaeontologists have described a new, 165 million year old dinosaur species from Northern China. Serikornis sungei –nickmane ‘Silky’ – is an important fossil in the evolution of feathers in dinosaurs. Silky had feathers on its four limbs, but could not fly. The discovery suggests that ground-dwelling dinosaurs had feathers, possibly to impress mating partners or to warn enemies, before adapting an arboreal lifestyle or flight.

When our palaeontologist Ulysse Lefèvre showed the Serikornis sungei fossil to a French colleague, she thought it looked like a Silky, a breed of chicken with atypically fluffy plumage. A nickname was born! ‘Silky’, around 48 cm long and 160 to 165 million years old, was found in the Tiaojishan formation in northern China. Like the Silky chicken it had feathers on both fore- and hindlimbs, but those feathers were not suitable for flight. This is one of the conclusions of the detailed description of the new dinosaur species (and genus) in The Science of Nature.

Flightless

Serikornis is the first fossil of a feathered dinosaur that visibly misses ‘barbicels’, minute hooks for cross-attachment. They make the feather stiff and resistant against air pressure. On Silky, the air blows right through the feathers. Apart from that, its feathers were symmetrical, and you need asymmetrical feathers to take off and steer. On Silky’s small sternum, there were not enough muscles to flap his wings with force. The bones in the forearm (ulna and radius) were not adapted for wingbeat.

‘Serikornis is an important fossil, because it gives us more insight in how flight evolved in dinosaurs’, says Ulysse Lefèvre (Royal Belgian Institute of Natural Sciences and University of Liege). ‘It shows that dinosaurs already had feathers when they were walking the earth on their hindlimbs, before the modern wing and feather structure developed that allowed them to fly.

Attract a Mate

If the feathers were not making the dinosaur airborne, what was their function? Lefèvre: ‘Feathered dinosaurs like Serikornis were probably not top predators, so they had to be able to move quickly to escape predation. Symmetrical feathers on the hindlimbs might be less efficient from an aerodynamic perspective, so we think it helped in attracting mates or to warn enemies.’

‘When feathers got barbicels, dinosaurs of the Jurassic could explore the sky while flapping their wings. This happened with the Eumaniraptora, a group including Velociraptor, Troodon and early and modern bird.’ Serikornis belongs to the more basal group within Paraves. We find similar primitive feathers on contemporaries like Aurornis, Eosinopteryx and Anchiornis. Two of those were described by our colleague, palaeontologist Pascal Godefroit. ‘These theropods, like Serikornis, had a long claw to grab on to tree bark and climb higher. It is not impossible that they jumped from there and parachuted down, gliding through the air. To decide whether flying originated from the ground or from trees, we need more fossils and research.’

Hotspot

Silky was found in 2014 in Daxishan, a village in the Liaoning province in northeastern China, and collected by the Palaeontological Museum of Liaoning. The fossil was in a layer of the Tiaojishan formation, a hotspot of feathered dinosaurs. Our palaeontologists got the permission from their Chinese colleagues to study the perfectly preserved Serikornis fossil. As a thank you, the species was named after Sun Ge, conservator of the palaeontological collections of the museum in Liaoning.

Ulysse Lefèvre also kept a living Silkie chicken in the Royal Belgian Institute of Natural Sciences. ‘My project leader Pascal Godefroit named her Penelope’, he says, referring to his special first name. ‘One day, Pascal put a cast of Serikornis next to it and yelled: “her grandmother”!’

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