Feathers evolved more than once

The theory that feathers evolved only once – in a group of dinosaurs known as therapods, from which birds descended – has been thrown into serious question.

In a paper published in the journal Nature Ecology and Evolution, palaeontologists led by Baoyu Jiang from China’s Nanjing University present evidence that another group of ancient vertebrates, pterosaurs, also sported feather-like structures.

Pterosaurs were the first animals to achieve true flapping flight, but have no extant descendants.

Previous research has established that the animals were covered with external structures, known as pycnofibres, which have generally been interpreted from fossil evidence as being hair-like. Pterosaurs, thus, were assumed to have been furry.

Jiang and colleagues now present findings which suggest otherwise, based on meticulous examination of two well-preserved Pterosaur specimens dating from the Middle–Late Jurassic Yanliao Biota, around 165 to 160 million years ago.

The researchers subjected the fossils to morphological, chemical and macroevolutionary analysis and concluded that the pycnofibres “bear key features of feathers: monofilaments, two types of non-vaned grouped filaments, bilaterally branched filaments”.

This was a surprise, because these structures were previously thought to be unique to therapods. Jiang and colleagues suggest that pterosaur feathers were not used only for flight, but instead “probably functioned in thermoregulation, tactile sensing, signalling and aerodynamics”.

The finding throws the emergence of feathers into question. The researchers raise two possibilities.

“These findings could imply that feathers had deep evolutionary origins in ancestral archosaurs, or that these structures arose independently in pterosaurs,” they write.