Exceptional preservation of soft tissues in the fossil record has provided information on the feathers of ancient birds, including some feather types that don't exist among modern species. Some Cretaceous birds possess a single pair of long tail feathers with an unusually wide central stalk, called rachis-dominated feathers (RDFs). In this study, Clark and colleagues describe a new species of ancient bird with the proportionally longest and best-preserved RDFs yet found, offering new insights into this extinct style of tail feather.
The new species has been named Plumadraco bankoorum, "the Banko's feather dragon". It is represented by a single specimen from Liaoning China, which is roughly 121 million years old. The bird measures just 15cm from beak to tail, but its twin tail feathers are nearly 30cm long. These feathers are not aerodynamic and were probably used for displays. Close observation revealed the central stalk of each feather increasingly diminished along their length, which would have enabled the latter half of each feather, and especially the end rackets, to make flexible motions such as the "flickering" seen in many modern bird displays.
Among modern birds such as peacocks and birds-of-paradise, long tail-region-feathers are typically found on males who use them in flashy displays to attract mates, while females often bear inconspicuous plumage to avoid notice by predators while tending their nests. The authors suggest that this specimen of Plumadraco likely represents a male individual whose exceptionally long tail feathers served a similar function. However, the authors also note that corroborating this interpretation will require more detailed evidence of the tail musculature and nesting strategies of this type of ancient bird.
The authors add: "This new fossil bird, Plumadraco, strongly suggests that elongate ornamental feathers, produced via sexually-selective pressures, have been present in birds since at least 121 million years ago."
"Detailed inspection of the tail feathers of Plumadraco suggest they potentially not only impressed females via their length, but also by their movement. The tail feathers, ending in delicate rackets, also have enfeeblement attributes, such as a diminished central support structure, resulting in either a flicker or waving movement if the feathers were moved along a dorsoventral plane."
Alexander Clark adds: "Working with fossil birds like Plumadraco continues to personally demonstrate to me that life is far more complex and richer than what we thought previously. To know that at one point in time, about 121 million years ago, this very individual flew through the dawn light with these incredible tail feathers streaming behind it is truly something to marvel. Even millions of years after its death, we can still appreciate just how spectacular this species would have looked like in life."
