The structures appear to be early feathers
The earliest dinosaur feathers were probably used for visual display, according to a new study.
The evidence comes from two 125-million-year-old dinosaur fossils unearthed in north-east China.
Writing in PNAS journal, the team says its findings may shed light on the origin of feathers.
They identified a previously unknown type of feather on the specimens which, they argue, could not have been used either for flight or for keeping warm.
The two specimens belong to the genus Beipiaosaurus, a member of the theropod group of dinosaurs.
The study was led by Xu Xing, a palaeontologist from the Chinese Academy of Sciences in Beijing.
Filamentous - and momentous?
The structures found on the fossils appear to be early feathers, based on their simple form.
The first type of feather is a short, slender filament that resembles those found on other flightless theropods.
The second type was previously unknown to science: it is a single, unbranched filament which is much longer than those seen before on theropod dinosaurs.
The researchers named these Elongated Broad Filamentous Feathers (EBFFs), because of their unique shape.
It is difficult to know what the principal function of these feathers was. But the researchers think the dinosaurs probably did not use them for flight or insulation.
Professor Xu and colleagues base this on the shape and distribution of the feathers.
By contrast, other types of theropod feathers are thought to have played a role in regulating body temperature.
Because EBFFs are found on parts of the body normally used for ornamentation in modern birds, visual display appears to have been a more likely function.
The researchers say this idea is supported by the great length and stiffness of the feathers.