The short, wing-like forelimbs of one of the adult ornithomimids were covered… (Julius Csotonyi / Science )
The first feathers that appeared on dinosaurs were most likely for the purpose of attracting mates, not for flying, researchers said Thursday. The new conclusion was provided by the first discovery of feathered dinosaurs in the Western Hemisphere, a feat reported in the journal Science. The discovery also demonstrated that feathered dinosaur fossils can be found in unexpected types of rocks, suggesting that there might be many more such fossils waiting to be discovered than had previously been expected.
Previous specimens of feathered dinosaurs have been found only in fine-grained rocks in China and Germany. Such rocks are formed from muddy sediment in quiet waters, and paleontologists had assumed that such conditions were necessary to form sufficient details in fossilized feathers. But the three new specimens of ostrich-like dinosaurs called ornithomimids were found in sandstone produced in flowing rivers in what is now the badlands of Alberta, Canada. The skeletons of two adults and a juvenile ornithomimid were discovered by a team headed by paleontologists Darla K. Zelenitsky of the University of Calgary and Francois Therrien of the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta.
In modern-day birds, feathers develop at a very young age, shortly after hatching. But the juvenile Ornithomimus edmontonicus discovered by the team was covered only with down-like feathers like those found on the bodies of the adults. The short, wing-like forelimbs of one of the adults, however, were covered with long feathers with stiff shafts down the middle, much like modern feathers. The dinos, however, were too big to fly or even too glide. That suggests, said the team, that the feathers were probably decorative for the purpose of attracting mates, much like those on a modern peacock. That suggests that the adult with the feathers was a male. The absence of feathers on the juvenile specimen suggests that the feathers appeared only when the males were old enough to mate.
The feathers may have taken on new roles, such as keeping the dinosaurs warm or making flight possible, as the animals evolved later.
A video of Zelenitsky discussing the specimens is available here.