For ancient birds, wing feathers were a serious drag

A new study of ancient feathers adds weight to the theory that primitive birds — close relatives of feathered dinosaurs — were far less versatile fliers than their modern descendants.

“We don’t think these things could take off from the ground,” said Nicholas R. Longrich, a postdoctoral fellow with Yale’s Department of Geology and Geophysics and lead author of a study appearing Nov. 21 online in the journal Current Biology. “They can’t fly like a modern bird.”

The researchers examined fossils of two types of primitive avians — the celebrated Jurassic bird Archaeopteryx lithographica and the feathered dinosaur Anchiornis huxley — and found that the type and arrangement of their wing feathers probably hindered liftoff.

Multiple overlapping layers of long wing feathers would have complicated feather separation, minimizing the bird’s ability to overcome drag on the upstroke. By contrast, the wings of modern flying birds typically have a single primary layer of easily separated long feathers overlain by short feathers.

Archaeopteryx and Anchiornis probably used their wings to glide from a height, possibly reached by climbing a tree, Longrich said.

While the wing feathers of Archaeopteryx and Anchiornis show striking similarities, they are not identical, and their differences appear to represent early experiments in the evolution of the wing, according to researchers. Archaeopteryx had multiple layers of long flight feathers. In contrast, the dinosaur Anchiornis had an abundance of simple, strip-like feathers that overlap.

Said Longrich, “The only bird that has anything remotely similar is a penguin.”

Furthermore, the major differences between the wing structure of the ancient avians and that of modern birds suggest that living birds offer few clues about the origins of wing design, the researchers said.

“We are starting to get an intricate picture of how feathers and birds evolved from within the dinosaurs,” said co-author Jacob Vinther, a 2011 Yale PhD now with the University of Bristol in the United Kingdom.

“We now seem to see that feathers evolved initially for insulation. More complex vaned or pinnate feathers evolved for display.

These display feathers turned out to be excellent membranes that could have been utilized for aerial locomotion, which only very late in bird evolution became what we consider flapping flight.”

Other authors are Qingjin Meng and Quangguo Li of the Beijing Museum of Natural History, and Anthony P. Russell of the University of Calgary. The Yale Institute for Biospheric Studies supported the research.