Archaeopteryx probably couldn’t fly

. . .but maybe they could glide and parachute out of trees.  If you’ve followed bird evolution, you know they evolved from theropod dinosaurs, and that feathers evolved before flight, probably for thermoregulation or sexual/species signalling. Some of the earliest “true” birds (and that’s a definition which is somewhat subjective), though, had feathers which were longer, superficially resembling those of modern birds.  These creatures included the famous Archaeopteryx (which lived about 145 mya), and Confuciusornis (125 mya, the first bird with a toothless beak).

There has been a lot of argument about whether these beasts, especially Archaeopteryx, could fly;  the controversy has involved scrutinizing the feathers, the structure of the wing, the bones, and the presumed muscle mass (for a summary of the arguments, go here).  The conclusion: we don’t know. Up to now the consensus seems to have been that it was a best a weak flyer.

A new paper in Science by Robert L. Nudds and Gareth Dyke (from University of Manchester and University College Dublin respectively) concludes, however, that both Archaeopteryx and Confuciusornis were non-fliers.  They arrived at this conclusion using measurements of feather characteristics (primary flight feathers) and Euler-Bernoulli beam theory, used in architecture to calculate the load-bearing ability of beams.  They measured five specimens of Confuciusornis (see Fig. 2) and one (the Munich specimen) of Archaeopteryx.

The upshot is that the rachis of the feather (the shaft) was too slender to support wing flapping, and that the wings of these birds would have buckled had they attempted powered flight.  The graph below shows how slender the shafts of the fossil species were compared to those of modern birds:

Fig. 1.  B: Plot of Feather length versus body mass (top line) and rachis diameter versus body mass (bottom line).  Black diamonds: Archaeopteryx, gray diamonds Confuciusornis; black circles: modern bird species.  The fossil birds have feathers as long as those of modern birds, but the rachis diameter is much smaller (note that data are on a log scale, which makes the differences look smaller than they really are).   C.  Plot of rachis diameter versus feather length, again on a log scale. Symbols the same for B. Fossil birds have much a much slimmer rachis for their feather length than do modern birds.

A slender feather shaft raises the danger of the feather buckling under the large stresses of powered flight, and the beam theory shows that the Confuciusornis primary feather would buckle at 1/90th of the force that would buckle the feathers of a modern bird of comparable size.  Archaopteryx feathers would have buckled at about 1/45th of that force.

The authors conclude that neither bird could fly:

With feathers structurally similar to those of modern birds, Confuciusornis and Archaeopteryx could only have parachuted with their wings held dorsally, reducing the forces acting on the primaries while providing drag to reduce descent speed. A parachuting arrangement seems incongruent with their overall wing morphologies.

The catch is “feathers structurally similar to those of modern birds.”  Modern birds have feathers with hollow shafts. It’s possible that these ancient ones had feathers with solid shafts. That, according to the authors’ calculations, would have enabled them to fly, albeit with much less of a “safety margin” for buckling than we see in  feathers of modern birds.  I’m not sure how likely it is that these feathers had solid shafts, and I suspect you can’t tell from fossils, or the authors would have mentioned it.

But this paper doesn’t completely end the controversy.  A news-and-views piece by Michael Balter at ScienceNow reports dissent from other paleontologists:

But some researchers are not ready to close the book on early flight. “I agree that Confuciusornis and Archaeopteryx were poor fliers,” says Luis Chiappe, a paleontologist at the Natural History Museum of Los Angeles County in California. “I don’t agree, however, that these birds were unable to fly by flapping their wings.” That’s because, he says, the fossilized shafts of the feathers of early birds are often not well defined, making them difficult to measure accurately.

Philip Currie, a paleontologist at the University of Alberta in Canada, says that although the paper provides the “most convincing evidence yet” that these birds did not do well in the air, he also questions the authors’ conclusions that they were capable of only gliding or parachuting. The birds’ fossils have been found both in marine and lake sediments, Currie says. “If they were only dropping out of trees, how did they end up so far from shore?”

Fig. 2. One of the Confuciusoris specimens analyzed in this study.  The primary feather measured is indicated by the black bar.  White scale bar is 2 cm.

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Nudds, R. L. and G. J. Dyke.  Narrow primary feather rachises in Confuciusornis and Archaeopteryx suggest poor flight ability.  Science 328:887-889.