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.

___________

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

18 Comments

  1. Don
    Posted May 14, 2010 at 3:02 pm | Permalink

    Does anyone else notice the scientology ad from google ads at the end of the article on the main blog page?

    • whyevolutionistrue
      Posted May 14, 2010 at 3:08 pm | Permalink

      Yes, yes, it is profoundly disturbing and I’ll do something about this tomorrow.

  2. MadScientist
    Posted May 14, 2010 at 5:06 pm | Permalink

    I can imagine a number of ways that gliding birds would find themselves in marine or lake sediments. As for the question of was the shaft hollow – if it wasn’t, how much extra weight would all that keratin put on? The other thing is, how do feathers develop? Is the hollow in the feather necessary for its development and maintenance or is it just a convenient artefact which makes them lighter?

    • Torbjörn Larsson, OM
      Posted May 14, 2010 at 5:57 pm | Permalink

      I can imagine a number of ways that gliding birds would find themselves in marine or lake sediments.

      That is not the problem, I believe.

      I take it Currie is saying that such an end is fairly common. While I doubt todays gliders would likely end up such, as the ones I know are living in wood habitats (flying squirrels, flying tree snakes, gliding tree frogs).

      [OK, those later seems to mate in or around ponds, so dead ones would more often associate with such.]

    • Torbjörn Larsson, OM
      Posted May 15, 2010 at 6:50 am | Permalink

      Btw, I found these University of Wisconsin movies on down and pennaceous feather development. Looks like the rachis is developed out of a fusion between keratin filaments. So at a guess it could develop both ways, hollow and solid.

      As I’m partly answering your question I believe, what about “maintenance”, in what regard? If feathers are like hair, both keratin infused structures, it is my understanding (easily mistaken, of course) that hair shafts comprises dead cells between keratin layers. If that is the case, there is no need for cellular reproduction or maintenance.

      [Wow! In posting, I googled hair evolution and come up with that some paper tie hairs to nails and ultimately claws. So much for “feathers are like hair”?]

  3. MadScientist
    Posted May 14, 2010 at 5:09 pm | Permalink

    Oh – I’m getting a creationist website rather than a scientology website.

    • NewEnglandBob
      Posted May 14, 2010 at 5:21 pm | Permalink

      Adblock Plus:

      2 out of 47 blocked (also whitelisted:0, hidden: 1)

  4. Posted May 14, 2010 at 5:41 pm | Permalink

    That’s really interesting, I’m continually amazed just how much people can learn from looking into the fossil record.

  5. Sigmund
    Posted May 14, 2010 at 10:57 pm | Permalink

    They couldn’t fly?
    This explains why they perished in the biblical flood!
    Religion is compatible with science yet again!

  6. SaintStephen
    Posted May 15, 2010 at 12:09 am | Permalink

    Okay. I guess those feather beams are thin enough to ignore transverse shear strain, so Euler-Bernoulli is fine.

    Stephen Timoshenko won’t be rolling over in his grave, in other words.

    (Finally, an ME gets his chance to shine on Coyne’s blog!)

    ;-P

  7. Posted May 15, 2010 at 10:58 am | Permalink

    I am just part way through Jack Horner’s fascinating book “How to build a Dinosaur”…I’ll report upon completion.

  8. Sili
    Posted May 16, 2010 at 6:08 am | Permalink

    Teach the controversy!

  9. Miranda
    Posted May 16, 2010 at 10:06 pm | Permalink

    “If you’ve followed bird evolution, you know they evolved from theropod dinosaurs,”

    Unless you belong to the PNAS, that is.

    http://www.physorg.com/news184959295.html

    “The weight of the evidence is now suggesting that not only did birds not descend from dinosaurs, Ruben said, but that some species now believed to be dinosaurs may have descended from birds.”

  10. Sven DiMilo
    Posted May 21, 2010 at 1:27 pm | Permalink

    I think in this case, the log scale is exaggerating the differences. Does not affect the conclusions of course.

  11. Jack
    Posted May 31, 2010 at 1:22 pm | Permalink

    Archaeoptryx feathers were “markedly asymmetrical”. Since they did not fly how is this explained?

  12. Delirious
    Posted June 17, 2010 at 2:18 pm | Permalink

    I’m kind of ok with Archaopteryx, since he wasn’t really a bird, but Confusciornis couldn’t fly?! Then why does it look so…able to fly, from its large wing-to-body ratio to its songbird build?

  13. Posted June 17, 2010 at 5:25 pm | Permalink

    Perhaps Confusciornis is a secondarily flightless bird.
    See pterosaurnet.blogspot.com


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