Colored dinosaurs: Part II

I recently posted about the discovery of pigment granules in a fossil feathered theropod dinosaur—the same type of pigment granules found in fossil early birds as well as modern birds.  This similarity not only strengthened the evolutionary argument that birds are the modern descendants of theropods, but also enabled scientists to crudely reconstruct the feathered dino’s color.

A related paper has just been published in Science, showing even better fossilization of the melanosomes and thus giving a better idea of the color and pattern of those dinos. The animal is Anchiornis huxleyi, a small (woodpecker-sized) feathered dinosaur from the late Jurassic, about 150 million years ago.  This nonflying theropod was pretty highly feathered, and those fossil feathers also contained fossil melanosomes.  Comparing the size and shape of the fossil melanosomes with those of melanosomes in modern birds, the authors were able to make educated guesses about whether the  granules contained red, gray, or black pigments.

Here’s their conclusion:

In summary Anchiornis huxleyi was darkly colored with gray and black body plumage (Fig. 4). The head was gray and mottled with rufous and black. Elongate gray feathers on the front and sides of the crest appear to frame a longer rufous hindcrown. Gray marginal wing coverts formed a dark epaulet that contrasted strongly with the black/gray-span light primaries, secondaries, and greater coverts of the forelimb. The large black spangles of the primaries and secondaries created a dark outline to the trailing edge of forelimb plumage. The spangles of the outer-most primaries were black. The greater coverts of the upper wing were spangled with gray or black, creating an array (secondary coverts) or rows (primary coverts) of conspicuous dots. The contour feathers of legs were gray on the shank, and black on the foot. Like the forelimb, the elongate feathers of the lateroplantar surface of the hind limb were white at their bases with broad black distal spangles.

I have only one comment on the paper.  At the end, the authors say this: “Thus, the first evidence for plumage color patterns in a feathered non-avian dinosaur suggests selection for signaling function may be as important as aerodynamics in the early evolution of feathers.” (The National Geographic website—see below—makes a similar suggestion.)  It seems to me that neither signaling nor aerodynamics can explain the early origin of feathers, if for no other reason that you can’t select for colored feathers until you first have feathers, and because early feathers—the filamentous structures on some feathered dinos—could hardly have had an aerodynamic function.  What seems more likely is that the origin of feathers involved some other selection pressure—perhaps a thermoregulatory one—and then those early feathers gave rise to the possibility that they could, via pigmentation, be used for intraspecific signalling.  Then, later, they could be coopted for flight.  In other words, flying and signaling are exaptations of a feature that originated for some other reason.

Here’s an artist’s reconstruction of the beast:

Fig. 1.  (Fig. 4 from Science paper): Reconstruction of the plumage color of the Jurassic troodontid Anchiornis huxleyi.   Color plate by Michael A. Digiorgio.

Looks a bit like this, no?

Fig. 2.  The roadrunner, Geococcyx californianus

The National Geographic website has more detail on this discovery, along with an animated 3-D reconstruction of A. huxleyi.

Greg has jogged my memory by reminding me that Anchiornis is very important in showing that feathered dinos actually preceded Archaeopteryx (a transitional form that might have flown).  I posted about this issue a while back, and quote Greg’s email here:

The Science paper actually says a lot more about dinosaur color than the Nature paper, but it’s drawing less attention because it’s coming out a few weeks later (the Science people also did the original work on fossilized melanosomes). One really interesting bit about this is that Anchiornis is the first feathered dinosaur that is older than Archaeopteryx, thus solving the “temporal paradox” which was one of the chief arguments used against dino-bird ancestry. This has only been known for a few months, and I did not see much about it at the time, but i think it’s actually more important (as opposed to astonishingly mind-blowing) than the colors. See here and here.

________________

Li, Q. et al. 2009.  Plumage color paterns of an extinct dinosaur.  Science (Sciencexpress online).

h/t: Carl Zimmer, Greg Mayer

19 Comments

  1. NewEnglandBob
    Posted February 6, 2010 at 4:19 pm | Permalink

    The feathers on the feet of Anchiornis huxley in figure 1 looks a bit odd to me. Don’t birds mostly retract their feet while flying?

    • llewelly
      Posted February 7, 2010 at 8:51 pm | Permalink

      The authors refer to it as a “nonflying theropod”.

  2. Posted February 6, 2010 at 5:23 pm | Permalink

    Herons’ sure don’t. Their feet just dangle down looking forgotten and in the way, in flight.

  3. Torbjörn Larsson, OM
    Posted February 6, 2010 at 6:11 pm | Permalink

    I don’t get it. It was nonflying, so how does flying (and in modern birds) figure into the feathers on the feet?

    Comparing the two it seems a pity birds developed naked legs.

  4. Posted February 6, 2010 at 7:26 pm | Permalink

    Put in an order to Acme, and commence pursuit!

    Glen Davidson

    http://tinyurl.com/mxaa3p

  5. littlejohn
    Posted February 6, 2010 at 7:30 pm | Permalink

    “Colored dinosaurs”? Have you no sensitivity, sir?
    They are “dinosaurs of color.”

  6. Josh Slocum
    Posted February 6, 2010 at 8:29 pm | Permalink

    DO WANT one. And also one of those cute little fellas with the banded tails, too. I shall have a menagerie of Dino-Chickens, and force them to sleep in a pile of prehistoric cute on my couch.

  7. Doc Bill
    Posted February 7, 2010 at 12:48 am | Permalink

    Brilliant research.

    The sort of stuff I wish I had done.

    Alas.

  8. BaldApe
    Posted February 7, 2010 at 8:55 am | Permalink

    While I agree that the initial selective value of feathers was most likely some other function like insulation, it is also true that even primitive filamentous feathers would make the animal look bigger, which can have some value in signaling a potential predator.

    Chicken? Egg? [ducks behind chair]

    • NewEnglandBob
      Posted February 7, 2010 at 8:57 am | Permalink

      Chicken? Egg? [ducks behind chair]

    • Posted February 7, 2010 at 12:36 pm | Permalink

      Like that terrifying bristling kitteh the other day. Gave me nightmares.

  9. MartinDH
    Posted February 7, 2010 at 9:16 am | Permalink

    Is that a beak or a jaw with teeth?

    Anyway, this is pretty amazing research.

  10. Steve
    Posted February 7, 2010 at 10:16 am | Permalink

    “you can’t select for colored feathers until you first have feathers” Early feathers may have arisen as means of thermoregulation but what would be the selective drive for color? Camouflage?
    Thermoregulation?

  11. Sili
    Posted February 7, 2010 at 11:29 am | Permalink

    Is it just me, or at dinosaurs looking less and less like – well – dinosaurs these days?

  12. Matthew Cobb
    Posted February 7, 2010 at 3:50 pm | Permalink

    There’s some argument over at the Z-letter whether all this coloured dino business isn’t a big scientific yawn…

    http://wp.me/puRgM-ey

  13. nanobot74
    Posted February 8, 2010 at 4:59 pm | Permalink

    Jerry,
    you wrote “A related paper has just been published in Science, showing even better fossilization of the melanosomes and thus giving a better idea of the color and pattern of those dinos.” This is not correct. The quality of fossilization had nothing to do with why the color predictions were better in the Science paper. The Nature authors simply eyeballed the shape of the melanosomes and used those to assign color, while the Science authors rigorously quantified melanosome shape and distribution in relation to color of modern birds. This is what allowed them to make more accurate color predictions.

  14. nanobot74
    Posted February 8, 2010 at 5:26 pm | Permalink

    Jerry,
    another thing. both the nature and science papers show that the earliest feathers were in fact colored, so your argument that you can’t select for colored feathers before you have feathers makes no sense. the color came with the feather

    • BaldApe
      Posted February 8, 2010 at 6:04 pm | Permalink

      It would kinda have to, wouldn’t it? I mean, they couldn’t very well have been invisible. :-)


3 Trackbacks/Pingbacks

  1. [...] if you want to see how science ideas get discussed, read this post about dinosaur coloring. Check out this comment: I have only one comment on the [...]

  2. [...] – that does the same trick, with a different dino. Jerry Coyne has blogged on this over at Whyevolutionistrue.com. The beast in question is Anchiornis huxleyi, a small (woodpecker-sized) feathered but non-flying [...]

  3. [...] this, among them Ed Yong (1, 2), Matthew Cobb from the Uni of Manchester(1, 2) and Jerry Coyne (1, 2). Basically they all blog about the same two articles but the points made at the end of Cobb-2 are [...]

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