Dinosaur feathers in amber!

The latest issue of Science contains a paper by McKellar et al, showing a number of examples of dinosaur and early bird feathers preserved in late Cretaceous amber (about 70 million years old) from Alberta, Canada (h/t to artist Kalliope Monoyios at Symbiartic for calling this work to my attention).  The feathers show almost all the stages in the evolution of those structures—beginning with simple filaments, presumably for thermoregulation, to coiled filaments used by diving birds like grebes to modify their buoyancy by absorbing water, to more complicated feathers similar to those in modern birds.

The hypothesized stages in the evolution of modern feathers are shown below (figure 1 from the paper); all of these stages are seen in the amber specimens.  The authors describe the stages:

The currently accepted (11, 12) evolutionary  developmental model for feathers (Fig. 1A) consists of a stage I morphology characterized by a single filament: This unfurls into a tuft of filaments (barbs) in stage II. In stage III, either some tufted barbs coalesce to form a rachis (central shaft) (IIIa), or barbules (segmented secondary branches) stem from the barbs (IIIb); then, these features combine to produce tertiary branching (IIIa+b). Barbules later differentiate along the length of each barb, producing distal barbules with hooklets at each node to interlock adjacent barbs and forma closed pennaceous (vaned) feather (stage IV). Stage V encompasses a wide range of additional vane and subcomponent specializations. Most modern birds possess stage IV or V feathers or secondary reductions from these stages (11, 16).

Here’s a feather from stage “1”: a simple filament, but note that some of these are coiled:

And more complicated feathers:

How do we know these feathers are from theropod dinosaurs (the ones that evolved feathers and whose descendants became modern birds) rather than more modern birds living at the time. The authors give several reasons, including the fact that some of the feather types are found only in fossilized dinosaurs like Sinornithosaurus millenii.  But I’m not convinced that at least some of the more complex feathers didn’t derive from what we’d consider “birds”, especially since bird fossils do occur in the area.

In his a Perspective piece accompanying this paper, Mark Norrell is more judicious, concluding that “complex ‘modern’ feather adaptations had already appeared before the extinction of the nonavian dinosaurs.” Norrell also sees the most surprising finding as that of feathers with coiled “barbules” (side structures in stage 3b above) suggesting that some of the early feathered dinos were diving animals.

If you want just a summary of the pictures and a brief description, check out Kapi’s post at Symbiartic (she was the illustrator of WEIT). Here’s one of the photo she presents, showing the feather in situ in an amber chunk, with the caption she gives:

Within this amber piece, six feather fragments partially overlap each other. The beaded appearance of the barbules (finest structures) in this image is a result of pigments concentrated within just a portion of each of the segments that make up the barbules. These barbule segments or “internodes” are connected in a fashion similar to the segments in a bamboo shoot. Photo: Ryan McKellar

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McKellar, R.,  B. D. E. Chatterton, A. P. Wolfe and P. J. Currie. 2011. A diverse assemblage of Cretaceous dinosaur and bird fossils from Canadian amber. Science 333:1619-1622.

13 Comments

  1. Posted September 18, 2011 at 6:35 am | Permalink

    Wow. I had no idea we actually had this sort of record. (I assumed that the discussion of feather evolution would be limited to the relevant Dna and occasional fossil.) Amazing!

    Of course, as usual, the creationists are going to jump all over the ambiguity and disagreement over whether some of these are bird “or” dino feathers, never mind that that’s precisely a consequence of evolution.

    Presumably, as with other major trait transitions, we’ll see some “holdover” of the “old models” for a few million years, no?

    • Frank
      Posted September 18, 2011 at 7:15 am | Permalink

      It is hard to define “holdover” traits, but if you are talking about primitive characters, all organisms abound with holdover traits – relative to some derived versions. From a horse’s perspective, your five digits on your hand is a holdover trait. So it is a bit of a non-sequitur to expect to see holdovers of old models for ONLY a few million years, since evolution does not proceed in any fixed direction. Monotreme mammals (the platypus and echidna) have had the ‘holdover’ of egg-laying for many millions of years, but they also have derived traits not found in any other mammals (such as the venomous spur on the leg of the platypus).

    • Torbjörn Larsson, OM
      Posted September 18, 2011 at 7:51 am | Permalink

      I had no idea we actually had this sort of record.

      Funny you say that, since it seems to have been a surprise to everyone:

      ““These were chance finds when we were preparing the amber to look for insects,” says Currie. “About half a dozen specimens were in my “research to do” specimen cabinet when Ryan ran across some more in his work.””

      • Torbjörn Larsson, OM
        Posted September 18, 2011 at 7:56 am | Permalink

        Of course, this comes to mind:

        “Dans les champs de l’observation le hasard ne favorise que les esprits préparés.”

        In the fields of observation chance favors only the prepared mind.

        Louis Pasteur, Lecture, University of Lille (7 December 1854)”

  2. Posted September 18, 2011 at 6:37 am | Permalink

    To clarily my tense: although I said “we’ll”, I was talking about the fossil record and not modern birds (although maybe modern birds show diversity in feather type? I have no idea).

    Also, I know DNA should be capped; writing on an iPad is tricky.

    • Rumtopf
      Posted September 18, 2011 at 8:26 am | Permalink

      I think flighted birds have examples of early stage feathers alongside the modern ones, like the downy underlayers used for insulation. Ratites like the kiwi have quite primitive plumage in general. There certainly is a bunch of feather diversity(I suddenly really want to read up on birds of paradise) including retained traits c:

  3. Hempenstein
    Posted September 18, 2011 at 8:46 am | Permalink

    Does amber typically contain embedded stuff, or is that more the exception? If the former, might we wonder if some of the same early feathers were in the panels of the Czar’s Amber Room?

    • Microraptor
      Posted September 18, 2011 at 10:06 am | Permalink

      I think it’s a case of the Law of Large Numbers- it’s somewhat rare for something to be preserved in amber, but enough amber has been found that we’ve still got a huge amount of pieces that did have something contained in them.

      I don’t know about the Amber Room, though- I think that most of the amber used for it was chosen for clarity so it’s unlikely that dino feathers would be found in them, assuming that the amber used there was even from the correct time period.

      • Microraptor
        Posted September 18, 2011 at 10:07 am | Permalink

        Also, subscribing.

  4. Marella
    Posted September 18, 2011 at 6:34 pm | Permalink

    I can recommend “Feathers: the Evolution of a Natural Miracle.” By Thor Hansen for those who’d like to read a bit more about feathers, I recently read it and it was very good.

  5. Posted September 19, 2011 at 7:57 am | Permalink

    There is an apparent misprint in the Science article (at least the HTML version). In the figure Jerry reproduces, the references to IIIa and IIIb are reversed: IIIb shows barbs condensed into a rachis (purple), while IIIa shows barbules (red) (not the other way around).

  6. Posted September 19, 2011 at 8:46 am | Permalink

    Thanks for the shout-out, Jerry!!

  7. BCoppola
    Posted February 6, 2012 at 10:09 am | Permalink

    I’m a fly fisherman/fly tyer. I’d love to use those filaments in fig. B for some wet flies!

    Just a general comment as a layperson: Evolution, cosmology, and discoveries like this are just so fascinating, why would anyone prefer the explanations of the world found in an ancient book of mythology?


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