Sep 25 2009

New Oldest Bird

archiornisI have been following the story of bird evolution for some time. My fascination began, appropriately, with Archaeopteryx – a beautifully transitional species from theropod dinosaurs to modern birds living about 150 million years ago. The Berlin specimen is simply a gorgeous fossil.

The story of bird evolution also has everything a paleontology enthusiast could want – impressive fossils, exotic extinct creatures, an unfolding mystery, and a bit of legitimate scientific controversy. There was also a case of fraud thrown in to keep things interesting.

So of course the news item about the oldest fossil bird being discovered – finally overtaking Archaeopteryx for the title, caught my eye.  Anchiornis huxleyi is a feathered theropod dinosaur from the Troodontidae family – the group of theropods most closely related to birds. The specimen was found in a formation in China now dated to between 161 and 151 million years old – making it older than Archaeopteryx. This specimen has great significance, but first let me set the stage with some background.

A Brief History of Bird Evolution

The first fossil species to link theropod dinosaurs and birds was Archaeopteryx, originally found in limestone formations in Germany (leading to the species name lithographica, as limestone from this quarry was used for making lithographs). For years this was the only link. Archaeopteryx is nicely morphologically transitional – it has teeth, a long bony tale, clawed hands and other reptilian features. Yet it also had fully formed feathers and could fly – although it lacked the more sophisticated features of flight seen in modern birds, so it was probably a poor flyer. You could not invent a more perfectly morphologically transitional species than Archaeopteryx.

I stress morphologically because this single species is probably not on the actual line that led to modern birds. There has also been a temporal paradox in that Archaeopteryx is older than many of the Troodontidae from which it allegedly evolved. This apparent paradox fueled much of the minority opposition (mainly held by one paleontologist, Alan Feduccia) that doubted the dino-bird connection.

However, the paradox really was never much of a problem. Species branch off from each other and then persist for millions of years. The spotty fossil record makes it likely that in many cases we will simply lack examples of older common ancestors, while having older specimens with later derived characteristic and younger specimens retaining “primitive” characteristics. For example, if a later paleontologist only had hominid fossils from 5 million years ago and ape fossil from today, they might find it paradoxical that humans evolved from ape-like ancestors.

To support the notion that the apparent temporal paradox is an artifact of a spotty fossil record is the fact that the record of theropod dinosaurs from the Jurassic – the time period before Archaeopteryx, is very sparse. So we lacked access to the very time period that would settle the question. But, the dino to bird hypothesis predicted that as we discovered more fossils we would find older Troodontidae, and that is in fact what happened, even before the Anchiornis huxleyi was discovered.

In recent years several Troodontid specimens from the Tiaojishan Formation of China have been discovered that are from the Jurassic era and are older than Archaeopteryx – so as predicted, the ancestral group to feathered dinosaurs are older than feathered dinosaurs – paradox resolved.

In the last 15 or so year China has also offered up a number of new feathered dinosaur finds. It now seems that feathers were a common feature of theropod dinosaurs of the time, especially the Troodontidae but also dromaeosaurids, another family of theropods. And also there was a robust adaptive radiation of feathered dinosaurs at that time, and surviving past the evolution of birds from one line of this bushy radiation. We now have specimens ranging the morphological range from slightly feathered dinosaurs to protobirds to Archaeopteryx to more bird-like specimens but still not fully modern birds. We have also documented more of the evolution of feathers themselves, and demonstrated a wide range of feathery adaptations in this group.

But still Archaeopteryx was more developed along the avian line than many of the later feathered dinosaurs, and we had not yet found a more primitive and older feathered dinosaur specimen – so the apparent temporal paradox continued.

Enter Anchiornis huxleyi

This brings us to the current specimen – Anchiornis huxleyi – which dates from 161-151 million years ago, is in the line that likely led to birds, and is feathered but more primitive than Archaeopteryx. This shatters the remnants of the alleged temporal paradox – as predicted by the dino to bird hypothesis.

Anchiornis huxleyi also shows a very interesting feature – it has long shafted feathers on all four limbs. In other words – it had four wings. This is not the first specimen to show this feature. Microraptor and Pedopenna are two other related species that have the four wing design. It seems that this feature evolved early in the branching point of what is called Paraves – which contains the Troodontids, the dromaeosaurids, and of course birds.

This makes sense – while wings were still small and not fully developed, you could get more lift from having four wings. Once the forelimbs developed more sophisticated wings, the hind wings became superfluous.

This raises the question of whether or not Anchiornis huxleyi could fly. Right now it seems that it probably could not. While the feathers are well developed, they are symmetrical in their design. Flight feathers are asymmetrical – they have an off-center shaft. Its hind legs also are large and seem well-adapted for running. Perhaps Anchiornis huxleyi was a glider, or used the feathers to pounce on prey from on high.

Creationist Cognitive Dissonance

Of course, I cannot help but contemplate how creationists (those who bother to be even minimally informed) resolve the cognitive dissonance that must result from such evidence. Up until the late 1990s, creationists like Duane Gish simply dismissed Archaeopteryx as a lone weirdo, and pointed out the apparent temporal paradox as well as the lack of more transitions to support the dino to bird hypothesis, and by extension evolution. The same was true of scientific dissenters, like Alan Feduccia (not a creationist, but he maintained that birds evolved from other reptiles, not dinosaurs).

But in 2009 all such objections have been dealt with. We now have a robust group of feathered dinosaurs showing a nice transition from early feathered theropods, with a variety of adaptations, including more and more “modern” feathers and bird-like creatures. The gaps have been shrinking, leaving the creationists like flopping fish in a dried up pond of denial. Anchiornis huxleyi is just the icing on the cake – showing that as we find more fossils the story just gets better and better.

The story of bird evolution also shows that new fossil evidence can simultaneously surprise paleontologists and confirm existing theories. This often confuses non-experts and provides fodder for a sensationalistic press and denying creationists. Specifically, as paleontologists discovered more and more feathered dinosaurs this evidence confirmed the theory that birds evolved from dinosaurs, specifically theropods, and probably Troodontidae. At the same time there were some surprising twists and turns in the story – such as the extent of feathered non-avian dinosaurs, and the evolution of four-winged theropods early on in the evolution of feathers.

Essentially, the evidence confirmed the big picture, while providing interesting and surprising details. This is a common point of confusion among creationists who often exploit surprising details as if they call into question the bigger question of evolution itself.

Conclusion

Anchiornis huxleyi is a nice addition to the story of bird evolution and the expanding picture of feathered dinosaurs. It also seems to put the final nail in the coffin of the (always weak) temporal paradox of bird evolution from theropods.

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13 responses so far

13 Responses to “New Oldest Bird”

  1. Hubbubon 25 Sep 2009 at 9:39 am

    Psh… it’s just a bird… -osaur…

    Anything interesting from Richard Prum on this?

  2. calinthaluson 25 Sep 2009 at 11:00 am

    Older, but could still get it’s tail whooped on by any monkey.

    Seriously, nice find. Too bad it won’t matter to anyone here in the home state of the creation “museum”.

  3. MarkWon 25 Sep 2009 at 11:06 am

    Yeah the Berlin Archaeopteryx…

    I was in Berlin a couple of years ago and managed to persuade my significant other to go to the Museum für Naturkunde just up the road from where we were staying. Only when we arrived did I make the link; Berlin… Archaeopteryx… in Berlin. (Yeah I can be slow on the uptake.)

    I’m not ashamed to admit that seeing it brought a tear to my eye.

  4. Benon 25 Sep 2009 at 11:39 am

    “But, the dino to bird hypothesis predicted that as we discovered more fossils we would find older Troodontidae, and that is in fact what happened, even before the Anchiornis huxleyi was discovered.”

    Don’t you have to qualify that claim a bit, since not finding AH would not falsify the dino/bird theory? Don’t you have to look at the grand scheme of the fossil record and make some kind of statistical argument for the likelihood of finding x number of transitional specimens per probable gaps of a generally established tree of life given the ratio of fossils we find from particular geological periods? It’s not a straight forward prediction. It’s a very messy one and you’ve used rather strong language. Just sayin.

    It is a nice retro-fit, I’ll say that, for sure.

    Ben

  5. Steven Novellaon 25 Sep 2009 at 12:37 pm

    Ben,

    I completely disagree. The fact is there are countless patterns in the fossil record that are not compatible with common descent. There are significantly fewer that are compatible (it is a tiny subset of the almost limitless possible morphologies and temporal sequences). I don’t know how you could do statistics on this.

    The fact is there is simply no reason, according to special creation, why we would have ever found feathered dinosaurs at all, let alone during the correct time periods. The hypothesis that birds evolved from dinosaurs predicted that we would. The finding of these specimens is powerful confirmation of not only evolution but of bird evolution from dinosaurs specifically.

    This also is more evidence that evolution has both extreme explanatory and predictive power.

  6. Alexon 25 Sep 2009 at 12:57 pm

    I think Ben’s point was that what you described as a prediction wasn’t a *hard* prediction in which the opposite outcome (not finding this fossil) would unequivocally falsify the hypothesis that theropods are the ancestors of birds.

    Of course, this isn’t a real objection to using common descent as a framework for paleontology, since anything close to *hard* predictions as described above are only made in the experimental, and not in the historical, sciences.

  7. daedalus2uon 25 Sep 2009 at 1:24 pm

    Alex, the “prediction” wasn’t that a dinosaur/bird intermediate fossil would be found, the prediction was that if a fossil was found it would have morphology intermediate between dinosaurs and birds.

    If a fossil was found that was only bird-like, that would have falsified the hypothesis. A fossil that was only dinosaur-like would not have falsified it because reminant dinosaurs may have still been extant.

  8. Steven Novellaon 25 Sep 2009 at 2:02 pm

    There are two ways to look at it. One is that evolution predicts will we find species occupying the morphological space between dinosaurs and birds (or whatever the common ancestor turned out to be, but it had to be something plausibly related to birds).

    Finding such a fossil confirms both evolution and the dino to bird hypothesis within evolution.

    Not finding such fossils does not immediately falsify the theory, but the longer and more thoroughly we look for such fossils without finding them the more unlikely they become and the theory starts to look shaky. If in the 150 years since Darwin we found few or no transitional fossils, the creationists might have a point. But the fact is we have found a steady stream of them.

    The third possibility is that we find fossils of species that are in a morphological and/or temporal sequence that are incompatible with common descent. This could mean finding birds in early strata, like the Cambrian, long long before they should exist. Or this could mean finding species that impossibly combine specific features (homologous, not just analogous) from disparate groups – horses with bird wings and feathers. Or, ironically, Cameron’s ridiculous crocoduck, which would actually count against evolution, not support it.

  9. Alexon 25 Sep 2009 at 8:16 pm

    daedalus: Not necessarily. If this particular fossil hadn’t been found, and an equally old “only bird-like” fossil would have been found, this would not disconfirm the hypothesis that birds evolved from theropods. It would simply mean that “true” birds already existed before morphological intermediates like Archaeopteryx did. That’s not a falsification of the theropod-to-birds hypothesis, anymore than Steve’s hypothetical example of fossil hominids and other apes is a falsification of current theories of human evolution. Imperfections of the fossil record, and the fact that evolution isn’t usually progressive, can readily account for such observations.

    A really old “true” bird” (i.e. from before theropods existed) would come close to falsifying the theropod-to-birds hypothesis, but not one as old as this fossil.

    I repeat, this isn’t at all a problem for a historical science like paleontology, where one has to work with very limited data (at least as compared to experimental sciences). It’s just not what Ben called a “straight forward prediction.”

  10. HHCon 25 Sep 2009 at 11:19 pm

    Could this fossil be the forerunner of the cuckoo family’s roadrunner?

  11. Doctor Evidenceon 26 Sep 2009 at 2:06 am

    somewhat related:

    Dr. Scott http://www.youtube.com/watch?v=mEnFJTgr9x4&feature=SeriesPlayList&p=F2E17B4CDCCE15F5

    Professor Dennett: http://www.youtube.com/watch?v=CimqEnhIAgw&feature=SeriesPlayList&p=F2E17B4CDCCE15F5

  12. eiskrystalon 29 Sep 2009 at 8:49 am

    What are they going to say? I’m betting:

    archeopterix was a bird…this is just a dino…it couldn’t even fly.
    So when are you going to show these transitional fossils you keep harping on about?

  13. [...] I wrote a couple of weeks ago about a new bird-dinosaur link and the new oldest bird, Anchiornis huxleyi, which took the title away from one of the iconic fossils of evolution – Archaeopteryx. A new study just published gives us some new information about Archaeopteryx. It turns out the structure of its bones was more like a dinosaur’s than a bird’s. [...]

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