Saturday, April 20, 2013

Supporting the Dinosaur/Bird Link in the Era of the MANIAC

I'm posting this more as an open question than a statement of my own opinion, so comments appreciated!

A new paper out in Paleobiology by Verracchio et al. describes the porosity of Troodon formosus eggs and uses the data as evidence to support the hypothesis that troodontids brooded their eggs, like modern birds and other known maniraptorans, rather than burying them, like crocodilians and some other modern birds. In and of itself, this conclusion is interesting in that it pretty much solidifies nest brooding (as opposed to burial) as the ancestral trait for modern birds, and for maniraptorans (or at least chuniaoans*) in general.

Study coauthor Darla Zelenitsky with Troodon formosus nest. Photo by Jay Im, University of Calgary.
I hate to admit it, but my first thought when reading the headline of this news article from PhysOrg was that, yeah, we all assumed that anyway. The unspoken "rule of cool" is that science tends to be more exciting when we find evidence that contradicts previously well-supported hypotheses, rather than confirming hypotheses we all took for granted. Sure, finding the Higgs-Boson was exciting, but not nearly as exciting as not finding it, which could have led to new physics. I assumed, and I'm sure many others did as well, that troodontids brooded their eggs, based on the reasonably secure hypothesis that oviraptorids (which are known to have done so) are more basal. This behavior in troodontids was even depicted nicely in 2011's Dinosaur Revolution. So score another one for phylogenetic bracketing!

(Of course, this is not to imply that all chuniaoans must have brooded their eggs. It's entirely possible that reversals to burial nesting occurred, as with modern megapodes, and this seems especially likely for very large species like some dromaeosaurines. But the odds that any given chuniaoan would not be a brooder are low.)
Arctic troodontids, anatomy based on Troodon formosus.
Matt Martyniuk, all rights reserved.
Aside from all that, the assertion in the PhysOrg headline struck me as particularly meaningless. How could a study of troodontid brooding lend support to the dinosaur/bird hypothesis? This statement would have been accurate a decade ago, but not today. The reason is the moving goalposts of the dinosaur/bird opposition.

Back in the 1990s, the small group of scientists who contend that birds are not dinosaurs (BANDits) spent most of their time arguing that deinonychosaurs like Troodon formosus were in no way, shape, or form related to birds, and that any similarities were due to convergent evolution.

And then we found Sinornithosaurus.

Suddenly, the BAND was faced with a dilemma. Here was an irrefutable deinonychosaur covered in irrefutable feathers, including irrefutable vaned wing and tail feathers. There's no way this this was not related to birds. Rather than acknowledge their error (to my knowledge, no BANDit has ever tried to explain why they were so wrong on this based on the skeletal evidence), the BAND engaged in the classic logical fallacy of moving the goalposts. Rather than admit defeat on this particular point, they said essentially that yes, deinonychosaurs were clearly related to closely related to birds, but were not themselves dinosaurs. They went from BANDits to MANIACs - Maniraptorans Are Not In Actuality Coelurosaurs!

So, in a way, continuing to use evidence from maniraptorans as evidence for the dinosaur/bird link is completely in vain. No scientist working today believes that these animals are anything but birds or bird relatives. If BADists (birds are dinosaurs hypothesis supporters) ignore the shifted goalposts, arguments like this are being made to nobody, and we may as well stop making them unless a serious counter-hypothesis is presented. Except that would be ignoring the fact that vocal opponents still exist, just not in the same form they did in the 1990s, when this sort of evidence would have been compelling.

So what to do? Continue trumpeting the ever-mounting evidence that deinonychosaurs are close evolutionary relatives of birds despite the fact that literally everybody is now on board with that idea? Or do we play the BANDits' game, addressing only actual holdouts to the hypothesis, but kicking for their new goalposts rather than their old ones?

Let's say we do go for the "new" goal as defined by BAND. What would constitute support for the dino/bird link today? A nest-brooding compsognathid or ornithomimid might do (and would be exponentially more exciting than a broodong troodontid, since it would push back the origins of brooding itself). But it's hard to tell what they would accept as evidence for BAD, since the BAND position seems to consist of little more than "BAD is wrong no matter what." I would assume that, according to BAND, it's now up to BAD to demonstrate that maniraptorans are related to compsognathids, coelurids, and other coelurosaurs. The caveat is that BAND has made it clear they are not convinced by cladistic, integumentary (other than vaned feathers), or osteological evidence. So maybe evidence based on eggs or brooding would do the trick after all, since that's really all there is left.

And if we found avian-style brooding in, say, a carnosaur or coelophysoid? Surely at least some in the BAND will simply move the goalposts again, declare all theropods to be birds, and dare BAD to demonstrate that they are related to sauropods and ornithischians.

So... should we keep playing this game of shifting hypotheses and moving goalposts? Or should we simply ignore these blatant uses of logical fallacy and acknowledge that no reasonable counter-hypothesis currently exists? It may be best to treat challenges to BAD like challenges to evolution itself--as not worthy of attention, or of headlines.

At this point, isn't the title "Egg Study Supports Evolutionary Link Between Birds and Troodontids" just as redundant as "Egg Study Supports Evolution"?

*Chuniaoae is the clade comprising oviraptorids and birds, usually called Aviremigia nowadays. However, Aviremigia is defined by the apomorphy of vaned feathers on the arms... and on the tail, for some reason. We now know that vaned arm feathers occur further down the tree in ornithomimosaurs. We don't yet know if they also had vaned tail feathers, so we can't yet sink Aviremigia as a synonym of Maniraptoriformes, and it technically remains a senior synonym of Chuniaoae. But since it is now a much shakier application of this particular apo-clade, I'm going to hedge my bets and start referring to Chuniaoae more often for the ovi+bird clade.

- Varricchio, D.J., Jackson, F.D., Jackson, R.A., and Zelenitsky, D.K. (2013). "Porosity and water vapor conductance of two Troodon formosus eggs: an assessment of incubation strategy in a maniraptoran dinosaur.Paleobiology, 39(2): 278-296.


  1. I don't think MANIACs care about brooding much. They seem to only care about 1. a manus consisting of digits II-III-IV, 2. pennaceous remiges/retrices, and 3. an arboreal stem leading back to the Triassic. Note in my conversation with Martin as posted on my blog, he didn't care much about ornithomimosaurs or tyrannosauroids being birds, since they could have 1 and 2 and could be neoflightless. You could probably use this reasoning to get all the way back to ceratosaurs assuming a BCF scenario of successive neoflightless branches, though once you get to coelophysoids' metacarpal V, that can't be a metacarpal VI, so things would fall apart.

    BANDits stopped paying attention to dinosaurs decades ago and refuse to use modern methodologies, so as far as published papers go I would let Prum's "ARE CURRENT CRITIQUES OF THE THEROPOD ORIGIN OF BIRDS SCIENCE? REBUTTAL TO FEDUCCIA (2002)" be the end of things. If Feduccia ever acknowledges counterarguments and stops using long-discredited arguments himself, maybe he'll deserve attention again.

  2. There's a tiny, thin, banal hope that one of these days, one of the BANDits or MANIACs will eventually listen, realized, and decide to do science again. I'd love it if they dis something substantive, rather than polemicizing. Rather they teach than hang themselves on crosses. I doubt it will be productive, and I don't think they'll listen.

    But they have an audience, they get editorials and papers with horrible analogies printed in them. Thye must be responded to. To ignore them is to imply they don't need responses, are sound. When several journals give them outlets, they MUST be responded to.

    1. I said we should stop responding to BAND with published papers. By all means continue to respond in popular media, blogs, etc.. Maybe it would be productive to put together a list of factual inaccuracies from Feduccia's 2013 paper and send it to the Auk editorial board, and ask how those errors were allowed to go through unchallenged with only a two month time between submission and acceptance.

    2. See, as long as they get editorial and article time in various journals, so too should any responses. Very rarely (not since Prum, in fact) have there been any direct responses to the bullshit peddled in those "papers" in the pages of the journal which produced them. A journal should INVITE responses to this "controversy," and also acknowledge that the proponents of this contrary view number around 10.

      As long as the readers of that journal see no particular response, they might see there is a valid controversy, instead of a fake one brought on by the argument from disbelief.

  3. What I'd really like to know is which clade of dinosaurs evolved a syrinx, and whether they used it for social communication just like birds do. I think a find like this would strengthen the perception of just how much dinosaurs are related to birds.
    I just watched a documentary on that Hadrosaur mummy, but sadly they didn't say anything on this topic.

    1. According to Senter (2008, p. 276), the presence of a syrinx corresponds with a clavicular air sac and pneumetized clavicles. Pneumatized clavicles are found in enantiornithes + aves (ornithothoracines), pterosaurs, and Aerosteon.

      It's possible that the syrinx didn't evolve until ornithothoracines, and that the clavicular air sac in pterosaurs and Aerosteon is a result of conversantly extensive air sacs in those form unrelated to the present of a syrinx. Alternately, I wonder if the syrinx evolved at the base of Ornithodira but only developed to the point that it invaded the clavicle in those three clades, existing in a more rudimentary form in all ornithodirans...

      Anyway, for what it's worth Senter uses this to suggest that given current evidence, non-ornithothoracine stem-birds did not vocalize at all, but relied on external sound (e.g. water slapping, drumming) sources and visual display.

  4. "I assumed, and I'm sure many others did as well, that troodontids brooded their eggs, based on the reasonably secure hypothesis that oviraptorids (which are known to have done so) are more basal."

    Besides that, the "brooding troodontid" hypothesis had already solidified by Varracchio et al. 1997.

    "A nest-brooding compsognathid or ornithomimid might do"

    That reminds me: Have any BANDits responded to the undeniably protofeathered Yutyrannus or the undeniably winged Ornithomimus? I would think that, if neither of these non-maniraptoran coelurosaurs shuts them up, then nothing will.

    1. Not that I know of, but it's not surprising. BAND does not consider those structures to be "protofeathers" at all. According to BAND, "protofeathers" are remix-like structures similar to the things on the back of Longisquama, not down-like filaments, and based on the interview with Marin Mickey posted at TTD Blog, they don't agree with Prum's developmental model. Surely they think the structures of Yutyrannus are collagen fibers. BAND does not accept something as a feather unless it is clearly vaned and pennaceous. As for Ornithomimus, even I would hesitate before I called the quill marks (not even quill knobs) unequivocal, though they are compelling IMO. It's not like any actual pennaceous feathers are preserved.

      Even if they were, the BAND would simply declare that tyrannosaurs and ornithomimids were not actually dinosaurs at all.