A new paper, and a pneumatic hiatus at last

February 11, 2009

I had a new paper come out today. Unofficial supplementary info here, PDF here. I would have had all this ready to go sooner, but the paper came out sooner than I expected. In fact, I didn’t even know that it had been published until Andy Farke (aka the Open Source Paleontologist) wrote me for a PDF. Turnabout’s fair play, I suppose, because last year I congratulated Stuart Sumida on his Gerobatrachus paper before he knew it was out. I guess letting the authors find out through the grapevine that their stuff has been published is part of the “value added” that commercial journals provide. ;-)

Anyway, I’m happy the paper is out, finally. It’s the third chapter of my dissertation, but with teaching and traveling to Spain and such I didn’t get it submitted until last January. I had to forcibly bite my tongue during the Aerosteon saga last fall, when such a big deal was made about the absence of pneumatic hiatuses in non-avian dinosaurs. This despite the facts that there are several good reasons to expect pneumatic hiatuses to be rare, and that pneumatic hiatuses are not the Rosetta Stone or magic bullet for air sacs in saurischian dinosaurs. They’re more like the cinderblock that broke the camel’s back, given all the other evidence for air sacs.

In fact, the structure of the new paper is built around the idea that there are several tiers of evidence for bird-like air sacs in saurischians. Those tiers are:

  1. The presence of postcranial pneumaticity at all. Some of the first authors to get interested in the implications of pneumaticity for dinosaurs argued that pneumaticity probably implies an air sac system, and left it at that. Later workers have tended to denigrate this argument as overly simplistic–just because some of the postcranial skeleton is pneumatic does not mean that the animal’s air sac system was necessarily like that of birds–but it’s not actually a bad argument. We can imagine lots of ways to get air into the postcranial skeleton, but for tetrapods the only system that we have any evidence for is diverticula of a lung/air sac system like we see in birds.
  2. The distribution of pneumaticity in the skeletons of most saurischians and pterosaurs is  diagnostic for specific air sacs, namely the cervical, clavicular, and abdominal air sacs that we see in birds. This is what Pat O’Connor and Leon Claessens established so firmly with their work on mapping parts of the respiratory system to skeletal domains in birds.
  3. The evolutionary patterns of pneumatization in sauropods and theropods parallel the development of pneumatization during ontogeny in birds. Or, more economically, ontogeny recapitulates phylogeny in this system. This is more evidence that the observed patterns of pneumaticity in the skeletons of birds and non-avian saurischians are produced by the same underlying process of diverticula developing from different air sacs in a highly conserved order–even if we don’t know why things evolved, and continue to develop, in the order that they do. And it’s better evidence, because it accounts for more observations (points 1 and 2 can be established from single specimens) and ties postcranial pneumaticity in all saurischians, living and extinct, into a more coherent picture.
  4. Pneumatic hiatuses are more evidence that the postcranial skeleton is pneumatized by diverticula from more than one part of the respiratory system. Not the only evidence–we already suspect this quite strongly based on points 2 and 3–but more evidence. It is possible that the diverticula of extinct animals behaved differently than those of all extant birds, and diverticula from a single source could conceivably pneumatize the whole vertebral column. Possible. Conceivably. How likely? Dunno–our n on this is either 1 (if you count all living birds as a batch) or several hundred (if you count each of the species that Pat O’Connor has dissected and injected). Pneumatic hiatuses offer another level of evidence, because they can potentially show that the patterns of pneumaticity in fossil taxa are inconsistent with pneumatization from a single point. That’s how they work in chickens, and that’s how they may work in non-avian dinosaurs, as long as diverticula don’t leapfrog over  some bones without leaving any traces, or at least don’t do that very often.

For the record, I don’t think that pneumatic hiatuses are stronger evidence than point 3; if I was ranking the tiers based on importance I would put 3 at the top. Pneumatic hiatuses ended up being last in the paper because 1-3 were basically review material, and it made sense to group them together before the big  bolus of description.

[UPDATE the next day: also, I just realized that those 4 are not the same as I used in the paper! In the paper I left out 1, advanced 2 and 3, and added a different number 3, which is pneumatization of the pelvic girdle and hindlimb. I tend to forget about that one because the evidence in sauropods is underwhelming so far. And arguably this is just another aspect of 2 (above), or if you like you can think of 5 tiers. They say consistency is the hobgoblin of small minds!]

The importance of pneumatic hiatuses remains to be seen; there might not be enough of them to tell us very much, or we might find that leapfrogging diverticula exist and are common (we’d then need a way to sort hiatuses caused by multiple sources of diverticula from those caused by leapfrogging diverticula). But they’re important to me, for a couple of reasons.

First, they’re probably one of the two or three best ideas that I’ve had in my life. When I realized that pneumatic hiatuses could potentially indicate pneumatization from multiple sources it really was like a light going on in my head. I walked around seeing stars all week.

I got the idea from this figure, from King (1957):

king_57_figs1-2-480On the left King has drawn the vertebral columns of several chickens, and shaded in the pneumatic regions. Blocks of pneumatic verts separated by apneumatic gaps represent pneumatization from different sets of diverticula. I remember very vividly sitting in the Padian lab reading this paper and thinking, “if we found one of those in a dinosaur it would be the money.” Then I suddenly sat up straight, then stood up, then paced around the room a few times to burn off the discovery energy. I had a very profound need to tell someone. I don’t remember who I told, but it was probably Mike.

The other reason that pneumatic hiatuses are important to me: they are now one of those cool little cases that show that paleontology can be a predictive science. If you want to test a hypothesis in the experimental sciences you manipulate the conditions and see what happens. Historical sciences don’t usually give you that option. But you can play What If? As in, “If hypothesis A is true then we ought to see such-and-such evidence.” In 2003, I predicted that if sauropods had abdominal air sacs we ought to see pneumatic hiatuses once in a while. Finding the evidence that validated the prediction was almost as much of a rush as having the idea in the first place.

haplo-skeleton-with-me-for-scale-480The owner of Sauropod Pneumatic Hiatus #1 is Haplocanthosaurus CM 879, which is a cool animal but fairly pathetic as sauropods go. In my dissertation/job talks I would show the above picture and joke that I could probably beat up that animal on a good day. I found out about the pneumatic hiatus by accident, when I was poring over Hatcher (1903). In one of the figures near the end of the paper, Hatcher shows the centra of the fourth and fifth sacral vertebrae. I noticed that sacral 4 had a pneumatic chamber of some sort but sacral 5 did not. Then a few minutes later I had gotten to the plates at the back of the paper, and saw what looked like a pneumatic chamber on the first caudal. Somewhere in the dank, beer-flooded grottoes of my skull, the neuron fired.

haplo-verts-v3-480This is the figure I put together, using images from Hatcher (1903), for a Jurassic Foundation grant to go see the material in the Carnegie Museum in 2005. It worked; they came through with $1500 for that trip and a week at BYU the same fall (to my immense shame, although the Jurassic Foundation is credited for funding on the first page, I see that I forgot to thank them in the acknowledgments. Belatedly: thanks, you guys rock, I suck). The pneumatic cavities are labeled as foramina because that’s what they look like in the drawing, and not having seen them I didn’t know any better. In fact they are fossae, but they are deep, invasive fossae and their morphology is not consistent with anything other than pneumatic invasion. (Pneumatic invasion!? Flee for your lives!!) See the paper for all the excruciating details. Note that the sacrals have unfused neurocentral sutures, so the animal was not fully mature when it died (there is probably a whole post ahead just on the neurocentral weirdness in this animal).

So that’s the story, for now at least. There are more pneumatic hiatuses coming, but those papers are still in the pipe so I can say no more for now. I’m sure when they come out some alert blogger will notice and e-mail me for a PDF, and then you’ll get the news here.

The moral of the story is that you can make real progress by reading lots of old, obscure stuff. Support–and abuse–your local academic library!



22 Responses to “A new paper, and a pneumatic hiatus at last”

  1. Mike Taylor Says:

    What, is no-one going to comment?

  2. Matt Wedel Says:

    We’ll never know now (assuming “no-one” equals “non-SV-POW!sketeers”).

    You’re as bad as that Dutch dude who separated the ducks. If you see something interesting happening–like no one commenting on my long semi-autobiographical post on what is objectively the most fascinating paper ever written–you have a responsibility to observe and report (later, in an appropriate venue), or at least not wreck the system for other observers. Sheesh!

  3. David Hone Says:

    No need to comment from here (apart form this to say I have no need to coment, obviously) since I can jsut read the actual paper. They are probably all off commenting on ‘Darwin’ posts on every other biology blg on Earth rather than dealing with the important issues of sauropod pneumaticy.

  4. Mike Taylor Says:

    Dude, I just didn’t want you to feel bad that no-one cares about your crappy paper.

  5. Matt Wedel Says:

    That’s sweet.

    I suspect that comments have been light because everyone is too busy retooling their entire research programs in light of my epochal discoveries. That’s the null hypothesis, anyway.

  6. Darren Naish Says:

    I have a comment. How the hell did you write the Aerosteon stuff without at least hinting at the existence of this (at the time) in-press paper? Man, I commend you for some powerful restraint. Or, as they say, for not Hulking-out.

  7. Darren Naish Says:

    Oh, and my comments have been non-existent until now because I’ve had no internet access. Tet Zoo readers might have noticed this.

  8. Nathan Myers Says:

    I can’t answer for anybody else, but I hadn’t commented because I was still too stunned at all the awesomeness. Give me a chance to catch my breath (re-inflate my sacs, as it were).

  9. Matt Wedel Says:

    How the hell did you write the Aerosteon stuff without […] Hulking-out.

    The really funny thing is that I illustrated the pneumatic hiatus in Haplocanthosaurus and waxed lyrical about its importance in my 2005 SVP talk, which was in the prosauropod symposium, which was attended by at least two of the principals in the Aerosteon saga. In this case, revenge is a dish best served publicly several years in advance.

    I hadn’t commented because I was still too stunned at all the awesomeness.

    See? I knew it.

  10. Andreas Johansson Says:

    I didn’t comment because I couldn’t think of anything to say. I mean, it’s awesome, but it’s not like you need to be told that by me, is it? Further, the presentation was clear enough I didn’t have any particular questions.

    Thus, if you want me to comment more, I’ll have to recommend you to write less awesome stuff less clearly. ;)

  11. Graham King Says:

    All this pneumaticity is very interesting. I’m glad the SVPOWers-that-be are pursuing it so intently.

    Congratulations on your new paper, Matt!

  12. Sean Craven Says:

    Just to be an internet jerk, I’m gonna pick on your quote about consistency. Nobody gets this one right and the inclusion of the word ‘foolish’ seems significant to petty writing freaks such as myself.

    “A foolish consistency is the hobgoblin of little minds,
    adored by little statesmen and philosophers and divines.”

    Ralph Waldo Emerson

  13. Zach Miller Says:

    Oooh, new paper. Congrats, Matt. I’d love to read it, though. :-D

  14. Matt Wedel Says:

    Sorry, I’m lost. Are you asking for the PDF? Or do you mean that if I got my logorrhea under control, you’d actually have time to read it? Because that I apparently can’t do anything about.

  15. Nathan Myers Says:

    I love the automatically generated “possibly related” link: PNEUMATIC FOUR-AXIS MATERIAL HANDLING EQUIPMENT . I suppose that stuff could be useful for moving some of these verts around.

    I suspect Zach hasn’t noticed the PDF link right at the top.

  16. Zach Miller Says:

    I did not, Nathan. I thought it would be in the references section, but when it wasn’t there, I wondered if it was “coming out soon” or something.

  17. Nathan Myers Says:

    Let that be a lesson to Matt: references go in the reference section (too).

  18. […] two important recent papers from the Journal of Experimental Zoology (other than my own). These are free right now but who knows for how long, so download them pronto before they go […]

  19. Scott Hartman Says:

    Congrats Matt, that’s really and truly awesome. Now I fully expect museum visitors to stop asking me “Why would big, overgrowed lizards get that size back in the day?” and instead ask me “Why would big, overgrowed lizards develop pneumatic hiatuses?”

    How sweet it will be…

    Also, as someone who has had more than a passing interest in saurischian respiration and pneumatization, I appreciate you doing all of the actual, you know, work. Keep it up!

  20. Matt Wedel Says:

    Dude, thanks! We appreciate your work, too. Speaking of, how’s that neck posture stuff coming along? Some of us are dying to cite it. :-)

  21. Matt Wedel Says:

    [Belatedly] All right, Zach, Nathan, I happily surrender. The paper is now in the references section. And just in case there is some benighted soul out there who has only learned of its existence in this comment thread and can’t be bothered to scroll back up, it is also available here. :-)

    Thanks to all of you for your kind words. You’re not helping me stay humble, but in my awesome beneficence, I forgive you.

  22. […] For more than you probably wanted to know about those specific holes in that specific bone, see this post and the linked […]

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