If you’re new to this thread, here’s a minimal reading list, in chronological order. I say ‘minimal’ because all of the relevant papers are freely available, and therefore all of the factual claims are easy to check.

The last is Paul Sereno’s response to my criticism of the Aerosteon paper. Here’s the full text, with my comments. Please go read the un-commented version at PLoS first, and see if you find it compelling.

In two trackbacks to our paper, Matt Wedel offers a misleading, longwinded, ad hominen critique of this paper on the new theropod dinosaur, Aerosteon riocoloradensis, and the significance of its pneumatic features.

There is a widespread misconception that if you say something unflattering about someone, that constitutes an ad hominem argument. In fact, an ad hominem argument has a specific form (quoted from Wikipedia):

  1. Person A makes claim X
  2. There is something objectionable about Person A
  3. Therefore claim X is false

If you actually read my critique, you’ll see that the form of my argument was more like:

  1. Sereno et al. claim X
  2. Claim X is misleading and easily falsifiable
  3. Sereno et al. probably claimed that X is true because it would support their hypothesis Y

I will not deny that I publicly speculated about the motivations of Sereno et al. (2008). Many of the arguments used in that paper are very difficult to explain unless Sereno et al. were trying to systematically discredit or suppress previous work (either by citing it misleadingly or not citing it at all). If you disagree, that’s fine. But don’t expect anyone to take your disagreement seriously unless you can back it up with evidence.

Anyway, remember what a real ad hominem argument looks like. We’ll see one later on.

Some personalized aspects of the commentary and erroneous claims push the limits of the “good practice” guidelines posted for commentary in this journal (http://www.plosone.org/static/commentGuidelines.action#goodpractice).

Here’s the last line of the good practice guidelines: “PLoS is the final arbiter of the suitability of content for inclusion in the PLoS Web sites.” In short, the guidelines are for commentary posted at PLoS, not about PLoS papers. A trackback is just a reciprocal hyperlink to material elsewhere on the ‘net–for example, a private blog, like this one. If the folks at PLoS don’t like the incoming links, they can always delete them and block my access.

And, hey, Darren put a trackback with his own critical review of the Aerosteon paper, but he doesn’t get mentioned at all here. Where’s the love?

Also, I’m curious to see which of my claims were erroneous. Presumably a fact-based rebuttal will be forthcoming, since Sereno does not engage my “misleading, longwinded” critique on a single point.

In this paper, we did our best to:

1) Present the pneumatic evidence as clearly as possible (Figs. 4-16).

2) Cite the literature thoroughly and fairly (95 citations).

3) Critique available hypotheses for the evolution of avian intrathoracic air sacs and respiratory mechanics.

4) Outline more clearly in tabular format our osteological correlates (Table 4).

5) Diagram more specifically particular stages as supported by current fossil evidence (Fig. 17).

In the short first trackback, Wedel outlines and agrees with all of the main points of the paper.

False. I said that the morphological description was mostly (not entirely) accurate. It’s the rest of the paper I have issues with, as I clearly and patiently explained. In fact, in the first trackback I hardly dealt with the Aerosteon paper at all; as the title suggests, I was laying out introductory and background material.

He then digresses to critique earlier papers and ends by explaining what “we’ve been up to”, referring to papers by himself, Pat O’Connor and Leon Claessens—research we cited many times in the paper, both positively for evidence and in critique.

…and other research they cited misleadingly or did not cite despite its relevance, as I’ve documented, and as Darren has further shown. Simply counting up cited references (ooh! 95!) does not demonstrate that previous work is cited “thoroughly and fairly”. I note that, in keeping with the rest of his comment, Sereno does not respond to any of my actual critiques, or try to defend the misleading citations.

Much of the personalized negativity of the second trackback is clearly generated by Wedel’s sense that the press unfairly aggrandized our work compared to theirs, which we somehow slighted and miscited.

Well, well, lots to dissect here.

First, they only address the “personalized negativity”. What about all the evidence? Not only is it not rebutted–it’s not even mentioned. Maybe they have an exhaustive, evidence-laden rebuttal lined up for that later. I honestly hope so.

Second, check out the form here:

  1. Wedel makes claim X
  2. But he’s jealous of our media exposure
  3. Therefore claim X is false

Textbook ad hom right here. Which is pretty ironic, since it’s the first pure example of the genre that has cropped up in this discussion so far, and it appears in a commentary that accuses me of ad hominem attacks.

Third, there is no question that Sereno made misleading statements to the media about the significance of Aerosteon. For example, when he claimed that it represented the first evidence of dinosaur sacs . . . about 150 years too late. That’s an easily verifiable fact, not an example of “personalized negativity”.

UPDATE: The “first evidence” thing was apparently hyperbole on the part of an underinformed journalist. At least, it’s not in the official press release, and Sereno denies ever saying it. He is right that one should never attribute to a possibly overzealous scientist what can be laid at the door of bad reporting–I’ve had some experience of this problem myself.

I wish now that I’d never brought up the misleading statements in the press. That opened me up to the ridiculous charge of being motivated by jealousy, and it’s quite beside the point. All of the important problems with the Aerosteon paper are scientific, not popular.

Fourth, I have no problem with other people working on pneumaticity and air sacs. Quite the contrary–it’s a big field and there’s plenty of work to be done. The more the merrier I say. I was very happy when Daniela Schwarz-Wings started working on pneumaticity in sauropods–her papers (including a new one out this week; congrats!) are thoughtful, innovative, and heck, just flat gorgeous:

Cervical diverticula in Brachiosaurus, from Daniela’s new paper (the original is a movie!).

So it doesn’t bother me that Sereno et al. (2008) wrote a paper about pneumaticity. What bothers me is the pervasive distortion of previous work and basic anatomy. I’m against that no matter what the subject.

Fifth, if anyone is curious about how it feels to languish in total obscurity, utterly ignored by the mainstream media, hoping against hope that someday I’ll make a valuable scientific contribution: I’m doing just fine, thanks. Fame’s a weed, repute a slow-growing oak, and I’m aiming for bark and acorns.

Neither we nor Pat O’Connor (pers. comm.) feel that personalized, ad hominem blogs like Wedel’s advance scientific understanding or enhance collegiality.

Hmm. I think it’s a bit pessimistic to say that my critiques didn’t advance scientific understanding. Certainly I’ve had a lot of people thank me for untangling the paper trail and showing what McLelland and others actually said about avian anatomy. A matter of taste, I suppose–although if Sereno was already familiar with what McLelland said, it’s odd that he got the cited information exactly backward.

Just for the record, I didn’t consult with Pat O’Connor or Leon Claessens about my critiques. We’re all big boys now, we can all speak for ourselves, and any fallout from SV-POW! will hopefully fall right where it belongs: on me. It’s not like I’m hiding.

As for collegiality . . . here’s where I stand:

  • As scientists we have a duty to obsessively document all previous relevant work and give credit where it is due, especially in cases where someone else got to the right answer first. I can’t speak for anyone else, but I got a real kick out of discovering that Heber Longman had worked out the basic dichotomy in internal structures of sauropod vertebrae decades before anyone else. And I made sure people knew about it (4th page here). I’ve always gratefully given credit to the giants upon whose shoulders I struggle to stand–among them, Owen, Seeley, Cope, Marsh, Longman, Janensch, Britt, Witmer, Wilson, Sereno (that’s right–he has done good and important work), O’Connor, Claessens, and Schwarz-Wings. Go look. Don’t forget to reread the Aerosteon paper while you’re at it. And then–yep, I am going to say it yet again–make up your own mind.
  • When authors engage in misleading citation and muddle the historical record–for example, by citing a paper in support of argument X when the cited paper actually states the precise opposite–people who are familiar  with the literature have a duty to explain how that literature is being misused. Collegiality doesn’t mean that we all keep our mouths shut no matter what (there’s a related word for doing that, and it also starts with a ‘c’). Sometimes we have to speak up and defend collegiality itself.
  • If someone brings a fact-based critique against your work, rebut them with facts or not at all. Calling names just makes you look weak and gives the impression that you have no factual case to pursue. My critique of the Aerosteon paper is “longwinded” only because it is so thoroughly documented. Sereno tries to paint it as a content-free exercise in pique–which is a pretty fair description of his own response. The irony could hardly be any richer.

I’m stuffed.

(On irony, not evidence. If anyone has any of the latter to bring against my critiques, I’ll be very happy to see it.)

Just got back from SVP, the annual meeting of the Society of Vertebrate Paleontology. SVP is always a blast; beyond the inherent coolness of four solid days of intense paleo-everything, I get a chance to catch up with my “SVP friends”–the pool of friends, some of them close, that I only see for a few days each year.

This year there was an extra bonus, which was making friends with a lot of paleobloggers that I’d previously only known as e-quaintances. There was even a paleoblogger lunch, which drew a big enough crowd that people at opposite ends of the table couldn’t effectively converse. That’s okay, though. I have a ‘critical mass’ theory about shared meals and parties, which is that they are usually lame unless there are enough people to sustain more than one conversation at the same time. By that standard, the paleoblogger lunch was a flying success. Unfortunately there weren’t any sauropods at the lunch, so it’s not really germane to our purpose here.

However, I did engineer a photo with a subset of paleobloggers that would be fair game, and you can see it above. This was at the welcome reception at the Cleveland Museum of Natural History. From left to right we’ve got Haplocanthosaurus (sauropod vertebra picture of the week: check), a disembodied floating T. rex head (it’s an oracle), a mosasaur, Megaloceros, Mammuthus (one of the least stinky of the stinkin’ mammals), and Allosaurus. Oh, and down in front are Julia Heathcote (Ethical Palaeontologist), moi, Amanda Northrop (Self-Designed Student), and Neil Kelley (microecos). Neil is the only real paleontologist of the bunch; you can tell because he’s holding a beer.

—————–

Mike drew the straw for our first birthday post, but I didn’t want to let it pass unremarked. This blog started as a joke on e-mail. “We ought to make a blog of nothing but sauropod vertebra pictures.” “Like APOD?” “Yeah, but weekly so we don’t drive ourselves crazy.” Next thing I knew, Mike had set up the blog and registered Darren and me as contributors. Then I posted a couple of times and BAM! we’re a year into it.

At first I thought we’d be struggling to get a year’s worth of material. I even made up a list of stuff I wanted to blog about, just in case I ever ran out of inspirado. I won’t tell you what’s on the list, but I will tell you that there are 27 things on the list and so far I’ve only gotten to six of them. So the outlook is good.

I have no idea how long we’ll be doing this. It never occurred to me after about the first month. If there is a Life Lesson (TM) in paleontology, it’s that nothing lasts forever. No sense getting an ulcer about it. Just enjoy what you have, and have a little fun.

We’ll do the same.

Every year the Fundación Conjunto Paleontológico de Teruel-Dinópolis in Teruel, Spain, gives out the International Award in Palaeontology Research, a.k.a. Paleonturology. ‘Paleonturology’ is a bit of a pun–it’s actually PaleonTurology; Turol is the old Roman name for the area, from which the Turia river, Turiasaurus, and the city and province of Teruel are all derived. (The photo above shows the sun setting over the hills near the Turiasaurus quarry.)

So what’s the deal with the award? You can find full rules and guidelines here, but here’s the short version: any paleontology paper published in the calendar year 2007 is eligible, just send in an application form (1 page) and a few copies of your paper or a PDF by November 15. If you win, you get a prize of 4500 Euros, which in the current economy is roughly a million dollars. You will also be invited to travel to Teruel next December to serve on the jury for Paleonturology 09, and attend a press conference where the book version of your winning paper will be unveiled and the next year’s winner will be announced. Depending on the state of the Paleonturology war chest, your trip may be partly or wholly paid for; all I paid for last year were souvenirs.

Those are merely the on-paper blandishments. If you take the trip to Spain, you’ll also get to:

. . . knock around some gorgeous medieval cities, like the 13th century fortress valley of Albarracin;

. . . hang out with the awesome folks at Dinópolis and other museums–here I am with Francisco “Paco” Gasco of Dinópolis (left) and Senor Maria, who runs a little museum in the village of Galve;

. . . visit incredible fossil quarries and tracksites (yes, that is an IKEA paper tape I have stretched out by the sauropod tracks–I keep one folded up in my wallet, where it takes up less space than a credit card, so I am never without an English/metric yard/meter tape, which is very handy when you work on sauropods),

. . . enjoy amazing food and drink, and be put up at a very nice hotel, probably with a view of a thousand-year-old church/fortress/tower out your window (there are four such towers in Teruel, so your odds are good). I got to go last December, and it was one of the greatest experiences of my life.

In the five years that the award has been given, winners have included grad students, young professionals, mid-career paleontologists, and near-retirees, from Spain, the US, Scotland, and Hungary, writing solo or with coauthors, on Pliocene hominins, clam shell construction, dinosaur gastralia, sauropod pneumaticity, and trilobite eyes. The point is that anyone, of any age, anywhere, writing about any paleontological subject has a chance to win.

To be as direct as possible: if you published a paper in paleontology in 2007 and don’t apply, you’re missing out on the chance of a lifetime.

That said, the recent winners have all had a few things in common. The papers have been about good-sized clades rather than single taxa, they’ve been well-illustrated and with a high general-interest factor (if I do say so myself), they’ve tended to address paleobiological questions, and none of them has been a shorty from one of the ‘high-impact’ journals (although such papers have been submitted). Still, even if your only paper from 2007 is a Nature note on a new Cambrian worm or the foot morphology of Pleistocene dragonflies, you’d be nuts not to submit, for two reasons: this year’s jury may be looking for something different, and yours might be the best paper they get.

Suppose your 2007 paper is on trilobite eyes or sauropod pneumaticity. Submit anyway. I was on the jury for Paleonturology 07, coming off two years of dinosaur papers, and a couple of dinosaur papers made it almost to the final cut. We all agreed that it didn’t matter what the paper was about, the qualities we were looking for were quality of research, broad interest, readability, and good (clear, helpful, aesthetically pleasing) illustrations. The trilobite eye paper won because it excelled in all of those areas, not because it was about trilobites rather than dinosaurs.

Did I mention that the province of Teruel is practically overrun with awesome sauropods? Aragosaurus (1987), Galveosaurus (2005), Turiasaurus (2006), and the newly-described Tastavinsaurus (2008) are just the tip of the iceberg. You will be hearing a LOT more about the Mesozoic biota of Teruel in the next few years. Here’s a dorsal vertebra of Tastavinsaurus, from Canudo et al. (2008:fig. 3).

I almost didn’t apply for Paleonturology 06. I was busy dissertating and it seemed like a long shot. But the application is one page long and I figured it would be stupid not to apply, so on the last possible day I printed it out, made copies of my paper, and dumped it all in the mail (that was back in the dark ages when you had to send paper copies; now you can apply over e-mail). When I think about how great my experience was, and how close I came to not applying, it makes me a little sick. Don’t be a doofus.

Reference

  • Canudo, J. I., Royo-Torres, R., and Cuenca-Bescós, G. 2008. A new sauropod: Tastavinsaurus sanzi gen. et sp. nov. from the Early Cretaceous (Aptian) of Spain. Journal of Vertebrate Paleontology 28(3):712-731.

What with all the fuss over Aerostron, it seems that we missed SV-POW!’s first birthday. Yes, it’s been just over a year since the very first post, Hello world!, showed us the Brachiosaurus brancai cervical vertebra HMN SII:C8 that we have seen so many times since in various ways. Since we kicked off on 1st October 2007, we’ve written a total of 82 posts (so more like one and a half per week than the one a week we advertised), and accumulated 1002 comments. (Congratulations to Andy Farke, who wrote the 1000th comment).

We’ve covered a lot of ground this year, from the the frivolous to the ferociously technical, so it’s hard to pick favourites. But from my own very biased perspective, I particularly enjoyed all eight days of the extended Xenoposeidon week, a rather exhausting series of posts that may make Xeno the most blogged dinosaur on the Internet — or at least, the most blogged mid-to-posterior partial dorsal vertebra. Also noteworthy was Matt’s flagrant playing-to-the-gallery “showdown” and Darren’s observation of a newly recognised site of pneumaticity (which I want to cite in a paper but won’t be allowed to). [Note added 22 June 2014: I did indeed cite it in a paper.]

Still, there’s no hesitation for me in picking my favourite series: it would have to be the four posts of axial-anatomy humiliation, Your neck is pathetic, Your torso is also pretty lame, Your sacrum is negligible and Your coccyx is contemptible.

A highlight this year was hearing SV-POW! namechecked by John Hutchinson in his introductory remarks at a workshop on functional morphology at the Natural History Museum. I also heard a rumour somewhere that Paul Upchurch tells his students to read this site. I have no idea whether that’s true or not, but I think it sounds pretty awesome so I am going to assume that it is until I hear otherwise.

I seem to recall when we kicked this thing off that we intended only to run it for one year, then archive it and shut it down. But it’s been going well enough, and we’ve enjoyed it enough, that there is no prospect of our calling it a day for a while yet. One of the reasons for that, I think, is that sharing a blog between three people has worked fantastically well. It’s meant that we’ve been able to keep up a half-decent rate of posting non-trivial articles without the load on any one of us being too great. (How on earth Darren manages to post daily on Tetrapod Zoology I can’t imagine). And this is my message to the world on the occasion of SV-POW!’s birthday: shared blogging is excellent, and I would love to see more team-run palaeo blogs out there. I’ve joked in the past about blogs like Basal Ornithopod Third Metatarsal Picture of the Week, but in all seriousness I would love to see people taking on super-specialised aspects of dinosaur palaeo as we’ve done here. I would read such blogs avidly, and our modest-but-non-negligible hit-counts here at SV-POW! (69,170 hits as I write this) suggests that there is a hardcore market for this kind of blog. So have at it, people!

As it happens, right around now is also an important time for me, Matt and Darren because on Friday night we submitted our first joint-authored paper. I’ll say no more about that now, because hopefully before too long we’ll be able to discuss the published version. [Note added 22 June 2014we did, extensively.] But making that submission was a landmark moment for The Three SV-POW!sketeers. Hopefully there’ll be more where that came from. [Note added 22 June 2014: there was.]

Finally, I give you the actual sauropod vertebra you’ve all been waiting for. It is a cast of the 2nd dorsal vertebra (the only one preserved ) of the holotype and only specimen of Puertasaurus reuili Novas et al. 2005, with lead author Fernando E. Novas himself for scale. This is one of those photos that just make you go “Woah!”; or, if you are so inclined, “Dude!”. Enjoy!

Puertasaurus reuili, second dorsal vertebra, anterior view.

Puertasaurus reuili, second dorsal vertebra, in anterior view, with Fernando E. Novas for scale.

Reference

In the last post I introduced Aerosteon, which has been touted as providing the first solid evidence for bird-like air sacs in non-avian dinosaurs, and I explained a little about how we know what we think we know about dinosaur air sacs. Aerosteon is legitimately cool and does show all of the features that Sereno et al. (2008) claim, and then some (see below). But the rest of the paper bugs me for several reasons: bad anatomy, bad phylogenetic reasoning, unfair criticism of other workers, and misleading citation of previous work. I’ll document every bit of this, but don’t forget that you can download almost all of the relevant papers for free. Don’t take my word for it, and don’t assume that any forthcoming rebuttals are accurate. Read the papers for yourself and make up your own mind.

Bad Anatomy #1: All cervical all the time (again)

In Part 1 we saw how Pat O’Connor and Leon Claessens (2005) cleared up about a century’s worth of confusion about how pneumatic bones map to specific parts of the avian respiratory system. In short, the cervical air sacs do not ever pneumatize any part of the skeleton past the mid-thoracic vertebrae, and the posterior thoracic, sacral, and caudal vertebrae are only pneumatized by diverticula of abdominal air sacs. Many non-avian dinosaurs have pneumatized vertebrae in the neck, thorax, sacrum, and tail, which are the diagnostic skeletal traces of air sacs both anterior and posterior to the lung, which are crucial for flow-through breathing like that of birds. O’Connor and Claessens never claimed that non-avian dinosaurs must have had flow-through breathing–that is unknowable for now–but they made a good case that most theropods, at least, had the requisite air sacs.

If there’s already great support for bird-like air sacs in non-avian theropods and has been for years, that would diminish the perceived importance of Aerosteon. Which may explain why Sereno et al. try to discredit O’Connor’s and Claessens’s work generally, and to discredit the importance of vertebral pneumaticity specifically. To do that, they resurrect the old canard about the cervical air sac pneumatizing the entire vertebral column.

Well, this is really something. I mean, O’Connor and Claessens (2005) looked at literally hundreds of birds and never found that once. What amazing new evidence do Sereno et al. bring to the table? Let’s find out:

“Second, cervical air sacs have been observed extending to the posterior end of the vertebral column in birds. Several authors have described cervical air sacs extending posteriorly beyond the abdominal air sacs in the ostrich (Struthio camelus) [21,36].” (p. 3)

So the case turns out to rest on refs 21 and 26, which are (thumbs through paper) McLelland (1989) [21] and Bezuidenhout et al. (1999) [36]. You’ll remember our old friend McLelland, who actually wrote:

“What can be stated with certainty is that in birds generally the cervical air sac aerates the cervical and thoracic vertebrae (Fig. 5. 22) and the vertebral ribs; the clavicular air sac aerates the sternum, sternal ribs, pectoral girdle and humerus (Fig. 5. 23); and the abdominal air sac aerates the synsacrum, pelvis and femur.” (pp. 271-272)

McLelland also mentions:

“In the Ostrich (Struthio camelus) a paired diverticulum arises from the vertebral diverticulum and extends through the peritoneal cavity beyond the abdominal air sac.” (p. 260)

The peritoneal cavity is the space containing the viscera, so these peritoneal diverticula are not going to the vertebrae, they’re going to the cloaca. Their existence provides no support for the contention of Sereno et al. that the entire vertebral column can be pneumatized by cervical air sacs, which is explicitly contradicted by the earlier McLelland quote (not to mention by the gigantic pile o’ dead birds cut up by O’Connor and Claessens).

Let’s go on to Bezuidenhout et al., who wrote:

“The caudal vertebral diverticula [of the cervical air sacs] extend caudally along the vertebral column, invading the spaces between the vertebrae and the vertebral ribs, and between the vertebrae and the oesophagus dorsally to the lungs, up to the level of the sixth vertebral ribs.” (p. 324)

“The cranial extension [of the diverticula perirenalia of the abdominal air sacs] formed secondary diverticula that invaded the spaces between the heads and tubercles of vertebral ribs 7-9 and the corresponding thoracic vertebrae (Fig. 3, 4, and 5). These diverticula were related to the dorsal border of the lung. The caudal extension was situated dorsally to the kidney. It formed secondary diverticula that invaded the spaces between the synsacrum and ilium (Fig. 3, 4, and 5).” (p. 322)

So far, so good. The vertebral diverticula of the cervical air sacs only go back as far as the middle of the thorax, and synsacrum is pneumatized by abdominal air sacs. But wait:

“Roche (1888) and McLelland (1989) describe paired extensions of the vertebral diverticula of the cervical air sacs in the ostrich that extend caudally into the peritoneal cavity beyond the abdominal air sacs. Although these extensions of the vertebral diverticula were not specifically identified in the present study, similar structures have been observed by the authors in post mortem material that was not part of this study.” (pp. 324-325)

So the story from Bezuidenhout et al. is precisely the same as from McLelland: the diverticula of the cervical air sacs that pneumatize the vertebral column only go back to the mid-thorax; secondary diverticula from the vertebral diverticula do extend all the way to the cloaca, but do so within the peritoneal cavity, where they are no longer in contact with the vertebrae; and the synsacrum is pneumatized by diverticula of the abdominal air sacs, which are in contact with the vertebrae.

Please, please, can we as a community drop the idea that the cervical air sacs can pneumatize the back half of the vertebral column? Nobody’s ever seen it happen, a gigantic search effort found no evidence that it’s possible (O’Connor and Claessens, 2005), and the refs that people keep citing on it–McLelland (1989) and Bezuidenhout et al. (1999)–actually talk about something completely different.

Bad Anatomy #2: Pleurocoels and the spectre of continuous pneumatization

“Pleurocoel” is an old term for the big pneumatic cavities that are often present in the vertebral centra of sauropods and theropods. For about a decade and a half, almost everyone who has worked on pneumaticity in dinosaurs has advocated abandoning the term, and calling these structures either pneumatic fossae (if they don’t lead to internal chambers) or pneumatic foramina (if they do)–see Britt (1993, 1997), Wedel et al. (2000), Wedel (2003b), O’Connor (2006), Taylor and Naish (2007), among others. Why? Because from the start the term “pleurocoel” was not rigorously defined, so it was variously used to mean pneumatic foramina, pneumatic fossae, internal pneumatic chambers, or some combination of the above. It is much better to just describe the actual morphology using informative terms.

Sereno et al. use the term pleurocoel. And the result is predictable: anatomical confusion.

“We are inclined to support the latter, more conservative interpretation that pleurocoels in nonavian dinosaurs are a product of paraxial cervical air sacs and provide, at best, ambiguous evidence for intrathoracic ventilatory air sacs. First, pleurocoels are rare in birds, and no living bird has an unbroken cervical-to-caudal series of pleurocoels as occurs in some nonavian dinosaurs, including the one we describe below [31]. As Wedel [26] has underscored, pleurocoels extend posteriorly in the axial column of saurischian dinosaurs to a variable extent, but neither adults nor juveniles of any species show an apneumatic gap. Allotting an unbroken series of pleurocoels of graded form, as in the case we describe below, to three different pneumatic sources (cervical air sacs, lung diverticulae, abdominal air sacs) is difficult to defend. Drawing a direct analogy based on birds for the source(s) of pneumaticity in the posterior axial column in nonavian dinosaurs [22,31,33], thus, is problematic.” (p. 3)

That all sounds pretty convincing . . . until you realize that “pleurocoels” are pneumatic foramina, in which case the entire paragraph becomes misleading at best and flatly incorrect at worst. I’ll show you–here are the key sentences with “pleurocoel” replaced with “pneumatic foramen”:

“First, [pneumatic foramina] are rare in birds, and no living bird has an unbroken cervical-to-caudal series of [pneumatic foramina] as occurs in some nonavian dinosaurs, including the one we describe below [31].”

Just flat wrong. In many birds the vertebral column is continuously pneumatized. That the pneumatic foramina of birds are typically small and tucked up inside the cervical rib loops (unlike the much larger pneumatic foramina of most saurischians) is beside the point. There certainly are interesting questions about why the size of pneumatic foramina varies among taxa and over evolutionary time, but in this context distinguishing between small pneumatic foramina and big “pleurocoels” only obscures the similarity of vertebral pneumatization in birds and other saurischians.

I really don’t want to talk about my own work here, but since it’s cited misleadingly, I have to do so for a while:

“As Wedel [26] has underscored, [pneumatic foramina] extend posteriorly in the axial column of saurischian dinosaurs to a variable extent, but neither adults nor juveniles of any species show an apneumatic gap.”

Neither do most adult birds, as I took pains to point out in the paper they cite (Wedel 2003a). Because the vertebral column of birds is invaded by up to three sets of diverticula–from the cervical air sacs, lungs, and abdominal air sacs–juveniles often have these apneumatic gaps. But in adults the diverticula from the different sources often meet up and anastomose, so you get a continuous series of pneumatic foramina right down the column. Oh, speaking of which:

“Allotting an unbroken series of [pneumatic foramina] of graded form, as in the case we describe below, to three different pneumatic sources (cervical air sacs, lung diverticulae, abdominal air sacs) is difficult to defend.”

Really? Because that’s exactly what happens in most birds.

The absence of an apneumatic gap (or “pneumatic hiatus” [Wedel 2003a]) in dinosaurs is not evidence of anything. If we found one, it would be additional evidence for pneumatization of the vertebral column from multiple sources, but that’s already well-supported. And if we don’t find one, we can’t assume they didn’t have multiple routes of pneumatization, because many birds also lack pneumatic hiatuses as adults. Even in birds that typically do have pneumatic hiatuses, like chickens, the hiatuses are not usually present in all adults. The absence of pneumatic hiatuses in described non-avian dinosaurs could easily be a side-effect of inadequate sampling, for three reasons:

  1. Pneumatic hiatuses are most likely to show up in very young individuals, before the diverticula from different sources have time to meet up. We have very few complete and well-preserved baby saurischians–and by well-preserved, I mean preserved well enough to be able to trace pneumatic features right down the column. The pretty but pancaked theropods from Liaoning won’t cut it (I know, I’ve looked).
  2. Nobody knew to be on the lookout for pneumatic hiatuses until 2003, when I coined the term and pointed out their importance, so there hasn’t been very much time in which to find them.
  3. Not everybody works on pneumaticity, and those of us who do have only seen a small fraction of the world’s dinosaurs. It is possible that pneumatic hiatuses are present in well-known dinosaurs and no one has noticed–yet.

Let’s finish up with the pleurocoel mess:

“Drawing a direct analogy based on birds for the source(s) of pneumaticity in the posterior axial column in nonavian dinosaurs [22,31,33], thus, is problematic.”

No, it’s not. But you can certainly make it seem problematic if you use ambiguous, uninformative terms that obscure the fundamental similarity in vertebral pneumatization in birds and other saurischians.

Bad Phylogenetic Reasoning

“Second, cervical air sacs have been observed extending to the posterior end of the vertebral column in birds. Several authors have described cervical air sacs extending posteriorly beyond the abdominal air sacs in the ostrich (Struthio camelus) [21,36]. Ratites have relatively smaller abdominal sacs than in other birds and, as nonvolant basal avians, serve as better analogs for nonavian saurischians than volant neognaths [37].” (p. 3)

We’ve already dealt with the first two sentences, now let’s handle the third:

“Ratites have relatively smaller abdominal sacs than in other birds”

True, but irrelevant. First, it’s not the size of the abdominal air sacs that’s at stake, it’s their ability to pneumatize the posterior part of the vertebral column. We’ve already seen that both of the papers Sereno et al. cite actually say explicitly that the posterior vertebral column of birds is pneumatized by diverticula of the abdominal air sac, even in the ostrich. Second, we can’t assume that the small abdominal air sacs of ratites represent the primitive condition. There are many cases of reduction, loss, or fusion of air sacs in birds, and the abdominal air sac is no exception. Since Sereno et al. like McLelland (1989) so much, we’ll see what he had to say:

“[The abdominal air sac] is reported to be very poorly developed in the Accipitridae, Fulica, Fregata and ratites (Groebbels, 1932); penguins (Spheniscidae), rheas (Rheidae) and loons (Gaviidae) (Duncker, 1971); and large passeriform species and parrots (Psittacidae) (Schulze, 1910). It appears to be especially small in hummingbirds (Trochilidae) (Stanislaus, 1937) and in Casuarius and Apteryx (Groebbels, 1932).” (p. 264)

If small abdominal air sacs are the criterion for choosing extant analogues, maybe we should be comparing sauropods to hummingbirds. Moving on:

“and, as nonvolant basal avians, serve as better analogs for nonavian saurischians than volant neognaths [37].”

Nonvolant here is a red herring; like non-avian saurischians, ratites are flightless, but they’re definitely secondarily flightless, so the apparent similarity is homoplasy, not plesiomorphy.

Sereno et al. think they’ve found a single taxon–the ostrich–in which the cervical air sac does pneumatize the entire vertebral column, and for their “all cervical all the time” model of dinosaurian pneumaticity to fly, they need to make the case that ostriches are the best possible models for all non-avian saurischians. But the similarities they use to argue this are either homoplastic throughout Aves (small abdominal air sacs) or homoplastic between ratites and non-avian saurischians (flightlessness). So it would be a lousy phylogenetic argument even if their anatomical assertion about the ostrich was correct–which it’s not.

Bad Behavior #1: Unfair Criticism

I urge you to just go read Sereno et al. and see how thoroughly dismissive they are of everything ever written by O’Connor and Claessens. I’ll only work through a couple of examples, but there are plenty of others.

Here’s a choice passage:

“Recently O’Connor proposed that axial pneumaticity in the abelisaurid theropod Majungasaurus can be used ‘‘to refine inferences related to pulmonary structure’’ [35: 159], because ‘‘it shows a reduction in the pneumaticity in the last two dorsal neural arches, with enhanced pneumaticity in sacral aches [31: 22]. Specifically, the ‘‘size and number of neural arch foramina’’ are reduced in dorsal vertebrae 12 and 13, whereas the same are ‘‘enhanced’’ in sacral vertebrae, indicating ‘‘two different sources of pneumatization’’ [33: 253]. The actual differences, however, were not described, and dorsal vertebrae 12 and 13 were not figured until recently [35: figs. 3, 12, 13].” (p. 11)

See, this is funny, because in the last sentence Sereno et al. are picking on O’Connor for the lag of a whole two years between the Nature paper (O’Connor and Claessens 2005) and the monographic description of the Majungasaurus vertebrae (O’Connor 2007). It’s funny because almost all of the many critters named by Sereno and various sets of coauthors have never received any morphological description beyond the original 3-5 page writeups in the weeklies. Here’s a short, non-exhaustive list, with original years of publication:

Eoraptor - 1993

Afrovenator - 1994

Deltadromeus - 1996

Suchomimus - 1998 (okay, this one did get its furcula described in 2007)

Jobaria - 1999

Rugops - 2004

Next to any of those, a two-year turnaround is practically instantaneous. Anyway, Sereno et al. go on to try to explain how the diminution of pneumaticity in the middle of the vertebral column of Majungasaurus is totally not like a pneumatic hiatus at all. Then it’s on to Aerosteon:

“The situation in Aerosteon is instructive for the contrast that it provides across the same vertebral transition. In this case, pneumaticity appears to peak in the last dorsal, with a large pneumatic canal in the transverse process that is not present in sacral vertebrae (Figure 4C). The pleurocoels, in addition, develop a posterodorsally inclined partition in the posteriormost dorsal vertebrae that passes into the sacral series unchanged. The axial column of Aerosteon does not suggest a clean partitioning based on the number or size of pneumatic spaces, but rather a gradation in pleurocoel form that extends from the anterior cervical vertebrae through the distal caudal vertebrae.” (p. 12)

Three things to note here. First, on the previous page, Sereno et al. bashed on O’Connor and Claessens for not figuring all of the relevant vertebrae in their first, short paper. But here they mention a partition in the pneumatic fossae that passes into the sacral vertebrae, without actually figuring any sacral vertebrae in the entire paper. PLoS ONE is online-only and doesn’t charge for length or figures, so there is really no reason not to show those vertebrae if they’re important. Second, their own figures are at odds with their argument. Figures 5 and 6 show cervical centra with big pneumatic foramina, and Figure 9 shows prominent pneumatic foramina in the caudal centra. But Figures 7 and 8 show that in the posterior dorsals the “pleurocoels” are reduced to shallow fossae. It’s been clear for a while that fossae are developmentally and evolutionarily antecedent to foramina (for a recent graphic example, see Wedel 2007:text-fig 8), so those middle dorsals appear to be stuck at a less pneumatized stage than the vertebrae on either side.* Which is exactly what O’Connor and Claessens (2005) described for Majungasaurus. Finally, it’s easy to miss the shift from foramina to fossae and back in the vertebral column of Aerosteon because they’re all collectively called pleurocoels–another case of an important morphological similarity being obscured by the use of an ambiguous term.

*It is true that the posterior dorsals of Aerosteon have highly pneumatic neural spines, but there is some evidence in sauropods that the vertebral centra and neural spines are pneumatized independently (see page 215 here). And regardless of what is going on in the neural spines, the “pneumatic diminution” (my term, newly coined) in the centra of Aerosteon is still interesting and worthy of comment. Odd that they didn’t mention it.

In short, Sereno et al. knock O’Connor and Claessens (2005) for

  • letting a little time pass between the short paper and the monograph, when Sereno and previous sets of coauthors hardly monograph anything;
  • not figuring all of the relevant vertebrae in the short paper, when they don’t, either, in their much longer paper; and
  • making a big deal about the “pneumatic diminution” in Majungasaurus, when the vertebral centra of Aerosteon show something very similar.

There are lots of things that I could say here. The driest and least loaded is that it’s difficult to take the criticisms of Sereno et al. seriously when they are guilty of the same or worse on every single point.

Bad Behavior #2: Misleading use of citations

Here’s another bit that requires some explanation:

“The posterior thoracic, synsacral, and caudal vertebrae, in contrast, are pneumatized by diverticula extending directly from the lung or from abdominal air sacs [1, 16, 19, 21, 22].”

One thing I just flat hate about a lot of “high-impact” journals is that they use numbered references instead of parenthetical citations by authors’ names. It makes it really easy to just read a paper without seeing who is being cited and who isn’t. And that can be a problem. The five refs cited in this sentence are King (1966), Muller (1908), Duncker (1971), McLelland (1989), and O’Connor (2004). Of those, King and McLelland are review papers; only Muller, Duncker, and O’Connor present the results of original research. But Sereno et al. do cite O’Connor here, so what’s my beef? They only cite his 2004 paper, which–crucially–does not include the devastating falsification of the “all cervical all the time model” that one can find in O’Connor and Claessens (2005) and O’Connor (2006). So even though the latter two papers are more recent, more comprehensive, and more relevant, they’re not cited here. Hmm. Is it because they contradict (with shedloads of evidence) the “all cervical all the time” model that Sereno et al. are trying to develop for non-avian saurischians?

The very next sentence:

“Some authors have concluded, therefore, that the lung and abdominal air sacs must also be responsible for pneumaticity in the posterior half of the axial column in nonavian dinosaurs and, on this basis, have packed the thoracic cavity of theropods with a full complement of avian ventilatory air sacs [33].”

If you’re keeping track at home, ref 33 is O’Connor and Claessens (2005). Now that Sereno et al. have something to slate them for, it’s time for a citation.

But wait. O’Connor and Claessens (2005) did not “pack the thoracic cavity with a full complement” of air sacs; they were very explicit in the text about having only found evidence for some of the air sacs (namely cervical and abdominal) from both the anterior and posterior functional sets. Their figure 4 shows a Majungasaurus with all of the regular avian air sacs, but they say in the caption that showing the other air sacs in light grey “represents tertiary-level inferences emphasizing the uncertainty surrounding the reconstruction of soft tissues not constrained by osteological evidence.” Hardly the reckless abandon one would assume from the rhetoric of Sereno et al. (This gets better–see Update 2 below.)

And it gets worse. O’Connor and Claessens (2005) are not the only authors who have inferred that all the basic components of the avian respiratory system were present in some or all non-avian saurischians. Brooks Britt (1993, 1997) came to the same conclusion. So have I (Wedel et al. 2000, Wedel 2003a,b, 2005, 2007). Sereno et al. don’t give Britt the same snide treatment they give O’Connor and Claessens, possibly because one of the authors is currently collaborating with Britt on describing a couple of new sauropods. They spare me for a different reason. Next sentence:

“An opposing view is that the continuous series of pleurocoels observed in many nonavian dinosaurs suggests that the nonventilatory, paraxial cervical air sacs extended posteriorly along the column [26,34]. We are inclined to support the latter, more conservative interpretation . . .”

Refs 26 and 34 are Wedel (2003a) and Chinsamy and Hillenius (2004), respectively. We’ve already seen Chinsamy and Hillenius in the last post; they recycled the mistaken text from Ruben et al. (2003) mis-citing McLelland (1989). And now my situation is clearer, too: Sereno et al. don’t include me in their slam of O’Connor and Claessens–even though I am every bit as ‘guilty’–because I am supposed to represent the counterargument.

But if you actually go read Wedel (2003a) you’ll see that the paper is about as pro-abdominal-air-sac as the available evidence allowed me to be. I raised the possiblity of “all cervical all the time” because this was back in the dark ages when no one knew for sure whether it happened in birds or not–i.e., before O’Connor and Claessens (2005) straightened everything out–but I didn’t sell it. In fact, in that paper I came up with pneumatic hiatuses as a way to falsify the “all cervical all the time” model in fossil taxa; the fact that no-one has published any yet doesn’t mean the hypothesis can’t be falsified from another route. And it has been, by O’Connor and Claessens (2005)–the very paper that Sereno et al. are trying to use my paper against!

So here’s the short version: Chinsamy and Hillenius (2004) were wrong, because they borrowed their text from Ruben et al. (2003), who misquoted McLelland (1989) (ironically, since Sereno et al. make precisely the same mistake). And I was wrong (for the purposes to which Sereno et al. put my work) because I thought that pneumatization of the whole vertebral column by the cervical air sacs was at least a possibility, before O’Connor and Claessens (2005) showed that it is not, for living saurischians at least. Sereno et al.’s critique of O’Connor and Claessens is empty fluff, and their counterargument is based on arguments that were either wrong in the first place or have already been falsified–by O’Connor and Claessens.

Conclusion

There are plenty of other places where Sereno et al. unfairly bash on O’Connor and Claessens and conveniently under-cite those authors who got to the pneumaticity party before them. I’d carefully explain them all, but life is too short and I’ve satisfied my conscience by exposing some of their worst excesses.

Sereno et al. are wrong about avian anatomy. Their phylogenetic inferences are wrong. They use selective citation to suppress genuine contributions and resurrect falsified hypotheses, but those hypotheses remain falsified. They use obfuscatory terminology to obscure important similarities between birds and non-avian saurischians, including Aerosteon. Their new model of avian lung evolution is based on old misconceptions about pneumatization in birds, and flatly contradicted by the very papers they cite to support it.

Verdict: COSMIC FAIL.

Thanks for slogging through all this. Here’s your sauropod vertebra:

UPDATE: I’ve been bad (or not)

I have been privately accused of ethical misconduct for something I said in this post, so I will now preeptively fisk myself by way of explanation.

A critic, whose name I will not mention (but it’s not Brooks Britt), accused me of publicly divulging information exchanged in confidence, in this section:

“Sereno et al. don’t give Britt the same snide treatment they give O’Connor and Claessens, possibly because one of the authors is currently collaborating with Britt on describing a couple of new sauropods.”

The critic claims that I learned of the collaboration between Britt and one of the authors of the Aerosteon paper in a private conversation, and that I was “out of line” in posting it in a public forum. The critic is partly right but mostly wrong. I did hear about the collaboration in a private conversation in either late 2006 or early 2007, but it was information I already knew from another, more public source. Brooks Britt delivered the talk for the Chure et al. (2006) abstract at the SVP meeting in October, 2006. At the podium, in front of a few hundred people, he mentioned that one of the Sereno et al. (2008) authors was collaborating with him on the description, and then showed a phylogenetic analysis generated by that collaborator (no prizes for guessing which Sereno et al. author). So all of the literally hundreds of people who were in that session knew about the collaboration, although I can’t say how many of them have remembered that it was mentioned.

The 2006 SVP abstract book carries this warning: “Observers are reminded that the technical content of the SVP sessions is not to be reported in any medium (print, electronic, or Internet) without the prior permission of the authors.” I’m not sure if knowing who is collaborating with whom counts as technical content or not. And I don’t really care. It’s not top-secret research results, and literally hundreds of people know about it, or did for a few minutes back in 2006 (probably just until Mary Schweitzer kicked us in the brainpan with her T. rex histo). And more importantly, when authors engage in selective citation, singling out some for praise and harshly condemning others when we were all about equally “guilty”, they shouldn’t be surprised if some of those so used publicly speculate about their motives in doing so. If nothing else, it may persuade them not to behave that way in the future.

UPDATE 2: Packing in the air sacs

There is an amusing coda to the bit where Sereno et al. (2008) accuse O’Connor and Claessens (2005) of having “packed the thoracic cavity of theropods with a full complement of avian ventilatory air sacs”. You’ll recall that O’Connor and Claessens did in fact show all of the avian air sacs, but greyed out the clavicular, anterior thoracic, and posterior thoracic sacs for which they had no direct evidence, and put a huge disclaimer about those air sacs in the figure caption.

I ignored the non-blog coverage of the Aerosteon story until recently, which is a shame, because it’s most interesting. Here’s the full-color Aerosteon restoration that went out to the media outlets from Sereno’s Project Exploration (borrowed from the National Geographic News page):

Notice that all of the air sacs are colored in, including those for which even Aerosteon has no direct evidence (i.e., the anterior and posterior thoracic air sacs). But wait–could the pneumatic gastralia be evidence of those phantom sacs? Not according to Sereno et al.:

“The external (ventral) position of the pneumatopores suggests that the pneumatic diverticulae lay in superficial tracts outside the gastral cuirass. It seems unlikely that pneumatic diverticulae would penetrated the ventral thoracic wall to access external pneumatopores, when entering the gastralia directly from their internal (dorsal) surface would be much easier. A plausible explanation may be that these ventral pneumatic tracts are part of a subcutaneous system, which is present to varying degrees in birds and is composed of diverticulae from cervical, clavicular, and abdominal air sacs [1,21,22]. Subcutaneous diverticulae usually exit the thoracic cavity and extend under the skin to distant body surfaces. In the brown pelican (Pelecanus occidentalis), for example, diverticulae of the clavicular air sac exit the thoracic cavity dorsally and extend under the skin to reach the entire ventral surface of the thorax [61].” (p. 13)

I have no quibbles with any of that. It’s just curious that Sereno et al. would eviscerate O’Connor and Claessens for going overboard on air sacs (when O&C were actually quite careful) and then do the same thing, sans caveats, in their press release.

Parting thought, from the National Geographic News story (emphasis added):

“The fossil [Aerosteon] provides the first evidence of dinosaur air sacs, which pump air into the lungs and are used by modern-day birds, said Paul Sereno, the project’s lead researcher and a National Geographic explorer-in-residence.” [NOTE: This overstatement is not in the Aerosteon press release, and may have been hyperbole by an underinformed journalist.]

References

Pneumatic dorsal vertebrae of Aerosteon (Sereno et al. 2008:fig 7)

Big news this week: Sereno et al. (2008) described a new theropod, aptly named Aerosteon (literally, “air bone”), with pneumaticity out the wazoo: all through the vertebral column, even into the distal tail; in the cervical and dorsal ribs; in the gastralia; in the furcula; and in the ilium. This is huge news, and it’s free to the world at PLoS ONE. Pneumatic vertebrae and ribs are the norm in theropods and most sauropods (hence our interest here), but the axial elements of Aerosteon are extremely pneumatic. A pneumatic furcula was reported in the dromaeosaur Buitreraptor (Makovicky et al. 2005), but Aerosteon appears to be a basal tetanuran so it pushes furcular pneumaticity a good distance down the tree. Most exciting are the pneumatic ilium and gastralia. Ilial pneumaticity has been suspected in some sauropods and non-avian theropods but the evidence has been lacking until now; either the ilial chambers could not be traced to pneumatic foramina, or the suspected pneumatic foramina could not be shown to lead to internal cavities. Pneumatic gastralia are really wacky–according to the paper, it is the first discovery of pneumatized postcranial dermal bone, and I certainly don’t know of any other examples.

Why is this important? In extant birds, the furcula is only pneumatized by diverticula of the interclavicular air sac, and the ilia are only pneumatized by the abdominal air sacs, so the presence of big pneumatic foramina leading to big internal chambers in both the furcula and ilia of Aerosteon is evidence not just for bird-like air sacs, but specifically air sacs from both the cranial and caudal groups within the thorax that are responsible for the flow-through lung ventilation of birds. It’s pretty dynamite stuff.

Right?

Right?

We-ell . . . There is no question that the fossil material is pretty stunning and shows all the morphological features that Sereno et al. claim (and even some that they don’t–stay tuned for Part 2). But there are parts of the paper that I disagree with, and to understand why, I have to tell you a little about recent research on pneumaticity in sauropods and theropods. In this post and the next I’ll be discussing papers by Pat O’Connor and Leon Claessens, as well as my own; all of these are freely available at the links just provided. So, please, if you have a beef with anything I say below, go read all the relevant literature for yourself, weigh the evidence, and make up your own mind.

First, a brief sketch of what we’ve been up to. Except for the occasional weirdo (surveyed on the third page here), the only extant tetrapods with postcranial pneumaticity are birds. In birds, postcranial pneumaticity is the skeletal footprint of the lung/air sac system. So if we find postcranial pneumaticity in dinosaurs–say, sauropods, or Aerosteon–we can use the ‘rules’ from birds to make inferences about the morphology of the respiratory system. We can’t tell which way the air was blowing in the lungs, but we can tell the minimum extent of the pneumatic diverticula, and we can make some inferences about lung structure. All of the logic of this is really nicely and concisely laid out in O’Connor and Claessens (2005), which is only three pages of text, so if you want to know more, just go read it.

The hypothesis that sauropods and theropods had air sacs like that of birds has been opposed in a couple of ways: pneumaticity doesn’t tell us anything, and vertebral pneumaticity only indicates cervical air sacs. Neither of these counterarguments has gotten much traction, probably because they’re so easily falsified. Let’s have a look.

Historical Misconception #1: Pneumaticity Is Completely Uninformative

“Without integrating functional data into the study, the most that can be inferred from post-cranial pneumaticity in extinct animals is that, as pointed out by Owen (1856), the pneumatized bones received parts of the lung in the living animal… Because pneumaticity has no known functional role in ventilation or thermoregulation or metabolic rates, its usefulness as a hard-part correlate for lung structure and metabolism is, unfortunately, questionable.” (Farmer 2006, pp. 91-92)

Farmer does not distinguish here between inferences based on the presence of postcranial pneumaticity and inferences based on the distribution of postcranial pneumaticity. If all we know about a bone is that it is pneumatic, then she is correct in stating that the most we can conclude is that it was connected to the respiratory system in some way. (The thermoregulatory function of pneumaticity discussed by Seeley [1870] has been demonstrated for cranial pneumaticity [Warncke and Stork 1977] but not for postcranial pneumaticity [Witmer 1997, O'Connor 2006]). But the inference of cervical and abdominal air sacs in non-avian dinosaurs does not depend simply on the existence of postcranial pneumaticity. Rather, these inferences are based on patterns of postcranial pneumaticity that are diagnostic for specific air sacs.

Verdict: Fail.

Historical Misconception #2: Vertebral Pneumaticity Only Comes From Cervical Air Sacs

“Pneumatization of the vertebrae and ribs is invariably accomplished by diverticuli [sic] of the cervical air sacs (McLelland 1989a), which are located outside the trunk and contribute little, if anything, to the respiratory air flow (Scheid and Piiper 1989). Presence of pneumatized vertebrae in non-avian dinosaurs therefore only speaks of the possible presence of such nonrespiratory diverticuli [sic], and cannot be regarded as indicative of an extensive, avian-style abdominal air-sac system.” (Ruben et al. 2003, p. 153)

This remarkable statement is repeated pretty much verbatim by Chinsamy and Hillenius (2004) and Hillenius and Ruben (2004). What’s remarkable about it is that is so thoroughly inaccurate. People have known for more than 100 years that the posterior parts of the vertebral column of birds are pneumatized by diverticula of the abdominal air sacs, and said as much in many papers–for example, Muller (1908), Cover (1953), King (1966, 1975), Duncker (1971), Hogg (1984a, b), and Bezuidenhout et al. (1999). Still, if McLelland said that the vertebrae and ribs are “invariably” pneumatized by diverticula of the cervical air sacs, it’s not their bad, right?

Okay, first, McLelland (1989) is a review paper and presents no new data (this will become really important later on, when we get back to Aerosteon). Second, here’s what McLelland actually said:

“What can be stated with certainty is that in birds generally the cervical air sac aerates the cervical and thoracic vertebrae (Fig. 5. 22) and the vertebral ribs; the clavicular air sac aerates the sternum, sternal ribs, pectoral girdle and humerus (Fig. 5. 23); and the abdominal air sac aerates the synsacrum, pelvis and femur.” (pp. 271-272)

By listing the synsacrum and pelvis separately, McLelland clearly meant that the synsacral vertebrae are pneumatized by the abdominal air sac, and this is confirmed by the sources he cited elsewhere: Hogg (1984a, b).

So Ruben et al. (2003)–and those who recycled that text–were relying not on any of their own research, or any primary research at all, but on a single review paper that actually says exactly the opposite of what they claim it does, based on other primary research papers (those by Hogg) that themselves say the same (opposite) thing.

Verdict: EPIC FAIL.

The Brave New Post-2005 World

He said, she said, yadda yadda. There are lots of inaccuracies in the literature, and it’s not like birds are extrasolar planets. If we want to know what is going on inside them, we can just look. That’s what O’Connor and Claessens (2005) did, by injecting and dissecting 200+ birds representing 19 avian orders. Know what they found? The cervical diverticula do not EVER go farther down the vertebral column than the middle of the thorax. NEVER EVER. So if you find pneumatic vertebrae in the posterior dorsals, sacrum, or tail, it’s pretty likely that they were pneumatized by diverticula of the abdominal air sacs.

I say “pretty likely” because it’s always possible that dinosaurian diverticula worked differently, and that the air that got into the posterior part of the vertebral column actually came from the cervical air sacs, or the lungs directly, or from arse gills, or possibly magic rocks. We can imagine lots of ways for air to get into the back half of the vertebral column, but the only one that we’ve ever seen work in a tetrapod* is diverticula of the abdominal air sacs. Dinosaurs may have worked differently, and had wacky cervical diverticula or arse gills or whatever. But those are not the obvious choices, and we don’t have any evidence for them; all the available evidence points to abdominal air sacs.

*Some osteoglossomorph fishes pneumatize the vertebral column from the swimbladder–strange but true!

So, great. The old confusion has been swept away by a blood-dimmed tide of bird carcasses and good science. Pneumatization of the posterior vertebral column implies abdominal air sacs. The combination of pneumaticity in the neck, trunk, sacrum, and even tail of many theropods and sauropods shows that both cervical and abdominal air sacs were present (as in Apatosaurus, above), which means air sacs both anterior and posterior to the lungs, which means that most (maybe all) saurischians had at least some of the gear they would need for flow-through breathing like that of birds (O’Connor and Claessens 2005, O’Connor 2006, Wedel 2007).

And yea, verily, anatomical accuracy and scientific clarity reigned throughout the land . . .

. . . until now.

TO BE CONTINUED.

References

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