Here’s the story of my fascination with supramedullary airways over the last 20 years, and how Jessie Atterholt and I ended up working on them together, culminating with her talk at SVPCA last week. (Just here for the preprint link? Here you go.)

Müller (1908: fig. 12). Upper respiratory tract, trachea, and lungs in pink, air sacs and diverticula in blue. DSPM = diverticulum supramedullare.

Way back when I was working on my Master’s thesis at the University of Oklahoma and getting into pneumaticity for the first time, Kent Sanders found Müller (1908) and gave me a photocopy. This would have been the spring or summer of 1998, because we used some of Müller’s illustrations in our poster for SVP that year (Wedel and Sanders 1998). Müller’s description of pneumatic diverticula in the pigeon formed part of my intellectual bedrock, and I’ve referenced it a lot in my pneumaticity papers (complete list here).

One of the systems that Müller described is the diverticulum supramedullare, a.k.a. supramedullary diverticula, or, informally, supramedullary airways (SMAs). Traditionally these are defined as pneumatic diverticula that enter the neural canal and lie dorsal (supra) to the spinal cord (medulla), although O’Connor (2006) noted that in some cases the diverticula could completely envelop the spinal cord in a tube of air. I yapped about SMAs a bit in this post, and they’re flagged in almost every ostrich CT or dissection photo I’ve ever published, here on the blog or in a paper.

CT sections of a Giraffatitan cervical, with connections between the neural canal and pneumatic chambers in the spine highlighted in blue. Modified from Schwarz & Fritsch (2004: fig. 4).

Fast forward to 2006, when Daniela Schwarz and Guido Fritsch documented pneumatic foramina in the roof of the neural canal in cervical vertebrae of Giraffatitan. As far as I know, this was the first published demonstration of SMAs in a non-bird, or in any extinct animal. Lemme repeat that: Daniela Schwarz found these first!

OMNH 60718: too ugly for radio. This is an unfused neural arch in ventral view. Anterior is to the left. Neurocentral joint surfaces are drawn over with ladders; pneumatic foramina lie between them.

Shortly thereafter I independently found evidence of SMAs in a sauropod, in the form of multiple pneumatic foramina in the roof of the neural canal in an unfused neural arch of a basal titanosauriform (probably a brachiosaurid) from the Cloverly Formation of Montana. It’s a pretty roadkilled specimen and I was busy with other things so I didn’t get around to writing it up, but I didn’t forget about it, either (I rarely forget about stuff like this).

Then in 2013 I went to the Perot Museum in Dallas to see the giant Alamosaurus cervical series, and I also visited the off-site research facility where juvenile Alamosaurus from Big Bend is housed. When Ron Tykoski let me into the collections room, I was literally walking through the door for the first time when I exclaimed, “Holy crap!” I had spotted an unfused neural arch of a juvenile Alamosaurus on a shelf across the room, with complex pneumatic sculpting all over the roof of the neural canal.

Title slide for the 2014 SVPCA presentation.

The Big Bend and Cloverly specimens were the basis for my talk on SMAs at SVPCA in 2014, coauthored with Anthony Fiorillo, Des Maxwell, and Ron Tykoski. As prep for that talk, I visited the ornithology collections at the Natural History Museum of Los Angeles County, photographed a lot of bird vertebrae with foramina inside their neural canals, and shot this pelican video. That was four years ago – why no paper yet? It’s because I wanted one more piece of smoking-gun evidence: a CT scan of a bird that would show a direct communication between the SMAs and the air spaces inside a vertebra, through one or more foramina in the roof, wall, or floor of the neural canal.

A spectrum of pneumatic traces in the neural canals of birds, including complexes of large or small foramina, isolated foramina, and sculpting without foramina.

In 2017, Jessie Atterholt taught in our summer anatomy course at WesternU as an adjunct (her full-time employment was at the Webb Schools in Claremont, home of the Alf Museum). Jessie and I had been acquainted for a few years, but we’d never had the opportunity to really talk science. As we chatted between dissections, I learned that she had a huge warchest of CT scans of whole birds from her dissertation work at Berkeley (we’d missed each other by a few years). My antennae twitched: one nice thing about SMAs is that, being bounded by bone, they can’t collapse after death, unlike more peripheral diverticula. And air is jet black on CT scans, so SMAs are easy to spot even on comparatively low-res scans. All you need is one or two black pixels. I proposed a collaboration: we could use her CT scans to survey the presence and distribution of SMAs in as many birds as possible.

Vertebral diverticula in two sagittally-exploded cervical vertebrae of a turkey. Anterior is to the left, #5 is the SMA. Cover (1953: fig. 2). Yes, I know this is gross – if anyone has a cleaner scan, I’m interested.

You might think that such a survey would have been done ages ago, but it’s not the case. A few authors have mentioned supramedullary airways, and O’Connor (2006) gave a good description of some of the variation in SMAs in extant birds as a whole. But the only detailed accounts to illustrate the morphology and extent of the SMAs in a single species are Müller (1908) on the common pigeon and Cover (1953) on the domestic turkey. I’d seen what I suspected were traces of SMAs in the vertebrae of many, mostly large-bodied birds, and I’d seen them in CTs of ostriches and hummingbirds, and in ostriches and turkeys in dissection. But Jessie was offering the chance to see both the SMAs and their osteological traces in dozens of species from across the avian tree.

SMAs in a micro-CT of a female Anna’s hummingbird, Calypte anna. Scale bars are in mm.

Real life intervened: we were both so busy teaching last fall that we didn’t get rolling until just before the holidays. But the project gradually built up steam over the course of 2018. One story that will require more unpacking later: everything I’ve written on this blog about neural canals, Haplocanthosaurus, or CT scanning in 2018 is something serendipitously spun out of the SMA survey with Jessie. Expect a lot more Atterholt and Wedel joints in the near future – and one Atterholt et al. (minus Wedel) even sooner, that is going to be big news. Watch this space.

It didn’t hurt that in the meantime Jessie got a tenure-track job teaching human anatomy at WesternU, to run the same course she’d taught in as an adjunct last year, and started here at the beginning of June. By that time we had an abstract on our findings ready to go for this year’s SVP meeting. Alas, it was not to be: we were out in the field this summer when we learned that our abstract had been rejected. (I have no idea why; we’ve increased the taxonomic sampling of SMAs in extant birds by a factor of six or so, most of our important findings are in the abstract, and we mentioned the relevance to fossils. But whatever.)

We were bummed for a day, and then Jessie decided that she’d submit the abstract to SVPCA, only slightly chopped for length, and go to Manchester to present if it was accepted – which it was. Unfortunately I’d already made other plans for the fall, so I missed the fun. Fortunately the SVPCA talks were livestreamed, so last Friday at 1:30 in the morning I got to watch Jessie give the talk. I wish the talks had been recorded, because she knocked it out of the park.

Title slide for the 2018 SVPCA presentation.

And now everything we’re in a position to share is freely available at PeerJ. The SVPCA abstract is up as a PeerJ preprint (Atterholt and Wedel 2018), the longer, rejected SVP abstract is up as a supplementary file (because it has a crucial paragraph of results we had to cut to make the length requirement for SVPCA, and because why not), and our slideshow is up now, too. I say ‘our’ slideshow but it’s really Jessie’s – she built it and delivered it with minimal input from me, while I held down the sauropod side of our expanding empire of neural canal projects. She has the paper mostly written, too.

Oh, and we did get the smoking-gun images I wanted, of SMAs communicating with pneumatic spaces in the vertebrae via foramina in the neural canal. Often these foramina go up into the neural arch and spine, but in some cases – notably in pelicans and the occasional ratite – they go down into the centrum. So I now have no excuse for not getting back to the sauropod SMA paper (among many other things).

We’re making this all available because not only are we not afraid of getting scooped, we’re trying to get the word out. SMAs are phylogenetically widespread in birds and we know they were present in sauropods as well, so we should see some evidence of them in theropods and pterosaurs (because reasons). I made such a nuisance of myself at the recent Flugsaurier meeting, talking to everyone who would listen about SMAs, that Dave Hone went and found some pneumatic foramina in the neural canals of Pteranodon vertebrae during the conference – I suspect just to shut me up. That’ll be some kind of Hone-Atterholt-Wedel-and-some-others joint before long, too.

Anyway, point is, SMAs are cool, and you now have everything you need to go find them in more critters. Jessie and I are happy to collaborate if you’re interested – if nothing else, we have the background, lit review, and phylogenetic sampling down tight – but we don’t own SMAs, and we’ll be nothing but thrilled when your own reports start rolling in. Unexplored anatomical territory beckons, people. Let’s do this.

References

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Remember this broken Giraffatitan dorsal vertebra, which Janensch figured in 1950?

It is not only cracked in half, anteroposteriorly, it’s also unfused.

Here’s a better view of the broken face, more clearly showing that the neural canal is (a) much taller than wide – unlike all vertebrate spinal cords – and (b) almost entirely situated ventral to the neurocentral joint, getting close to the condition in the perverted Camarasaurus figured by Marsh.

Here’s a dorsal view, anterior to the top, with Mike’s distal forelimbs for scale.

Left lateral view.

Right lateral view – note the subtle asymmetries in the pneumatic foramen/camera. A little of that might be taphonomic distortion but I think much of it is real (and expected, most pneumatic systems produce asymmetries).

And postero-dorsal view, really showing the weird neural canal to good advantage. In this photo and in the pure dorsal view, you can see that the two platforms for the “neural arch” – which, as in the aforementioned Camarasaurus, is neither neural nor an arch – converge so closely as to leave only a paper-thin gap.

A few points arise. As explained in this post, it makes more sense to talk about the neurocentral joint migrating up or down relative to the neural canal, which is right where it always is, just dorsal to the articular faces of the centrum.

So far, in verts I’ve seen with “offset” neurocentral joints, the joint tends to migrate dorsally in dorsal vertebrae, putting the canal inside the developmental domain of the centrum (which now includes a partial or total arch in an architectural sense, even though the chunk of bone we normally call the neural arch develops as a separate bit) – as shown in the first post in this series. In sacral and caudal vertebrae, the situation is usually reversed, with the joint shifted down into what would normally be the centrum, and the canal then mostly or completely surrounded by the arch – as shown in the second post in the series. This post then doesn’t really add any new concepts, just a new example.

Crucially, we can only study this in the vertebrae of juveniles and subadults, because once the neurocentral joints are fused and remodeled, we usually can’t tell where the old joint surface was. So it’s like cervicodorsal and caudal dorsal pneumatic hiatuses, in that the feature of interest only exists for part of the ontogeny of the animal, and our sample size is therefore inherently limited. Not necessarily limited by material – most museums I’ve visited have a fair amount of juvenile and subadult material in the collections – but limited in published visibility, in that for many sauropods only the largest and most complete specimens have been monographically described.

So once again, the answer is simply to visit collections, look at lots of fossils, and stay alert for weird stuff – happily, a route that is open to everyone with a legitimate research interest.

Reference

  • Janensch, W. 1950. Die Wirbelsaule von Brachiosaurus brancai. Palaeontographica (Suppl. 7) 3:27-93.

Computer programmer, essayist and venture capitalist Paul Graham writes:

In most fields, prototypes have traditionally been made out of different materials. Typefaces to be cut in metal were initially designed with a brush on paper. Statues to be cast in bronze were modelled in wax. Patterns to be embroidered on tapestries were drawn on paper with ink wash. Buildings to be constructed from stone were tested on a smaller scale in wood.

What made oil paint so exciting, when it first became popular in the fifteenth century, was that you could actually make the finished work from the prototype. You could make a preliminary drawing if you wanted to, but you weren’t held to it; you could work out all the details, and even make major changes, as you finished the painting.

You can do this in software too. A prototype doesn’t have to be just a model; you can refine it into the finished product. I think you should always do this when you can. It lets you take advantage of new insights you have along the way. But perhaps even more important, it’s good for morale.

– Paul Graham, “Design and Research

Mike and I have long been drawn by the idea that blog posts, like conference talks and posters, could be first drafts of research papers. In practice, we haven’t generated many successful examples. We basically wrote our 2013 neural spine bifurcation paper as a series of blog posts in 2012. And Mike’s 2014 neck cartilage paper grew out of this 2013 blog post, although since he accidentally ended up writing 11 pages I suppose the blog post was more of a seed than a draft.

I should also note that we are far from the first people to do the blog-posts-into-papers routine. The first example I know of in paleo was Darren’s Tet Zoo v1 post on azhdarchid paleobiology, which formed part of the skeleton of Witton and Naish (2008).

Nevertheless, the prospect of blogging as a way to generate research papers remains compelling.

And as long as I’m on about blogging and papers: sometimes people ask if blogging doesn’t get in the way of writing papers. I can’t speak for anyone else, but for me it goes in the opposite direction: I blog most when I am most engaged and most productive, and drops in blogging generally coincide with drops in research productivity. I think that’s because when I’m rolling on a research project, I am constantly finding or noticing little bits that are cool and new, but which aren’t germane to what I’m working on at the moment. I can’t let those findings interfere with my momentum, but I don’t want to throw them away, either. So I blog them. Also the blog gives me a place to burn off energy at the end of the day, when I can still produce words but don’t have the discipline to write technical prose.

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The photo at the top of the post is of Giraffatitan dorsal vertebrae in a case at the MfN Berlin, from Mike’s and my visit with the DfG 533 group back in late 2008. I picked that photo so I could make the following dumb off-topic observation: with its upturned transverse processes, the dorsal on the right looks like it’s being all faux melodramatic, a la:

This post started out as a comment on this thread, kicked off by Dale McInnes, in which Mike Habib got into a discussion with Mike Taylor about the max size of sauropods. Stand by for some arm-waving. All the photos of outdoor models were taken at Dino-Park Münchehagen back in late 2008.

I think it’s all too easy to confuse how big things do get from how big they could get, assuming different selection pressures and ecological opportunities. I’m sure someone could write a very compelling paper about how elephants are as big as they could possibly be, or Komodo dragons, if we didn’t have indricotheres and Megalania to show that the upper limit is elsewhere. This is basically what Economos (1981) did for indricotheres, either forgetting about sauropods or assuming they were all aquatic.

Truly, a mammal of excellence and distinction. With Mike and some dumb rhino for scale.

In fact, I’ll go further: a lot of pop discussions of sauropod size assume that sauropods got big because of external factors (oxygen levels, etc.) but were ultimately limited by internal factors, like bone and cartilage strength or cardiovascular issues. I think the opposite is more likely: sauropods got big because of a happy, never-repeated confluence of internal factors (the Sander/et al. [2008, 2011, 2013] hypothesis, which I think is extremely robust), and their size was limited by external, ecological factors.

Take a full-size Argentinosaurus or Bruhathkayosaurus – even modest estimates put them at around 10x the mass of the largest contemporary predators. Full-grown adults were probably truly predator-immune, barring disease or senescence. So any resources devoted to pushing the size disparity higher, instead of invested in making more eggs, would basically be wasted.

If there was reproductive competition among the super-giants, could the 100-tonners have been out-reproduced by the 70-tonners, which put those extra 30 tonnes into making babies? Or would the 100-tonners make so many more eggs than the 70-tonners (over some span of years) that they’d still come out on top? I admit, I don’t know enough reproductive biology to answer that. (If you do, speak up in the comments!) But if – if – 70-tonners could out-reproduce 100-tonners, that by itself might have been enough to put a cap on the size of the largest sauropods.

Another possibility is that max-size adult sauropods were neither common nor the target of selection. In most populations most of the time, the largest individuals might have been reproductively active but skeletally-immature and still-growing subadults (keep in mind that category would encompass most mounted sauropod skeletons, including the mounted brachiosaurs in Chicago and Berlin). If such individuals were the primary targets of selection, and they were selected for a balance of reproductive output and growth, then the few max-size adults might represent the relatively rare instances in which the developmental program “overshot” the selection target.

Dave Hone and Andy Farke and I mentioned this briefly in our 2016 paper, and it’s come up here on the blog several times before, but I still have a hard time wrapping my head around what that would mean. Maybe the max-size adults don’t represent the selective optimum, but rather beneficial traits carried to extreme ends by runaway development. It seems at least conceivable that the bodies of such animals might have been heavily loaded with morphological excrescences – like 15- to 17-meter necks – that were well past the selective optimum. As long as those features weren’t inherently fatal, they could possibly have been pretty darned inefficient, riding around on big predator-immune platforms that could walk for hundreds of kilometers and survive on garbage.

What does that swerve into weird-but-by-now-well-trod ground have to do with the limits on sauropod size? This: if max-size adults were not heavy selection targets, either because the focus of selection was on younger, reproductively-active subadults, or because they’d gotten so big that the only selection pressure that could really affect them was a continent-wide famine – or both – then they might not have gotten as big as they could have (i.e., never hit any internally-imposed, anatomical or biomechanical limits) because nothing external was pushing them to get any bigger than they already were.

Or maybe that’s just a big pile of arm-wavy BS. Let’s try tearing it down, and find out. The comment thread is open.

References

As Matt recently noted, we both have a ton of photos from various expeditions that we’ve never got around to posting — not to mention a ton of specimens that we’ve seen but never got around to working on. Here is one of the most exciting:

As you can see, this is a massive cervical vertebra from a sauropod, probably a brachiosaurid, eroding right out of the ground. It’s in an undisclosed location in the Arches National Park, which we visited in May 2016. The neural arch is in amazingly good shape, though the end of the right prezygapophysis has broken off and been displaced slightly upwards. The postzygapophysesal facet is difficult to make out. Here’s a rough-and-ready interpretive drawing to get you oriented, with the completely missing parts speculatively sketched in light grey. (We don’t know how much more of this vertebra might be preserved underground.)

Apart from its size, the most striking thing about this vertebra is how very pneumatic it is — corroborating the long-standing hypothesis that pneumaticity tends to be positively allometric. If you compare with the much-loved 8th cervical vertebra of the Giraffatitan brancai paralectotype MB.R.2181 (formerly HMN SII), you can see similar “sculpted” features on the arch of that vertebra, but they are much less developed and ramified:

(This photo is in of course in left dorsolateral view, whereas the aspect of the Arches vertebra available to us is right lateral, and slightly ventral of true lateral.)

How big is the Arches vertebra? Stupidly, we didn’t have measuring equipment with us when we were visiting the park, so we don’t have an exact figure. But we can get some idea by extrapolating from the photo above. The stretched-out arm-span of an adult man is close to his height. I’m 1.8 m tall, so allowing for the downward slope of my arms, we might guess that the fingertip-to-fingertip measurement is about 1.7 m. If that’s right, measuring off the photo, the preserved portion of the vertebra is nearly twice that, at 3.3 m — and the complete length must have been somewhat longer, as the back end of the centrum is completely missing. Something in the region of 3.6 m might not be too far out. But as always, note that these are extremely speculative figures based on multiple layers of approximation.

We really need to get back out there, measure that thing properly, and of course try to find a way to have it excavated.

Amazingly (to me, anyway), SV-POW! is ten years old today. It was on 1st October 2007 that we published Hello world!, our first post, featuring a picture of what may still be our favourite single sauropod vertebra: the ?8th cervical of the Giraffatitan brancai paralectotype MB.R.2181. Of course, back then, we thought it was the type (it’s not), it was thought to belong to Brachiosaurus brancai (mea culpa), and the specimen number was HMN SII. A lot has changed in ten years, but the vertebra is still heart-breakingly beautiful.

Some other things have changed in those ten years, of course. Three of us started the blog, but one (Darren) has become a sleeping partner due to the enormous success of his other blog, Tetrapod Zoology. We began intending to be a picture blog, but we’ve ended up as a 50-50 blend of sauropod palaeontology and open-access advocacy. Along the way, I (Mike) got my Ph.D, and Matt moved from UC Merced to Western University of Health Sciences, where both he and his wife Vicki now have tenure. Darren meanwhile has carved out a unique niche for himself as a writer and consultant, and has his own cconference.

We never thought this blog would run for so long — I seem to remember the original plan was to make 52 weekly posts, then call it a day after one year. In fact, over the last ten years, we’ve posted 1160 articles, for an average of one every 3.15 days: more than twice as often as the weekly schedule that the blog title suggests. But not all those posts have included sauropod vertebrae — so, guessing that about half of them have, we’re more or less on target.

In the mean time, you have written 16820 comments, for a pretty healthy average of 14.5 per post. One of the things I’m proudest about regarding this blog is that we’ve only once had to shut a thread down because it became unproductive; and I think on only two other occasions have we had to issue a public warning. We have a fantastic community of commenters here, and my deeply felt gratitude goes out to you all.

Our most-read post at the time of writing is Every attempt to manage academia makes it worse (with 214,438 views), followed by Elsevier is taking down papers from Academia.edu (62,695), SV-POW! showdown: sauropods vs whales (35,944) and How big was Amphicoelias fragillimus? I mean, really? (35,531). These lead a list of 35 posts that have each garnered more than 10,000 views, contributing to an overall total of 3,573,821 views (which gives us an average of 3,080 views per post). We are alternately delighted, baffled and impressed that the world has shown such interest.

We have one or two things planned for this week of the 10th anniversary, but for this post I just want to leave it like this: THANK YOU ALL for reading, commenting and engaging with this blog. Thank you, palaeontologists for putting up with the open-access posts, and thank you scholarly communication specialists for putting up with the sauropods. We hope it’s been interesting, entertaining and sometimes thought-provoking; and we hope we can continue in the same vein. (We certainly have no plans to stop any time soon.)

We love you guys.

Suppose that I and Matt were right in our SVPCA talk this year, and the
Supersaurus” cervical BYU 9024 really is the C9 of a gigantic Barosaurus. As we noted in our abstract, its total length of 1370 mm is exactly twice that of the C9 in AMNH 6341, which suggests its neck was twice as long over all — not 8.5 m but 17 m.

How horrifying is that?

I realised one good way to picture it is next to the entire mounted skeleton of Giraffatitan at the Museum für Naturkunde Berlin. That skeleton is 13.27 m tall. At 17 m, the giant barosaur neck would be 28% longer than the total height Giraffatitan.

Giraffatitan brancai mounted skeleton MB.R.2181 at the Museum für Naturkunde Berlin, with neck of Barosaurus ?lentus BYU 9024 at the same scale. Photo by Axel Mauruszat, from Wikipedia; drawing from Scott Hartman's Supersaurus skeleton reconstruction.

Giraffatitan brancai mounted skeleton MB.R.2181 at the Museum für Naturkunde Berlin, with neck of Barosaurus ?lentus BYU 9024 at the same scale. Photo by Axel Mauruszat, from Wikipedia; drawing from Scott Hartman’s Supersaurus skeleton reconstruction.

Yes, this looks ridiculous. But it’s what the numbers tell us. Measure the skeleton’s height and the neck length off the image yourself if you don’t believe me.

(Note, too, that the size of the C9 in that big neck is about right, compared with a previous scaled image that Matt prepared, showing the “Supersaurus” vertebra in isolation alongside the Chicago Brachiosaurus.)