Sauro-throat, Part 3: what does Dolly’s disease tell us about sauropods?

February 17, 2022

Naturally I was grateful when Cary invited me to be part of the team working on Dolly, the diplodocid with lesions in its neck vertebrae (Woodruff et al. 2022; see previous posts on Dolly here and here). I was also intellectually excited, not only to see air-filled bones with obvious pathologies, but also for what those pathologies could tell us about Dolly and other sauropods. That’s the part of our new paper I want to unpack in this post.

We have a lot of evidence that air-filled bones in birds are a good model for air-filled bones in extinct dinosaurs. And we have several lines of evidence (not just air-filled bones; see Schachner et al. 2009, 2011, 2020) that the respiratory systems of many dinosaurs functioned broadly like those of living birds. But we have less direct evidence than we’d like, so every additional bit of information is welcome.

Diving into Diverticula

In birds, the air-filled bones in the neck and body are connected to the respiratory system by air-filled tubes. These tubes sometimes get called air sacs, in the sense that they are sacs filled with air, but we also refer to them pneumatic diverticula, to distinguish them from the respiratory air sacs in the torsos of birds that ventilate the lungs. Imagine blowing up some rubber gloves and sticking them inside a bird* and you’ll have a pretty good mental model of the system — the inflated ‘palm’ area of each glove is like one of the respiratory air sacs, the air-filled glove fingers are the diverticula, and the rubber material of the glove is the pneumatic epithelium that lines the air sacs and the diverticula alike. 

* Please don’t actually try that.

The cartoon above presents an unrealistically simplified picture of the respiratory system in dinosaurs and birds. For one thing, I omitted the windpipe or trachea — that blue tube going up the neck represents the diverticula that run alongside, and often inside, the neck vertebrae, parallel to the trachea but separated from it by whole sheets of muscle. Also, the cartoon only shows diverticula of the air sacs, but diverticula can also originate from the lungs themselves (see O’Connor 2006: 1211 and Schachner et al. 2020: 16-19). Here’s the actual respiratory system of a pigeon, with the trachea and lungs in pink and the air sacs and their diverticula in blue (Muller 1908 fig. 11):

I think it’s pretty natural to look at that illustration and wonder where the heck the guts go, since it certainly looks like the air sacs are occupying the entire volume of the torso. The answer is that the air sacs enclose the viscera “as do the shells of a nut”, in the memorable formulation of Wetherbee (1951: p. 243), describing the air sacs of the English sparrow.


Fig. 4. Reconstruction of the distribution of pneumatic diverticula in diplodocids and dicraeosaurids. A. Schematic drawing of midcervical vertebra of Diplodocus in left lateral aspect (A1), in dorsal aspect with single neural spine (A2) and in dorsal aspect with bifurcate neural spine (A3). The partitioning of pneumatic diverticula at the lateral surface of the vertebral corpus is hypothetical, based on the strongly divided pneumatic fossae. Schwarz et al. (2007: fig. 4A).

Furthermore, the pneumatic diverticula around the vertebrae in birds are complex, and we are fairly certain that they were also complex in sauropods, because they left so many distinct traces. The most detailed reconstructions of the cervical diverticula in sauropods that I know of are those of Daniela Schwarz and colleagues (2007), as shown above. For what it’s worth, I think those reconstructions are not just reasonable but perhaps conservative; I think there’s a good chance that the diverticular network around the vertebrae was even more complex and extensive. 

The rubber-glove model also lets us see that the diverticula are cul-de-sacs. We know that diverticula can anastomose, or merge, to form networks, and there is a possibility that if diverticula from different air sacs anastomosed, different pressures in those air sacs might allow some air to circulate through the diverticular network. Maybe — the anterior and posterior air sacs fill and empty at the same time, so there might not be a pressure differential to exploit. If air circulates in the diverticula at all in birds, it probably happens in the dorsal vertebrae, where diverticula from different parts of the respiratory system have the best opportunity to anastomose. But the far ends of the diverticular network are always dead ends, and we assume that air diffuses in and out of those terminal diverticula fairly slowly. We’re stuck with assumptions because no-one’s ever checked, experimentally, to determine the rate of diffusion or circulation of air in the diverticula. But it’s hard to imagine much circulation in the terminal diverticula, with no air reservoir or pump at the far end.

Reconstruction of soft−tissues in the neck of Diplodocus. A. Transverse cross−sections through cervical vertebra with bifurcate neural spine in the diapophysis region (A1) and in caudal third of vertebra (A2). B. Transverse cross−sections through cervical vertebra with single neural spine in diapophysis region (B1) and in caudal third of vertebra (B2), dashed outlines representing possible craniocervical extensor muscle analogous to m. biventer cervicis of extant birds or m. transversospinalis capitis of extant crocodylians. Schwarz et al. (2007: fig. 7A-B).

Here’s another great illustration from Schwarz et al. (2007), showing cross-sections of the neck of Diplodocus with hypothetical soft tissues restored. Bone is black, muscle is pink, and the pneumatic diverticula are blue. As this diagram makes clear, the air spaces in the bones are themselves extensions of the diverticula (that much is true regardless of how extensive we make the reconstructed diverticula outside the vertebrae). Instead of smooshing an inflated rubber glove into a duck, imagine smooshing one into a vertebra of a duck — or a Diplodocus — so that all of the empty spaces are occupied by some blobby bit of inflated-glove finger. All of air spaces in the bone would be lined by rubber-glove material, which in this metaphor is the same pneumatic epithelium that lines both the respiratory air sacs and their pneumatic diverticula, outside the bones or inside them.

I get to see this firsthand in the gross anatomy lab in our unit on head and neck anatomy. As we open up the skulls of the cadavers, the air-filled epithelial balloons that fill the sinuses sometimes pull away from, or completely out of, their bony recesses. (I’ll bet I could demonstrate the same thing with the sinuses of a pig or sheep head — I should give that a shot and post the resulting photos or videos here.) The point is, the pneumatic epithelium is in intimate contact with the bone, lining every pneumatic fossa, foramen, and internal chamber; this will be really important later on.

Incidentally, one question I get a lot is whether the diverticula, inside or outside the bones, contributed to gas exchange in sauropods. The answer is, probably not. We know from dissections and histological work on birds that the respiratory air sacs, their diverticula, and the diverticular spaces inside the skeleton are all relatively avascular, meaning that the tissues get enough blood to stay alive, but aren’t specialized for gas exchange. Furthermore, physiological experiments on living birds have shown that about 95% of the gas exchange happens in the lungs, and almost all of the remaining 5% happens in the paired abdominal air sacs (Magnussen et al. 1976), probably because they are so large and so intimately in contact with the guts (Wetherbee’s nutshell metaphor), which are well-supplied with blood. We also know from bone histology that the air-filled bones of extinct dinosaurs are essentially identical to those of modern birds (Lambertz et al. 2018), so there’s no evidence that they functioned any differently.

A simplified diagram of the sauropod respiratory system. What I’ve labeled “air tubes” here are the pneumatic diverticula. Air holes in the vertebrae are also known as pneumatic foramina. The shapes of the lungs and air sacs are speculative, but the minimum extent of the pneumatic diverticula is not–although it could be an underestimate (e.g., diverticula might have gone even further down the tail, and just not left any diagnostic traces on those vertebrae).

A final piece before we get back to Dolly: we know from lots of anecdotal observations, and some actual experiments, that air-filled bones have to stay connected to the outside to form in the first place, and to stay healthy afterward. This is true of both human sinuses and postcranial pneumatic bones in birds, so it’s reasonable to assume that it’s a general feature of all air-filled bones (see Witmer 1997 for lots of relevant citations and discussion). This is a pretty handy thing to know, because if we find an air-filled vertebra way out in the tail, we know pneumatic diverticula of the respiratory system got at least that far. ‘At least’ because pneumatic diverticula can make diagnostic traces on bones, but they don’t always do so. That means that the diverticular network can easily be more extensive than its skeletal traces, but not less so — see Wedel and Taylor (2013) for more on that.

To sum up, we suspect the following things about pneumatic diverticula around the vertebrae of sauropods, including Dolly:

  1. The diverticula were complex, based on the traces they left on the bones, and similarly complex diverticula in birds.
  2. The diverticula were patent, or open, maintaining an open connection to the outside by way of the respiratory air sacs, lungs, and trachea, because that’s how air-filled bones work in living birds and mammals.
  3. Despite being complex and ultimately open to the outside in one direction, the diverticula were cul-de-sacs, with little or no active circulation of air — especially in the neck.

With that in mind, what does the distribution of infected bone in Dolly tell us about sauropods?

Infections and inferences

Here’s another illustration of the respiratory system of the pigeon, this time a dorsal or top-down view, from Muller (1908: fig. 12):

Okay, that was a bit of a bait-and-switch: I promised you Dolly and gave you another pigeon. But that’s only to help you understand this similar cartoon I drew, which represents Dolly’s respiratory system and neck vertebrae, also seen from the top down:

Like the earlier cartoon, this is pretty simplified. For instance, I got lazy and didn’t draw all of the neck vertebrae. In life, Dolly probably had 15 or 16 neck vertebrae, like other diplodocids, and we know that the three with lesions are C5-C7 because they were found articulated. Here I drew just enough vertebrae to make my points, and I left off the head and all the other extraneous bits. Also, I’ve drawn the diverticula that run up the neck originating from cervical air sacs, as in pigeons (Muller 1908), but there is evidence that in ostriches those diverticula may originate from the lungs themselves (Schachner et al. 2020). Whether the diverticula come from the lungs or the air sacs is probably not an answerable question for sauropods, and for my purposes here, it doesn’t matter, only that the diverticula are connected back to the core respiratory system.

Three things struck us about the distribution of the infected bone in Dolly’s neck:

  1. The lesions are all in vertebrae that are a long way up the neck, far from the lungs and respiratory air sacs in the torso.
  2. The lesions are clustered in serially-adjacent vertebrae, instead of being scattered up and down the neck randomly.
  3. The lesions are present bilaterally, on both left and right sides of the affected vertebrae.

Well, as opposed to what? We can imagine a scenario in which the lesions were scattered randomly, not just up and down the neck, but also on left and right sides, like so:

If the infection had been carried in the blood, we might expect such a random pattern. In that case, it would be an extreme coincidence if a blood-borne infection, which could go anywhere in the body, only manifested in the air spaces on the sides of three consecutive vertebrae. The clustering of the Dolly’s lesions, in the air spaces on both sides in three adjacent vertebrae, far up the neck, points to a different cause.

Recall that diverticula are lined by epithelium, and that in air-filled bones, the epithelium is right up against the bone tissue. The infection in Dolly almost certainly started out as an infection in the diverticulum, which was so severe that it spread to the underlying bone. In exactly the same way that the air spaces in the bones are the skeletal footprints of the diverticula, the lesions in Dolly’s vertebrae are the skeletal footprints of infected epithelium lining the diverticula, like so:

The infection may have gotten so severe, far up Dolly’s neck, precisely because there was little airflow so far from the lungs and air sacs. Airborne bacteria or fungal spores could have floated into the diverticula by diffusion, come to rest against the epithelium in warm, dark, humid conditions, and gone wild. It’s also possible that a huge swath of Dolly’s respiratory system was infected, but the infection only got severe enough to spread to the underlying bone in cervical vertebrae 5-7, in which case the actual infection might have looked something like this:

Just like a diverticulum can contact a bone without producing a distinct trace, the pneumatic epithelium could be infected without producing a bony lesion. Thought experiment: how many times have you had a sinus infection, and how many people do you know who have had sinus infections? And how many of those sinus infections were severe enough, and lasted long enough, to produce bony lesions like we see in Dolly? Probably very few — such things do happen in humans, and the medical literature has plenty of cases (and if this has happened to your or a loved one, you have my full sympathy) — but on a population level, the fraction of respiratory infections that produce bony lesions is miniscule. Similarly, it’s very likely that much more of Dolly’s respiratory system was infected than we can tell from the skeleton.

A cervical vertebra of an ostrich with some of the pneumatic diverticula traced on.

The presence of infected bone on both left and right sides of C5-C7 in Dolly is also telling. If the diverticula on the left and right sides of the neck were separate, the symmetrical pattern of infection would be another extreme coincidence. But in birds there are opportunities for diverticula from the left and right sides of the neck to meet and anastomose, especially the supravertebral diverticula on the neural arch (shown above), and the supramedullary diverticula inside the neural canal. Based on pneumatic traces on the vertebrae we infer that the same diverticula were present in sauropods, as shown up above in the Diplodocus figures from Schwarz et al. (2007), and those left-and-right communications probably allowed the infection to develop more or less symmetrically. Or to put it another way, the symmetrical infections are additional evidence that the diverticula on the left and right sides of the neck were connected across the midline, and birds show that there are several ways that could have happened.

CT scans of cervical 7 of MOR 7029. Photograph and scan model of the vertebra ((A,B) respectively). The colored lines in (B) correspond to the scan slices (and scan interpretative drawings below). White arrows point to the external feature, while black arrows denote the hyperintense bone and irregular voids. (C) Comparison of the abnormal tissue composition of MOR 7029 (left), compared to that of a ‘normal’ diplodocine (right). Text and white arrows indicate the various features different shared/differentiated between the two. For the interpretative drawings, white = ‘normal’ bone, grey = hyperintense bone, black = irregular voids. Woodruff et al. (2022: fig. 2).

Another possibility is that a good chunk of the internal structure Dolly’s vertebrae was infected, and the lesions that we see on the surface are just the groady tips of big, disgusting icebergs of infected bone. In fact, that’s pretty much what the CT scans show. So possibly the infection started on one side of each vertebra and basically burrowed through to reach the other side. That would probably take weeks or months, whereas the infection could have spread across the midline through diverticula in hours or days, so I think the latter scenario is still the most plausible explanation for the presence of the lesions on both sides of the affected vertebrae.

In summary, I don’t think Dolly tells us anything surprising that we didn’t suspect before. Rather, the pattern of infection in Dolly makes perfect sense if the diverticula of sauropods were essentially bird-like, and that pattern is difficult to explain any other way.

Finding skeletal traces of a respiratory infection in Dolly was still a crazy lucky break, and that’s something I’ll discuss more in the next post in this series.

References

Posted by Matt Wedel
Filed in diplodocids, Dolly, paleopathology, pigeon, pneumaticity, stinkin' theropods
8 Comments »

Sauro-throat, Part 2: Dolly in 3D

February 14, 2022

Okay, this is cool: with the help of Ryan Ridgely, my coauthor* Larry Witmer used the CT scans of the two best infected vertebrae of Dolly to create 3D models, which are now viewable on Sketchfab. (See the announcement post about Dolly here, and our open-access paper on her pathological vertebrae here.)

*Yes, it is super-awesome to have Larry as a coauthor, after almost a quarter-century of admiring his work and standing on his shoulders.

The lesions are pretty subtle, and I intend to update this post with screenshots of the models with the infected bone highlighted, but I didn’t want to hold up getting the models out. UPDATE a couple of hours later: Cary kindly gave me a hand figuring out which bits of the vertebrae are infected. It’s not super-obvious at the resolution of these models, and not all of the infected bone is bubbling outward like cauliflower. More information is coming! Also, I tagged the vertebrae with their serial positions. C7 is in front of C6 because that’s how they went through the CT scanner. 

We’ve deliberately been a bit vague about what, exactly, Dolly is, beyond a diplodocid from the Morrison Formation of Montana. The answer is that Cary Woodruff is leading a team on a very well-illustrated monographic description of Dolly, which will be along in due time. So expect even more goodies in the future. Follow Cary on Twitter (@DoubleBeam, a reference to Diplodocus) for updates on all kinds of interesting stuff.

In the meantime, go have fun with the new toys!

Reference

 

Posted by Matt Wedel
Filed in 3D models, cervical, diplodocids, Dolly, paleopathology
3 Comments »

New paper: Dolly, the dinosaur with a sauro-throat

February 10, 2022

I was at the SVP meeting in Albuquerque in 2018 when Cary Woodruff called me over and said he had something cool to show me. “Something cool” turned out to be photos of infected sauropod vertebrae from the Morrison Formation of Montana. Specifically, some gross, cauliflower-looking bony lesions bubbling up in the air spaces on the sides of the vertebrae.

Pathologic pneumatic tissue in MOR 7029. (A) Schematic map of the neck of Diplodocus (Hatcher 1901; bones not present in grey), with the pathologic structures denoted in red. (B) Cervical 5 of MOR 7029 with red box highlighting the pathologic structure; close up in (C) with interpretative drawing in (D) (by DCW) (pathology in red). Woodruff et al. (2022: fig. 1).

I was stoked, because I’ve been working on air-filled bones in sauropods since 1998, and in that time I’ve gotten countless versions of this question: “Do you ever see any evidence of respiratory infections in those air spaces?” For 20 years, the answer had been ‘no’, but now Cary was showing me a likely ‘yes’.

Better still, Cary asked me if I wanted to collaborate on writing up the case. He could have done it on his own, but right out of the gate he wanted to assemble a collaborative team. He also got paleopathologist and veterinarian Ewan Wolff, veterinary radiologist Sophie Dennison, and anatomist and paleontologist Larry Witmer. It was my first time collaborating with all of those folks, and it was really cool firing around ideas, observations, and references. Cary coined the clever title “Sauro-Throat” when we presented our preliminary results at SVP (Woodruff et al. 2020), and you’ll probably see it a lot in conjunction with this paper.

The elaborate and circuitous pulmonary complex of the sauropod, with the hypothetical route of infectious pathway in MOR 7029. Skeletal reconstruction of the diplodocine Galeamopus pabsti by and copyright of Francisco Bruñén Alfaro to scale with MOR 7029. Human scale bar is the exemplar of pandemic education and rationalism, Dr. Anthony Fauci, at his natural height of 170 cm. Woodruff et al. (2022: fig. 3).

A little over three years after our meet-up in Albuquerque, one global pandemic notwithstanding, our results are out this morning in Scientific Reports (Woodruff et al. 2022). Normally I’d write a mini-dissertation about our findings, but I decided to do a little video explainer instead. That’s the video linked up top — many thanks to Fiona Taylor (music), Brian Engh (paleoart), and Jennifer Adams (filming and editing) for the timely help in getting it done.

I’ll have more to say about this in the future. For now, the paper is a free download at this link. Go have fun!

UPDATE later the same day:

Woo-hoo! Dolly is the top science story on Google News:

Google News UK:

The Guardian — with fabulous quotes by Steve Brusatte and, especially, Mike Benton:

…and probably others, but that’s enough navel-gazing for one afternoon.

References

Posted by Matt Wedel
Filed in cervical, diplodocids, Dolly, paleopathology, pneumaticity
25 Comments »

The Wiren Apatosaurus femur is on exhibit in the Moab Museum

October 19, 2021

 

The last time we saw the sauropod femur that Paige Wiren discovered sticking out of a riverbank, it had been moved into the prep lab at the Moab Museum, with the idea that it would eventually go on exhibit as a touch specimen for the public to enjoy and be inspired by. That has come to pass.

I was in Moab last month with Drs. Jessie Atterholt and Thierra Nalley and we stopped in the Moab Museum to digitize some vertebrae from SUSA 515, an unusual specimen of Camarasaurus that I’ve blogged about before, and will definitely blog about again. While we were there, we got to see and touch the Wiren femur. The museum folks told us that femur has been the first dinosaur bone that a lot of schoolkids and tourists have seen up close, or gotten to touch. As a former dinosaur-obsessed kid who never stopped being excited about touching real dinosaur bones–and as one of the lucky folks that got to rescue this particular fossil from erosion or poaching–that pleases me deeply. 

So, obviously, you should go see this thing. And the rest of the museum–as you can see from the photos above, the whole place has been renovated, and there are lots of interesting fossils from central and eastern Utah on display, not to mention loads of historical artifacts, all nicely presented in a clean, open, well-lit space that invites exploration. Go have fun!

Posted by Matt Wedel
Filed in Apatosaurus, diplodocids, femur, Museum of Moab, museums, public galleries, stinkin' appendicular elements, stinkin' mammals, stinkin' SV-POW!sketeers
8 Comments »

What’s the difference between a cervical and dorsal vertebra?

June 6, 2021

In mammals — certainly the most-studied vertebrates — regional differentiation of the vertebral column is distinct and easy to spot. But things aren’t so simple with sauropods. We all know that the neck of any tetrapod is made up of cervical vertebrae, and that the trunk is made up of dorsal vertebrae (subdivided into thoracic and lumbar vertebrae in the case of mammals). But how do we tell whether a given verebra is a posterior cervical or an anterior dorsal?

Here two vertabrae: a dorsal vertebra (D3) and a cervical vertebra (C13) from CM 84, the holotype of Diplodocus carnegii, modified from Hatcher (1901: plates III and VII):

It’s easy to tell these apart, even when as here we have only lateral-view images: the dorsal vertebra is tall, its centrum is short, its neural spine is anteroposteriorly compressed and its parapophysis is up on the dorsal half of the centrum; but the cervical vertebra is relatively low, its centrum is elongated, its neural spine is roughly triangular and its parapophysis hangs down well below the centrum (and has a cervical rib fused to it and the diapophysis).

But things get trickier in the shoulder region because, in sauropods at least, the transition through the last few cervicals to the first few dorsals is gradual — the vertebrae become shorter, taller and broader — and tends to have no very obvious break point. In this respect, they differ from mammals, in which the regional differentiation of the spinal column is more abrupt. (Although even here, things may not be as simple as generally assumed: for example, Gunji and Endo (2016) argued that the 1st thoracic vertebra of the giraffe behaves functionally like an 8th cervical.)

So here are those two vertebrae in context: the sequence D3 D2 D1 C15 C14 C13 in CM 84, the holotype of Diplodocus carnegii, modified from Hatcher (1901: plates III and VII):

Given that the leftmost is obviously a dorsal and the rightmost obviously a cervical, where would you place the break-point?

The most usual definition seems to be that the first dorsal vertebra is the first one that has a free rib, i.e. one not fused to the vertebra: in the illustration above, you can see that the three cervicals on the right all have their cervical ribs fused to their diapophyses and parapophyses, and the three dorsals on the left do not. This definition of the cervical/dorsal distinction seems to be widely assumed, but it is rarely explicitly asserted. (Does anyone know of a paper that lays it out for sauropods, or for dinosaurs more generally?)

But wait!

Hatcher (1903:8) — the same dude — in his Haplocanthosaurus monograph, writes:

The First Dorsal (Plate I., Fig. 1). […] That the vertebra now under consideration was a dorsal is conclusively shown not by the presence of tubercular and capitular rib facets showing that it supported on either side a free rib, for there are in our collections of sauropods, skeletons of other dinosaurs fully adult but, with the posterior cervical, bearing free cervical ribs articulating by both tubercular and capitular facets as do the ribs of the dorsal region. The character in this vertebra distinguishing it as a dorsal is the broadly expanded external border of the anterior branch of the horizontal lamina [i.e. what we would now call the centroprezygapophyseal lamina]. This element has been this modified in this and the succeeding dorsal, no doubt, as is known to be the case in Diplodocus to give greater surface for the attachment of the powerful muscles necessary for the support of the scapula.

Hatcher’s illustrations show this feature, though they don’t make it particularly obvious: here are the last two cervicals and the first dorsal, modified from Hatcher (1903:plate I), with the facet in question highlighted in pink: right lateral view at the top, then anterior, and finally posterior view at the bottom. (The facet is only visible in lateral and anterior views):

Taken at face value, Hatcher’s words here seem to imply that he considers the torso to begin where the scapula first lies alongside the vertebral column. Yet if you go back to the Diplodocus transition earlier in this post, a similar scapular facet is not apparent in the vertebra that he designated D1, and seems to be present only in D2.

Is this scapular-orientation based definition a widespread usage? Can anyone point me to other papers that use it?

Wilson (2002:226) mentions a genetic definition of the cervical/dorsal distinction

Vertebral segment identity may be controlled by a single Hox gene. The cervicodorsal transition in many tetrapods, for instance, appears to be defined by the expression boundary of the Hoxc-6 gene.

But this of course is no use in the case of extinct animals such as sauropods.

So what’s going on here? In 1964, United States Supreme Court Justice Potter Stewart, in describing his threshold test for obscenity, famously said “I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description, and perhaps I could never succeed in intelligibly doing so. But I know it when I see it.” Is that all we have for the definition of what makes a vertebra cervicals as opposed to dorsal? We know it when we see it?

Help me out, folks! What should the test for cervical-vs-dorsal be?

References

  • Gunji, Mego, and Hideki Endo. 2016. Functional cervicothoracic boundary modified by anatomical shifts in the neck of giraffes. Royal Society Open Science 3:150604. doi:10.1098/rsos.150604
  • Hatcher, Jonathan B. 1901. Diplodocus (Marsh): its osteology, taxonomy and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum 1:1-63 and plates I-XIII.
  • Hatcher, J. B. 1903b. Osteology of Haplocanthosaurus with description of a new species, and remarks on the probable habits of the Sauropoda and the age and origin of the Atlantosaurus beds; additional remarks on Diplodocus. Memoirs of the Carnegie Museum 2:1-75 and plates I-VI.
  • Wilson, Jeffrey A. 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136:217-276.

Posted by Mike Taylor
Filed in cervical, Diplodocus, dorsal, Haplocanthosaurus, help SV-POW!, ribs, Thinking it through
19 Comments »

A third pneumatic hiatus in a specimen of Barosaurus

May 27, 2021

Here’s a pretty cool image: Plate 7 from Lull (1919), showing the partial skeleton of Barosaurus YPM 429 (above), compared to the much more complete skeleton of Diplodocus CM84/94 (below).

I’ve been pretty familiar with that Barosaurus skeleton diagram since I was about 9 years old, because it’s in Donald Glut’s New Dinosaur Dictionary, which I’ve written about here before. In particular, I like that Lull was scrupulous about drawing in the lateral pneumatic cavities in the caudal vertebrae. It’s pretty common in Diplodocus for the tail to be pneumatized out to somewhere between caudal 15 and 19, and the same is true in Barosaurus. I’m not just relying on the figure–Lull was also good about saying explicitly what was going on with the pneumatization in the centrum of each vertebra.

I returned to this image as an adult doing research on sauropod pneumaticity, and I read big swaths of Lull (1919), but never the bit about the sacrum. Why would I? The sacrum of YPM 429 is pretty scrappy, and I was mostly interested in the big honkin’ cervicals, and in learning how to distinguish bones of Barosaurus and Diplodocus. I always assumed that the sacrum of Barosaurus was pneumatized right the way through.

Only, er, it ain’t. As I just discovered.

Lull (1919: p. 22):

See that second sentence? “The central fragment is extremely massive, with no adaptation for lightening the weight appreciable in the portion preserved.” That’s old-timey talk for, “the chunk of centrum has no pneumatic openings or cavities”. Which is kind of a big deal, because:

…a gap of one or more apneumatic vertebrae with pneumatic vertebrae on either side constitutes a pneumatic hiatus. Why that’s a big deal is explained in this post.

If I had read this in the early 2000s, I would have flipped out. I did flip out when I discovered what seemed to be a pneumatic hiatus at the base of the tail in Haplocanthosaurus. Just that possibility sent me scurrying off to the Carnegie Museum to investigate, and precipitated both a dissertation chapter, later published as Wedel (2009), and an enduring fascination with Haplocanthosaurus. If I’d been reading Lull instead of Hatcher, my air sac paper would have been about Barosaurus, probably, and I wouldn’t have known enough about Haplo to get interested in the other specimens, which would have been a real shame.

A pneumatic hiatus in Barosaurus would have been big news in 2009. In 2021, it’s still nice, but not groundbreaking. The groundbreaking pneumatic hiatuses in Barosaurus were described in two different juvenile skeletons by Melstrom et al. (2016) and Hanik et al. (2017). Those were both mid-thoracic hiatuses, which probably separated the pneumatization domains of the cervical air sacs anteriorly and the abdominal air sacs posteriorly. A mid-sacral hiatus in YPM 429 is probably within the domain of the abdominal air sac, just like the hiatus in sacral 5 of CM 879 that I described in my 2009 paper. It’s still exciting, in that it shows that there were abdominal air sacs, and they were separate from the lungs and cervical air sacs, but this example in YPM 429 is now third in line in terms of priority, just within this one genus. Which is why I’m telling the world with a blog post, instead of hopping on a plane (or, er, planning a very long road trip) to New Haven. I’ll check on YPM 429 the next time I’m out there, but the specifics will keep for now.

References

  • Hanik, Gina M., Matthew C. Lamanna and John A. Whitlock. 2017. A juvenile specimen of Barosaurus Marsh, 1890 (Sauropoda: Diplodocidae) from the Upper Jurassic Morrison Formation of Dinosaur National Monument, Utah, USA. Annals of Carnegie Museum 84(3):253–263.
  • Lull, R.S. 1919. The sauropod dinosaur Barosaurus Marsh. Memoirs of the Connecticut Academy of Arts and Sciences 6:1-42.
  • Melstrom, Keegan M., Michael D. D’Emic, Daniel Chure and Jeffrey A. Wilson. 2016. A juvenile sauropod dinosaur from the Late Jurassic of Utah, USA, presents further evidence of an avian style air-sac system. Journal of Vertebrate Paleontology 36(4):e1111898. doi:10.1080/02724634.2016.1111898
  • Wedel, M.J. 2009. Evidence for bird-like air sacs in saurischian dinosaurs. Journal of Experimental Zoology 311A:611-628.
Posted by Matt Wedel
Filed in Barosaurus, diplodocids, pneumatic hiatus, pneumaticity
4 Comments »

Cross-sectional asymmetry of sauropod vertebrae

March 13, 2021

 

FIGURE 7.1. Pneumatic features in dorsal vertebrae of Barapasaurus (A–D), Camarasaurus (E–G), Diplodocus (H–J), and Saltasaurus (K–N). Anterior is to the left; different elements are not to scale. A, A posterior dorsal vertebra of Barapasaurus. The opening of the neural cavity is under the transverse process. B, A midsagittal section through a middorsal vertebra of Barapasaurus showing the neural cavity above the neural canal. C, A transverse section through the posterior dorsal shown in A (position 1). In this vertebra, the neural cavities on either side are separated by a narrow median septum and do not communicate with the neural canal. The centrum bears large, shallow fossae. D, A transverse section through the middorsal shown in B. The neural cavity opens to either side beneath the transverse processes. No bony structures separate the neural cavity from the neural canal. The fossae on the centrum are smaller and deeper than in the previous example. (A–D redrawn from Jain et al. 1979:pl. 101, 102.) E, An anterior dorsal vertebra of Camarasaurus. F, A transverse section through the centrum (E, position 1) showing the large camerae that occupy most of the volume of the centrum. G, a horizontal section (E, position 2). (E–G redrawn from Ostrom and McIntosh 1966:pl. 24.) H, A posterior dorsal vertebra of Diplodocus. (Modified from Gilmore 1932:fig. 2.) I, Transverse sections through the neural spines of other Diplodocus dorsals (similar to H, position 1). The neural spine has no body or central corpus of bone for most of its length. Instead it is composed of intersecting bony laminae. This form of construction is typical for the presacral neural spines of most sauropods outside the clade Somphospondyli. (Modified from Osborn 1899:fig. 4.) J, A horizontal section through a generalized Diplodocus dorsal (similar to H, position 2). This diagram is based on several broken elements and is not intended to represent a specific specimen. The large camerae in the midcentrum connect to several smaller chambers at either end. K, A transverse section through the top of the neural spine of an anterior dorsal vertebra of Saltasaurus (L, position 1). Compare the internal pneumatic chambers in the neural spine of Saltasaurus with the external fossae in the neural spine of Diplodocus shown in J. L, An anterior dorsal vertebra of Saltasaurus. M, A transverse section through the centrum (L, position 2). N, A horizontal section (L, position 3). In most members of the clade Somphospondyli the neural spines and centra are filled with small camellae. (K–N modified from Powell 1992:fig. 16.) [Figure from Wedel 2005.]

Here’s figure 1 from my 2005 book chapter. I tried to cram as much pneumatic sauropod vertebra morphology into one figure as I could. All of the diagrams are traced from pre-existing published images except the horizontal section of the Diplodocus dorsal in J, which is a sort of generalized cross-section that I based on broken centra of camerate vertebrae from several taxa (like the ones shown in this post). One thing that strikes me about this figure, and about most of the CT and other cross-sections that I’ve published or used over the years (example), is that they’re more or less bilaterally symmetrical. 

We’ve talked about asymmetrical vertebrae before, actually going back to the very first post in Xenoposeidon week, when this blog was only a month and a half old. But not as much as I thought. Given how much space asymmetry takes up in my brain, it’s actually weird how little we’ve discussed it.

The fourth sacral centrum of Haplocanthosaurus CM 879, in left and right lateral view (on the left and right, respectively). Note the distinct fossa under the sacral rib attachment on the right, which is absent on the left.

Also, virtually all of our previous coverage of asymmetry has focused on external pneumatic features, like the asymmetric fossae in this sacral of Haplocanthosaurus (featured here), in the tails of Giraffatitan and Apatosaurus (from Wedel and Taylor 2013b), and in the ever-popular holotype of Xenoposeidon. This is true not just on the blog but also in our most recent paper (Taylor and Wedel 2021), which grew out of this post.

Given that cross-sectional asymmetry has barely gotten a look in before now, here are three specimens that show it, presented in ascending levels of weirdness.

First up, a dorsal centrum of Haplocanthosaurus, CM 572. This tracing appeared in Text-fig 8 in my solo prosauropod paper (Wedel 2007), and the CT scout it was traced from is in Fig 6 in my saurischian air-sac paper (Wedel 2009). The section shown here is about 13cm tall dorsoventrally. The pneumatic fossa on the left is comparatively small, shallow, and lacks very distinct overhanging lips of bone. The fossa on the right is about twice as big, it has a more distinct bar of bone forming a ventral lip, and it is separated from the neural canal by a much thinner plate of bone. The fossa on the left is more similar to the condition in dorsal vertebrae of Barapasaurus or juvenile Apatosaurus, where as the one on the right shows a somewhat more extensive and derived degree of pneumatization. The median septum isn’t quite on the midline of the centrum, but it’s pretty stout, which seems to be a consistent feature in presacral vertebrae of Haplocanthosaurus.

 

Getting weirder. Here’s a section through the mid-centrum of C6 of CM 555, which is probably Brontosaurus parvus. That specific vert has gotten a lot of SV-POW! love over the years: it appears in several posts (like this one, this one, and this one), and in Fig 19 in our neural spine bifurcation paper (Wedel and Taylor 2013a). The section shown here is about 10cm tall, dorsoventrally. In cross-section, it has the classic I-beam configuration for camerate sauropod vertebrae, only the median septum is doing something odd — rather than attaching the midline of the bony floor of the centrum, it’s angled over to the side, to attach to what would normally be the ventral lip of the camera. I suspect that it got this way because the diverticulum on the right either got to the vertebra a little ahead of the one on the left, or just pneumatized the bone faster, because the median septum isn’t just bent, even the vertical bit is displaced to the left of the midline. I also suspect that this condition was able to be maintained because the median septa weren’t that mechanically important in a lot of these vertebrae. We use “I-beam” as a convenient shorthand to describe the shape, but in a metal I-beam the upright is as thick or thicker than the cross bits. In contrast, camerate centra of sauropod vertebrae could be more accurately described as a cylinders or boxes of bone with some holes in the sides. I think the extremely thin median septum is just a sort of developmental leftover from the process of pneumatization.

EDIT 3 days later: John Whitlock reminded me in the comments of Zurriaguz and Alvarez (2014), who looked at asymmetry in the lateral pneumatic foramina in cervical and dorsal vertebrae of titanosaurs, and found that consistent asymmetry along the cervical column was not unusual. They also explicitly hypothesized that the asymmetry was caused by diverticula on one side reaching the vertebrae earlier than diverticula on other other side. I believe they were the first to advance that idea in print (although I should probably take my own advice and scour the historical literature for any earlier instances), and needless to say, I think they’re absolutely correct.

Both of the previous images were traced from CTs, but the next one is traced from a photo of a specimen, OMNH 1882, that was broken transversely through the posterior centrum. To be honest, I’m not entirely certain what critter this vertebra is from. It is too long and the internal structure is too complex for it to be Camarasaurus. I think an apatosaurine identity is unlikely, too, given the proportional length of the surviving chunk of centrum, and the internal structure, which looks very different from CM 555 or any other apatosaur I’ve peered inside. Diplodocus and Brachiosaurus are also known from the Morrison quarries at Black Mesa, in the Oklahoma panhandle, which is where this specimen is from. Of those two, the swoopy ventral margin of the posterior centrum looks more Diplodocus-y than Brachiosaurus-y to me, and the specimen lacks the thick slab of bone that forms the ventral centrum in presacrals of Brachiosaurus and Giraffatitan (see Schwarz and Fritsch 2006: fig. 4, and this post). So on balance I think probably Diplodocus, but I could easily be wrong.

Incidentally, the photo is from 2003, before I knew much about how to properly photograph specimens. I really need to have another look at this specimen, for a lot of reasons.

Whatever taxon the vertebra is from, the internal structure is a wild scene. The median septum is off midline and bent, this time at the top rather than the bottom, the thick ventral rim of the lateral pneumatic foramen is hollow on the right but not on the left, and there are wacky chambers around the neural canal and one in the ventral floor of the centrum. 

I should point out that no-one has ever CT-scanned this specimen, and single slices can be misleading. Maybe the ventral rim of the lateral foramen is hollow just a little anterior or posterior to this slice. Possibly the median septum is more normally configured elsewhere in the centrum. But at least at the break point, this thing is crazy. 

What’s it all mean? Maybe the asymmetry isn’t noise, maybe it’s signal. We know that when bone and pneumatic epithelium get to play together, they tend to make weird stuff. Sometimes that weirdness gets constrained by functional demands, other times not so much. I think it’s very seductive to imagine sauropod vertebrae as these mechanically-optimized, perfect structures, but we have other evidence that that’s not always true (for example). Maybe as long as the articular surfaces, zygapophyses, epipophyses, neural spine tips, and cervical ribs — the mechanically-important bits — ended up in the right places, and the major laminae did a ‘good enough’ job of transmitting forces, the rest of each vertebra could just sorta do whatever. Maybe most of them end up looking more or less the same because of shared development, not because it was so very important that all the holes and flanges were in precisely the same places. That might explain why we occasionally get some really odd verts, like C11 of the Diplodocus carnegii holotype.

That’s all pretty hand-wavy and I haven’t yet thought of a way to test it, but someone probably will sooner or later. In the meantime, I think it’s valuable to just keep documenting the weirdness as we find it.

References

Posted by Matt Wedel
Filed in camarasaurs, cervical, cross sections, diplodocids, Diplodocus, dorsal, Haplocanthosaurus, pneumaticity, sacral, Saltasaurus, titanosaur
8 Comments »

Equatorial Minnesota on Alamosaurus

February 21, 2021

Figure 3. BIBE 45854, articulated series of nine mid and posterior cervical vertebrae of a large, osteologically mature Alamosaurus sanjuanensis. Series is estimated to represent the sixth to fourteenth cervical vertebrae. A, composite photo-mosaic of the cervical series in right lateral view; identification of each vertebra indicated by C6 to C14, respectively. B, line drawing based on the photo-mosaic in A. C, line drawing in B with labels shown and vertebral fossae indicated by solid grey fill; cross-hatching represents broken bone surfaces and reconstructive material. Abbreviations: C, cervical vertebra; cdf, centrodiapophyseal fossa; clf, centrum lateral fossa; pocdf, postzygapophyseal centrodiapophyseal fossa; prcdf, prezygapophyseal centrodiapophyseal fossa; prcdf1, dorsal prezygapophyseal centrodiapophyseal fossa; prcdf2, ventral prezygapophyseal centrodiapophyseal fossa; sdf, spinodiapophyseal fossa; spof, spinopostzygapophyseal fossa; sprf, spinoprezygapophyseal fossa. (Tykoski and Fiorillo 2016)

Have you been reading Justin Tweet’s series, “Your Friends the Titanosaurs“, at his awesomely-named blog, Equatorial Minnesota? If not, get on it. He’s been running the series since June, 2018, so this notice is only somewhat grotesquely overdue. The latest installment, on Alamosaurus from Texas and Mexico, is phenomenal. I have never seen another summary or review that pulled together so much of the relevant literature and explained it all so well. Seriously, that blog post deserves to be a review paper; it could be submitted pretty much as-is, although it would be even better with his two other Alamosaurus posts integrated (this one, and this one). It’s great work, is what I’m saying, and it needs to be acknowledged.

In particular, I was struck by the note by Anonymous in 1941 on the discovery of a cervical vertebra 1.2 meters long. I’d never heard of that ref, and I’ve never seen that vert, but at 120cm it would be in the top 7 longest cervical vertebrae on the planet (see the latest version of the list in this post), narrowly beating out the 118-cm cervical of Puertasaurus. In fairness, the preserved cervical of Puertasaurus is probably a posterior one, and more anterior cervicals might have been longer. Then again, in the big Alamosaurus neck the longest verts are pretty darned posterior, so…we need more Puertasaurus.

EDIT a few hours later: Thanks to the kind offices of Justin Tweet, I’ve now seen Anonymous (1941), and the exact wording is, “A single vertebra, or neck joint bone, is three feet across, only two inches less than four feet long, and in its present fossilized state weighs 600 pounds.” ‘Two inches less than four feet long’ is 46 inches or a hair under 117cm, which puts the supposed giant cervical just behind Puertasaurus after all, but still firmly in the top 10. And depending on how one interprets the passage in Anonymous (1941), it might not have been any bigger than BIBE 45854–see this comment for details.

Big cervical showdown. From the top left: BYU 9024, originally referred to Supersaurus but more likely representing a giant Barosaurus (137cm); the single available cervical of Puertasaurus (118cm); a world-record giraffe neck (2.4m); Alamosaurus referred cervical series BIBE 45854, longest centra are ~81cm; Sauroposeidon holotype OMNH 53062, longest centrum is 125cm. This image makes it very clear that whatever Sauroposeidon was doing, it was a way different thing from Alamosaurus.

Crucially, the longest vertebrae in the BIBE 45854 series are about 80 or 81 cm long, which means that a 1.2-meter cervical would be half again as large. That is a pretty staggering thought, and that individual of Alamosaurus–assuming it was the same taxon as BIBE 45854, and not some other, longer-necked critter–would definitely be a contender for the largest sauropod of all time.

Illustrations here are of the big Alamosaurus cervical series from Big Bend, which was comprehensively described by Ron Tykoski and Tony Fiorillo in 2016, and which we have covered in these previous posts:

References

  • Anonymous. 1941. Find dinosaur neck bone nearly four feet long. The Science News-Letter 39(1):6–7.
  • Tykoski, R.S. and Fiorillo, A.R. 2016. An articulated cervical series of Alamosaurus sanjuanensis Gilmore, 1922 (Dinosauria, Sauropoda) from Texas: new perspective on the relationships of North America’s last giant sauropod. Journal of Systematic Palaeontology 15(5):339-364.
Posted by Matt Wedel
Filed in Alamosaurus, Barosaurus, cervical, credit where it's due, diplodocids, giraffe, Sauroposeidon, showdown, size, stinkin' mammals, Things I should have posted a year ago, titanosaur
11 Comments »

How can we get post-publication peer-review to happen?

February 20, 2021

Today marks the one-month anniversary of my and Matt’s paper in Qeios about why vertebral pneumaticity in sauropods is so variable. (Taylor and Wedel 2021). We were intrigued to publish on this new platform that supports post-publication peer-review, partly just to see what happened.

Taylor and Wedel (2021: figure 3). Brontosaurus excelsus holotype YPM 1980, caudal vertebrae 7 and 8 in right lateral view. Caudal 7, like most of the sequence, has a single vascular foramen on the right side of its centrum, but caudal 8 has two; others, including caudal 1, have none.

So what has happened? Well, as I write this, the paper has been viewed 842 times, downloaded a healthy 739 times, and acquired an altmetric score 21, based rather incestuously on two SV-POW! blog-posts, 14 tweets and a single Mendeley reader.

What hasn’t happened is even a single comment on the paper. Nothing that could be remotely construed as a post-publication peer-review. And therefore no progress towards our being able to count this as a peer-reviewed publication rather than a preprint — which is how I am currently classifying it in my publications list.

This, despite our having actively solicited reviews both here on SV-POW!, in the original blog-post, and in a Facebook post by Matt. (Ironically, the former got seven comments and the latter got 20, but the actual paper none.)

I’m not here to complain; I’m here to try to understand.

On one level, of course, this is easy to understand: writing a more-than-trivial comment on a scholarly article is work, and it garners very little of the kind of credit academics care about. Reputation on the Qeios site is nice, in a that-and-two-bucks-will-buy-me-a-coffee kind of way, but it’s not going to make a difference to people’s CVs when they apply for jobs and grants — not even in the way that “Reviewed for JVP” might. I completely understand why already overworked researchers don’t elect to invest a significant chunk of time in voluntarily writing a reasoned critique of someone else’s work when they could be putting that time into their own projects. It’s why so very few PLOS articles have comments.

On the other hand, isn’t this what we always do when we write a solicited peer-review for a regular journal?

So as I grope my way through this half-understood brave new world that we’re creating together, I am starting to come to the conclusion that — with some delightful exceptions — peer-review is generally only going to happen when it’s explicitly solicited by a handling editor, or someone with an analogous role. No-one’s to blame for this: it’s just reality that people need a degree of moral coercion to devote that kind of effort to other people’s project. (I’m the same; I’ve left almost no comments on PLOS articles.)

Am I right? Am I unduly pessimistic? Is there some other reason why this paper is not attracting comments when the Barosaurus preprint did? Teach me.

References

 

Posted by Mike Taylor
Filed in Brontosaurus, caudal, help SV-POW!, papers by SV-POW!sketeers, Peer review, pneumaticity, Shiny digital future, stinkin' reviewers, What counts?, Yale Peabody Museum
12 Comments »

Happy Valentine’s Day from Apatosaurinae

February 15, 2021

This is RAM 1619, a proximal caudal vertebra of an apatosaurine, in posterior view. It’s one of just a handful of sauropod specimens at the Raymond M. Alf Museum of Paleontology. It’s a donated specimen, which came with very little documentation. It was originally catalogued only to a very gross taxonomic level, but I had a crack at it on a collections visit in 2018, when I took these photos. I told Andy Farke and the other Alf folks right away, I just never got around to blogging about it until now.

Why do I think it’s an apatosaurine? A few reasons: 

  • it’s slightly procoelous, which is pretty common for diplodocids, whereas caudals of Haplocanthosaurus, Camarasaurus, and Brachiosaurus are all either amphicoelous or amphiplatyan;
  • it has big pneumatic fossae above the transverse processes, unlike Haplo, Cam, and Brachio, but it lacks big pneumatic fossae below the transverse processes, unlike Diplodocus and Barosaurus. 
  • and finally the clincher: the centrum is taller than wide, and broader dorsally than ventrally.

In the literature this centrum shape is described as ‘heart-shaped’ (e.g., Tschopp et al. 2015), and sometimes there is midline dorsal depression that really sells it. That feature isn’t present in this vert, but overall it’s still much closer to a heart-shape than the caudals of any non-apatosaurine in the Morrison. Hence the literal 11th-hour Valentine’s Day post (and yes, this will go up with a Feb. 15 date because SV-POW! runs on England time, but it’s still the 14th here in SoCal, at least for another minute or two).

RAM 1619 in postero-dorsal view.

Back to the pneumaticity. Occasionally an apatosaurine shows up with big lateral fossae ventral to the transverse processes–the mounted one at the Field Museum is a good example (see this post). And the big Oklahoma apatosaurine breaks the rules by having very pneumatic caudals–more on that in the future. But at least in the very proximal caudals of non-gigantic apatosaurines, it’s more common for there to be pneumatic fossae above the transverse processes, near the base of the neural arch. You can see that in caudal 3 of UWGM 15556/CM 563, a specimen of Brontosaurus parvus:

I don’t think I’d figured out this difference between above-the-transverse-process (supracostal, perhaps) and below-the-transverse-process (infracostal, let’s say) pneumatic fossae when Mike and I published our caudal pneumaticity paper back in 2013. I didn’t start thinking seriously about the dorsal vs ventral distribution of pneumatic features until sometime later (see this post). And I need to go check my notes and photos before I’ll feel comfortable calling supracostal fossae the apatosaurine norm. But I am certain that Diplodocus and Barosaurus have big pneumatic foramina on the lateral faces of their proximal caudals (see this post, for example), Haplocanthosaurus and brachiosaurids have infracostal fossae when they have any fossae at all in proximal caudals (distally the fossae edge up to the base of the neural arch in Giraffatitan), and to date there are no well-documented cases of caudal pneumaticity in Camarasaurus (if that seems like a hedge, sit tight and W4TP). 

RAM 1619 has asymmetric pneumatic fossae, which is pretty cool, and also pretty common, and we think we have a hypothesis to explain that now–see Mike’s and my new paper in Qeios.

And if I’m going to make my midnight deadline, even on Pacific Time, I’d best sign off. More cool stuff inbound real soon.

References

Posted by Matt Wedel
Filed in Apatosaurus, Brontosaurus, caudal, diplodocids, pneumaticity
12 Comments »
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