“Look at all the things you’ve done for me
Opened up my eyes,
Taught me how to see,
Notice every tree.”
So sings Dot in Move On, the climactic number of Stephen Sondheim’s Pulitzer Prize-winning music Sunday in the Park with George, which on the surface is about the post-impressionist painter Georges Seurat, but turns out to be a study of obsession and creativity.“Taught me how to see”? What kind of talk is that? One the surface, it seems silly — we all know how to see. We do it constantly, without thinking. Yet it’s something that artists talk about all the time. And anyone who’s sat down and seriously tried to paint or draw something will have some understanding of what the phrase means. We have such strong implicit ideas of what things look like that we tend to reproduce what we “know” is there rather than what’s actually there. Like I said, we see without thinking.
In fact, the psychology of perception is complicated and sophisticated, and the brain does an extraordinary amount of filtering of the visual signals we get, to save us the bother of having to consciously process way too much data. This is a whole scientific field of its own, and I’m going to avoid saying very much about it for fear of making a fool of myself — as scientists so often do when wandering outside their own field. But I think it’s fair to say that we all have a tendency to see what we expect to see.
In the case of sauropods, this tendency has meant that we’ve all been startlingly bad at seeing pneumaticity in the caudal vertebrae of sauropods. Because the literature has trained us to assume it’s not there. For example, in the two competing sauropod phylogenies that dominated the 2000s, both Wilson (2002) and Upchurch et al. (2004) scored caudal pneumaticity as very rare: Wilson’s character 119, “Anterior caudal centra, pneumatopores (pleurocoels)”, was scored 1 only for Diplodocus and Barosaurus; and Upchurch et al. (2004:286) wrote that “A few taxa (Barosaurus, Diplodocus, and Neuquensaurus) have pleurocoel-like openings in the lateral surfaces of the cranial [caudal] centra that lead into complex internal chambers”. That’s all.
And that’s part of the reason that every year since World War II, a million people have walked right past the awesome mounted brachiosaur in the Museum Für Naturkunde Berlin without noticing that it has pneumatic caudals. After all, we all knew that brachiosaur caudals were apneumatic.
But in my 2005 Progressive Palaeontology talk about upper limits on the mass of land animals estimated through the articular area of limb-bone cartilage, I included this slide that shows how much bigger the acetabulum of Giraffatitan is than the femoral head that it houses:
And looking at that picture made me wonder: those dark areas on the sides of the first few caudals (other than the first, which is a very obvious plaster model) certainly look pneumatic.
Then a few years later, I was invited to give a talk at the Museum Für Naturkunde Berlin itself, on the subject “Brachiosaurus brancai is not Brachiosaurus“. (This of course was drawn from the work that became my subsequent paper on that subject, Taylor 2009) And as I was going through my photos to prepare the slides of that talk, I thought to myself: darn it, yes, it does have pneumatic caudals!
So I threw this slide into the talk, just in passing:
Those photos were pretty persuasive; and a closer examination of the specimen on that same trip was to prove conclusive.
Earlier in 2009, I’d been in Providence, Rhode Island, with my Index Data colleagues. I’d managed to carve a day out of the schedule to hope along the coast to the Yale Peabody Museum in New Haven, Connecticut. My main goal was to examine the cervicals of the mounted Apatosaurus (= “Brontosaurus“) excelsus holotype (although it was also on that same trip that I first saw the Barosaurus holotype material that we’ve subsequently published a preprint on).
The Brontosaurus cervicals turned out to be useless, being completely encased in plaster “improvements” so that you can’t tell what’s real and what’s not. hopefully one day they’ll get the funding they want to take that baby down off its scaffold and re-prep the material.
But since I had the privilege of spending quality time with such an iconic specimen, it would have been churlish not to look at the rest of it. And lo and behold, what did I see when I looked at the tail but more pneumaticity that we thought we knew wasn’t there!
What does this mean? Do other Giraffatitan and Apatosaurus specimens have pneumatic tails? How pervasive is the pneumaticity? What are the palaeobiological implications?
Stay tuned! All will be revealed in Matt’s next post (or, if you can’t wait, in our recent PLOS ONE paper, Wedel and Taylor 2013b)!
- Taylor, Michael P. 2009. A re-evaluation of Brachiosaurus altithorax Riggs 1903 (Dinosauria, Sauropoda) and its generic separation from Giraffatitan brancai (Janensch 1914). Journal of Vertebrate Paleontology 29(3):787-806.
- Upchurch, Paul, Paul M. Barrett and Peter Dodson. 2004. Sauropoda. pp. 259-322 in D. B. Weishampel, P. Dodson and H. Osmólska (eds.), The Dinosauria, 2nd edition. University of California Press, Berkeley and Los Angeles. 861 pp.
- Wedel, Mathew J., and Michael P. Taylor. 2013. Caudal pneumaticity and pneumatic hiatuses in the sauropod dinosaurs Giraffatitan and Apatosaurus. PLOS ONE 8(10):e78213. 14 pages. doi:10.1371/journal.pone.0078213
- Wilson, J.A. 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136:217-276.
October 31, 2013
First, there’s a nice write-up of one of our papers (Wedel and Taylor 2013b on pneumaticity in sauropod tails) in the Huffington Post today. It’s the work of PLOS blogger Brad Balukjian, a former student of Matt’s from Berkeley days. The introduction added by the PLOS blogs manager is one of those where you keep wanting to interrupt, “Well, actually it’s not quite like that …” but the post itself, once it kicks in, is good. Go read it.
Brad also has a guest-post on Discover magazine’s Crux blog: How Brachiosaurus (and Brethren) Became So Gigantic. He gives an overview of the sauropod gigantism collection as a whole. Well worth a read to get your bearings on the issue of sauropod gigantism in general, and the new collection in particular.
PLOS’s own community blog EveryONE also has its own brief introduction to the collection.
And PLOS and PeerJ editor Andy Farke, recently in these pages because of his sensational juvenile Parasaurolophus paper, contributes his own overview of the collection, How Big? How Tall? And…How Did It Happen?
Finally, if you’re at SVP, go and pick up your free copy of the collection. Matt was somehow under the impression that the PLOS USB drives with the sauropod gigantism collection would be distributed with the conference packet when people registered. In fact, people have to go by the PLOS table in the exhibitor area (booth 4 in the San Diego ballroom) to pick them up. There are plenty of them, but apparently a lot of people don’t know that they can get them.
- Wedel, Mathew J., and Michael P. Taylor. 2013. Caudal pneumaticity and pneumatic hiatuses in the sauropod dinosaurs Giraffatitan and Apatosaurus. PLOS ONE 8(10):e78213. 14 pages. doi:10.1371/journal.pone.0078213 [PDF]
October 30, 2013
This is an exciting day: the new PLOS Collection on sauropod gigantism is published to coincide with the start of this year’s SVP meeting! Like all PLOS papers, the contents are free to the world: free to read and to re-use. (What is a Collection? It’s like an edited volume, but free online instead of printed on paper.)
There are fourteen papers in the new Collection, encompassing neck posture (yay!), nutrition (finally putting to bed the Nourishing Vomit Of Eucamerotus hypothesis), locomotion, physiology and evolutionary ecology. Lots every sauropod-lover to enjoy.
Matt and I are particularly excited that we have two papers in this collection: Taylor and Wedel (2013c) on intervertebral cartilage in necks, and Wedel and Taylor (2013b) on pneumaticity in the tails of (particularly) Giraffatitan and Apatosaurus. So we have both ends of the animal covered. It also represents a long-overdue notch on our bed-post: for all our pro-PLOS rhetoric, this is the first time either of has had a paper published in a PLOS journal.
It’s a bit of a statistical anomaly that after a decade of collaboration in which there was never a Taylor & Wedel or Wedel & Taylor paper, suddenly we have five of them out in a single year (including the Barosaurus preprint, which we expect to eventually wind up as Taylor and Wedel 2014). Sorry about the alphabet soup.
Since Matt is away at SVP this week, I’ll be blogging mostly about the Taylor and Wedel paper this week. When Matt returns to civilian life, the stage should be clear for him to blog about pneumatic caudals.
- Taylor, Michael P., and Matthew J. Wedel. 2013c. The effect of intervertebral cartilage on neutral posture and range of motion in the necks of sauropod dinosaurs. PLOS ONE 8(10): e78214. 17 pages. doi:10.1371/journal.pone.0078214 [PDF]
- Wedel, Mathew J., and Michael P. Taylor. 2013. Caudal pneumaticity and pneumatic hiatuses in the sauropod dinosaurs Giraffatitan and Apatosaurus. PLOS ONE 8(10):e78213. 14 pages. doi:10.1371/journal.pone.0078213 [PDF]
July 16, 2013
Here is Tataouinea, named by Fanti et al. (2013) last week — the first sauropod to be named after a locality from Star Wars (though, sadly, that is accidental — the etymology refers to the Tataouine Governatorate of Tunisia).
No doubt Matt willl have much more to say about this animal, and especially its pneumatic features. I just thought it was time for a picture-of-the-week post.
UPDATE: Matt here, just a few quick thoughts (I’m in the middle of my summer anatomy lectures so they will be less extensive than this animal deserves). First, it’s awesome to see so much pneumaticity, and in elements that have not previously been reported as pneumatic in sauropods. The authors make a good case that we’re looking at actual pneumaticity here, for example in the pelvic elements, and not something else. So that’s cool.
What’s even cooler is that we’re seeing this in a diplodocoid: Tataouinea is a rebbachisaurid. We’ve seen extreme pneumaticity in saltasaurines, and now we’ve got a parallel evolution of this character complex in diplodocoids. That’s cool by itself, and it’s further evidence that the underlying generating mechanism–the air sacs and their diverticula–were all in place long before they started leaving traces on the skeleton. The case for a birdlike lung-air sac system in sauropods, in saurischians, and in ornithodirans generally only keeps getting stronger. That is, we’re seeing more evidence not just that air sacs were there, but that they were bird-like in their layout, e.g., pneumatization of the pectoral girdle by clavicular air sacs, in both saltasaurines and theropods (avian and otherwise), and now extensive pelvic pneumatization (i.e., going beyond what we’ve seen previously in saltasaurines) by abdominal air sacs in rebbachisaurids and theropods (and pterosaurs, can’t forget about them). Happy times.
Fanti, Federico, Andrea Cau, Mohsen Hassine and Michela Contessi. 9 July 2013. A new sauropod dinosaur from the Early Cretaceous of Tunisia with extreme avian-like pneumatization. Nature Communications 4:2080. doi:10.1038/ncomms3080
March 26, 2013
Another raw photo from the road.
The Morrison fossils from the Oklahoma panhandle were dug up and prepped out by WPA workers in the 1930s, and their preparation toolkit consisted of hammers, chisels, pen-knives, and sandpaper. (Feel free to take a minute if you need to get your nausea under control.) And whereas most Morrison fossils are much darker than the surrounding matrix, in the Oklahoma panhandle the bone and matrix are about the same color. Sometimes the prep guys didn’t know they’d gone too deep until they sanded into the trabecular bone. Or in this case, into the air spaces in the condyle of this anterior dorsal of Apatosaurus.
Still, we have lots of anterior dorsals of Apatosaurus, and very few we can see inside, and they’re too darned big to scan, so this gives us useful information that a more perfect specimen would not. So I salute you, underemployed dude from eighty-odd years ago. Thanks for showing me something cool.
August 22, 2012
No time for anything new, so here’s a post built from parts of other, older posts.
The fourth sacral centrum of Haplocanthosaurus CM 879, in left and right lateral view. This is part of the original color version of Wedel (2009: figure 8), from this page. (Yes, I know I need to get around to posting the full-color versions of those figures. It’s on my To Do list.)
Note the big invasive fossa on the right side of the centrum. The left side is waisted (narrower at the middle than the ends) like most vertebrae of most animals, but has no distinct fossa on lateral face of the centrum. What’s up with that? Here’s an explanation from an old post (about another sauropod) that still fits:
Now, this asymmetry is also weird, but it’s expected weirdness. Pneumaticity seems to just be inherently variable, whether we’re talking about human sinuses or the facial air sacs of whales or the vertebrae of chickens. It appears that the form of pneumatic features is entirely determined by local tissue interactions, with little or no genetic control of the specific form. Think of it this way: genes prescribe certain developmental events, and those events bring tissues into contact–such as pneumatic epithelium and bone. The morphology of the bone arises out of that interaction, and each interaction of bone and pneumatic epithelium has the potential to produce something new. In this case, the diverticula on the left side of the vertebral column come from the lungs or air sacs on the left, and those on the right side come from the lungs or airs sacs on the right, so it’s really two sets of diverticula contacting the bone independently. The wonder, then, is not that pneumatic bones are so variable, but that we see any regularities at all.
Earlier this month I was amazed to see the new paper by Cerda et al. (2012), “Extreme postcranial pneumaticity in sauropod dinosaurs from South America.” The title is dramatic, but the paper delivers the promised extremeness in spades. Almost every figure in the paper is a gobsmacker, starting with Figure 1, which shows pneumatic foramina and cavities in the middle and even distal caudals of Rocasaurus, Neuquensaurus, and Saltasaurus. This is most welcome. Since the 1990s there have been reports of saltasaurs with “spongy bone” in their tail vertebrae, but it hasn’t been clear until now whether that “spongy bone” meant pneumatic air cells or just normal marrow-filled trabecular bone. The answer is air cells, loads of ‘em, way farther down the tail than I expected.
Here’s why this is awesome. Lateral fossae occur in the proximal caudals of lots of neosauropods, maybe most, but only a few taxa go in for really invasive caudal pneumaticity with big internal chambers. In fact, the only other sauropod clade with such extensive pneumaticity so far down the tail are the diplodocines, including Diplodocus, Barosaurus, and Tornieria. But they do things differently, with BIG, “pleurocoel”-type foramina on the lateral surfaces of the centra, leading to BIG–but simple–camerae inside, and vertebral cross-sections that look like I-beams. In contrast, the saltasaurines have numerous small foramina on the centrum and neural arch that lead to complexes of small pneumatic camellae, giving their vertebrae honeycomb cross-sections. So caudal pneumaticity in diplodocines and saltsaurines is convergent in its presence and extent but clade-specific in its development. Pneumaticity doesn’t get much cooler than that.
But it does get a little cooler. Because the stuff in the rest of the paper is even more mind-blowing. Cerda et al. (2012) go on to describe and illustrate–compellingly, with photos–pneumatic cavities in the ilia, scapulae, and coracoids of saltasaurines. And, crucially, these cavities are connected to the outside by pneumatic foramina. This is important. Chambers have been reported in the ilia of several sauropods, mostly somphospondyls but also in the diplodocoid Amazonsaurus. But it hasn’t been clear until now whether those chambers connected to the outside. No patent foramen, no pneumaticity. It seemed unlikely that these sauropods had big marrow-filled vacuities in their ilia–as far as I know, all of the non-pneumatic ilia out there in Tetrapoda are filled with trabecular bone, and big open marrow spaces only occur in the long bones of the limbs. And, as I noted in my 2009 paper, the phylogenetic distribution of iliac chambers is consistent with pneumaticity, in that the chambers are only found in those sauropods that already have sacral pneumaticity (showing that pneumatic diverticula were already loose in their rear ends). But it’s nice to have confirmation.
So, the pneumatic ilia in Rocasaurus, Neuquensaurus, and Saltasaurus are cool because they suggest that all the other big chambers in sauropod ilia were pneumatic as well. And for those of you keeping score at home, that’s another parallel acquisition in Diplodocoidea and Somphospondyli (given the apparent absence of iliac chambers in Camarasaurus and the brachiosaurids, although maybe we should bust open a few brachiosaur ilia just to be sure*).
* I kid, I kid.**
** Seriously, though, if you “drop” one and find some chambers, call me!
But that’s not all. The possibility of pneumatic ilia has been floating around for a while now, and most of us who were aware of the iliac chambers in sauropods probably assumed that eventually someone would find the specimens that would show that they were pneumatic. At least, that was my assumption, and as far as I know no-one ever floated an alternative hypothesis to explain the chambers. But I certainly did not expect pneumaticity in the shoulder girdle. And yet there they are: chambers with associated foramina in the scap and coracoid of Saltasaurus and in the coracoid of Neuquensaurus. Wacky. And extremely important, because this is the first evidence that sauropods had clavicular air sacs like those of theropods and pterosaurs. So either all three clades evolved a shedload of air sacs independently, or the basic layout of the avian respiratory system was already present in the ancestral ornithodiran. I know where I’d put my money.
There’s loads more interesting stuff to talk about, like the fact that the ultra-pneumatic saltasaurines are among the smallest sauropods, or the way that fossae and camerae are evolutionary antecedent to camellae in the vertebrae of sauropods, so maybe we should start looking for fossae and camerae in the girdle bones of other sauropods, or further macroevolutionary parallels in the evolution of pneumaticity in pterosaurs, sauropods, and theropods. Each one of those things could be a blog post or maybe a whole dissertation. But my mind is already thoroughly blown. I’m going to go lie down for a while. Congratulations to Cerda et al. on what is probably the most important paper ever written on sauropod pneumaticity.
- Cerda, I.A., Salgado, L., and Powell, J.E. 2012. Extreme postcranial pneumaticity in sauropod dinosaurs from South America. Palaeontologische Zeitschrift. DOI 10.1007/s12542-012-0140-6
- Janensch, W. 1947. Pneumatizitat bei Wirbeln von Sauropoden und anderen Saurischien. Palaeontographica, Supplement 7, 3:1–25.
- Osborn, H. F. 1899. A skeleton of Diplodocus. Memoirs of the American Museum of Natural History 1:191–214.
March 10, 2012
Those ostrich necks I went to Oro Grande to get last Thursday? Vanessa and I started dissecting them last Friday. The necks came to us pre-cut into segments with two to three vertebrae per segment. The transverse cuts were made without regard for joints so we got a bunch of cross sections at varying points through the vertebrae. This was fortuitous; we got to see a bunch of cool stuff at the cut faces, and those cut faces gave us convenient avenues for picking up structures and dissecting them out further.
In particular, the pneumatic diverticula in the neck of this ostrich were really prominent and not hard at all to see and to follow. The photo above shows most of the external diverticula; click through for the full-resolution, unlabeled version. The only ones that aren’t shown or labeled are the diverticula around the esophagus and trachea (which had already been stripped off the neck segments, so those diverticula were simply gone), those around carotid arteries, which are probably buried in the gloop toward the bottom of the photo, and the intermuscular diverticula, of which we found a few in parting out the dorsal and lateral neck muscles.
There is one final group of diverticula that are shown in the photo but not labeled: the interosseous diverticula that fill the air spaces inside the bone.
We have tons of cool photos from this dissection, so expect more posts on this stuff in the future.
For previous posts showing diverticula in bird neck dissections, see:
Things to Make and Do, part 7b: more fun with rhea necks (admittedly, not the most creative title ever)
January 6, 2012
We’re starting the new year with a new feature, in which we answer questions that have come our way. We never had a policy about not answering questions, it’s just that previous ones have tended to arrive in the comments section and have been dealt with there. But suddenly in the last few days I’ve gotten two questions from extrabloggular sources, and rather than hide the replies I thought I’d make them available to all.
One of my cohort at Berkeley texted me the other day with the following questions:
OK, phylobuddy: can you suck the marrow from a chicken bone? If they have hollow bones, where’s the marrow?!? Google is getting me nowhere.
Short answer: yes, one can get marrow from chicken bones, from those bones that contain marrow rather than air. In most fully mature chickens, the pneumatic bones include the braincase, the cervical, dorsal, and most or all synsacral vertebrae, some of the dorsal ribs, the central portion of the sternum, the coracoids, and the humeri (if you’re not a regular and some of these terms are unfamiliar, check out these handy guides [1, 2] to the vertebrate skeleton). That leaves marrow in everything else, although the only bones with large marrow cavities–as opposed to tiny trabecular spaces, which also house marrow–are the radii, ulnae, femora, tibiotarsi, and tarsometatarsi. So if you want to actually see large amounts of chicken marrow, or suck the marrow out of chicken bones, you’re basically stuck with the big distal bones of the wing, the thigh, and the drumstick (tibiotarsus). If you are boiling chicken bones to get stock for soups or stews, might as well throw them all in; even the pneumatic bones will still have bits of adhering meat, cartilage, and ligaments that will give up molecules and flavor to the stock.
The long answer is that the expression “hollow bones” has caused no end of confusion, because there are at least two ways to interpret hollow: filled with air, or not filled with bone (the former is a subset of the latter). If you mean “not filled with bone”, then the bones of almost all amniotes* are hollow, and the spaces inside are occupied by marrow (most commonly) or air. If filled with air, the bones are referred to as pneumatic, and an accessible introduction to them is here.
* At least; I know less about amphibians and fish, although at least one osteoglossomorph (IIRC) pneumatizes its vertebrae from its swim bladder!
The reasons it gets confusing are twofold. First, sometimes authors describe bones as hollow and mean only that they have chambers inside, but later readers see ‘hollow’ and infer ‘pneumatic’. Not all hollow bones are pneumatic; in fact, the vast majority of them are not, including the long bones of your arms and legs. The criteria for inferring pneumaticity from dry bones are more strict, and are explored in this paper and this one. Anyway, this point is just confusion caused by an ambiguous term.
The second case is more interesting, because it involves real unknowns. In the fossil record we can almost always tell if a bone is hollow, sensu lato, but sometimes it is not possible to say for certain whether the hollow space(s) inside were filled with marrow or air. Particularly vexing and intriguing examples include the humerus of Eotyrannus and the iliac chambers of some sauropods, which are discussed in this paper. My guess is that the iliac chambers of sauropods are genuinely pneumatic, because they only occur in sauropods that already have sacral pneumaticity, and we know from broken ilia of more basal sauropods and sauropodomorphs that large marrow-filled chambers are not present in those taxa. Conversely, I suspect that the humerus of Eotyrannus was apneumatic (marrow-filled), given that humeral pneumaticity is otherwise unknown in non-avian theropods, although the pneumatic furcula of Buitreraptor at least shows that the necessary clavicular air sac was present in some.
Next question! This one came to me on Facebook, from ReBecca Hunt-Foster, whom you may know from her awesome Dinochick Blogs. You should also envy her and hubby John Foster for getting the most awesome wedding present of all time: a 1/12 scale skeleton of Apatosaurus sculpted by Phil Platt, which you can read about here. That’s cool enough that I am stealing it for this otherwise picture-challenged post.
ANYWAY, ReBecca wrote on my FB wall today to ask:
Random question: Have you seen many tooth marks on sauro cervical verts? I am debating on whether something I have is a dessication crack or really some tooth marks. Thanks :)
In all the 15 years that I have spent looking at sauropod remains in the bowels of many, many museums, I have never seen a single tooth mark on a sauropod vertebra.
[Update the next day: Er, except for the bitten Apatosaurus tail on display in the AMNH! Many thanks to reptilianmonster and steve cohen for reminding me about this in the comments. I'm going to go hide for a while now.]
Now, that doesn’t mean that they aren’t there. Truth be told, I’ve never looked for them, and my usual mental search pattern for pneumatic traces (large, irregular) would probably exclude tooth scratches (small, linear) as noise. But I’ve certainly never seen any vertebrae with easily recognizable signs of predation or scavenging or with obvious bites removed.
People also sometimes ask me what kinds of healed traumas I’ve seen in pneumatic sauropods bones. That’s easy: apart from vertebral fusions, most of which probably have nothing to do with trauma, I’ve seen zip. Nada. Null set. The wingspan of the average tadpole. I’ve seen some pretty cool pneumatic bones from extant birds that were broken and later healed, including a eagle femur in the UCMP comparative collection that is now shaped like the letter Z, but nothing in sauropods.
I can think of three possible reasons for this, which sort of flow into each other. The first is that apart from the very solid and blocky centra of apneumatic vertebrae, sauropod verts were pretty fragile, and prone to getting distorted and busted up even when they started out intact, and those verts that started out broken just had a tougher time with the taphonomic lottery.
The second is that pneumatic sauropod bones would been nothing to most predators other than a mouthful of relatively dry bone shards, so either carnivores left them alone, or if they were osteovores like T. rex, they ate the shards and whatever is left over is unrecognizable. I have seen, and mostly ignored, plenty of vert-shrapnel in quarries and in collections, and maybe sharper eyes than mine could have discerned evidence of predation from those bits. To me it mostly looked like trampling, hydraulic transport, erosion, and other mundane ways to explode a vertebra.
The third is that in addition to a preservation bias against half-destroyed verts, there is probably also a collection bias against them. I’m probably not the only one would pass up a few shards of excellence to dig out the complete fibula sitting next to them in the quarry, and I love this stuff. That said, we did get a LOT of blasted vert bits out of the Wolf Creek quarry in the Cloverly, so if you want to pore over sauropod shards looking for tooth marks, visit the OMNH.
And, if you do know of tooth marks on sauropod vertebrae, please let us know in the comments. And consider publishing them, given the apparent vacuum of such things.
August 23, 2011
freezer full of interesting dead animals + great anatomy student who actually wants to get up on Saturday morning and dissect = happiness
The rhea has been the gift that keeps on giving. Saturday was my fourth session with some part of this bird, going back to 2006 (previous posts are here, here, and here). The first two sessions were just about reducing the bird to its component parts, and the last session was all about midline structures.
The goal for the neck is to dissect down to the vertebrae and document everything along the way–muscles, tendons, fascia, blood vessels, and especially diverticula. In the past I have been pessimistic about the chances of seeing diverticula without having them injected with latex or resin or something. But this bird is changing my mind, as we saw in a previous post and as you can see below.
The goal for Vanessa is to grok all of this anatomy, and hopefully make some publishable observations along the way. She has a chance to do something that I think is rather rare for a sauropod paleobiologist, which is to get a firm, dissection-based grounding in bird and croc anatomy before she first sets foot in a museum collection to play with sauropod bones.
That sounds awesome, and probably will be awesome, but before there can be any awesomeness, the fascia has to be picked off the neck. And by ‘picked’ I mean ‘actually cut away, millimeter by arduous millimeter’. It wasn’t that bad everywhere–the fascia over the long dorsal muscles came off very easily. But the lateral neck muscles were actually originating, in part, from the inner surface of the fascia. That’s not unheard of, it happens in the human forearm and leg all the time, but I’ve never seen it as consistently as in this rhea. So picking fascia took a loooong time–that’s what Vanessa is doing in the photo at top.
Once the fascia was off, Vanessa started parting out the long tendons of the hypaxial muscles in the left half of the neck. Meanwhile, I started stripping fascia from the right half. I had forgotten that the right half of the neck still had the trachea and esophagus adhered to the side. That probably sounds weird, given that our trachea and esophagus–and those of most mammals–run right down the middle of our necks and aren’t free to move around much. In birds, they’re more free-floating and can drift around between the skin and the vertebral muscles, sometimes even ending up dorsal to the vertebral column–there’s a great x-ray of a duck in a 2001 paper that shows this, which I’ll have to blog sometime.
Anyway, when I cut the fascia to pull back the trachea and esophagus, I found that they were separated from the underlying tissues by a dense network of pneumatic diverticula winding through the fascia.
I had heard, anecdotally, of networks of diverticula described as looking like bubble wrap. I can now confirm that is true, for at least some networks. What was especially cool about these is that they were occupying space that would be filled with adipose or other loose connective tissue in a mammal, which illustrates the point that pneumatic epithelium seems to replace many kinds of connective tissue, not just bone–something Pat O’Connor has talked about, and which I also briefly discussed in this post.
I should mention that there was no connection between these diverticula and the trachea, as there is between the subcutaneous throat sac and the trachea in the emu (story and pictures here).
While I was geeking out on diverticula, Vanessa was methodically separating the long hypaxial muscles, which looked pretty cool all fanned out.
And that’s all we had time for on Saturday. But we’re cutting again soon, so more pictures should be along shortly.