February 12, 2013
Today our paper on sauropod neck anatomy is formally published in PeerJ.
There’s not much new to say about the paper, since we posted it to arXiv last year and told the world about it then (post 1, post 2, post 3). Although a lot more attractive in form, this version is almost identical in content, modulo some changes requested by the PeerJ reviewers, and some changes to the figures to make sure every part of every figure was CC BY or otherwise in the public domain. Many thanks to everyone who gave us permission to use their images, especially Scott Hartman, who is rapidly getting to be the go-to person for this sort of thing just by doing good work and being a nice guy.
The big news, of course, is not the paper but the outlet. We’re excited about PeerJ because it promises to be a game-changer, for lots of reasons. Mike has a nice article in the Guardian today about the thing that is getting the most attention, which is the cost to publish. I blogged about it last fall, when I bought the max bling lifetime membership–for about one-tenth of the OA publication fee for a single article from one of the big barrier-based publishers.
Then there’s turnaround time: for our paper, a mere 72 days, including both submission day (Dec. 3) and publication day (Feb. 12). My fastest turnaround before this was 73 days for my sauropod nerve paper, but that was from submission to posting of the accepted manuscript, not publication of the final version of record. Prior to that I’d had a couple of papers published within six months of submission, but that was definitely the exception rather than the rule. And sadly, I’ve had several situations now where a paper languished in peer review for six months.
And that brings me to peer review–the real “peer” in PeerJ. When you sign up a lifetime membership, you agree to review one paper a year for them to keep your membership active. Certainly not a crushing amount of work, especially since I’ve been averaging 5 or 6 reviews a year for much less congenial outlets.
I’ve seen this from both sides now, since I was tapped to review a manuscript for PeerJ back in December. The first thing I liked is that they asked for the review back within 10 days. That’s just about right. I can see a thorough review taking three days (not working straight through, obviously, but taking time to carefully read, digest, look stuff up, and compose the review), and a busy academic maybe needing a week to find that kind of time. If one is too busy to get it done within 10 days, better to just be honest, say that, and decline the review. There is certainly no reason to let reviewers have manuscripts for four to six weeks, let alone the three to four months that was standard when I got into this business.
The second thing I liked is that they gave me the option to sign the review (which is almost always implicitly present, whether reviewers take advantage of it or not), and they gave the authors of the manuscript the option to publish my review alongside the paper. I love that. It means that, for the first time ever*, maybe the time and effort I put into the review will not disappear without a trace after I send it off. (It is astonishingly wasteful that we write these detailed technical critiques and then consign them to never be seen by any but a handful of people.) And it had a salutary effect on my reviewing. I always strive to be thoughtful and constructive in my reviews, but the knowledge that this review might be published for the world to see made me a lot more careful, both in what I said and how I said it. Hopefully, the authors I reviewed for will opt to publish my review, so you will be able to judge for yourself whether I succeeded–I’ll keep you posted on that. UPDATE: Hooray! The paper is out, and it’s a beaut, and the authors did publish the review history, which is excellent. The paper is Schachner et al. (2013), “Pulmonary anatomy in the Nile crocodile and the evolution of unidirectional airflow in Archosauria”, the reviews by Pat O’Connor and myself and the author responses and the editor’s letters are all available by clicking the “Peer review history” link on the sidebar, and you should go read all of it right now.
* There are a bare handful of other outlets that publish reviews alongside papers, but I’ve never been tapped to review for them, so this was my first experience with a peer review that might be published.
Naturally Mike and I took the maximum openness option and had our reviews and all the rest of the paper trail published alongside our paper, and I intend to do this every time from here on out. As far as I’m concerned, the benefits of open peer review massively outweigh those from anonymous peer review. There will always be a few jackasses in the world, and if openness itself doesn’t force better behavior out of them, at least they’ll be easier to identify and route around in an open world. Anyway, to see our reviews, expand ‘Author and article information’ at the top of this page, and click the link in the green box that says, “The authors have chosen to make the review history of this article public.”
One happy result of this will manifest in just a few weeks. Bunny-wrangler and sometime elephant-tracker Brian Kraatz and I co-teach a research capstone course for the MS students at WesternU, and one of the things we cover is peer review. Last year I had to dig up a couple of my reviews that were sufficiently old and anonymous that no harm could come from sharing them with the students, but even so, they only got half the story, because I no longer had the manuscripts and couldn’t have shared them if I had. This year I’ll be able to point the students at PeerJ and say, “Go look. There’s the back-and-forth. That’s how we do this. Now you know.”
Science, process and product alike, out in the open, freely available to the world: that’s why I’m proud to be a member of PeerJ.
(And I haven’t even mentioned the preprint server, or all the thought the PeerJ team put into the graphic design of the papers themselves, or how responsive the production team was in helping us get the finished product just right, or….)
The pictures in this post have nothing to do with our paper, other than showing off one of the beautiful products of the factors we discuss therein. The images are all borrowed from Brant Bassam’s amazing BrantWorks, which we will definitely be discussing more in the future. Explicit permission to reproduce the images with credit can be found on this page. Thanks, Brant!
UPDATE: Bonus Figure
January 31, 2013
You may remember this:
…which I used to make this:
…and then this:
The middle image is just the skeleton from the top photo cut out from the background and dropped to black using ‘Levels’ in GIMP, with the chevrons scooted up to close the gap imposed by the mounting bar.
The bottom image is the same thing tweaked a bit to repose the skeleton and get rid of some perspective distortion on the limbs. The limb posture is an attempt to reproduce an elephant step cycle from Muybridge.
That neck is wacky. Maybe not as wrong as Omeisaurus, but pretty darned wrong. As I mentioned in the previous Rapetosaurus skeleton post, the cervicals are taller than the dorsals, which is opposite the condition in every other sauropod I’ve seen. All in all, I find the reposed Rapetosaurus disturbingly horse-like. And oddly slender through the torso, dorsoventrally at least. The dorsal ribs look short in these lateral views because they’re mounted at a very odd, laterally-projecting angle that I think is probably not correct. But the ventral body profile still had to meet the distal ends of the pubes and ischia, which really can’t go anywhere without disarticulating the ilia from the sacrum (and cranking the pubes down would only force the distal ends of the ilia up, even closer to the tail–the animal still had to run its digestive and urogenital pipes through there!). So the torso was deeper than these ribs suggest, but it was still not super-deep. Contrast this with Opisthocoelicaudia, where the pubes stick down past the knees–now that was a tubby sauropod. Then again, Alamosaurus has been reconstructed with a similarly compact torso compared to its limbs–see the sketched-in ventral body profile in the skeletal recon from Lehman and Coulson (2002: figure 11).
I intend to post more photos of the mount, including some close-ups and some from different angles, and talk more about how the animal was shaped in life. And hopefully soon, because history has shown that if I don’t strike while the iron is hot, it might be a while before I get back to it. For example, I originally intended this post to follow the last Rapetosaurus skeleton post by about a week. So much for that!
Like everything else we post, these images are CC BY, so feel free to take them and use them. If you use them for the basis of anything cool, like a muscle reconstruction or life restoration, let us know and we’ll probably blog it.
April 30, 2012
In the recent post on OMNH 1670, a dorsal vertebra of a giant Apatosaurus from the Oklahoma panhandle, I half-promised to post the only published figure of this vertebra, from Stovall (1938: fig. 3.3). So here it is:
And in the second comment on that post, I promised a sketch from one of my notebooks, showing how much of the vertebra is reconstructed. Here’s a scan of the relevant page from my notebook. Reconstructed areas of the vert are shaded (confusingly, using strokes going in opposite directions on the spine and centrum, and the dark shaded areas on the front of the transverse processes are pneumatic cavities), and measurements are given in mm.
Next item: is this really a fifth dorsal vertebra?
Here are D4 and D5 of A. louisae CM 3018. They sort of bracket OMNH 1670 in terms of morphology. D4 has a broader spine, and D5 has a narrower one. The spine of D5 lacks the slight racquet-shaped expansion seen in OMNH 1670, but the overall proportions of the spine are more similar. On the other hand, the transverse processes of D4 taper a bit in anterior and posterior view, as in OMNH 1670, and unlike the transverse processes of D5 with their more parallel dorsal and ventral margins. But honestly, neither of these verts is a very good match (and the ones on either side, D3 and D6, are even worse).
Here are D3 and D4 of A. parvus UWGM 15556. D3 is clearly a poor match as well–it is really striking how much the vertebral morphology changes through the anterior dorsals in most sauropods, and Apatosaurus is no exception. D3 looks like a dorsal in lateral view, but in anterior or posterior view it could almost pass for a posterior cervical. If I was going to use the term “cervicodorsal”, indicating one of the vertebrae from the neck/trunk transition, I would apply it as far back as D3, but not to D4. That thing is all dorsal.
And it’s a very interesting dorsal from the perspective of identifying OMNH 1670. It has fairly short, tapering transverse processes. The neural spine is a bit shorter and broader, but it has a similar racquet-shaped distal expansion. I’m particularly intrigued by the pneumatic fossae inscribed into the anterior surface of the neural spine–in Gilmore’s plate they make a broken V shapen, like so \ / (or maybe devil eyes). Now, OMNH 1670 doesn’t have devil eyes on its spine, but it does have a couple of somewhat similar pneumatic fossae cut into the spine just below the distal racquet–perhaps a serially modified iteration of the same pair of fossae as in the A. parvus D4. It’s a right sod that D5 from this animal has its spine blown off–but it still has its transverse processes, and they are short and tapering as in OMNH 1670.
Here are all the dorsals and the first couple sacrals of FMNH P25112, which was originally described as A. excelsus but in the specimen-level analysis of Upchurch et al. 2005) comes out as the sister taxon to the A. ajax/A. parvus/A. excelsus clade. Note the striking similarity of the D5 here with D4 of the A. parvus specimen in Gilmore’s plate (until the careful phylogenetic work up Upchurch et al. 2005, that A. parvus specimen, once CM 563 and now UWGM 15556, was considered to represent A. excelsus as well). But also notice the striking similarity of D6 to OMNH 1670. It’s not quite a dead ringer–the transverse processes are longer and have weird bent-down “wingtips” (XB-70 Valkyrie, anyone?)–but it’s pretty darned close, especially in the shape of the neural spine.
So what does this all mean? First, that trying to specify the exact serial position of an isolated vertebra is nigh on to impossible, unless it’s something that is one-of-a-kind like an axis. Second, after doing all these comparos I think it’s unlikely that OMNH 1670 is a D4–those are a bit too squat across the board–but it could plausibly be either a D5 or a D6. Third, I’m really happy that it doesn’t seem to match any particular specimen better than all the rest. What I don’t want to happen is for someone to see that this vertebra looks especially like specimen X and therefore decide that it must represent species Y. As I said in the comments of the previous post, what this Oklahoma Apatosaurus material needs is for someone to spend some quality time seeing, measuring, and photographing all of it and then doing a phylogenetic analysis. That sounds like an ambitious master’s thesis or the core of a dissertation, and I hope an OU grad student takes it on someday.
If you were intrigued by my suggestion that the big Oklahoma Apatosaurus rivalled Supersaurus in size, and wanted to see a technical comparison of the two, I am happy to report that Scott Hartman has done the work for you. Here’s one of his beautiful Apatosaurus skeletal reconstructions, scaled to the size of OMNH 1670, next to his Supersaurus silhouette. This is just a small teaser–go check out his post on the subject for a larger version and some interesting (and funny) thoughts on how the two animals compare.
- Gilmore, C.W. 1936. Osteology of Apatosaurus with special reference to specimens in the Carnegie Museum. Memoirs of the Carnegie Museum 11:175-300.
- Riggs, E.S. 1903. Structure and relationships of opisthocoelian dinosaurs, part I: Apatosaurus Marsh. Field Columbian Museum Publications, Geological Series 2(4): 165–196.
- Stovall, J.W. 1938. The Morrison of Oklahoma and its dinosaurs. Journal of Geology 46:583-600.
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.
November 30, 2011
- Part 1: intro
- Part 2: the head
- Part 3: the neck
- Part 4: body, tail, limbs, base, and skull
- Part 6: texture and color
- Part 7: verdict
There are really only a couple of interesting points to discuss for posture: the neck and the feet.
The neck posture is fine. Easy to say, but since I’m one of the “sauropods held their necks erect” guys, it might need some unpacking.
On one hand, animals really do use stereotyped postures, especially for the neck and head (Vidal et al. 1986, Graf et al. 1995, van der Leeuw et al. 2001). The leading hypothesis about why animals do this is that the number of joints and muscle slips involved in the craniocervical system permits an almost limitless array of possible postures, and that having a handful of stereotyped postures cuts down on the amount of neural processing required to keep everything going. That doesn’t mean that animals only use stereotyped postures, just that they do so most of the time, when there’s no need to deviate.
This might work something like the central pattern generators in your nervous system. When you’re walking down the sidewalk thinking about other things or talking with a friend, a lot of the control of your walk cycle is handled by your spinal cord, not your brain. Your brain is providing a direction and a speed, but the individual muscles are being controlled from the spinal cord. Key quote from the Wikipedia article: “As early as 1911, it was recognized, by the experiments of T. Graham Brown, that the basic pattern of stepping can be produced by the spinal cord without the need of descending commands from the cortex.”
But then you see a puddle or some dog doo and have to place your foot just so, and your brain takes over for a bit to coordinate that complex, ad hoc action. After the special circumstance is past, you go back to thinking about whatever and your spinal cord is back in charge of putting one foot in front of the other. This is the biological basis of the proverbial chicken running around with its head cut off: thanks to the spinal cord, the chicken can still run, but without a brain it doesn’t have anywhere to go (I have witnessed this, by the way–one of the numerous benefits to the future biologist of growing up on a farm).
Similarly, if the craniocervical system has a handful of regular postures–alert, feeding, drinking, locomoting, and so on–it lightens the load on the brain, which doesn’t have to figure out how to fire every muscle slip inserting on every cervical vertebra and on the skull to orient the head just so in three-dimensional space. That doesn’t mean that the brain doesn’t occasionally step in and do that, just like it takes over for the spinal cord when you place your feet carefully. But it doesn’t have to do it all the time.
van der Leeuw et al. (2001) took this a step further and showed that birds not only hold their heads and necks in stereotyped postures, they move between stereotyped postures in very predictable ways, and those movement patterns differ among clades (fig. 7 from that paper is above). There is a lot of stuff worth thinking about in that paper, and I highly recommend it, along with Vidal et al. (1986) and Graf et al. (1995), to anyone who is interested in how animals hold their heads and necks, and why.
So, on one hand, its wrong to argue that stereotyped postures are meaningless. But it’s also wrong to infer that animals only use stereotyped postures–a point we were careful to make in Taylor et al. (2009). And it’s especially wrong to infer that paleoartists only show animals doing familiar, usual things–I wrote the last post partly so I could make that point in this one.
For example, I think it would be a mistake to look at Brian Engh’s inflatable Sauroposeidon duo and infer that he accepts a raised alert neck posture for sauropods. He might or might not–the point is that the sauropods in the picture aren’t doing alert, they’re doing “I’m going to make myself maximally impressive so I can save myself the wear and tear of kicking this guy’s arse”. The only way the posture part of that painting can be inaccurate is if you think Sauroposeidon was physically incapable of raising its neck that high, even briefly (the inflatable throat sacs and vibrant colors obviously involve another level of speculation).
Similarly, the Sideshow Apatosaurus has its neck in the near-horizontal pose that is more or less standard for depictions of diplodocids (at least prior to 2009, and not without periodic dissenters). But it doesn’t come with a certificate that says that it is in an alert posture or that it couldn’t raise its neck higher–and even if it did, we would be free to ignore it. Would it have been cool to see a more erect-necked apatosaur? Sure, but that’s not a new idea, either, and there are other restorations out there that do that, and in putting this apatosaur in any one particular pose the artists were forced to exclude an almost limitless array of alternatives, and they had to do something. (Also, more practically, a more erect neck would have meant a larger box and heftier shipping charges.)
So the neck posture is fine. Cool, even, in that the slight ribbing along the neck created by the big cervical ribs (previously discussed here) gives you a sense of how the posture is achieved. Visible anatomy is fun to look at, which I suspect is one of the drivers behind shrink-wrapped dinosaur syndrome–even though it’s usually incorrect, and this maquette doesn’t suffer from it anyway.
Next item: the famous–or perhaps infamous–flipped-back forefoot. I have no idea who first introduced this in skeletal reconstructions and life restorations of sauropods, but it was certainly popularized by Greg Paul. It’s a pretty straightforward idea: elephants do this, why not sauropods?
Turns out there are good reasons to suspect that sauropods couldn’t do this–and also good reasons to think that they could. This already got some air-time in the comments thread on the previous review post, and I’m going to start here by just copying and pasting the relevant bits from that discussion, so you can see four sauropod paleobiologists politely disagreeing about it. I interspersed the images where they’re appropriate, not because there were any in the original thread.
Mike Taylor: the GSP-compliant strong flexion of the wrist always look wrong to me. Yes, I know elephants do this — see Muybridge’s sequence [above] — but as John H. keeps reminding us all, sauropods were not elephants, and one might think that in a clade optimsied for size above all else, wrist flexibility would not be retained without a very good reason.
Adam Yates: Yes I agree with Mike here, the Paulian, elephant-mimicking hyperflexion of the wrist is something that bugs me. Sauropod wrist elements are rather simple flat structures that show no special adaptation to achieve this degree of flexion. [Lourina sauropod right manus below, borrowed from here.]
Heinrich Mallison: Hm, I am not too sure what I think of wrist flexion. Sure it looks odd, but if you think it through the very reasons elephant have it is likely true in sauropods. And given the huge amount of cartilage mossing on the bones AND the missing (thus shape unknown) carpals I can well imagine that sauropods were capable of large excursions in the wrist.
Mike: What are those reasons?
Heinrich: Mike, long humeri, very straight posture – try getting up from resting with weak flexion at the wrist. Or clearing an obstacle when walking. I can’t say too much, since this afternoon this has become a paper-to-be.
Mike: OK, Heinrich, but the Muybridge photos (and many others, including one on John H.’s homepage) show that elephants habitually flex the wrist in normal locomotion, not just when gwetting up from resting or when avoiding obstacles. Why?
The interesting thing here is that this is evidence of how flawed our (or maybe just my) intuition is: looking at an elephant skeleton, I don’t think I would ever have guessed that it would walk that way. (That said, the sauropod wrist skeleton does look much less flexible than that of the elephant.)
Matt: (why elephants flex their wrists) Possibly for simple energetics. If the limb is not to hit the ground during the swing phase, it has to be shortened relative to the stance limb. So it has to be bent. Bending the limb at the more proximal joints means lifting more weight against gravity. Flexing the wrist more might be a way to flex the elbow less.
(sauropod wrists look less flexible) Right, but from the texture of the ends of the bones we already suspect that sauropods had thicker articular cartilage caps than do mammals. And remember the Dread Olecranon of Kentrosaurus (i.e., Mallison 2010:fig. 3).
Mike: No doubt, but that doesn’t change the fact that elephant wrists have about half a dozen more discrete segments.
Matt: Most of which are very tightly bound together. The major flexion happens between the radius and ulna, on one hand, and the carpal block on the other, just as in humans. Elephants may have more mobile wrists than sauropods did–although that is far from demonstrated–but if so, it’s nothing to do with the number of bony elements. [Loxodonta skeleton below from Wikipedia, discovered here, arrow added by me.]
(Aside: check out the hump-backed profile of the Asian Elephas skeleton shown previously with the sway-backed profile of the African Loxodonta just above–even though the thoracic vertebrae have similar, gentle dorsal arches in both mounts. I remember learning about this from the wonderful How to Draw Animals, by Jack Hamm, when I was about 10. That book has loads of great mammal anatomy, and is happily still in print.)
And that’s as far as the discussion has gotten. The Dread Olecranon of Kentrosaurus is something Heinrich pointed out in the second of his excellent Plateosaurus papers (Mallison 2010: fig. 3).
Heinrich’s thoughts on articular cartilage in dinosaurs are well worth reading, so once again I’m going to quote extensively (Mallison 2010: p. 439):
Cartilaginous tissues are rarely preserved on fossils, so the thickness of cartilage caps in dinosaurs is unclear. Often, it is claimed that even large dinosaurs had only thin layers of articular cartilage, as seen in extant large mammals, because layers proportional to extant birds would have been too thick to be effectively supplied with nutrients from the synovial fluid. This argument is fallacious, because it assumes that a thick cartilage cap on a dinosaur long bone would have the same internal composition as the thin cap on a mammalian long bone. Mammals have a thin layer of hyaline cartilage only, but in birds the structure is more complex, with the hyaline cartilage underlain by thicker fibrous cartilage pervaded by numerous blood vessels (Graf et al. 1993: 114, fig. 2), so that nutrient transport is effected through blood vessels, not diffusion. This tissue can be scaled up to a thickness of several centimeters without problems.
An impressive example for the size of cartilaginous structures in dinosaurs is the olecranon process in the stegosaur Kentrosaurus aethiopicus Hennig, 1915. In the original description a left ulna (MB.R.4800.33, field number St 461) is figured (Hennig 1915: fig. 5) that shows a large proximal process. However, other ulnae of the same species lack this process, and are thus far less distinct from other dinosaurian ulnae (Fig. 3B, C). The process on MB.R.4800.33 and other parts of its surface have a surface texture that can also be found on other bones of the same individual, and may indicate some form of hyperostosis or another condition that leads to ossification of cartilaginous tissues. Fig. 3B–D compares MB.R.4800.33 and two other ulnae of K. aethiopicus from the IFGT skeletal mount. It is immediately obvious that the normally not fossilized cartilaginous process has a significant influence on the ability to hyperextend the elbow, because it forms a stop to extension. Similarly large cartilaginous structures may have been present on a plethora of bones in any number of dinosaur taxa, so that range of motion analyses like the one presented here are at best cautious approximations.
One of the crucial points to take away from all of this is that thick cartilage caps did not only expand or only limit the ranges of motions of different joints. The mistake is to think that soft tissues always do one or the other. The big olecranon in Kentrosaurus probably limited the ROM of the elbow, by banging into the humerus in extension. In contrast, thick articular cartilage at the wrist probably expanded the ROM and may have allowed the strong wrist flexion that some artists have restored for sauropods. I’m not arguing that it must have done so, just that I don’t think we can rule out the possibility that it may have. And so the flipped-back wrist in the Sideshow Apatosaurus does not bother me–but not everyone is convinced. Welcome to science!
Ever since I saw Jensen’s (1987) paper about how mammals are so much better than dinosaurs because their limb-bones articulate properly, I’ve been fuming on and off about this — the notion that the clearly unfinished ends we see are what was operating in life. No.
Finally, interest in articular cartilage is booming right now, as Mike blogged about here. In addition to the Dread Olecranon of Kentrosaurus, see the Dread Elbow Condyle-Thingy of Alligator from Casey Holliday’s 2001 SVP talk, and of course the culmination of that project in Holliday et al. (2010), and, for a more optimistic take on inferring the shapes of articular surfaces from bare bones, read Bonnan et al. (2010).
Next time: texture and color.
- Bonnan, M.F., Sandrik, J.L., Nishiwaki, T., Wilhite, D.R., Elsey, R.M., and Vittore, C. 2010. Calcified cartilage shape in archosaur long bones reflects overlying joint shape in stress-bearing elements: Implications for nonavian dinosaur locomotion. The Anatomical Record 293: 2044-2055.
- Graf, W., Waele, C. de, and Vidal, P.P. 1995. Functional anatomy of the head−neck movement system of quadrupedal and bipedal mammals. Journal of Anatomy 186: 55–74.
- Holliday, C.M., R.C. Ridgely, J.C. Sedlmayr and L.M. Witmer. 2010. Cartilaginous epiphyses in extant archosaurs and their implications for reconstructing limb function in dinosaurs. PLoS ONE 5(9): e13120. doi:10.1371/journal.pone.0013120
- Mallison, H. 2010. The digital Plateosaurus II: An assessment of the range of motion of the limbs and vertebral column and of previous reconstructions using a digital skeletal mount. Acta Palaeontologica Polonica 55 (3): 433–458.
- Taylor, M.P., Wedel, M.J. and Naish, D. 2009. Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54(2): 213-220.
- van der Leeuw, A.H.J., Bout, R.G., and Zweers, G.A. 2001. Evolutionary morphology of the neck system in ratites, fowl, and waterfowl. Netherlands Journal of Zoology 51(2):243-262.
- Vidal, P.P., Graf, W., and Berthoz, A. 1986. The orientation of the cervical vertebral column in unrestrained awake animals. Experimental Brain Research 61: 549-559.
November 23, 2011
Here at SV-POW! we are ardently pro-turkey. As the largest extant saurischians that one can find at most butchers and grocery stores, turkeys (Meleagris gallopavo) are an important source of delicious, succulent data. With Thanksgiving upon us and Christmas just around the corner, here’s an SV-POW!-centric roundup of turkey-based geekery.
The picture at the top of the post shows a couple of wild turkeys that frequented our campsite in Big Bend in the winter of 2007. Full story here.
If you’re wondering what to do with your turkey, the answer is GRILL IT. I use the recipe (available on Facebook) of my good friend and colleague, Brian Kraatz, who has fallen to the Dark Side and works on mammals–rabbit tooth homology, even (Kraatz et al. 2010)–but still grills a mean theropod. (In his defense, Kraatz has published on extinct saurischians–see Bibi et al. 2006.) My own adventures in turkey grilling are chronicled in this post, which will show you the steps to attaining enlightenment, or at least a larger circumference.
While you’re cooking and eating, you might as well learn something about muscles. This shot of the fanned-out longus colli dorsalis muscles in a turkey neck was the raison d’etre for this post, and turned up again with different muscles labeled in one of the recent Apatosaurus maquette review posts. Mike and I ate those muscles, by the way.
After the meal, you’ll have most of a turkey skeleton to play with. This diagram is from my other ‘holiday dinosaur’ page, which I put together for the Lawrence Hall of Science and UCMP back in 2005. That page has instructions on how to turn your pile of greasy leftovers into a nice set of clean white bones. Tom Holtz is widely acknowledged as King of the Dino-Geeks, and in kingly fashion he took the above diagram and turned the geek-o-meter up to 11. Steel yourself, gentle reader, before checking out the result here.
Speaking of bones, here’s a turkey cervical from Mike’s magisterial work in this area, which first appeared as a tack-on to a post about the holotype dorsal vertebra of the now-defunct genus Ultrasauros. The huge version of the composite photo has its own page on Mike’s website, where it is available in three different background colors. The lateral view also turned up in one of my rhea neck posts.
From the serving platter to publication: when I was young and dumb, I used a photo of a broken turkey vert to illustrate the small air spaces, or camellae, that are commonly found in the pneumatic bones of birds and some sauropods (Wedel and Cifelli 2005:fig. 11F).
I made a much better version by sanding the end off a cleaned-up vertebra, and used that in Wedel (2007), in this popular article on pneumaticity (which has instructions for making your own), and way back in Tutorial 3–only the 12th ever post on SV-POW!
Finally, it would be remiss of me not to point out that turkeys are not only readily accessible, tasty sources of anatomical information, they are also pretty interesting while they’re still alive. Don’t stare at the disgusting freak in the photo above or you might lose your will to eat. Instead, head over to Tetrapod Zoology v2 for Darren’s musings on caruncles, snoods, and other turkey parts that don’t even sound like words.
That does it for now. If you actually follow all of the links in this post, you might just have enough reading to keep you occupied during that post-holiday-meal interval when getting up and moving around is neither desirable nor physically possible. If you’re in the US, have a happy Thanksgiving; if you’re not, have a happy Thursday; and no matter where you are, take a moment to give thanks for turkeys.
- Bibi, F., Shabel, A.B., Kraatz, B.P., and Stidham, T.A. 2006. New fossil ratite (Aves: Palaeognathae) eggshell discoveries from the Late Miocene Baynunah Formation of the United Arab Emirates, Arabian Peninsula. Palaeontologia Electronica Vol. 9, Issue 1; 2A:13p.
- Kraatz, B.P., Meng, J., Weksler, M., and Li, C. 2010. Evolutionary patterns in the dentition of Duplicidentata (Mammalia) and a novel trend in the molarization of premolars. PLoS ONE 5(9): e12838. doi:10.1371/journal.pone.0012838
- Wedel, M.J. 2007. Aligerando a los gigantes (Lightening the giants). ¡Fundamental! 12:1-84. [in Spanish, with English translation]
- Wedel, M.J., and Cifelli, R.L. 2005. Sauroposeidon: Oklahoma’s Native Giant. Oklahoma Geology Notes 65 (2):40-57.
November 21, 2011
- Part 1: intro
- Part 2: the head
- Part 3: the neck
- Part 5: posture
- Part 6: texture and color
- Part 7: verdict
A long-running theme here at SV-POW! is that the torsos of most sauropods were not just deep and slab-sided, they were unusually deep and slab-sided, more so than in most other tetrapods (see this and this, and for a more pessimistic take, this). This is something that is easy to get wrong; we are used to seeing round mammalian torsos and a lot of toy sauropods have nearly circular cross-sections. A lot of sculptors of collectible dinos do get the torso cross-section right, though, and the folks who made this Apatosaurus are no exception.
Next item: there’s an upward kink at the base of the tail, as there should be. Gilmore was the first to point this out, in his 1932 paper on the mounting of the Smithsonian Diplodocus (that’s plate 6 from that paper above; the skeleton on the bottom is the more correct one). This came up in the comment thread of the first post in this series, and since I haven’t had any deeper thoughts on the issue in the past week, I’m just going to copy and paste what I wrote then:
The upkink at the base of the tail is unavoidable; the sacrum is shaped like an inverted keystone and there’s no way to get the proximal caudals to do anything but angle upward without disarticulating them…. The reverse keystoning of sauropod sacra is weird. And it’s in every sauropod sacrum I can remember seeing with my own eyes, including Brachiosaurus altithorax. And yet the only authors I can think of off the top of my head who have discussed it seriously are Gilmore (1932), Greg Paul (2010, maybe a magazine article or two I haven’t seen), maybe Jim Jensen (1988), and IIRC Salgado et al. (1997). If there are more, please let me know–this is something I’m very curious about.
The back is gently arched, with the highest point about midway between the shoulder and hip joints. Where the highest point in the back falls depends on a host of factors, including the relative lengths of the forelimb and hindlimb bones, the amount of cartilage on the ends of those bones, the position and angle of the scapula on the ribcage, and the intrinsic curvature, if any, of the articulated series of dorsal vertebrae, which were themselves separated by an unknown amount of cartilage. Opinions are all over the map on most of these issues, particularly scapular orientation. As a scientist, I am agnostic on most of these points; I don’t think that they’re beyond being sorted out, but there’s a lot of work in progress right now and I haven’t seen evidence that would definitely convince me one way or another. So in lieu of saying that Apatosaurus must have had this scapular orientation and that dorsal curvature and so on, I’ll just note that the maquette has been a dominant feature in my office for a few weeks now and nothing about the body profile, shoulder position, or limb length has ever struck me as odd or worthy of comment. It looks like Apatosaurus to me. Moving on…
In the last post I talked about the visible bulges in the neck that allow one to count the cervical vertebrae. The maquette also has low bumps along the back that mark the neural spines of the dorsal vertebrae. This doesn’t strike me as unreasonable. Attachment scars for interspinous ligaments run all the way up to the tips of the neural spines in most sauropods, so the entire height of one neural spine was often webbed to the next by a continuous ligamentous sheet, as Janensch (1929: plate 4) drew for Dicraeosaurus in the illustration above (isp.L). I don’t think those ligaments would have prevented the bony tips of the vertebrae from being visible, necessarily, and the epaxial muscles should have been on either side of the interspinous ligaments and in the triangular spaces between the spine tips and the transverse processes.
What might have smoothed out the dorsal body profile are supraspinous ligaments (ssp.L in the plate above). These are present in crocs (Frey 1988: figs. 14, 16, 17) but apparently absent in most birds; at least, I haven’t seen any myself, and the Nomina Anatomica Avium does not mention any (Baumel et al. 1993: 156-157). So on phylogenetic grounds their presence in sauropods is equivocal. That said, the tips of the neural spines in most sauropods are fairly rugose. Does that mean that they were webbed one to the next by interspinous ligaments only, or that they were embedded in supraspinous ligaments as well? I don’t know the answer, and I don’t know if anyone else does, either. The whole issue of intervertebral ligaments in sauropods has received too little attention to date. In the absence of better data, I’ll just say that although I wouldn’t put any money on the proposition that the spines made externally visible bumps in life, neither does it offend me.
There is one fairly nit-picky point that I am honor-bound to mention. Because the dorsal neural spines make bumps, it is possible to count the dorsals, just like the cervicals last time. And this count doesn’t work out quite as well. Apatosaurus should have 10 dorsal vertebrae, but try as I might I can’t see more than 8 bumps along the back, and that’s generously assuming that c14′s spine is pretty well ahead of its rib. Is this pathologically anal to complain about? Quite possibly. On the other hand, by sculpting in those details the artists were basically begging geeks like me to come along and count vertebrae just because we could.
The tail is pretty cool. It is appropriately massive where it leaves the body, and has a visible bulge for the caudofemoralis muscle, which originated in the tail and inserted on the fourth trochanter of the femur. The caudofemoralis is the major femur retractor in lizards and crocs and in most non-avian dinosaurs, and rather than go on about it I’ll just point you to Heinrich Mallison’s awesome post about dinosaur butts. The tail of the maquette also has an awesome whiplash. I could say a ton more about the hypothesized uses of whiplash tails in diplodocids and other sauropods, but I don’t feel like climbing that hill just now. Suffice it to say that the maquette’s whiplash is pretty sweet, and avoids the “scale is too small so I just stuck in a piece of wire” mode of making whiplashes that I’ve seen in other, smaller diplodocid sculpts.
The tail has a row of little spines running down the dorsal midline, which have been de rigeur for life restorations of diplodocids and many other sauropods (ahem) since they were first reported by Czerkas (1993). AFAIK, such spines have only been found preserved in the tail region of diplodocids. That’s not to say that they weren’t present in the neck or the back of diplodocids, or in other sauropod taxa, just that the only good fossil traces of them to date have been from the tails of diplodocids, and maybe just one or two tails. So the presence of little spines in the tail of the maquette and not the back or the neck is perfectly–one might even say slavishly–consistent with the fossil evidence. I’ll discuss the flamboyancy or lack thereof in the maquette in another post, so I’ll say no more about this design choice for now.
The limbs are mostly good. The muscles under the skin look plausible, with one exception. As noted before in this series, Apatosaurus was a freakishly robust critter, and the limbs look appropriately sturdy and well-muscled, except where the thigh meets the hip. There is a visible bulge for the ilium, and the anterior margin of the thigh should converge with the most forward point on the ilium. That’s what the preacetabular blade of the ilium is for: to anchor thigh muscles (discussed here, and also nicely illustrated here). Unless the animal had some kind of wasting disease, there was no bone sticking out beyond the muscle, and so the anterior-most point of the ilium has to be the start of the anterior margin of the thigh.
On the positive side, there’s a little ridge running down from the anterior arm onto the forearm for the biceps tendon, which is a nice touch. The manus shows the short, solid arc of metacarpals typical for diplodocids, and an inward-curving thumb claw. The hind feet have the big laterally-curving claws on the first three digits that one expects.
In a way that is difficult to describe in words, the feet really look they are bearing a lot of weight, and this impression of solidity helps to ground the whole maquette. It doesn’t look like a sauropod-shaped balloon that just happens to be poling itself along with limbs that barely touch the ground–an impression that I have gotten occasionally from some other sculptures with overly skinny limbs and too-small feet. This critter looks big, heavy, and powerful, and those are exactly the adjectives one wants to come to mind when looking at Apatosaurus. (I do wonder if doing a Diplodocus in the same scale would be more difficult. How do you convey ‘multi-ton animal’ and ‘gracile’ at the same time?)
To sum up, in the trunk, tail, and limbs I find much to like and little to criticize. The only noteworthy problems are the insufficient dorsal count and the mismatch between the ilium and anterior thigh profile. On one hand these are puzzling goofs, given the overall attention to detail and the numerous points at which the sculpt is not just good but surprisingly good. On the other hand, I didn’t notice the dorsal thing until I bothered to count, and I didn’t notice the thigh thing until the other day when I was writing the first draft of this post, so both problems went unnoticed for weeks and are probably below the threshold of perception for the vast majority of people. The accuracy of the sculpt is so high that my approach to its problems has not been, “Where do I begin?” but rather, “What is keeping this thing from being perfect?” And the answer is, not very much.
The base is nice. It’s not just a generic slab of earth, it’s a muddy surface marked with the tracks of other dinosaurs, including a couple of theropods. The base sits nice and flat, and the Apatosaurus sits nice and flat on it, with no rocking at either point of contact. Not only do the feet of the Apatosaurus fit neatly into the sculpted footprints, one of the hindfeet has a little metal rod that slots into a socket in one of the hindfoot prints, to keep the maquette firmly on the base. That means that if you want to display the maquette off the base, you’ll have to either cut off the rod or make sure that your alternative surface will accommodate it.
The skull is…less satisfying. It’s a nice enough rendition of an Apatosaurus skull, and if it had come by itself I would have been very happy with it. The trouble is that the maquette is considerably more detailed, so when the skull sits next to the maquette it suffers by comparison. But what else are you going to do with it? Make a separate shrine to Apatosaurus somewhere else?
The difference in sculpt quality between the maquette and base on one hand and the skull on the other is apparent even on casual inspection. My copies are sitting on a bookcase adjacent to my office door. Sometimes people walking down the hall pop their heads in, and so far the most common comments are that the maquette is “awesome” and that the base is “cool”. People have been genuinely impressed that the base is a realistically detailed chunk of the environment and not just a flat slab. The only people who have commented on the skull have said that it seems “lame” compared to the maquette.
The base is included in the basic package with the maquette, in a limited edition of 500, which as of this writing goes for $289.99 (here). The package with the skull accessory is in an edition of 100, and goes for $299.99 (here). So the skull is only $10 more, and although it is not quite as nice as the maquette, I think it’s a steal at the price. Mine is certainly not going anywhere.
So much for the gross anatomy. You probably noticed that I haven’t said anything about how the maquette is posed or textured or colored. Those will all be topics for next time.
- Baumel, J.J., King, A.S., Breazile, J.E., Evans, H.E., and Vanden Berge, J.C. (eds.) 1993. Handbook of Avian Anatomy: Nomina Anatomica Avium, 2nd ed. Publications of the Nuttall Ornithological Club, No. 23. Cambridge, Massachusetts, 779 pp.
- Czerkas, S.A. 1993. Discovery of dermal spines reveals a new look for sauropod dinosaurs. Geology 20:1068–1070.
- Frey, E. 1988. Anatomie des Körperstammes von Alligator mississippiensis Daudin.
- Gilmore, C. W. 1932. On a newly mounted skeleton of Diplodocus in the United States National Museum. Proceedings of the United States National Museum 81:1-21.
- Janensch, W. 1929. Die Wirbelsäule der Gattung Dicraeosaurus. Palaeontographica Suppl. 7(1), 3(2), 37-133.
- Jensen, J.A. 1988. A fourth new sauropod dinosaur from the Upper Jurassic of the Colorado Plateau and sauropod bipedalism. Great Basin Naturalist 48(2):121-145.
- Paul, G.S. 2010. The Princeton Field Guide to Dinosaurs. Princeton University Press, 320 pp.
- Salgado, L., R.A. Coria, and J.O. Calvo. 1997. Evolution of titanosaurid sauropods. I: Phylogenetic analysis based on the postcranial evidence. Ameghiniana 34:3-32.
October 3, 2011
Just a quick note to let anyone who’s not on the Dinosaur Mailing List know that the DML has spawned a new list dedicated to the history of palaeontology. It’s hosted at Google Groups, so you have the choice of subscribing to it as a mailing list or reading it as a forum.
September 8, 2011
Last time, we looked at the bones of the sauropod skeleton, and I mentioned that “thanks to the wonder of homology, it doubles as a primer for dinosaur skeletons in general”. To prove it, here everyone’s favourite vulgar, overstudied theropod Tyrannosaurus rex, in L. M. Sterling’s reconstruction from Osborn 1906:plate XXIV, published just one year after the big guy’s initial description. (The pose is somewhat outdated, but it’s a classic):
Click through for the full-sized version (2897 by 1755 pixels), which — like yesterday’s Camarasaurus — you are welcome to print out and hang on your wall as a handy reference. (Sterling’s original is out of copyright; I hereby make my modified version available under the CC-BY-NC-SA licence.)
The thing to notice is that the Camarasaurus and Tyrannosaurus have exactly the same bones, excepting only that theropods had gastralia (belly ribs) and sauropods probably did not. If you doubt it, here are the two animals composited together. Print it out! Print lots of copies! Hand them out to your friends!
September 7, 2011
We should have done this long ago. Back in the early tutorials, we covered skeletal details such as regions of the vertebral column, basic vertebral anatomy, pneumaticity and laminae, but we never started out with an overview of the sauropod skeleton.
Time to fix that. This is numbered as Tutorial 15 but you can think of it as Tutorial Zero if you prefer. Thanks to the wonder of homology, it doubles as a primer for dinosaur skeletons in general.
Here is a complete, labelled sauropod skeleton, modified from Erwin S. Christman’s reconstruction of Camarasurus supremus in Ostrom and Mook 1921:plate LXXXIV:
Click through for the full-sized version (2897 by 1280 pixels), which you are welcome to print out and hang on your wall as a handy reference. (Christman’s original is out of copyright; I hereby make my modified version available under the CC-BY-NC-SA licence.)
Since that’s a lot to take in all at once, we’ll walk through the regions of the skeleton: the head and neck, the rest of the vertebral column, the forelimb and girdle, and the hindlimb and girdle. But first, a little bit of …
Skeletons consist of bones. The study of skeletons and of bones is called osteology. There are several ways of dividing up the skeleton into manageable chunks. One is to consider cranial vs. postcranial bones. In this division, cranium just means skull (though see below) and postcranium means “everything except the skull”. Here at SV-POW!, of course, we consider skulls beneath our notice, so this division seems silly to us. We have been known to refer to the skull as the prepostcranium on occasion.
A more useful division of the skeleton is into axial and appendicular. The axial skeleton includes the skull, hyoid apparatus (little bones in the neck that anchor tongue and throat muscles), vertebrae, ribs and chevrons (i.e. everything on the midline), and the appendicular bones are those of the limbs and their girdles, i.e. shoulders and hips. (I learned only very recently that, although they seem to be part of the forelimb girdle, the sternal plates are actually part of the axial skeleton, being related to the ribs rather than the shoulders.)
Head and neck
Let’s start with the head. Although “cranium” is sometimes used to mean the whole head, as noted above, it more strictly refers to the rigid upper portion of the skull which attaches to the neck and includes the upper jaw. The lower jar, which moves independently, is called the mandible. Both of these units are made up of many smaller bones. There is of course much, much more to say about skull anatomy, but that is another tutorial for another day. For now, we will just pretend that the skull is made of two lumps of bone and move swiftly onwards.
The back of the skull articulates with the neck, which is part of the spine, or vertebral column. All vertebrates have a spine; and in all tetrapods it’s divided into neck, trunk (or torso), sacrum and tail. The spine is composed of vertebrae: those in the neck are called cervical vertebrae, or cervicals for short; those in the trunk are called dorsal vertebrae (in crocs and mammals these are further broken down into the thoracic vertebrae, which bear mobile ribs, and the lumbar vertebrae which do not); those in the sacrum are called sacral vertebrae and those in the tail are called caudal vertebrae. But you already know that if you read Tutorial 1.
In some kinds of tetrapods, including all dinosaurs, the cervical vertebrae have backward-pointing ribs; these are called the cervical ribs. Birds have these (in reduced form) and so do crocs and mammals, but they are absent in at least some lizards and turtles. Contrary to popular belief, mammals do have bicipital (two-headed) cervical ribs, they are just very short and fused to the vertebrae. Even most human osteology textbooks refer to them as transverse process. But developmentally and functionally they are ribs; they bound the transverse foramina through which the vertebral arteries pass, and they anchor deep neck muscles. The “cervical ribs” that occasionally crop up as a pathology in humans are large, mobile, thoracic-style ribs, and represent segmentation anomalies during early development.
The cervical vertebrae are numbered backwards from the head. Each cervical can be identified by number, so that the tenth is called “cervical 10″, or C10 for short. Sauropods have between eleven and nineteen cervicals — a lot more than the feeble seven that nearly all mammals have, but well short of the seventy or so that Elasmosaurus could boast.
In most tetrapods, the cervicals from C3 backwards are similar in shape, although they tend to get bigger as they approach the torso; but the first two are distinctive, so they have special names. C1 is called the atlas — easy to remember as it holds up the head, just as the titan Atlas held up the sky (not the Earth as often thought). It doesn’t really look like a vertebra at all, being ring-shaped and (in sauropods) tiny. C2 is called the axis. It looks much more like a normal vertebra, but has an odd articulation at the front, a distinctive blunt spike that the atlas sits on (it also has small prezygapophyses for the neural arch elements of the atlas–these little bits of bone are often lost in fossil skeletons). It’s smaller than the succeeding vertebrae — unlike the situation in mammals, in which the axis is ususally the largest cervical — and has a big, blade-like neural spine.
Torso and tail
The vertebral column continues back from the base of the neck, as the torso, which consists of dorsal vertebrae.
In the region of the hips, several vertebrae fuse together: this is true to some extent in most or all tetrapods, but in many groups it’s only two or three vertebrae that fuse, whereas in sauropods (and most dinosaurs) it’s four or more. This set of fused vertebrae is the sacrum, and the vertebrae that make it up are the sacral vertebrae.
Behind the sacrum is the tail, which is composed of caudal vertebrae. Hanging beneath these — or, specifically, between the intervertebral joints — are transversely flattened bones called chevrons or haemopophyses. These exist in most reptiles, but have been lost in most mammals. (They do exist in wallabies, but they are a very different shape.) Developmentally the chevrons mirror the neural arch, and form a canal for the caudal aorta in the same way that the neural arch forms a canal for the spinal cord.
Just as the cervical vertebrae have cervical ribs, so the dorsal vertebrae have dorsal ribs. These are longer and more vertically oriented than the cervical ribs. The sacral vertebrae, too, have sacral ribs, but you rarely see them because in lateral view they are obscured by the ilium — as is the case here. You might, then, wonder whether the caudal vertebrae have caudal ribs, but the answer is not clear. The first few caudals, at least, do have lateral processes, but surprisingly there is no consensus about what they actually are: ribs that are fused to the vertebrae, or paraphophyses/diapophyses that are fused together. See the overview in Wilson (1999:642).
How can you tell where the neck ends are the torso begins? The traditional answer is that the first dorsal vertebrae is the first one with a “free” (i.e. unfused) rib, but it’s not always that clear. Although cervical ribs generally fuse to their vertebrae and dorsal ribs rarely or never do, there are plenty of exceptions — for example, the last few cervical ribs of the Mamenchisaurus hochuanensis holotype appear unfused. Also, in specimens where the cervicodorsal transition is well preserved, it’s apparent that the switch from short backward-directed cervical ribs to long downward-directed dorsal ribs may be abrupt, between adjacent vertebrae, or a gradual transition spread out over several vertebrae. Since the shoulder girdle bones don’t articulate with the torso, that clue’s also unavailable, so all in all it can be hard to nail down where the transition was. You just sort of know it when you see it.
The final axial bones are the sternal plates, which belong somewhere in the breast area. The exact placement and orientation of these bones is not agreed, and they are rarely if ever preserved in place.
Shoulder and forelimb
The bones of the shoulder are the elongate scapula, or shoulder-blade, on the side of the torso; and the coracoid, lower down wrapping round to the front. Together, these bones make up the shoulder girdle. Unlike the pelvis, the shoulder is not fused to the bones of the torso, but would have been bound to it by ligament and muscle. Because of this, the exact position of the scapula and coracoid are not known, and remain the subject of controversy. The reconstruction above shows a fairly vertical scapula; some others make it more nearly horizontal.
Where the scapula and coracoid meet, they form a hollow on the underside, called the glenoid. The head of the humerus fits in here; two parallel bones form the lower limb segment: the ulna and radius. In sauropods, the ulna is a rounded triangle in cross-section, with a hollow on the front face of the triangle which the radius fits into.
At the bottom of the lower limb segment are the carpals, or wrist bones; then the manus, or hand. The upper bones of the manus are the metacarpals, which in sauropods are held near-vertical in a semi-circular arcade with the hollow directed backwards and slightly inwards. Below the metacarpals are the phalanges (singular phalanx); each finger may have multiple phalanges, but sauropods tend to have very few. When the last phalax of a digit is claw-shaped, it’s called an ungual.
Because both forefeet and hindfeet have phalanges and unguals, we distinguish by saying manual phalanges and manual unguals for the bones of the forelimb, and pedal phalanges and pedal unguals for those of the hindlimb.
Hip and hindlimb
The pelvis, or hip girdle, is made up of three bones on each side: the ilium, on top, is roughly semi-circular; the pubis, at the front, and the ischium, at the back, are more elongate. Where these three bones meet, they form a circular hole called the acetabulum, or hip socket. Unlike the shoulder girdle, the pelvis is fused to the torso: specifically, the ilium is fused to the sacrum via the transverse processes of the sacral vertebrae and their sacral ribs. The pubes and ischia do not fuse.
The femur, or thigh bone, has a head that projects into the acetabulum. At the knee, it meets two parallel lower-limb bones, the tibia and fibula. The former is the main weight-bearing bone and is nearest the midline. The fibula sits to the side of it. Unlike mammals, most reptiles including non-avian dinosaurs have no kneecap, or patella; but birds do. Sesamoids or “floating” bones like the patella seem to be evolved and lost more readily than the normally-connected bones of the skeleton.
Below these two bones are the tarsals, or ankle bones. In sauropods there are one or two of these: a large, disc-shaped astragalus beneath the tibia, and sometimes a smaller globular calcaneum below the fibula. (For some reason, the carpals don’t seem to have names.) Beneath these is the pes, or hindfoot. The upper bones of the pes are the elongate metatarsals. Beyond these are the short pedal phalanges and unguals.
What did we miss?
The bones listed account for nearly all the skeleton. There are, however, a few extra bones that are rarely recovered or not always present. Clavicles, or collar bones, have been reported in the limb girdles of some sauropods. Gastralia, or belly ribs, were probably present in all sauropods, but are fragile and very rarely preserved. Finally, some sauropods had osteoderms — small, isolated bones embedded in the skin and serving as armour. None of these are illustrated in Christman’s Camarasaurus.
Because the basic tetrapod body-plan is so conservative — many bones change size and shape, but it’s comparatively rare for bones to evolve away or for new ones to evolve — you can look at skeletons of all sorts of animals in a museum and recognise nearly all the bones I’ve listed here. Birds, the closest living relatives of sauropods, have everything I’ve listed here, though their sternal plates have merged into a single big sternum and their forelimbs are obviously highly modified. Crocs have everything. Lizards have everything except cervical ribs. Even mammals are surprisingly similar, though all the pelvis bones fuse together and the coracoid is lost (the coracoid process of the scapula in humans and other mammals is a different, non-homologous bit of bone).
In particular, you have nearly all the bones in a sauropod skeleton, though of course many of the bones are very different in shape, or fused together, and your tail is contemptible. You might like to try re-reading this tutorial, finding all the relevant bones in your own body. You have a few extras as well: most obviously, your kneecaps, but also extra bones in the wrist and ankle.
SEE ALSO: the same thing done for Tyrannosaurus.
Wilson, Jeffrey A. 1999. A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs. Journal of Vertebrate Paleontology 19(4): 639-653. [Wilson used to have a freely available PDF on his site, but he seems to have removed it, and substituted a link to a paywalled PDF.]