February 2, 2015
Introduction and Background
I have three goals with this post:
- To document the range of variation in epipophyses in the cervical vertebrae of sauropods.
- To show that the “finger-like processes” overhanging the cervical postzygapophyses in the newly described Qijianglong are not novel or mysterious structures, just very well developed epipophyses.
- Finally, to show that similar long, overhanging epipophyses are present in other mamenchisaurids, although as far as I can tell no-one has noted them previously.
Epipophyses are muscle attachment points dorsal to the postzygapophyses, for the insertion of long, multi-segment epaxial (dorsal) neck muscles in birds and other dinosaurs. I know that they turn up occasionally in non-dinosaurian archosaurs, and possibly in other amniotes, but for the purposes of this post I’m only considering their distribution in sauropods. For some quick background info on epipophyses and the muscles that attach to them, see the second half of this post, and see Wedel and Sanders (2002) and Taylor and Wedel (2013a) for further discussion and more pictures.
Before we start with the pictures, a fiddly nomenclatural point: this muscle attachment point dorsal to the postzyg has traded under at least six names to date.
- The ‘Owenian’ term, used by virtually all non-avian theropod workers, by Sereno et al. (1999) for Jobaria, and probably by loads of other sauropod workers (including myself, lately) is epipophysis.
- Beddard (1898) referred to this feature in birds as the hyperapophysis; this term seems to have fallen completely out of use.
- Boas (1929), again referring to birds, called it the processus dorsalis. Zweers et al. (1987: page 138 and table 1) followed this terminology, which is how I learned of it when I was an undergrad at OU.
- Baumel and Witmer (1993) called this feature in birds the torus dorsalis (note 125 on page 87), which some authors have informalized to dorsal torus (e.g., Harris 2004: page 1243 and fig. 1). Baumel and Witmer (1993: page 87) note that, “the use of ‘Torus’ is preferable since it avoids confusion with the spinous [dorsal] process of the neural arch”.
- In my own early papers (e.g., Wedel et al. 2000b) and blog posts I called this feature the dorsal tubercle, which was my own attempt at an informal term matching ‘processus dorsalis’ or ‘torus dorsalis’. That was unfortunate, since there are already several other anatomical features in vertebrates that go by the same name, including the dorsal-facing bump on the dorsal arch of the atlas in many vertebrates, and a bump on the humerus in birds and some other taxa. In more recent papers (e.g., Taylor and Wedel 2013a) I’ve switched over to ‘epipophysis’.
- In the last post, Mike coined the term parapostzygapophysis for this feature in Qijianglong. [Note: he now regrets this.]
As usual, if you know of more terms for this feature, or additional history on the ones listed above, please let us know in the comments.
Now, on to the survey.
I haven’t seen very many prominent epipophyses in basal sauropodomorphs. Probably the best are these in the near-sauropod Leonerasaurus, which is very sauropod-like in other ways as well. Modifed from Pol et al. (2011: fig. 5).
This combination of photograph and interpretive drawing neatly shows why it’s often difficult to spot epipophyses in photos: unless you can make out the postzygapophyseal facet, which is often located more anteriorly than you might guess, you can’t tell when the epipophysis projects further posteriorly, as in the last of these vertebrae. In this case you can make it out, but only because the interpretive drawing shows the facet much more clearly than the photo.
The most basal sauropod in which I have seen clear evidence of epipophyses is Tazoudasaurus. They’re not very apparent in lateral view, but in posterior view the epipophyses are clearly visible as bumps in the spinopostzygapophyeal laminae (SPOLs). Modified from Allain and Aquesbi (2008: fig. 9).
In addition to Qijianglong, some other basal eusauropods have prominent epipophyses. Probably the best known is Jobaria; Sereno et al. (1999: fig. 3) figured and labeled the epipophysis in one of the cervical vertebrae. The vertebra image in that figure is tiny (nice work, glam-magz!), so here are some sketches of Jobaria mid-cervicals (from two different individuals) that I made back in the day when I was doing the research for Gary Staab’s Jobaria neck sculpture (see Sanders et al. 2000 for our SVP abstract about that project).
Turiasaurus also has prominent, overhanging epipophyses in at least some of its cervical vertebrae. You can just make one out as a tiny spike a few pixels long in Royo-Torres et al. (2006: fig. 1K). I have seen that cervical firsthand and I can confirm that the epipophyses in Turiasaurus are virtually identical to those in Jobaria.
It’s not air-tight, but there is suggestive evidence of projecting epipophyses in some other mamenchisaurids besides Qijianglong.
If you’re really hardcore, you may remember that back in 2005, Mike got to go up on a lift at the Field Museum of Natural History to get acquainted with a cast skeleton of Mamenchisaurus hochuanensis that was mounted there temporarily. During that adventure he took some photos that seem to show projecting epipophyses in at least two of the mid-cervicals. At least, if they’re not epipophyses, I don’t know what they might be.
Here they are again in medial view. My only reservation is that these vertebrae were distorted to begin with, and some features of the cast are very difficult to interpret. So, probably epipophyses, but it would be nice to check the original material at some point.
Something similar may be present in some posterior cervical vertebrae of Mamenchisaurus youngi. Here’s Figure 17 from Ouyang and Ye (2002). The “poz” label does not not seem to be pointing to the articular facet of the postzygapophysis, which looks to be a little more anterior and ventral, below the margin of the PODL. If that’s the case, then C15 has long, overhanging epipophyses like those of Jobaria. C16 has a more conservative bump, which is to be expected – the epipophyses typically disappear through the cervico-dorsal transition.
Finally, here’s a cervical vertebra of Omeisaurus junghsiensis from Young (1939: fig. 2). I don’t want to hang very much on just a few pixels, but my best guess at the extent of the postzygapophyseal articular facet is shown in the interpretation above. If that’s correct, then this specimen of Omeisaurus had really long epipophyses, rivaling those of Qijianglong. Unfortunately that’s impossible to check, because this specimen has been lost (pers. comm. from Dave Hone, cited in Taylor and Wedel 2013).
Haplocanthosaurus nicely shows that the epipophyses can be large in terms of potential muscle attachment area without projecting beyond the posterior margins of the postzygapophyses. Here is C14 of H. priscus, CM 572, in posterior and lateral views, modified from Hatcher (1903: plate 1).
Epipophyses that actually overhang the postzygapophyses are not common in Diplodocidae but they do occasionally occur. Here are prominent, spike-like epipophyses in Diplodocus (upper left, from Hatcher 1901: plate 3), Barosaurus (upper right), Kaatedocus (lower left, Tschopp and Mateus 2012: fig. 10), and Leinkupal (lower right, Gallina et al. 2014: fig. 1).
Of course, the champion epiphysis-bearer among diplodocoids is the weird little rebbachisaurid Nigersaurus. Here’s a Nigersaurus mid-cervical, from Sereno et al. (2007: fig. 3). Note that the projecting portions of the epipophysis is roughly as long as the articular surface of the postzygapophysis.
The epipophysis in this cervical of Australodocus just barely projects beyond the posterior margin of the postzygapophysis.
In Giraffatitan, epipophyses are absent or small in anterior cervicals but they are prominent in C6-C8. Here’s a posterolateral view of C8, showing very large epipophyses that are elevated several centimeters above the postzygapophyses. You can also see clearly in this view that the spinopostzygapophyseal lamina (SPOL) and postzygodiapophyseal lamina (PODL) converge at the epipophysis, not the postzygapophysis itself.
The holotype of Sauroposeidon, OMNH 53062, is similar to Giraffatitan in that the two anterior cervical vertebrae (possibly C5 and C6) have no visible epipophyses, but epipophyses are prominent in the two more posterior vertebrae (possibly C7 and C8). Click to enlarge – I traced the articular facet of the postzygapophysis in ?C8 to more clearly separate it from the epipophysis. For a high resolution photograph of that same vertebra that clearly shows the postzyg facet and the epipophysis dorsal to it, see this post.
Oddly enough, I’ve never seen prominent epipophyses in a titanosaur. In Malawisaurus, Trigonosaurus, Futalognkosaurus, Rapetosaurus, Alamosaurus, and Saltasaurus, the SPOLs (such as they are – inflated-looking titanosaur cervicals do not have the same crisply-defined laminae seen in most other sauropods) merge into the postzygapophyseal rami and there are no bumps sticking up above or out beyond the articular facets of the postzygs. I don’t know what to make of that, except to note that several of the animals just mentioned have mediolaterally wide, almost balloon-shaped cervical neural spines. In our 2013 PeerJ paper, Mike and I argued that the combination of tall neural spines and tall epipophyses in the cervical vertebrae of sauropods made them functionally intermediate between crocs (huge neural spines, no epipophyses) and birds (small or nearly nonexistent neural spines, big epipophyses). Perhaps most titanosaurs reverted to a more croc-like arrangement with most of the long epaxial neck muscles inserting on the neural spine instead of the postzygapophyseal ramus. I’ve never seen that possibility discussed anywhere, nor the apparent absence of epipophyses in most titanosaurs. As usual, if you know otherwise, please let me know in the comments!
And as long as we’re discussing the phylogenetic distribution of epipophyses, it is interesting that long, overhanging epipophyses are so broadly but sporadically distributed. They turn up in some non-neosauropods (Jobaria, Turiasaurus, Omeisaurus) and some diplodocoids (Nigersaurus, the occasional vertebra in Diplodocus and Leinkupal), but not in all members of either assemblage, and they seem to be absent in Macronaria (although many non-titanosaurs have shorter epipophyses that don’t overhang the postzygs). I strongly suspect that a lot of this is actually individual variation that we’re not perceiving as such because our sample sizes of almost all sauropods are tiny, usually just one individual. Epipophyses are definitely muscle attachment sites in birds and no better hypothesis has been advanced to explain their presence in other archosaurs. Muscle attachment scars are notoriously variable in terms of their relative development and expression among individuals, and it would be odd if epipophyses were somehow exempt from that inherent variability.
It also seems more than likely that ontogeny plays a role: progressive ossification of tendons attached at the epipophyses would have the effect of elongating the preserved projection. And since for some aspects of sauropod vertebral morphology, serial position recapitulates ontogeny (Wedel and Taylor 2013b), it shouldn’t be surprising that we see differences in the prominence of the epipophyses along the neck.
Back to Qijianglong
By now it should be clear that the “finger-like processes” in Qijianglong are indeed epipophyses, and although they are quite long, they aren’t fundamentally different from what we see in many other sauropods. I haven’t gone to the trouble, but one could line up all of the vertebrae figured above in terms of epipophysis size or length, and Qijianglong would sit comfortably at one end with Omeisaurus and Mamenchisaurus, just beyond Nigersaurus and Jobaria.
The strangest thing about the epipophyses in Qijianglong is that they seem to be bent or broken downward in two of the vertebrae (B and H in the figure above). I assume that’s just taphonomic distortion – the cervical shown in H wouldn’t even be able to articulate with the vertebra behind it if the epipophysis really drooped down like that. The epipophyses in Qijianglong seem to mostly manifest as thin spikes of bone (or maybe plates, as shown in B and I), so it’s not surprising that they would get distorted – most of the vertebrae shown above have cervical ribs that are incomplete or missing as well.
One more noodle-y thought about big epipophyses. I wrote in the last section that I’ve never seen them in titanosaurs, possibly because titanosaurs have big neural spines for their epaxial muscles to attach to. Maybe long, overhanging epipophyses are so common in mamenchisaurids because their neural spines are so small and low. Although we tend to think of them as a basal group somewhat removed from the “big show” in sauropod evolution – the neosauropods – mamenchisaurids did a lot of weird stuff. At least in terms of their neck muscles, they may have been the most birdlike of all sauropods. Food for thought.
- Allain, R., & Aquesbi, N. (2008). Anatomy and phylogenetic relationships of Tazoudasaurus naimi (Dinosauria, Sauropoda) from the late Early Jurassic of Morocco. Geodiversitas, 30(2), 345-424.
- Baumel, J. J., & Witmer, L. M. (1993). Osteologia; pp. 45–132 in Baumel, J.J. (ed.), Handbook of avian anatomy: Nomina anatomica avium. Publications of the Nuttall Ornithological Club (USA). no. 23.
- Beddard, F. E. (1898). The structure and classification of birds. Longmans, Green, and Company.
- Boas, J. E. V. (1929). Biologisch-anatomische Studien über den Hals der Vögel. Det Kongelige Danske Videnskabernes Selskabs Skrifter. Naturvidenskabelig og Mathematisk Afdeling.
- Gallina PA, Apesteguía S, Haluza A, Canale JI (2014) A Diplodocid Sauropod Survivor from the Early Cretaceous of South America. PLoS ONE 9(5): e97128. doi:10.1371/journal.pone.0097128
- Gomani, E.M., 2005. Sauropod dinosaurs from the Early Cretaceous of Malawi, Africa. Palaeontologia Electronica 8(1) 27A:37p.
- Harris, J. D. (2004). Confusing dinosaurs with mammals: tetrapod phylogenetics and anatomical terminology in the world of homology. The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology, 281(2), 1240-1246.
- Hatcher, J.B. 1901. Diplodocus (Marsh): its osteology, taxonomy and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum 1:1-63 and plates I-XIII.
- Hatcher, J.B. 1903. Osteology of Haplocanthosaurus with description of a new species, and remarks on the probable habits of the Sauropoda and the age and origin of the Atlantosaurus beds; additional remarks on Diplodocus. Memoirs of the Carnegie Museum 2:1-75.
- Ouyang Hui and Ye Yong. 2002. The first mamenchisaurian skeleton with complete skull: Mamenchisaurus youngi. 111 pages + 20 plates. Sichuan Science and Technology Press, Chengdu.
- Pol D, Garrido A, Cerda IA (2011) A New Sauropodomorph Dinosaur from the Early Jurassic of Patagonia and the Origin and Evolution of the Sauropod-type Sacrum. PLoS ONE 6(1): e14572. doi:10.1371/journal.pone.0014572
- Royo-Torres, R., Cobos, A., & Alcalá, L. (2006). A giant European dinosaur and a new sauropod clade. Science, 314(5807), 1925-1927.
- Sanders, R.K., Wedel, M.J., Sereno, P.C., and Staab, G. 2000. A restoration of the cranio-cervical system in Jobaria. Journal of Vertebrate Paleontology 20, Supplement to Issue 3: 67A.
- Sereno, Paul C., Allison L. Beck, Didier. B. Dutheil, Hans C. E. Larsson, Gabrielle. H. Lyon, Bourahima Moussa, Rudyard W. Sadleir, Christian A. Sidor, David J. Varricchio, Gregory P. Wilson and Jeffrey A. Wilson. 1999. Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs. Science 282:1342-1347.
- Sereno PC, Wilson JA, Witmer LM, Whitlock JA, Maga A, et al. (2007) Structural Extremes in a Cretaceous Dinosaur. PLoS ONE 2(11): e1230. doi:10.1371/journal.pone.0001230
- Taylor, Michael P., and Mathew J. Wedel. 2013a. Why sauropods had long necks; and why giraffes have short necks. PeerJ 1:e36. 41 pages, 11 figures, 3 tables. doi:10.7717/peerj.36
- Tschopp, Emanuel, and Octávio Mateus. 2012. The skull and neck of a new flagellicaudatan sauropod from the Morrison Formation and its implication for the evolution and ontogeny of diplodocid dinosaurs. Journal of Systematic Palaeontology. doi:10.1080/14772019.2012.746589
- Wedel, M.J., and Sanders, R.K. 2002. Osteological correlates of cervical musculature in Aves and Sauropoda (Dinosauria: Saurischia), with comments on the cervical ribs of Apatosaurus. PaleoBios 22(3):1-6.
- Wedel, M.J., Cifelli, R.L., and Sanders, R.K. 2000b. Osteology, paleobiology, and relationships of the sauropod dinosaurSauroposeidon. Acta Palaeontologica Polonica 45(4): 343-388.
- Xing Lida, Tetsuto Miyashita, Jianping Zhang, Daqing Li, Yong Ye, Toru Sekiya, Fengping Wang & Philip J. Currie. 2015. A new sauropod dinosaur from the Late Jurassic of China and the diversity, distribution, and relationships of mamenchisaurids. Journal of Vertebrate Paleontology. doi:10.1080/02724634.2014.889701
- On a new Sauropoda, with notes on other fragmentary reptiles from Szechuan. Bulletin of the Geological Society of China 19:279-315.
- Acta Morphologica Neerlando-Scandinavica 25:131-155 Avian cranio-cervical systems. Part I: Anatomy of the cervical column in the chicken (Gallus gallus L.)
After a completely barren 2008, this year is turning out to be a good one for me in terms of publications. Today sees the publication of Taylor (2009b), entitled Electronic publication of nomenclatural acts is inevitable, and will be accepted by the taxonomic community with or without the endorsement of the code — one of those papers where, if you’ve read the title, you can skip the rest of the paper. (Although on that score, my effort is knocked into a cocked hat by Hulke 1880.)
The message of the paper will be familiar to anyone who’s been following the Shiny Digital Future thread on this site; as indeed will parts of the text, as the paper is basically a more carefully worked and cohesive form of an argument that I’d previously spread across half a dozen blog posts, a similar number of emails on the ICZN mailing list and any number of comments on other people’s blogs. The sequence of section headings in the paper tells its own story:
And that conclusion reads as follows:
While we were looking the other way, the digital revolution has happened: everyone but the ICZN now accepts electronic publication. The Code is aﬀorded legitimacy by workers and journals only because it serves them; if we allow it to become anachronistic then they will desert it – or, at best, pick and choose, following only those provisions of the Code that suit them. Facing this reality, the Code has no realistic option but to change – to recognise electronic publishing as valid.
I have no detailed recommendations to make regarding the recently proposed amendments to the Code (ICZN, 2008). Instead I ask only this simple question: will the Code step up to the plate and regulate electronic publications as well as printed publications? Because this is the only question that remains open. Simply rejecting electronic publication is no longer a valid option.
Which I’m sure is familiar rhetoric to long-time SDF advocates, but which I hope will rattle a few cages in the more conservative ranks of specialist taxonomists. I think it’s a very promising sign that BZN, the official journal of the ICZN, is prepared to publish this kind of advocacy — they didn’t even ask me to tone down the language. I hope it indicates that in high places, they are sensing which way the wind is blowing.
Here’s a reminder of why electronic publishing is so desirable: figure 3 from Sereno et al.’s (2007) paper on the bizarre skull of the rebbachisaurid Nigersaurus:
Let me remind you that this was a paper about skulls — vertebrae were not even on the agenda. Yet click through the image (go on, you have to) and you will see them each presented in glorious high-resolution detail. That paper was of course published in the PLoS ONE — a journal that, because it is online only, can provide this quality of figure reproduction, which shames even the very best of printed journals. To see printed-on-paper figures this detailed and informative, you have to right back to Osborn and Mook (1921).
Which is why I recently decided to put my open-access money where my electronic-only mouth is, and submit the forthcoming Archbishop description to a PLoS journal. In response to a challenge from Andy Farke, I rather precipitately made a public commitment to do my level best to get that paper submitted this calendar year; and while that may not actually happen, having that goal out there can only help. Seeing that gorgeous quarry photo of Spinophorosaurus was what tipped me over the edge into wanting to use PLoS. My plan is to describe the living crap out of that bad boy, photograph every element from every direction and put the whole lot in the paper — make the paper as close as possible as a surrogate for the specimen itself. Only PLoS (to my knowledge) can do this.
(Of course, once you start wanting to include other kinds of information in your publications — videos, 3d models, etc. — then an electronic-only venue is literally your only option.)
I leave you with two photos of “Cervical P” of the Archbishop; commentary by Matt. These images are copyright the NHM since it’s their specimen.
- Hulke, J. W. 1880. Iguanodon Prestwichii, a new species from the Kimmeridge Clay, distinguished from I. Mantelli of the Wealden Formation in the S.E. of England and Isle of Wight by differences in the shape of the vertebral centra, by fewer than five sacral vertebrae, by the simpler character of its tooth-serrature, &c., founded on numerous fossil remains lately discovered at Cumnor, near Oxford. Quarterly Journal of the Geological Society 36:433-456. doi:10.1144/GSL.JGS.1880.036.01-04.36
- International Commission on Zoological Nomenclature. 2008. Proposed amendment of the International Code of Zoological Nomenclature to expand and refine methods of publication. Zootaxa 1908: 57-67, Bulletin of Zoological Nomenclature 65(4): 265-275 and various other places.
- Osborn, H. F. and C. C. Mook. 1921. Camarasaurus, Amphicoelias and other sauropods of Cope. Memoirs of the American Museum of Natural History, n.s. 3: 247-387, and plates LX-LXXXV. [HUGE download, but totally worth it.]
- Sereno, Paul C., Jeffrey A. Wilson, Lawrence M. Witmer, John A. Whitlock, Abdoulaye Maga, Oumarou Ide and Timothy A. Rowe. 2007. Structural Extremes in a Cretaceous Dinosaur. PLoS ONE 2 (11): e1230 (9 pages). doi:10.1371/journal.pone.0001230
- Taylor, Michael P. 2009. Electronic publication of nomenclatural acts is inevitable, and will be accepted by the taxonomic community with or without the endorsement of the Code. Bulletin of Zoological Nomenclature 66(3):205-214.
June 5, 2009
Man, I hate making mistakes. The only thing worse than making mistakes is making them in public, and the only thing worse than that is finding them in published papers when it’s too late to do anything about them. About the only consolation left–if you’re lucky–is getting to be the one to rat yourself out (we have to do this a lot). So here goes.
In our figure 4 (from Taylor et al. 2009) we showed the skulls of three sauropodomorphs, Massospondylus, Camarasaurus, and Diplodocus, posed with horizontal semicircular canals (HSCCs) level, angled 30 degrees above horizontal, and angled 20 degrees below horizontal, as it is written (by Duijm 1951). We also showed the angle of the occipital condyle when the HSCCs are level; if the craniocervical joint was in osteologically neutral pose (ONP), that line would indicate the angle of the anterior cervicals.
Trouble is, we put the neck lines for Diplodocus and Camarasaurus in the wrong places.
As any idiot can see from Sereno et al. (2008: fig 1), the brain, brainstem, and occipital condyle form a line that runs from roughly the upper part of the orbit (in lateral see-through view) out the back of the head. Now if you look at our fig. 4 you’ll see that the ONP lines for Camarasaurus and Diplodocus are much too inclined, so that if the brain was in line with the anterior neck–which it should be, in ONP–it would be sticking out the back of the head.
If that doesn’t make sense, just look at the above illustration, imagine the brain and spinal cord in a straight line parallel to the black neck line but also dorsal to it, and you’ll see that the brain would be outside the skull. Those incorrect neck lines don’t represent impossible postures, but they don’t represent ONP, either.
Here’s a corrected up version of the figure to show what I mean. The black lines are still the ONP neck lines, and now I’ve put in shadowy necks at +30 and -20 to go with the shadowy heads. The 50 degree spans marked out by the shadowy necks are the ranges within which the neck could articulate in ONP with skulls stuck in the 50-degree “Duijm window”.
Caution: it is very easy to misread the shadowy necks as showing a range of movement within an individual; in fact, the neck lines are ‘anchored’ to the skulls in ONP as the skulls rotate through the 50 degrees allowed by the HSCCs. They are not individual movement but the possible range of taxonomic variation in HSCC orientation according to Duijm (1951).
Worth noting here is the likelihood that Massospondylus had a more elevated neck than any of the neosauropods studied so far–certainly a finding at odds with the traditional depictions of basal sauropodomorphs. (It is just a likelihood, though, since the top, neck-wise, of Massospondylus‘s Duijm window overlaps with the windows of the other taxa a bit.)
In this version I’ve gone one step farther and included Nigersaurus (modified from Sereno et al. (2008: fig 1). Nigersaurus differs from Diplodocus in the angle of the face from the HSCCs and occipital condyle, not in the angle between the HSCCs and the occipital condyle, which is remarkably similar in Camarasaurus, Diplodocus, and Nigersaurus. This suggests that Nigersaurus held its head differently than other sauropods, but not necessarily its neck.
Keep in mind, though, that the difference in facial angle between Diplodocus and Nigersaurus is less than 50 degrees, and that some of the head postures in the respective Duijm windows of the two taxa are identical. So we can’t say for certain that Nigersaurus held its head differently than Diplodocus; it is possible that they held their heads at the same angle and that Nigersaurus just carried its HSCCs at a different angle. If that were the case, the neck of Nigersaurus would have been more inclined than that of Diplodocus. I’m not arguing that that’s likely–it seems perfectly plausible that the two taxa might have held their necks similarly and their heads differently, as suggested above–I’m just pointing out the very wide range of possibilities allowed by the data. To reiterate one of the points of the paper, HSCCs aren’t useless for determining habitual head posture, they just can’t narrow things down very far on their own.
Also note that some of the neck postures allowed by the Duijm window have the anterior cervicals running down, below horizontal, not up. And many of the allowed neck postures for the neosauropods are close to horizontal. So, we were wrong and HSCCs + occipital condyles show that most sauropods held their necks close to level and not strongly elevated after all, right?
Onward and Upward, or Down in Flames?
Not so fast. Remember that all of the neck lines in the above figures show the angle of the anterior neck if the neck was in ONP with the skull. But Vidal et al. (1986) found that the skull is habitually flexed on the neck, even in lizards, and we have since verified this for salamanders, turtles, and more. And sometimes the flexion is dramatic.
Our figure 1 (from Taylor et al. 2009) shows the cranium, cervicals, and first few dorsals from a hare in ONP and in the posture shown by Vidal et al. (1986: fig. 4b). The difference between the anteriorly-directed ONP pose and the backward-leaning Vidal-compliant pose is striking. I measured the angle between the cervical column and the maxillary toothrow to be ~110 degrees in the ONP pose and ~70 degrees in the Vidal-compliant pose (try it yourself with Paint or Photoshop, or download some free image manipulation software). That means the head is flexed on the neck by 40 degrees! That is a big angle. If sauropods did the same, you could take the neck lines shown above and crank them down by 40 degrees (remember that the heads are “fixed” into the 50-degree Duijm windows allowed by the HSCCs), which would make Mike’s elevated Diplodocus look not just achievable, but perhaps even conservative.
Where does all that leave us? In sauropods for which HSCC orientation is known, putting the HSCCs level the anterior neck is still inclined, and even with the HSCCs angled 20 degrees down the ONP neck would only be slightly below horizontal, and if the head was Vidal-compliant (strongly flexed on the neck), the neck would have to be above horizontal. So heads still tell us about necks, and in particular they tell us that the necks angled up. Our neck lines for Camarasaurus and Diplodocus are not correct for ONP, but probably represent attainable postures. My first head ‘n necks post has the angles too exaggeraged for ONP, too, but again all of those poses are not just possible but likely if the head was flexed on the neck.
We owe mad props to Brian Engh, a.k.a. The Historian, who burst on the paleo-rap scene with a rap video about crocodilian predation and almost certainly the first ever kung-fu rap video to name-check titanosaurs. Brian stumbled across Mike’s extra goodies page for the new paper about week before the paper was due out, and kindly suppressed the information until after D-Day. You can and should download his entire album, Earth Beasts Awaken (open access, yo), and kick it old school.
Congratulations to Francisco “Paco” Gasco, who just got funding for a PhD to do a complete morphological and paleobiological workup on the giant Spanish sauropod Turiasaurus. You’ll be hearing more about Paco in the not-too-distant future, we promise.
Finally, here’s that video of an elephant grabbing an ostrich by the neck that you ordered.
The End of the Beginning?
This brings us to the end of ten solid days of new posts, which is a new record for us and one not likely to be broken for a long time, if ever. We never planned to do all this; in the beginning we each were going to contribute one post and that would have been that. But we kept finding things that we felt needed to be discussed.
As all of us have been saying in every available medium, this is not the end of anything. The sauropod neck posture debate is not over; in a few years we may look back and see that in 2009 we were still stumbling to the real starting line. We don’t think this stuff is unimportant or unknowable, and we’re going to keep working on it, and we hope lots of others do as well.
We’ll see you out there.
- Duijm, M. 1951. On the head posture in birds and its relation to some anatomical features. II. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen, Series C 54: 260–271.
- Sereno, Paul C., Jeffrey A. Wilson, Lawrence M. Witmer, John A. Whitlock, Abdoulaye Maga, Oumarou Ide and Timothy A. Rowe. 2007. Structural Extremes in a Cretaceous Dinosaur. PLoS ONE 2 (11): e1230 (9 pages). doi:10.1371/journal.pone.0001230
- 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.
June 15, 2008
Paul Sereno’s Project Exploration has a traveling exhibit called The Science of SuperCroc, which I recently visited at my old stomping grounds, the Oklahoma Museum of Natural History. The exhibit focuses on Sarcosuchus, the improbably large and possibly Kryptonian crocodilian from the Cretaceous of Niger, but it also includes nice mounted skeletons of the spinosaur Suchomimus and–relevant to our purposes here–the just plain improbable sauropod Nigersaurus.
At least one of my co-bloggers probably thinks I should stop pandering to the crowds with my mounted skeleton posts and get back to hardcore vertebral anatomy. After all, that’s the raison d’etre of SV-POW!, and I have been falling behind a little lately. Still, I’m going to risk the Wrath of Mike and go ahead and post about the mounted Nigersaurus skeleton, and why you should definitely go see it if you get the chance.
Here are my reasons for doing so:
1. It is a demonstrated scientific fact, as rock-solid as the value of c or the proposition that the Amazon basin is damp, that Nigersaurus is Damn Weird. In a clade of little-known weirdos (Rebbachisauridae), it promises to be an exceedingly well-known ultra-weirdo, thanks to (1) the large number of skeletons that have been discovered, including both juveniles and adults, and (2) the sheer vastness of its weirdness, which you can sample immediately and without charge courtesy of Sereno et al. (2007) and the kind offices of the Public Library of Science (translation: free paper here).
2. Although Nigersaurus was named in 1999 and has been the subject of three peer-reviewed publications, not much of the skeleton has been figured to date. So the opportunity to see the whole critter up close is pretty remarkable. If sauropods were heavy metal, the traveling Nigersaurus mount would be an evening backstage getting high with Led Zeppelin, circa 1973. Certainly if you work on sauropods, the morphology of Nigersaurus will make you think that someone has been under the influence of powerful illicit substances, and that someone is Mother Nature (or Gaia, or the overused/sexist/quasi-pantheistic biosphere personification of your choice).
3. It’s a really nice mount. It’s fiberglass, but the quality of the casts is first rate. I have seen a lot of traveling skeletons that looked like they were made out of Play-Doh by speed-sculpting chimps, but the mounts in the SuperCroc exhibit are all well cast, gracefully mounted, and nicely displayed, by which I mean that you can get up close to them and walk most or all of the way around them, which is my major pet peeve about mounted skeletons: I want to be able to see them from any angle, or at least many angles. SuperCroc delivers.
4. The exhibit includes a lot of display cases that explain the detailed anatomy of the beasts. For Nigersaurus alone, there were cases on vertebral pneumaticity (yay!), the vertebrae themselves (real bones), the detailed anatomy of the jaws (real bones, from the holotype!), the head and neck skeleton plus life sculpture (shown at the top), adult and baby femora (real bones), probable feeding ecology, and maybe one or two others I can’t remember, plus a giant wall hanging of the full-color life restoration painting that came out with the 2007 paper.
So if you get a chance to see SuperCroc, it’s worth it just for the sauropod.
I’ll have tons more to say about the Nigersaurus vertebrae in future posts, but the short version is that they are small and unbelievably delicate. Mike and I always characterize Camarasaurus vertebrae as coarse, fat, and kind of ugly; the vertebrae of Nigersaurus are the aesthetic opposite. They look like they might have been constructed out of toothpicks and white glue. And they are crazy pneumatic. In one of his essays, outdoor humorist Patrick F. McManus characterized a poorly-maintained country bridge as consisting mostly of holes that were elevated and loosely defined by a few rotting beams. Similarly, the skull and cervical vertebrae of Nigersaurus seem to be mostly holes, with just enough bone around them to suggest the form of a sauropod. One more half-baked comparison: the mounted Nigersaurus looks like the skeleton of a skeleton, at least in the craniocervical region.
I want to make a final point that is not really about vertebrae. As you can see in the photo above, and to beat a dead thunder-lizard, sauropods had erect limbs, compact feet, and deep, slab-sided bodies. You don’t have to be a zoologist to see that this is a body-form made for roaming the land, not for bobbing around slurping up pond scum. That’s not to say that sauropods didn’t go into the water. They probably did so all the time. Elephants do, almost every chance they get. Heck, elephants may even be descended from aquatic ancestors. But no one would characterize elephants as aquatic or even semi-aquatic. Sauropods weren’t elephants, and they weren’t giraffes, and facile comparisons of sauropods to big mammals have probably done more harm than good to sauropod paleobiology. But sauropods weren’t hippos or manatees, either, despite decades of ecological characterization as such. The Aquatic Sauropod era officially ended the same year I was born, so you may rightly wonder why I am tilting at this particular windmill. It’s because ideas are seductive, and sometimes we allow them to make us blind to the obvious. I don’t know of any way to fight that tendency other than to keep asking questions.
And I don’t know of a sauropod that is more likely to provoke questions than Nigersaurus. Go see it if you can.