February 8, 2015
Here, for example, is the basal archosauriform Vancleavea. (Thanks to Mickey Mortimer, whose a comment on an earlier post put us onto this, and various other candidate epipohysis-bearers which we’ll see below.)
Here is a pair of Vancleavea cervical vertebrae:
No ambiguity here: the epipophysis is even labelled.
But we can find epipophyses even outside Archosauriformes. Here, for example, is the the rhynchosaur Mesosuchus:
Check out the rightmost vertebra (C7), clicking through for the full resolution if necessary. There is a definite eminence above the postzyg, separated from it by a distinct groove. Unless the drawing is wildly misleading, that is a definite epipophysis, right there.
But even more basal archosauromorphs have epipophyses. Check out Teraterpeton, described by Hans-Dieter Sues in 2003:
This is another one where the epipophysis is labelled (though not recognised as such — it’s just designated an “accessory process”).
Can we go yet more basal? Yes we can! Here are cervicals 2 and 3 of the trilophosaur Trilophosaurus (in an image that I rearranged and rescaled from the published original for clarity):
The parts of this image to focus on (and you can click through for a much better resolution) are the postzyg at top right of the left-lateral view, which has a distinct groove separating the zygapophyseal facet below from the epipohysis above; and the posterior view, which also shows clear separation on both sides between these two structures.
While we’re playing with trilophosaurs here’s here’s another one (probably), Spinosuchus:
Again, the groove separating postzygapophyseal facet from epipophysis (at top right in the image) is clear.
But there’s more! Even the protorosaurs, pretty much the most basal of all archosauromorphs, have convincing epipophyses. Here are two that I found in Dave Peters’ post from two years ago, which I only discovered recently. [Here I must insert the obligatory disclaimer: while Dave Peters is a fine artist and has put together a really useful website, his ideas about pterosaur origins are, to put it mildly, extremely heterodox, and nothing that he says about phylogeny on that site should be taken as gospel. See Darren’s write-up on Tet Zoo for more details.]
Dave shows some probable, but not super-convincing epipophyses in the protorosaur Macrocnemus (shaded purple here) …
… and some much more convincing epipophyses in the better known and more spectacular protorosaur Tanystropheus:
Frustratingly, Dave doesn’t attribute these images, so I don’t know where they’re originally from (unless they’re his own artwork). Can anyone enlighten me? There’s a nice illustration in figure 57 of Nosotti’s (2007) epic Tanystropheus monograph that is at least highly suggestive of epipophyses:
But it’s not as good as the one Peters used, as that one shows a distinct notch between postzyg and epipophysis, so I’d like to track that down if I can.
With this, I believe I am done on cataloguing and illustrating epipophyses, unless something dramatic turns up. (For example, this commenter thinks that nothosaurs have epipophyses, but I’ve not been able to verify that.) Here’s what we’ve found — noting that we’ve illustrated epipophyses on every taxon on this tree except Crocodylia:
So it seems that epipophyses may well be primitive at least for Archosauromorpha — which implies that they were secondarily lost somewhere on the line to modern crocs.
With this lengthy multi-part digression complete, hopefully, we’ll get back to sauropods next time!
- Dilkes, David W. 1998. The Early Triassic rhynchosaur Mesosuchus browni and the interrelationships of basal archosauromorph reptiles. Philosophical Transactions of the Royal Society of London B 353:501-541.
- Kellner, Alexander W. A., and Yukimitsu Tomida. 2000. Description of a new species of Anhangueridae (Pterodactyloidea) with comments on the pterosaur fauna from the Santana Formation (Aptian-Albian), Northeastern Brazil. National Science Museum monographs, Tokyo, 17. 135 pages.
- Nesbitt, Sterling J., Michelle R. Stocker, Bryan J. Small and Alex Downs. 2009. The osteology and relationships of Vancleavea campi (Reptilia: Archosauriformes). Zoological Journal of the Linnean Society 157:814-864.
- Nosotti, Stefania. 2007. Tanystropheus longobardicus (Reptilia, Protorosauria): re-interpretations of the anatomy based on new specimens from the Middle Triassic of Besano (Lombardy, Northern Italy). Memorie della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano 35(III). 88pp.
- Spielmann, Justin A., Spencer G. Lucas, Larry F. Rinehart and Andrew B. Heckert. 2008. The Late Triassic Archosauromorph Trilophosaurus. New Mexico Museum of Natural History and Science Bulletin 43.
- Justin A. Spielmann, Spencer G. Lucas, Andrew B. Heckert, Larry F. Rinehart and H. Robin Richards III. 2009. Redescription of Spinosuchus caseanus (Archosauromorpha: Trilophosauridae) from the Upper Triassic of North America. Palaeodiversity 2:283-313.
- Sues, Hans-Dieter. 2003. An unusual new archosauromorph reptile from the Upper Triassic Wolfville Formation of Nova Scotia. Canadian Journal of Earth Science 40:635-649.
August 28, 2014
I’m scrambling to get everything done before I leave for England and SVPCA this weekend, so no time for a substantive post. Instead, some goodies from old papers I’ve been reading. Explanations will have to come in the comments, if at all.
For more noodling about nerves, please see:
- The world’s longest cells? Speculations on the nervous systems of sauropods
- Oblivious sauropods being eaten
- Butler, A.B., and Hodos, W. 1996. Comparative Vertebrate Neuroanatomy: Evolution and Adaptation. 514 pp. Wiley–Liss, New York.
- Nieuwenhuys, R. (1964). Comparative anatomy of the spinal cord. Progress in Brain Research, 11, 1-57.
- Streeter, G. L. (1904). The structure of the spinal cord of the ostrich. American Journal of Anatomy, 3(1), 1-27.
June 16, 2014
We feature a lot of Brian Engh’s stuff here–enough that he has his own category. But lately he has really been outdoing himself.
The wave of awesome started last year, when Brian started posting videos showing builds and suit tests for monsters–monster suits, monster puppets, monster you-name-its. Like this monster-sculpting timelapse from last August:
And this suit test from last October:
Brian even wrote a blog post about how he builds monsters.
Things really ramped up this May with the release of “In Mountains”, the first video in a three-part series from Brian’s Earth Beasts Awaken album (which is badass, and available for free here).
If you’re thinking that the Mountain Monster has some Estemmenosuchus in its background, you are correct–that astonishing real-world critter was one of Brian’s inspirations, among many others.
More awesomeness is coming in July, when the next video, “Call to Awaken”, is slated to be released. Here’s a teaser:
I have even more exciting Brian-Engh-related news, but I am not at liberty to discuss that just yet. Hopefully sometime this fall. Stay tuned, true believers. UPDATE: Now I’m at liberty to discuss it!
November 6, 2013
Last time, we looked at how including intervertebral cartilage changes the neutral pose of a neck — or, more specifically, of the sequence of cervical vertebrae. The key finding (which is inexplicably missing from the actual paper, Taylor and Wedel 2013c) is that adding cartilage of thickness x between vertebrae whose zygapophyses are height y above the mid-height of the centra elevates the joint’s neutral posture by x/y radians.
But how thick was the intervertebral cartilage in sauropods?
Determining the ONP of a sauropod’s cervical vertebral column given only its bones requires is necessarily speculative since the cartilage, and thus the intervertebral spacing, is unknown.
Part of the our goal in our own PLOS collection paper (Taylor and Wedel 2013c) was to take some very tentative first steps towards estimating the cartilage thickness. To do this, we used two approaches. First, we looked at CT scans of articulated vertebrae; and second, we measured the cartilage thickness in a selection of extant animals and thought about what we could extrapolate.
Since the CT scans were Matt’s domain, I’m going to pass over those for now, in the hope that he’ll blog about that part of the paper. Here, I want to look at the extant-animal survey.
The first thing to say is that our survey is inadequate in many ways. We worked with the specimens we could get hold of, in the state we had them. This means that:
- we have a very arbitrary selection of different animals,
- they are at different ontogenetic stages, and
- their cartilage thickness was measured by a variety of methods.
Our goal was not at all to reach anything like a definitive answer, but just to get the question properly asked, and so hopefully to catalyse much a more detailed survey.
With that proviso out of the way, here are our main results (from Table 4 of the paper, though here I have removed the sauropod CT-scan rows since we’ll be writing about those separately).
|Turkey||4.56%||This study||Difference in measurements of intact neck and articulated sequence of cleaned, degreased and dried vertebrae.|
|Ostrich||6.30%||Cobley et al. (2013)||Difference in measurements of individual vertebrae with and without cartilage.|
|Rhea||2.59%||This study||Measurement of in situ cartilage in bisected neck.|
|Alligator||14.90%||This study||Measurement of in situ cartilage from photograph of cross section.|
|Horse||6.90%||This study||Measurement of in situ cartilage from photograph of cross section.|
|Camel||13.00%||This study||Crude measurement from condyle margin to cotyle lip of lateral-view X-ray. This is an interim measurement, which we hope to improve on when we obtain better images.|
|Dog||17.00%||This study||Measurement of intervertebral gaps in lateral-view X-ray, uncorrected for likely concavity of cotyles.|
|Giraffe||24.00%||This study||Difference in measurement of intact neck and closely articulated sequence of cleaned vertebrae. Young juvenile specimen.|
|Muraenosaurus||14.00%||Evans (1993)||Measurement of in situ cartilage in fossils.|
|Cryptoclidus||20.00%||Evans (1993)||Measurement of in situ cartilage in fossils.|
We’ve expressed the measurements as a ratio between cartilage thickness and the length of the bone itself — that is, cartilage/bone. Another way to think of this is that the percentage is a correction factor which you need to add onto bone length to get whole-segment length. Note that this is not the same ratio as the proportion of total segment length that consists of cartilage: that would be (cartilage thickness + bone length) / bone length.
(We also tossed in some measurements of plesiosaur neck cartilage that Mark Evans made way back when. Get that thing properly published, Mark!)
Even this small survey throws up some interesting points.
First, there is a huge range of proportional cartilage thicknesses: almost an order of magnitude from the 2.59% of the Rhea up to the 24% of the juvenile giraffe — or, even if you discard that because of its ontogenetic stage, up to 17% for the dog. And note that the 17% for the dog is probably an under-estimate, since we were working from an X-ray that doesn’t show the concavity of the vertebral cotyles.
(Two reviewers expressed scepticism that this is the usual condition for dogs, but this X-ray is consistent with those of other dogs illustrated in the veterinary literature.)
The second thing to note is that the cartilage measurements for birds (average 4.5%) are are much lower than those of crocodilians (14.9%) or mammals (15.2%). What does this mean? Among these groups, sauropods are most closely related to birds; but birds and crocs form the extant phylogenetic bracket, so we can’t tell from phylogeny alone whether to expect them to more closely approach the avian or crocodilian condition. Furthermore, in being opisthocoelous (condyle in front, cotyle at the back) sauropod cervicals most closely resemble those of mammals in gross structure — and they have the thickest cartilage of all.
The third thing to note is that there is considerable variation within groups. Although the cartilage is proportionally thin for all three birds, it’s more than twice as thick in the ostrich as in the rhea (although some of this could be due to the different measurement methods used for these two birds). More interestingly, among mammals the cartilage is twice as thick in camels as in horses. In the horse, the condyles are deeply inserted into the cotyles of the preceding vertebrae; but in camels, they don’t reach even the lip of the cotyle. This should worry us, as horse and camel cervicals are grossly similar, and no osteological correlates have been identified that would allow us to determine from the bones alone how very different the cartilage is between these two mammals. So it seems possible that there were similarly dramatic differences in the neck-cartilage thickness of different sauropods.
Note: I said that no osteological correlates have been identified. That doesn’t mean they don’t exist. One thing I would love to see is a serious attempt to analyse cartilage thickness across a broad range of mammals, and to examine the corresponding dry bones to see whether in fact there are correlates that could be informative in this respect. One lesson that Matt and I have learned over and over again is that there’s often plenty of data in places that are out in the open, but where no-one’s thought to look.
Next time: more on searching for osteological correlates of cartilage. Then, measurements of sauropod-neck cartilage from CT scans, and likely implications for cartilage thickness in life.
- Cobley, Matthew J., Emily J. Rayfield, and Paul M. Barrett. 2013. Inter-vertebral flexibility of the ostrich neck: implications for estimating sauropod neck flexibility. PLOS ONE 8(8):e72187. 10 pages. doi:10.1371/journal.pone.0072187 [PDF]
- Evans, Mark. 1993. An investigation into the neck flexibility of two plesiosauroid plesiosaurs: Cryptoclidus eurymerus and Muraenosaurus leedsii. University College London: MSc thesis. London.
- Stevens, Kent A. 2013. The articulation of sauropod necks: methodology and mythology. PLOS ONE 8(10): e78572. 27 pages. doi:10.1371/journal.pone.0078572 [PDF]
- Taylor, Michael P., and Matthew J. Wedel. 2013c. The effect of intervertebral cartilage on neutral posture and range of motion in the necks of sauropod dinosaurs. PLOS ONE 8(10): e78214. 17 pages. doi:10.1371/journal.pone.0078214 [PDF]
October 4, 2013
For a palaeontology blog, we don’t talk a lot about geology. Time to fix that, courtesy of my middle son Matthew, currently 13 years old, who made this helpful guide to the rock cycle as Geology homework.
September 17, 2013
I liked it, but I thought it could use some color, so I hacked a crude version in GIMP and sent it to Mark with a, “Hey, please put this on a t-shirt so I can throw money at you” plea. Lo and behold, he did just that.
You can get your own from Mark’s Zazzle store. And apparently he will have more sauropod-themed merch coming soon.