How crazy are the cervicals of Mendozasaurus?

February 1, 2018

There’s a new paper out, describing the Argentinian titanosaur Mendozasaurus in detail (Gonzalez Riga et al. 2018): 46 pages of multi-view photos, tables of measurement, and careful, detailed description and discussion. But here’s what leapt out at me when I skimmed the paper:

Gonzalez Riga et al. (2018: figure 6). Mendozasaurus neguyelap cervical vertebra (IANIGLA-PV 076/1) in (A) anterior, (B) left lateral, (C) posterior, (D) right lateral, (E) ventral and (F) dorsal views. Scale bar = 150 mm. Sorry it’s monochrome, but that’s how it appears in the paper.

Just look at that thing. It’s ridiculous. In our 2013 PeerJ paper “Why Giraffes have Short Necks” (Taylor and Wedel 2013), we included a “freak gallery” as figure 7: five very different sauropod cervicals:

Taylor and Wedel (2013: figure 7). Disparity of sauropod cervical vertebrae. 1, Apatosaurus “laticollis” Marsh, 1879b holotype YPM 1861, cervical ?13, now referred to Apatosaurus ajax (see McIntosh, 1995), in posterior and left lateral views, after Ostrom & McIntosh (1966, plate 15); the portion reconstructed in plaster (Barbour, 1890, figure 1) is grayed out in posterior view; lateral view reconstructed after Apatosaurus louisae (Gilmore, 1936, plate XXIV). 2, “Brontosaurus excelsus” Marsh, 1879a holotype YPM 1980, cervical 8, now referred to Apatosaurus excelsus (see Riggs, 1903), in anterior and left lateral views, after Ostrom & McIntosh (1966, plate 12); lateral view reconstructed after Apatosaurus louisae (Gilmore, 1936, plate XXIV). 3, “Titanosaurus” colberti Jain & Bandyopadhyay, 1997 holotype ISIR 335/2, mid-cervical vertebra, now referred to Isisaurus (See Wilson & Upchurch, 2003), in posterior and left lateral views, after Jain & Bandyopadhyay (1997, figure 4). 4, “Brachiosaurus” brancai paralectotype MB.R.2181, cervical 8, now referred to Giraffatitan (see Taylor, 2009), in posterior and left lateral views, modified from Janensch (1950, figures 43–46). 5, Erketu ellisoni holotype IGM 100/1803, cervical 4 in anterior and left lateral views, modified from Ksepka & Norell (2006, figures 5a–d).

But this Mendozasaurus vertebra is crazier than any of them, with its tiny centrum, its huge, broad but anteroposteriorly flattened neural spine, and its pronounced lSPRLs.

I just don’t know what to make of this, and neither does Matt. And part of the reason for this may be that neither of us has had that much to do with titanosaurs. As Matt said in email, “Those weird ballooned-up neural spines in titanosaurs kind of freak me out.” And I could not agree more.

And of course as sauropodologists, we really should familiarise ourselves with titanosaurs. There are a lot of them, and they account for a lot of sauropod evolution. Someone recently made the point, either in an SV-POW! comment or on Facebook, that titanosaurs may be to sauropods what monkeys and apes are to primates: a subclade that is way more diverse than the rest of the clade put together.

It’s starting to look like an extreme historical accident that Camarasaurus, diplodocines and brachiosaurids — all temporally and/or geographically restricted groups — were the first well-known sauropods, and for decades defined our notion of what sauropods were like. Meanwhile, the much more widespread and long-surviving rebbachisaurs and titanosaurs were poorly understood until really the last 25 years or so. For the first century of sauropodology, our ideas about sauropods were driven by weird, comparatively short-lived outliers.

That our appreciation of titanosaur diversity has come so late says something about how our discovery of the natural world is more to do with geopolitics and the quirks of exploration than what’s actually out there. Sauropods were defined by diplodocids for so long because that’s what happened to be in the ground in the exposed rocks of North America, and that’s where the well-funded museums and expeditions were.

We at SV-POW! towards have often wondered how different our idea of what dinosaurs even were would be if the Liaoning deposits had been available to Buckland, Mantell, and Owen. It seems like that unavoidable that, if they’d first become familiar with feathered but osteologically aberrant (by modern standards) birds, one of two things would have happened. Either they would either have never coined the term “Dinosauria” at all, recognizing that Megalosaurus (and later Allosaurus and Tyrannosaurus) were just big versions of their little feathered ur-birds. Or they would have included Dinosauria as a primitive subclass of Aves.

References

  • González Riga, Bernardo J., Philip D. Mannion, Stephen F. Poropat, Leonardo D. Ortiz David and Juan Pedro Coria. 2018. Osteology of the Late Cretaceous Argentinean sauropod dinosaur Mendozasaurus neguyelap: implications for basal titanosaur relationships. Zoological Journal of the Linnean Society, 46 pages, 28 figures. doi:10.1093/zoolinnean/zlx103
  • Taylor, Michael P., and Mathew J. Wedel. 2013. 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

 


Note. This post contains material from all three of us (Darren included), harvested from an email conversation.

 

Advertisements

10 Responses to “How crazy are the cervicals of Mendozasaurus?”


  1. On Monday I will send you the 3D PDF I made of this vertebra when I was in Mendoza (which, in retrospect, we really should have included in this paper… it completely slipped my mind, since I made it more than three years ago). It _is_ weird, but I have to wonder what its internal structure would tell us about how much it has been compressed. All of the bones that we observed from Mendozasaurus were really distorted (partially, I imagine, a consequence of Mendoza’s proximity to the Andes, but possibly also a result of plastic deformation under sediment load prior to lithification)…

    Would it be safe to assume, given that sauropod presacral vertebrae were pneumatised, that they were particularly susceptible to ductile deformation post mortem? Especially if the coels were not infiltrated by sediment prior to more sediment being lain down above…

    In the Winton Formation, limb/girdle bones that show evidence of trampling evidently held up better than presacral (or even sacral) vertebrae subjected to the same.

  2. Mike Taylor Says:

    Thanks, Stephen, that would be great! Better still would be to deposit the 3D model in a recognised repository such as FigShare so that anyone can use it — this is what I did with the Xenoposeidon 3D model: https://figshare.com/articles/Untitled_Item/5605612

    It’s interesting to think about distortion and compression: stupidly, I had not even given that any thought as an explanation for the shape of IANIGLA-PV 076/1. But, while it’s possible that some anteroposterior crushing has exaggerated the oddities I drew attention to, it would take a perfectly aligned force to achieve that without other asymmetrical distortions — so I am not inclined to think that’s what happened, but bear in mind that all I know about this bone is what I’ve gleaned from your figure 6.

    It certainly seems feasible that pneumatic bones would be not only more vulnerable to crushing than solid ones, but also more liable to ductile distortion. But that’s only my intuition speaking. It would be good to see actual experiments, perhaps on bird-vs.-mammal vertebrae. Or maybe this has already been done: does anyone out there know if it’s in the literature?

  3. Matt Wedel Says:

    In the text, González Riga et al. attribute the odd shape of that vert partly to its being a posterior cervical, and partly to taphonomic distortion. That seems reasonable to me. Mike, I wonder if you and I have both been overly influenced by Diplodocus carnegii, which is actually pretty weird among sauropods in that its posterior cervicals aren’t more transitional or dorsalized. A lot of other sauropods have weird and awkward-looking transitional vertebrae at the base of the neck.

    It also doesn’t seem unreasonable to me that the distortion might have been orthogonal in this one vert. It’s not in most of the other cervicals of this animal, but each vertebra is a roll of the taphonomic dice and they gotta come up boxcars sometimes. Especially if this vert was taller than long to begin with and ended up lying flat on its front or back surface before the sediment load was applied.

    As for whether pneumatic bones would be more susceptible to deformation – I don’t know. It seems perfectly reasonable that pneumatic bones would be at more risk of damage from trampling. But for ductile distortion, I wonder if moisture content might not be more important. Dry bone is pretty brittle, but wet bone can bend a surprisingly long way before it breaks. There are some great photos demonstrating this with a human femur in Brookes & Wardle (1962) – I will get those posted soon.

    It does not seem a priori unreasonable to me that pneumatic bones might be less good at ductile deformation. In a more solid bone, the change in geometry is spread across a lot more bone tissue, whereas in a pneumatic bone, all of the deformation would have to be handled by the comparatively meager internal struts and septa. I suspect that pneumatic bones might just break instead of bending.

    Some pneumatic vertebrae look pretty good from the outside, but when they’re scanned, the internal structure is pretty busted up. Others have intact internal structures despite looking somewhat distorted externally. That’s part of what makes me think that moisture content is as least as important as pneumaticity in determining the deformability of a bone.

    Whew – that was a much longer comment than I intended! But interesting discussion. Let’s keep it rolling – especially folks with relevant knowledge on distortion of bone.

    That ref:
    Brookes, M., and Wardle, E.N. 1962. Muscle action and the shape of the femur. The Journal of Bone and Joint Surgery 44B(2): 398-411.

    …which looks like it might be a free download here (link) – someone try it and let me know (I’m on a university computer and can’t rule out that my access is invisibly facilitated that way).

  4. Mike Taylor Says:

    What’cha talkin’ ’bout, Willis? C15 of Diplodocus carnegii is totally transitional: compare C15 (Hatcher 1901: plate III) with D1 (plate VII). Very similar.

    Fair point on the possibility of orthogonal compression.

    On ductile distortion: we’ve both been surprised at the flexibility of bone, and how much it can bend before it breaks. So I am open to at least the possibility that the thin layers of pneumatised vertebrae are capable of surprising distortions before it becomes outright crushing. But this is something that really wants experimentation. (Or even, and I tremble to admit this, maybe an FEA study.)

  5. Matt Wedel Says:

    I would say that D1 of D. carnegii is surprisingly cervicalized, not that C15 is surprisingly dorsalized. Which maybe makes sense? In light of the fact that diplodocids apparently got to 15 cervicals in the first place by cervicalizing a couple of dorsals (relative to most other sauropods), and that Barosaurus has 16/9 instead of 15/10 – maybe Diplodocus is a transitional form here.

    Oh dear, I foresee a series on the cervico-dorsal transition in sauropods.

  6. Mike Taylor Says:

    … If indeed “D1” is the first dorsal and not the last cervical.

    But my real point is of course that there is a smooth transition in Diplodocus, not a sequence of 15 obvious cervicals and then 10 obvious dorsals. Really, you’d be hard-pressed to say where the heck the transition is.

  7. Marja Erwin Says:

    “We at SV-POW! towards have often wondered how different our idea of what dinosaurs even were would be if the Liaoning deposits had been available to Buckland, Mantell, and Owen.”

    I haven’t studied Hitchcock’s work, but I think he shows that scientists were ready for large pre-Birds, but he at least wasn’t ready to recognize the available skeletal material as pre-Birds.

  8. Matt Wedel Says:

    Good point about Hitchcock. If people really do spin in their graves, he must be approaching relativistic rotation rates these days.

  9. Marja Erwin Says:

    Might they have percieved two groups: “Proaves” (Theropoda, and possibly Pterosauria in early systems; Seeley or another would eventually redefine this as what we call Saurischia), and “Dinosauria” (Ornithischia), at first without any clear classification for Dongbeititan and Cetisaurus?

    They might see this narrower “Dinosauria” as a mammal-like counterpart to the bird-like but more diverse “Proaves,” and they probably wouldn’t accept a lizard-like “Dinosauria.”

    I imagine Charles R. Knight paintings with feathery and properly bipedal theropods, scattered feathers on sauropods, and very hairy mammal-like ornithischia.

  10. Marja Erwin Says:

    I don’t know what the Crystal Palace sculptures would look like, though.


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: