Supersaurus, Ultrasaurus and Dystylosaurus in 2019, part 2b: the size of the BYU 9024 animal

June 16, 2019

In part 2, we concluded that BYU 9024, the large cervical vertebra assigned by Jensen to the Supersaurus holotype individual, is in fact a perfectly well-behaved Barosaurus cervical — just a much, much bigger one than we’ve been used to seeing. Although we heavily disclaimered our size estimates, Andrea Cau quite rightly commented:

Thanks for the disclaimer: unfortunately, it is going to be ignored by the Internet.
[…]
So, my boring-conservative mind asks: what is the smallest size that is a valid alternative explanation? I mean, if we combine all possible factors (position misinterpretation, deformation effects, allometry and so on) what could be the smallest plausible size? Only the latter should be taken as “the size” of this animal, pending more material.

Andrea is right that we should take a moment to think a bit more about the possible size implications of BYU 9024.

BYU 9024, the huge cervical vertebra assigned to Supersaurus but which is actually Barosaurus, in left dorsolateral view, lying on its right side with anterior to the right. In front of it, for scale, a Diplodocus cervical from about the same serial position. (Note that the Diplodocus vertebra here appears proportionally bigger than it really is, due to being much closer to the camera.)

What we know for sure is that the vertebra is 1380 mm long (give or take a centimeter or two due to the difficulties of measuring big complex bones in an objective way, something we should write about separately some time.)

We are 99% certain that the bone is a Barosaurus cervical.

We are much less certain about the serial position of that bone. When we were at BYU, we concluded that it most resembled C9 of the AMNH specimen, but I honestly can’t remember the detail of our reasoning (can you, Matt?) and our scanned notebooks don’t offer much in the way of help. We know from McIntosh (2005) that the neural spine of C8 is unsplit and that C9 has the first hint of a cleft.  How does that compare with BYU 9024? Here’s a photo to help you decide:

BYU 9024, large cervical vertebra in left dorsolateral view, inverted (i.e. with dorsal towards us and anterior to the right). Note the shallow cleft between metapophyses at bottom left.

And here’s an anaglyph, to help you appreciate the 3D structure. (Don’t have any red-cyan glasses? GET SOME!)

BYU 9024, oriented similarly to the previous photograph.

The morphology around the crown of the neural spine is difficult to interpret, partly just because the fossil itself is a bit smashed up and partly because the bone, the (minimal) restoration and the matrix are such similar colours. But here’s my best attempt to draw out what’s happening, zoomed in from last non-anaglyph photo:

As you start at the prezygapophyses and work backwards, the SPRLs fade out some way before you reach the crown, and disappear at or before what appears to be an ossified midline ligament scar projecting anteriorly from very near the top of the vertebra. Posterior to that are two small, tab-like metapophyses that appear almost like separate osteological features.

Now this is a very strange arrangement. Nothing like it occurs in any of the cervicals of Diplodocus, where all the way from C3 back to the last cervical, the SPRLs run continuously all the way up from the prezygs to the metapophyses:

Hatcher (1901:plate V). Diplodocus carnegii holotype CM 84, cervical vertebra 2-15 in anterior view.

What we’d love to do of course is compare this morphology with a similar plate of the AMNH Barosaurus cervicals in anterior view, but no such plate exists and no such photos can be taken due to the ongoing entombment of the vertebrae. So we’re reduced to feeding on scraps. McIntosh (2005:47) says:

The neural spine of cervical 8 is flat across the top, and that of cervical 9 shows the first trace of a divided spine (Fig. 2.2A). This division increases gradually in sequential vertebrae, being moderately developed in cervicals 12 and 13, and as a deep V-shape in cervicals 15 and 16.

Sadly, McIntosh illustrates only cervicals 8 and 13 in anterior view: Fig 2.2A does not illustrate C9, as the text implies. And neither of the illustrated vertebrae much resembles what we see in BYU 9024.

So while in 2016 we interpreted BYU 9024 is having “the first trace of a divided spine”, we do hold open the possibility that what we’re seeing is a vertebra in which the spine bifurcation is a little more developed than we’d realised, but with strange morphology that does not correspond closely to any well-preserved vertebra we’ve seen of any sauropod. (Most Barosaurus cervicals are either crushed and damaged; the well preserved ones outside of the AMNH walkway tomb are from a more anterior part of the neck where there is no bifurcation of the spine.)

There is one more possibility. Here is a truly lovely (privately owned) Barosaurus cervical in the prep lab at the North American Museum of Ancient Life (NAMAL):

Uncrushed Barosaurus cervical vertebra, serial position uncertain, in the NAMAL prep lab.

In this blessedly undistorted vertebra, we can see that the summit of the neural spine is flared, with laterally projecting laminae that are likely homologous with metapophyses. (The vertebra is symmetrical in this respect.) Might it be possible that the tab-like metapophyses of BYU 9024 were like this in life, but have been folded upwards post-mortem?

All of this leaves the serial position of the vertebra far from certain. But what we can do is compare it with the lengths of all the known AMNH Barosaurus vertebrae. Columns 1 and 2 in the table below show the serial position and total length of the AMNH cervicals. Column 3 shows the factor by which the 1370 mm length of BYU 9024 exceeds the relevant cervical, and column 4 shows the corresponding estimate for total neck length, based on 8.5 m (Wedel 2007:206–207) for AMNH Barosaurus.

Cv# Length (mm) BYU 9224 ratio BYU 9024 neck length
8 618 2.217 18.84
9 685 2.000 17.00
10 737 1.859 15.80
11 775 1.768 15.03
12 813 1.685 14.32
13 850 1.612 13.70
14 865 1.584 13.46
15 840 1.631 13.86
16 750 1.827 15.53

So to finally answer Andrea’s question from waaay back at the start of this post, the smallest possible interpretation of the BYU 9024 animal gives it a neck 1.584 times as long as that of the AMNH individual, which comes out around 13.5 m (and implies a total length of maybe 43 m).

But I don’t at all think that’s right: I am confident that the serial position of BYU 9024 is some way anterior to C14, likely no further back than C11 — which gives us a neck at least 15 m long (and a total length of maybe 48 m and a mass of maybe 12 × 1.768^3 = 66 tonnes).

 

References

  • Hatcher, Jonathan 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.
  • McIntosh, John S. 2005. The genus Barosaurus Marsh (Sauropoda, Diplodocidae). pp. 38-77 in: Virginia Tidwell and Ken Carpenter (eds.), Thunder Lizards: the Sauropodomorph Dinosaurs. Indiana University Press, Bloomington, Indiana. 495 pp.
  • Wedel, Mathew J. 2007. Postcranial pneumaticity in dinosaurs and the origin of the avian lung. Ph.D dissertation, Integrative Biology, University of California, Berkeley, CA. Advisors: Kevin Padian and Bill Clemens. 290 pages.

15 Responses to “Supersaurus, Ultrasaurus and Dystylosaurus in 2019, part 2b: the size of the BYU 9024 animal”


  1. […] the next day: see the next post for more on the serial position of the vertebra and the size of the […]

  2. Matt Wedel Says:

    There’s one more factor to consider: allometric growth of the neck. We know it happens through sauropod phylogeny (Parrish 2006) and in the ontogeny of a single individual (Wedel et al. 2000b, probably others). I don’t think we know enough about it in general, and certainly not enough about it in Barosaurus, to say how much difference it would make for this individual, but it’s a factor to consider. And not just for BYU 9024, but for any sauropod known only from big cervicals (I’m looking at you, Sauroposeidon holotype).

    Parrish, J.M., 2006. The origins of high browsing and the effects of phylogeny and scaling on neck length in sauropodomorphs. Amniote paleobiology: perspectives on the evolution of mammals, birds and reptiles. University of Chicago Press, Chicago, pp.201-244.

  3. Mike Taylor Says:

    Yep — that’s why I majored on neck lengths, and left the total lengths and masses in parenthetical comments.

    Aside from that, are you basically happy that I’ve accurately represented our thinking on all this?

  4. Matt Wedel Says:

    Yep. Looking at Jack’s photos of the AMNH specimen, I don’t think that BYU 9024 can possibly be C14 or any further back. I can juuust about accept it as a C13 based on centrum dimensions — it has a honking condyle — but the neural spine says C10 or C11. And allometry or no, there’s no avoiding that this was a truly immense animal.

  5. Mike Taylor Says:

    Wait wait wait! By “Jack’s photos”, do you just mean the tiny tiny tiny monochrome stippled bigfoot-quality photos in the Thunder Lizards volume? Or do you have something better than that?

  6. Matt Wedel Says:

    No, just the bigfoot-quality ones in TL. Unfortunately.

  7. Illiterate Scholar Says:

    This is 3rd hand info, so take it with a grain of salt. Someone said on Facebook that they spoke to Mark Norrell about Patagotitan with Norrell suggesting the current mount that estimated to be around 36 meters is still not fully grown. That at 36 meters, it’s still only 70% grown. Reading about BYU 9024 really does make me think that comment isn’t all that far fetched. I know Patagotitan is a Titanosaur and direct comparison might not be the best with BYU 9024.

  8. Andrea Cau Says:

    Many thanks for this post, which confirms why I’ve always considered SVPoW one of the best paleo sites and blogs.
    So, taking into account a plausible “neck vs body” positive allometry, a rough, conservative minimum size estimation of the beast is around 40 m. Which satisfies the boring side of my brain ;-)

  9. Mike Taylor Says:

    I would not be at all surprised to learn that the Patagotitan material was sub-adult: as we’ve often argued here, almost all sauropod material is. I pointed out in my 2009 brachiosaur paper, for example, that both the Brachiosaurus altithorax holotype FMNH P 25107 and the Giraffatitan brancai paralectotype MB.R.2181, massive though they are, are well short of skeletal maturity, as can be seen by their unfused coracoids. (We know that brachiosaur coracoids do eventually fuse to their scapulae from the Jensen’s “Ultrasaurus” scapulocoradoid.)


  10. […] and what Matt and I concluded about its big cervical BYU 9024, and though a bit more about the size of the BYU 9024 animal, it’s finally time to consider what all this means for Jensen’s […]

  11. Dean Hester Says:

    There is no way to ascertain skeletal maturity from a cervical vert is there? If not, we must labour under the lurking notion that BYU 9024 could also be immature. I’ve always been interested in the mathematics of average and maximum size in a poorly sampled population, and I wonder if models could be produced to estimate standard deviations around a sample of individuals given their wild Gaussian distributions. For instance if you found 6 3-ton elephants, twenty 5-ton elephants, three 7-tonners, could you simulate a normal distribution for the entire population? Do most species show similar amounts of deviation from the mean, or is it highly variable? Does larger absolute body size in a species constrain mass variability? Just need to win the lottery and quit my day-job.

  12. Mike Taylor Says:

    You can determine immaturity from a single vertebra, if its neural arch is not fused to its centrum — or if the fusion has commenced but the suture not yet obliterated. But quite a bit of growth is possible after the arch and centrum are fully fused, so we can’t tell from a fused vertebra that it is from a fully grown animal. (In any case, I’m not sure BYU 9024 is sufficiently well preserved for that to be observable.)

    It would be great to have ways of modelling likely size distributions in a population, and probably such techniques do exist. But we have two problems with sauropods. First, and most obviously, our sample sizes are absolutely tiny. Most sauropods are known from a single individual. There can’t be more than ten or so sauropods for which we have more than half a dozen specimens, and even for most of those (e.g. Apatosaurus) it’s likely that they represent several different species. But the second problem is in some ways ever harder to deal with: we simply have no idea what the population structure was like for sauropods. For all we know, there would typically be one super-giant alpha male in a given area, and all the other individuals would stop growing at half of its size. We can make guesses based on the population dynamics of extant species, but that’s all they are — better or worse informed guesses.

    (Hone et al. 2016 has something to say about this, mostly I guess due to Matt’s involvement. See Dinosaur life histories are plicomcated.


  13. Patagotitan has histologically been determined to be “subadult” (more specifically, that its growth rate has slowed but not stopped as there’s no EFS), but I wouldn’t necessarily interpret that as meaning it could get much bigger. I don’t think we know enough about the growth of giant titanosaurs to be able to rule out the possibility that they just took so long to grow that they inevitably died before growth stopped.


  14. […] (If you don’t have the 3D glass that you need to see this, get some. Seriously, how many times do I have to tell you?) […]


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