Beware over-interpreting photos of fossils

January 2, 2017

Welcome to 2017! Let’s start the year with a cautionary tale. I’ll leap straight to the moral, then give an example: it’s very easy to reach the wrong conclusion about fossils from photos. That’s because no single photo can give an accurate impression of distortion. For that, you need at least a much bigger selection of photos; or better still, a 3d model; or of course best of all, the fossil itself.

Here’s the motivating example:

unnamed

Cervical vertebrae 8-16 of Barosaurus lentus AMNH 6341; and BYU 9024 “Supersaurus” cervical ?9. All in left lateral view.

A correspondent — I will not divulge his or her name unless the person in question chooses to reveal it — had looked over the slides for our 2016 SVPCA talk on new Barosaurus specimens, which claims that Jensen’s Dry Mesa “Supersaurus” cervical BYU 9024 actually belongs to Barosaurus.

Matt and I felt, based largely on the degree of neural spine bifurcation, that the BYU vertebra compares most similarly to C9 of the AMNH specimen — the middle one in the top row of the composite illustration above. But my correspondent put together the composite, and wrote [lightly edited for clarity]:

I’ve already compared BYU 9024 with the AMNH cervicals, I attach a photo, because for me it is also very similar to C14: the centrum is much more similar to C14 than C9, I think. What do you think about this?

Like I said: you always need to be careful about interpreting any one view of a fossil. In this case, BYU 9024 is misleading in lateral view because the CPOLs are folded upwards and inwards, and the ventrolateral flanges are (to a lesser extent) folded downwards and inwards — making the posterior part of the centrum look much taller (and rather narrower) than it really is.

This is hard to see in photos, because the fossil is so smashed up and the matrix is so visually similar to the bone, but take a look at the posterior view (with anterior to the right of the photo):

img_3516

Here are the key parts, annotated, as best I can make out. (And bear in mind that even I am not sure, after having spent a whole day with the fossil, and with literally hundreds of photos to consult.)

img_3516-annotated

As you can see, the centrum accounts for only a small proportion of the apparent height of the posterior end of the vertebra — and even that is probably exaggerated, as the eccentricity of the condyle indicates that crushing has increased its height at the expense of its width.

Put it all together, and Jensen’s much-derided sculpture of what the vertebra should have looked like is actually pretty good:

img_3399

The upshot of this anecdote is an obvious one, but it bears repeating: you simply cannot do a meaningful description of a fossil without seeing it yourself — or at the very least a high-quality 3d model. Photos just won’t cut it.

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18 Responses to “Beware over-interpreting photos of fossils”

  1. Shahen Says:

    It was me, no problem this article is very interesting and helpfull, many thanks for more details
    “Who asks not stray” :) Thanks for answer

  2. bricksmashtv Says:

    Hey guys! I know you’re busy, but I was wondering your thoughts on this: http://comments.deviantart.com/1/652945233/4297495623

    Nima disagrees that the BYU vert is Barosaurus, & posted his argument there on DA. Thoughts/rebuttals?

  3. Mike Taylor Says:

    Thanks for the heads-up, bricksmashtv. I’ll take a look.

  4. Mike Taylor Says:

    I read it. I find it very unconvincing, at least until Nima produces illustrations that show why he thinks what he thinks. But having spend significant time with BYU 9024 and with several different unambiguous Barosaurus specimens, I am very confident that the former is the latter. For the full explanation of why, see the paper that we will surely write once we get a ton of tedious revision-and-resubmission off our desks.

  5. Matt Wedel Says:

    Okay, I’ll bite. Let’s look at Nima’s claims in detail.

    It’s got an apparently broken neural spine which when complete would have been rather different than those in Barosaurus

    Flatly false. I’ve heard this other places and I’m not sure how it got started. The neural spine of BYU 9024 is complete, including both metapophyses of the shallowly divided spine apex. The lateral profile is intact and uninterrupted. In life, the bone looked pretty much like it does now.

    … also the parapophysis is a different shape than in Barosaurus

    Umm, no, it’s not. Just look at the comparative photographs of BYU 9024 and the AMNH Barosaurus in this very post. In fact, the positions and shapes of the diapophyses and parapophyses are strikingly similar in BYU 9024 and Barosaurus.

    and the bone was found in Dry Mesa Quarry with the other initial Jensen Supersaurus material. No verifiable Barosaurus specimens were found there. So it’s most likely this was Supersaurus.

    Plausible, maybe, if you’ve never seen all of the material from that quarry. There is a LOT, and most of it has never been described. BYU 11617, which I showed photos of in this post, is probably from a subadult Barosaurus, based on the characters shown in this post.

    So I’d argue that (1) assigning a bone to a taxon because they came out of the same hole is bad practice at best, kinda dumb in the Morrison where there are so many multi-taxon quarries, and extremely unwise at Dry Mesa where there are at least five genera (Apatosaurus, Diplodocus, Supersaurus, Camarasaurus, and Brachiosaurus – see Curtice and Wilhite 1996) not counting Barosaurus. And (2), there almost certainly are other Barosaurus elements from Dry Mesa, they’ve just never been described in the literature.

    Also while this bone does have some features in common with Barosaurus, it has been mangled quite a bit…

    No, no, NO! Where did this stupid idea come from, that BYU 9024 is ‘mangled quite a bit’? It’s not! It’s mediolaterally crushed a bit and the end of prezyg is probably missing, but other than that it’s complete and largely undistorted.

    …so if you really wanted to, I suppose you could make the case for it being not just Barosaurus, but also an unusually large species of any of several genera of diplodocids: Barosaurus, Diplodocus, Seismosaurus, Galeamopus, the Dana Quarry diplodocid, etc.

    Fantasy. BYU 9024 has a lot of characters in common with Barosaurus to the exclusion of all those other genera. See Mike’s talk from SVPCA last fall for details (slides in PDF format are here). The idea that “it could be anything” is only supportable from a position of deep and at this point willful ignorance.

    The stratigraphy with Barosaurus may not match Dry Mesa either.

    …which means basically nothing. The “stratigraphy of Barosaurus” is wherever Barosaurus has been found. If there’s Barosaurus at Dry Mesa – and we have good reason to think so, even apart from BYU 9024 – then Dry Mesa is part of the “stratigraphy of Barosaurus”. Morrison strat is not nailed down enough yet that we can go around overruling piles of shared characters based on careful morphological comparisons.

    If it does then great for the Barosaurus theory… but I don’t know of any other “Barosaurus” remains turning up at that locale.

    Unintentionally correct – there are other Barosaurus specimens from Dry Mesa, he was just unaware of them.

    Also lets keep in mind that Supersaurus (including the Jimbo specimen) was initially considered a barosaurine until new research in Lovelace, et. al. (2007) showed it to be an unusual apatosaurine.

    And then Tschopp et al. (2015) showed it to be a diplodocine after all. Keep up, folks. With all due respect to Lovelace et al. (2007), which was fine for its time, the analysis with 238 characters in 33 OTUs is not at the mercy of the analysis with 477 characters in 81 OTUs.

    So Supersaurus overall does converge on Barosaurus in some respects, but that doesn’t mean the BYU cervical is Barosaurus, given the general similarities Jimbo’s neck also has with Barosaurus.

    This is so confused I can hardly parse it. There is no reason to think that BYU 9024 is Supersaurus other than (1) it’s really big, and (2) it came from Dry Mesa. Morphologically, it has more in common with Barosaurus than with Jimbo. Also, there are other meter-class Barosaurus cervicals in the world, so although BYU 9024 would still be a very big Barosaurus – and indeed a very big anything – it’s not entirely unprecedented. We could be wrong about BYU 9024 being Barosaurus, but we’re not wrong about it having more characters in common with Barosaurus than with any other dinosaur.

    Bottom line, if you want to know what these things are, it helps if you keep up with the literature and actually go look at bones.

  6. Shahen Says:

    Then if is really C9, and AMNH Barosaurus is around 25 m , then BYU 9024 could be ~44,6 (neck twice as long, but rest of body shorter – Parrish 2006) – probably longest know sauropod but maybe not heaviest.

  7. Mike Taylor Says:

    Yes, that seems about right.


  8. thanks to you both! Another question, this time on the other part of your SVP 2016 abstract (which has pretty much been forgotten I’ve noticed): you mentioned *Dystylosaurus* could be valid again. Any other news on that?

  9. Mike Taylor Says:

    Just to clarify: that’s an SVPCA abstract, not SVP — it’s a smaller meeting, held in Europe, usually somewhere in the UK.

    We have no more news on Dystylosaurus, no. We said about all we have to say about it in the abstract, to be honest: we had so much to see and do when we were in Utah, we only spent a few minutes on poor Dystylo, so we never even got it down off the shelf. As a result, we never saw its anterior or posterior faces, or a good laterial view from either side.

  10. luigigaskell Says:

    And this is precisely why I don’t take claims of Amphicoelias fragillimus being 60+ meters long and over 100 tons in mass based on nothing but a century-old drawing of a single, distorted dorsal with no corresponding description or field notes.

  11. Mike Taylor Says:

    It’s almost as though you read my post on exactly that.


  12. @luigigaskell

    “no corresponding description”?

    It does, actually. It’s not a single isolated drawing like you seem to think it is. And the dorsal isn’t really very distorted, it’s just heavily eroded, but the upper portion is still pretty recognizable as a diplodocoid neural arch.

    Cope basically described basically as much as you can get from a single eroded neural arch.

    @Mike Taylor and @Matt Wedel

    I have some questions:

    1. Do you place the giant BYU 9024 Barosaurus as a B. lentus or it’s own new species?
    2. What is your stance on the phylogenetic affinity of A. fragillimus? Some think it’s a rebbachisaurid, others think it’s diplodocid. May as well place this question here after luigigaskell brought Amphicoelias up.

    Thanks in advance :)

  13. Mike Taylor Says:

    Sauropodomorph, we have not seen any characters separating BYU 9024 from Barosaurus lentus. (And in any case, I think all sauropod genera should be monospecific, so if we did think it was something different, we wouldn’t contribute to further instability by naming it Barosaurus somethingelse.)

    Who think Amphicoelias fragillimus is a rebbachisaurid? I don’t recall reading that anywhere. As far as I know, everyone who’s looked into it seriously has been happy enough with a diplodocid identity. But, not being one of those people myself, I don’t have an opinion one way or the other.


  14. “Who think Amphicoelias fragillimus is a rebbachisaurid? I don’t recall reading that anywhere.”

    Zach Armstrong wrote a lengthy post a couple of years ago giving his thoughts on the matter, & his post is still an excellent summary of the entire hypothesis: http://palaeozoologist.deviantart.com/journal/Was-Amphicoelias-a-rebbachisaur-440611550

    Personally I think it’s more likely, but it can certainly go either way.


  15. @Mike Taylor

    Well, if the D. carnegii-sized B. lentus is mature in any way, BYU 9024 seems much too big to belong to the same species XD. I mean, that’s basically a ~700% size disparity or so if it’s twice the dimensions, that would have to be some insane individual variation lol.


  16. (continuation of above post)

    And as for the rebbachisaur Amphicoelias hypothesis, Zach, Gunnar Bivens (who just replied above), and Nima believes that.

  17. Mike Taylor Says:

    Sauropodomorph, thanks for the link to Zach Armstrong’s post. I’ll take a brief look, but I am very short of time right now so I may not be able to write up my thoughts.

    Yes, we have good reason to think there was great variation in “adult” sauropod size within species — as with modern crocs. See also Dinosaur life histories are plicomcated.


  18. For my photogrammetric 3D models I sometimes have to manually place control points – i.e. mark the same location of a specimen in several photographs. And although I do this quite a lot and am used to it, I am often totally blown away by how much changes in the appearance a tiny shift in point-of-view makes.

    Interpreting shape (presence, size, shape) of characters based on photographs? Get lost!


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