Sauro-throat, Part 4: the osteological paradox

February 19, 2022

I closed the last post by claiming that finding the infected bone in Dolly was “a crazy lucky break”. Here’s why:

Another point made by Wood et al. (1992) concerns our perceptions of frailty and robustness. They were talking about archaeological populations, mostly from cemeteries, but the point is equally valid for non-human animals. We could look at Dolly and her infected vertebrae and say, “Ah, poor Dolly, she was too frail to fight off the infection” — implicitly comparing her to the individuals in the three left columns of the cartoon, which either never got sick, never developed lesions, or fully recovered. Or we could say, “Look how tough Dolly was, she must have survived with this infection for years!” — implicitly comparing her to the individuals in the right-most column, which all died too fast to develop lesions in the first place. The heck of it is, we can’t tell those comparison groups apart. Both stories about Dolly are true…from a certain point of view.

As a parting shot, here’s something to think about: a lot of the big mounted sauropod skeletons in museums are from individuals that are not skeletally mature — so they didn’t die of old age — and they also lack any evidence that they were killed by predators or even scavenged. There are some dramatic tooth-marked sauropod bones out there (f’rinstance), but not among the “monographically prominent” specimens like CM 3018 (Apatosaurus louisae), AMNH 5761 (Camarasaurus supremus), and MB.R.2181 (Giraffatitan brancai). I wonder how many of the latter were brought down by disease or parasites, and just don’t have any diagnostic traces of the maladies that killed them? Maybe the world’s museums are full of right-column sauropods.

References

7 Responses to “Sauro-throat, Part 4: the osteological paradox”

  1. llewelly Says:

    Great diagram for showing the filters at play (well, some of them, anyway.) Thank you for continuing this series.

    It does make me wonder about the other end of the odds question: How many sauropod specimens of sufficient preservation have been seen by people who would recognize the osteological signs of air-saculitus? (Total, including all the others that didn’t show signs of air-saculitus.)

  2. Matt Wedel Says:

    How many sauropod specimens of sufficient preservation have been seen by people who would recognize the osteological signs of air-saculitus?

    I don’t have anything like exact numbers, but it’s probably thousands for me alone.

    One of the reasons we all keyed so quickly on Dolly was that those lesions are exactly what we’d all been waiting to see. If you’d asked me, pre-2018, to predict what an infected pneumatic vertebra would look like, I would have drawn something so close to what Dolly shows that you’d have a hard time picking it out of a lineup.

    The biggest specific thing is that the lateral pneumatic chambers in sauropods, be they fossae or foramina, are often complexes of overlapping and interdigitating excavations, like someone went after the side of the vertebra with an ice cream scoop or a melon baller. If anything sticks out of that mess, it’s generally an accessory lamina, which will be thin and straight. Dolly’s lesions jumped right out because they were growing outward, and as irregular lumps, bubbling up like some gross blob monster from a 50s sci-fi movie.

    So I’m pretty confident that there aren’t a lot more Dolly-type lesions waiting to be discovered in museum collections. I’ll grant that there could be a few, but I think it must be a *very* few, because they just look wrong, like studded mud tires on a Formula 1 race car.

    I think it’s more likely that there are more subtle lesions that have been missed. At one point Dolly’s lesions were just rough patches of bone. Those could easily be mistaken for taphonomic or preparation damage, especially if they don’t grab the eye with any excessive blobbiness.

    The thought that really bothers me is this: what if the infection had only spread inside the vertebrae, instead of on the outside where it was easy to see? The number of sauropod vertebrae that have been CT scanned is still comparatively tiny, and even broken specimens don’t get us super far in terms of sampling, not least because the break would have to go right through the lesion to be useful. So I wonder if there are internally-infected sauropod vertebrae, hiding their secrets from us and waiting to be CT scanned. Maybe not — if the infection has to be in the epithelium of the diverticulum before it spreads to the bone, it’s always going to hit the outside of the vertebra before it hits the internal structure. But still, it doesn’t seem like it’s beyond the bounds of possibility.

  3. Katherine Honish Says:

    Could the same be said for malnutrition? My understanding of the Morrison Formation is that the inhabitants were dependent on good wet seasons to spur vegetation during the dry ones. I would tend to think that droughts would be on average the bigger threat to animals that had to eat such great quantities of food than disease, but would the fossil record show evidence of that, or would the same issues as disease affecting the bone apply?

  4. Matt Wedel Says:

    Good questions! I have two thoughts on this.

    First, we know what malnutrition looks like in the skeletons of humans and a lot of domesticated animals, and we might be able to diagnose specific conditions like rickets in an extinct dinosaur, but that’s a different thing from starving from a lack of food. I could easily be wrong, and if I am I hope someone speaks up, but I’m not sure that we have the criteria to diagnose starvation in a non-avian dinosaur. Especially sauropods, which are already a bit weird histologically (at least, that’s my takeaway from Stein and Prondvai 2014). And if we could diagnose starvation, it would probably take histological sampling, which, like CT scanning, has not been done for the vast majority of specimens.

    Second, malnutrition manifesting in the skeleton is usually a chronic condition (months or years), whereas starvation from a drought is more likely to be an acute condition (days or weeks), and I think a lot of animals that starve during droughts probably have few or no diagnostic traces of their starvation in their skeletons — in terms of the diagram in the post, they’re right-column victims. Again, that’s a guess, and I’d be happy to be corrected.

    Reference:
    Stein, K. and Prondvai, E. 2014. Rethinking the nature of fibrolamellar bone: an integrative biological revision of sauropod plexiform bone formation. Biological Reviews 89(1): 24-47.

  5. Jura Says:

    An additional line worth adding to the flow chart would be “portions of skeleton that get preserve” If you have a sauropod with air saculitis infecting 3 cervical vertebrae out of 10 and none of those 3 get preserved, it gets funneled back into “looks healthy”. Another sobering reminder of how little we actually know about extinct critters.

  6. Nathan Myers Says:

    It would be helpful if you were to come up with another column for your diagram — maybe “not exposed” (because they were on wanderjahr?) so that the museums could be suggested to be full of “sixth-column” specimens. Thank you for your cooperation in making a better paleoontological world.

  7. Matt Wedel Says:

    Yeah, right? _So_ close!


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