Analysing the distribution of complete sauropod necks

March 27, 2021

Matt dropped me a line midweek about the catalogue of complete sauropod necks, with some interesting thoughts. He broke down the necks as listed across a basic phylogeny of sauropods, and counted the occurrences:

Simplified phylogeny of Sauropoda, showing counts of complete and near-complete necks. Captions: C, complete and described; U, complete but undescribed; –1, missing the atlas but otherwise complete; O, other near-complete necks; T, total.

Matt and I were both surprised to see that non-neosauropods are quite well represented, both inside and outside of Mamenchisauridae — although it’s a pity that two of those ten specimens are of Jobaria, for which we have next to zero information.

Diplodocoids are surprisingly poorly represented, with essentially just one each in Dicraeosauridae and Diplodocidae that are complete. And brachiosaurids are a black hole, with absolutely no representation — see the 2015 preprint for details on how unconvincing the neck of Giraffatitan is.

But camarasaurids are crushing it, probably just by being the most abundant sauropods of all time in terms of individual specimens in museums. (Of course when we say “camarasaurids”, we just mean Camarasaurus, which is the only named sauropod currently considered to belong to Camarasauridae unless you follow Mateus and Tschopp (2013) in considering Cathetosaurus to be generically distinct. But Matt and I both suspect that Camarasaurus is way over-lumped, so we’ll see how this pans out over the next decade or two.)

It’s surprising, though, that the second and third best represented sauropods in museums, Diplodocus and Apatosaurus, are both barely represented in terms of complete necks. And while it’s encouraging to see quite a few complete and nearly-complete necks among somphospondyls, including titanosaurs,it’s disappointing that about half of them are not yet described.


4 Responses to “Analysing the distribution of complete sauropod necks”

  1. llewelly Says:

    I did not expect Mamenchisaurids to do so well because it seems to me that more vertebrate means a neck is more likely to come up missing some.

  2. Mike Taylor Says:

    That’s a good point.

  3. I would guess that it doesn’t have to do with mamenchisaurids per se so much as it has to do with where they’re fossilized; five of the 27 sauropod necks here are from the Shaximiao Formation and one is from the overlying Suining Formation, and those six Sichuan necks include four of the five (or six, counting Euhelopus) mamenchisaur necks.

    Or maybe it does have something to do with mamenchisaurids per se—maybe they favored habitats that were better for getting fossilized. I know the converse has been suggested as an explanation for why titanosaurs have such a scrappy record.

    It’s notable that of the 27 necks on this list, six are from the Sichuan Basin, eight are from the Morrison Formation, five are from the Neuquén Basin, and three are from the Irhazer Group. Only five are from anywhere else. I dare say that that’s probably a pretty strong Lagerstätte effect on our understanding of sauropod necks (and sauropod diversity more generally).

  4. Andrea Cau Says:

    Ok, the sample is way too small for inferring something robust, but it would be intriguing if such result is due to different ecological preferences among sauropods biasing their rate of preservation in the fossil record.

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