A Phylogeny of Pure Sacral Characters

I have for a while been intrigued by sauropods, and how Atlantosaurus related to Apatosaurus. Of course because the former would be the senior synonym. But I didn’t want to code it into a large analysis. So I decided to place it in a purely sacral-based analysis. So I (somehow, honestly I’m not sure how, but I think it was a trial version) got PAUP* for free and added in my matrix. In the analysis, with the matrix based on my observations of photographs, with characters after multiple authors including Tschopp et al..

There were 25 characters, and 13 taxa, so not exactly the most comprehensive analysis. The outgrip was hypothetical, and all zeros. Taxa included were CetiosaurusFutalognkosaurusBrachiosaurusCamarasaurusElosaurusApatosaurus ajax, A. minimumAtlantosaurus, and the three proposed species of Haplocanthosaurus in addition to H sp. I expected to see the normal group with Cetiosaurus as most basal, diplodocoidea formed, and macronaria together. However, something strange happened.

Like proposed by Mike Taylor and Matt Wedel, Apatosaurus minimus grouped with Camarasaurus and Brachiosaurus. Both the strict consensus and 50% majority trees were similar, with the strict consensus simply more dissolved. Cetiosaurus was most basal other than the outgroup. But up next was a polytomy of Futalognkosaurus and Atlantosaurus. This is strange, as normally these two fall into the ends of separate neosauropoda. Up next was what would normally be Neosauropoda. This split into two groups, Presumably diplodocoidea and macronaria. However, the split seemed to be more Rebbachisauridae/Diplomacronaria. In Rebbachisauridae was a clade of (Haplo delfsi, Haplo priscus (Haplo sp. (Haplo utterbacki + Tataouinea) ) ). And then there is Diplomacronaria, which is just a name I made up. It includes (Apato ajax ( Elosaurus ( Apato minimus (Camarasaurus + Brachiosaurus) ) ) ). This is really quite a weird result, but I think it could be expected with the small number of taxa and the purely sacral-based matrix. Both the strict consensus and 50% majority trees are shown below.

50% majority tree

50% majority tree

Strict consensus tree

Strict consensus tree

Things to note include that there were 15 possible trees for the strict consensus. In the analysis, when there was more than one species the first letter is directly following the generic name. I can provide people with the nexus file if they would like it.


About ijreid

I am an amateur palaeontologist thats hobbies include studying extinct amniotes, specifically dinosaurs, birds, and mammals. Occasionally, I focus my time on detailed and accurate illustrations of dinosaurs, and I have completed drawings of Dysalotosaurus, Micropachycephalosaurus, Zhuchengtyrannus, Troodon, Eotyrannus, Europelta, and Achillobator. I do not believe in copyrights, and think that the world would be better if everything was open access.
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2 Responses to A Phylogeny of Pure Sacral Characters

  1. Mike Taylor says:

    A really useful exercise, which is going to set you up will for more detailed phylogenetic analysis work in the future.

    As a next step, I suggest that you try adding characters to your matrix, and see how the results are affected. If your experience is like mine, you will find that apparently innocuous changes have dramatic and unexpected consequences.

    Part of the value of such an exercise is that it teaches you a proper degree of scepticism regarding the results of phylogenetic analysis 🙂


    • ijreid says:

      Oh, I’m already plenty sceptical. This just shows how different bones change the phylogenies. But I will try to add more characters, although since I’m not really vertebral laminae inclined I may stick to appendicular and cranial features.


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