Correction: there is no support for Haestasaurus as a derived titanosaur

June 6, 2015

In my blog-post announcing Haestasaurus as the new generic name for the misassigned species “Pelorosaurusbecklesii, I briefly surveyed the three phylogenetic analyses in the paper. Of the third — the one based on the Mannion et al. (2013) Lusotitan matrix using both discrete and continuous characters — I wrote that it …

… recovers Haestasaurus as a titanosaur — as sister to Diamantinasaurus and then Malawisaurus, making it a lithostrotian well down inside Titanosauria.

My mistake! I was working from the result of an earlier version of that analysis. In the final version included in the paper, things are rather different:

Fig 17. Strict consensus tree (LCDM). A strict consensus tree based on the 17 most parsimonious trees generated by analysis of the Mannion et al. [18] LCDM with the revised scores for Haestasaurus and the addition of six new characters. GC values (multiplied by 100) are shown in square brackets for all nodes where these values are greater than 0. Abbreviations: Brc, Brachiosauridae; Dd, Diplodocoidea. N.B. the tree topology shown here means that the clades defined by Brachiosaurus+Saltasaurus (Titanosauriformes) and Andesaurus+Saltasaurus (Titanosauria) are identical. See main text for details.

Upchurch et al. (2015: Fig 17). Strict consensus tree (LCDM).
A strict consensus tree based on the 17 most parsimonious trees generated by analysis of the Mannion et al. [18] LCDM with the revised scores for Haestasaurus and the addition of six new characters. GC values (multiplied by 100) are shown in square brackets for all nodes where these values are greater than 0. Abbreviations: Brc, Brachiosauridae; Dd, Diplodocoidea. N.B. the tree topology shown here means that the clades defined by Brachiosaurus+Saltasaurus (Titanosauriformes) and Andesaurus+Saltasaurus (Titanosauria) are identical. See main text for details.

As you can see, Haestasaurus is indeed a titanosaur in this analysis — but not a derived one at all. In fact, it’s part of the most basal clade of titanosaurs, along with Janenschia and Dongbeititan. In this tree, we have a really nice, big Brachiosauridae, containing 19 OTUs split fairly evenly between two subclades.

[Side-note: Upchurch et al. (2015) uses phylogenetic definitions that I’m not crazy about. I prefer the arrangement that I followed in my brachiosaur paper (Taylor 2009), in which Titanosauriformes = Brachiosauridae + Titanosauria is a node-stem triplet. Hopefully, some time soon, the wretched PhyloCode will finally be implemented, and we’ll be in a position to nail down a single set of definitions for the whole community to use.]

Anyway, the upshot of all this is that all three phylogenetic analyses in the paper return Haestasaurus as a pretty basal macronarian, and on the balance of evidence it’s likely not a titanosaur after all. (That’s why the name “Haestatitan“, which was in some earlier drafts of the paper, was changed to Haestasaurus. Kind of a shame, given how mundane -saurus names are, but probably the wisest course of action.)

What is the takeaway lesson from this? It’s not just “Haestasaurus is not a derived titanosaur”. It’s that all our phylogenetic hypotheses are just that — hypotheses. Papers that publish only a single cladogram are always at risk of being misinterpreted as conveying much more certainty than they really do, and Paul and Phil are to be commended for including the whole messy story in this paper. The position of Haestasaurus shifts around far too easily for us to have a strong sense of what it is, and it’s good that the paper makes that clear.

(It also makes me glad that way back in Taylor and Naish (2007), I and Darren didn’t give a more precise position of Xenoposeidon than that it’s probably some kind of neosauropod. And even that is not something I would put money on.)

References

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7 Responses to “Correction: there is no support for Haestasaurus as a derived titanosaur”

  1. Brad McFeeters Says:

    “In this tree, we have a really nice, big Brachiosauridae, containing 19 OTUs split fairly evenly between two subclades.”

    But according to the label on the figure, only one of those subclades is Brachiosauridae. So, a nice big “Brachiosauroidea,” including Brachiosauridae and Chubutisauridae?

  2. Brad McFeeters Says:

    Actually, no need for a “Brachiosauroidea,” the clade of all sauropods closer to Tastavinsaurus than Saltasaurus is named Laurasiformes.

  3. Mike Taylor Says:

    “According to the label on the figure, only one of those subclades is Brachiosauridae.”

    Yes, I’m not sure how that happened. The only phylogenetic definition I’ve ever seen for Brachiosauridae is (Brachiosaurus not Saltasaurus).


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  5. Where is Brontosaurus in that list? I know they were reclassified as a separate genus earlier this year…

  6. Mike Taylor Says:

    In what list? If you mean in the cladogram, then it’ll be right next to Apatosaurus as usual. No-one challenged the idea that those two animals are closely related.

  7. Matt Wedel Says:

    I think what Brady is asking (please correct me if I’m wrong) is why Brontosaurus isn’t shown in the cladogram. It’s because this cladogram focuses on relationships among titanosauriforms, so it only includes a representative handful of diplodocids. Similarly, analyses that focus on diplodocids – like Tschopp et al. (2015) – would probably not include more than a representative handful of titanosauriforms.


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