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Hot sauropod news, part 2: A new look for Sauroposeidon

Wednesday, September 5, 2012 2:50

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(Before It's News)

YPM 5449, a posterior dorsal vertebra of Sauroposeidon, from D’Emic and Foreman (2012:fig. 6A and C).

Another recent paper (part 1 is here) with big implications for my line of work: D’Emic and Foreman (2012), “The beginning of the sauropod dinosaur hiatus in North America: insights from the Lower Cretaceous Cloverly Formation of Wyoming.” In it, the authors sink Paluxysaurus into Sauroposeidon and refer a bunch of Cloverly material to Sauroposeidon as well. So in one fell swoop Sauroposeidon goes from being one of the most poorly represented Early Cretaceous North American sauropods, based on just four vertebrae from a single individual, to one of the best-known, most complete, and most widespread, based on at least seven individuals from Texas, Oklahoma, and Wyoming.

The web of connections among the different sets of material is complex, and involves the Sauroposeidon holotype OMNH 53062 from the Antlers Formation of southeastern Oklahoma, the type and referred material of Paluxysaurus from the Twin Mountains Formation of northern Texas described by Rose (2007), sauropod material from the Cloverly Formation of north-central Wyoming described and illustrated by Ostrom (1970), and UM 20800, a scap and coracoid newly excavated from one of Ostrom’s old quarries. D’Emic and Foreman argue that (1) the Cloverly material is referable to Sauroposeidon based on the shared derived characters of a juvenile cervical, YPM 5294, and the Sauroposeidon holotype, and (2) Paluxysaurus is not distinguishable from the Cloverly material and in fact shares several autapomorphies with the Cloverly sauropod. Which means that (3) Paluxysaurus is Sauroposeidon.

But that’s not all! All the new material suggests different phylogenetic affinities for Sauroposeidon. Instead of a brachiosaurid, it is now posited to be a basal somphospondyl. That’s not super-surprising; as we noted back in 2000 (Wedel et al. 2000), if Sauroposeidon was a brachiosaurid it had evolved some features in parallel with titanosaurs, most notably the fully camellate internal structure of the cervical vertebrae. And it also makes sense because other basal somphospondyls include Erketu and Qiaowanlong, the cervicals of which are similar to Sauroposeidon in some features. D’Emic and Foreman (2012) cite a forthcoming paper by Mike D’Emic in the Journal of Systematic Paleontology that contains the cladistic analysis backing all this up, but the case based on comparative anatomy is already pretty strong.

If anyone is unconvinced by all of these referrals, please bear in mind that we haven’t heard the whole story yet, quite probably for reasons that are outside of the authors’ control. I am inclined to be patient because I have been in that situation myself: Wedel (2003a) was intended to stand on the foundation of evidence laid down by Wedel (2003b), but because of the vagaries of publication schedules at two different journals, the interpretive paper beat the descriptive one into press by a couple of months.

Mid-cervical originally described as Paluxysaurus, now referred to Sauroposeidon, from Rose (2007:fig. 10).

Anyway, if anyone wants my opinion as “Mr. Sauroposeidon“, I think the work of D’Emic and Foreman (2012) is solid and the hypothesis that Paluxysaurus is Sauroposeidon is reasonable. So, if I think it’s reasonable now, why didn’t I synonymize the two myself? Partly because I thought there was a pretty good chance the two were not the same, based mostly on FWMSH 93B-10-8 (which I referred to as FWMSH “A” in Wedel 2003b, since I had only seen in on display without a specimen number), which I thought looked a lot more like a titanosaur cervical than a brachiosaur cervical. But of course I thought Sauroposeidon was a brachiosaur until a couple of months ago, and if it ain’t, and if brachiosaurs and basal somphospondyls have similar cervicals, that objection is considerably diminished. And partly because I’ve had other things to be getting on with, and stopping everything else to spend what would realistically be a few months looking into a possible synonymy (that I didn’t strongly suspect) wasn’t feasible in terms of time or geography. So I’m glad that D’Emic and Foreman have done that work, and I’m excited about the new things they’ve uncovered.

And I’m honored to bring you a new life restoration of Sauroposeidon by uber-talented Bob Nicholls, which we think is the first to show Sauroposeidon in its new guise as a basal somphospondyl. Click through for the mega-awesome version.

Same critter, different views. If anyone wants to GDI this baby, you now have everything you need. Many thanks to Bob for permission to post these and the following making-of images. Please visit him at Paleocreations.com to see a ton of awesome stuff, and give him some love–or at least a few thousand “likes”–on Facebook.

This is Bob’s first foray into 3D modeling, but you’d never know from the quality of his virtual sculpt. And let me tell you, that dude works fast. He sent this initial version, showing Sauroposeidon as an attenuated brachiosaur (sorta like this) on August 23, to solicit comments from Mike and me.

I wrote back and let Bob know about the new work of D’Emic and Foreman, and suggested that he could probably be the first to restore Sauroposeidon as a somphospondyl. Mike and I also voiced our opposition to the starvation-thinned neck, and Mike suggested that the forelimb was too lightly muscled and that the ‘fingers’ were probably too prominent. The very next day, this was in our inboxes:

I wrote back:

Whatever Sauroposeidon was, its neck was fairly tall and skinny in cross-section. It looks like the neck on your model sort of tapers smoothly from the front of the body to the head. I think it would be much narrower, side-to-side, along most of its length, and would have a more pronounced shoulder-step where it met the body.

The bottom view is very useful. It shows the forefeet as being about the same size as the hindfeet. AFAIK all or nearly all known sauropod tracks have much bigger hindfeet than forefeet. Certainly that is the case with Brontopodus birdi, the big Early Cretaceous sauropod tracks from Texas that were probably made by Sauroposeidon. The forefeet should be about 75-80% the width of the hindfeet, and only about half a long front-to-back. Even if you don’t quite get to those numbers, shrinking the forefeet a bit and subtly up-sizing the hindfeet would make the model more accurate.

Mike’s commentary was much shorter–and funnier:

I like how freaky it looks. It looks WRONG, but in a good way.

Bob toiled over the weekend and came back with this subtly different, subtly better version:

I had one more change to recommend:

I’m sorry I didn’t suggest this sooner, but it only just now occurred to me. With the referral of Paluxysaurus and the Cloverly material to Sauroposeidon, we now have dorsal vertebrae, and they are loooong, much more similar in proportion to the dorsals of Brachiosaurus altithorax than those of Giraffatitan brancai. So, as much as I like the compact little body on your Sauroposeidon, I think it was probably fairly long in the torso. You probably already have Mike’s Brachiosaurus paper [Taylor 2009] with the skeletal recon showing the long torso–in the absence of an updated skeletal recon for Sauroposeidon, I’d use Mike’s Figure 7 as a guide for reconstructing the general body proportions.

Bob lengthened the torso to produce the final version, which is the first one I showed above. He sent that over on August 29–the delay in getting this post up rests entirely with me.

So. It is still very weird to think of “my” dinosaur as a somphospondyl rather than a brachiosaur. I had 15 years to get used to the latter idea. But suddenly having a lot more material–essentially the whole skeleton, minus some stinkin’ skull bits–is pretty darned exciting, and the badass new life restoration doesn’t hurt, either.

Now, would it be too much to wish for some more Brontomerus?

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