“Biconcavoposeidon”
August 15, 2017
Here is a fascinating sequence of five consecutive posterior dorsal vertebra — AMNH FARB 291 from the”Big Bone Room” at the AMNH:
AMNH FARB 291, five consecutive posterior dorsal vertebrae of a probably brachiosaurid sauropod, in right lateral view. The vertebrae are embedded in a plaster block, which has been desaturated in this image.
Matt and I first saw this specimen back in February 2009, when we were mostly there to look at “Apatosarus” minimus (and then again in 2012). As soon as our eyes lit on it, we couldn’t help but be captivated by its bizarre biconcave centra. We immediately started flippantly referring to it as “Biconcavoposeidon” — the ugliest name we could come up with — and in our subsequent discussions the name has stuck (often abbreviated to “BCP”).
- Taxonomic note: for avoidance of doubt, “Biconcavoposeidon” is not and will never be a formal taxonomic name, only an informal specimen nickname. If at some future point we conclude that this specimen represents a new taxon, and name it, we will definitely not use the name “Biconcavoposeidon”. If you ever use the name, please do not set it in italics.
As you can see in this front view, the specimen is sheared: the upper part of the vertebrae have been displaced to their left (which is the right as we see it in this image):
AMNH FARB 291, most anterior of five consecutive posterior dorsal vertebrae of a probably brachiosaurid sauropod, in anterior view.
Apart from the shearing, though, and the truncation of the neural spines shortly above the transverse processes, the specimen is in pretty good nick. Crucially, it’s not been “restored” in plaster to conceal what is and is not real bone — unlike many specimens of that era. It came out of the Bone Cabin quarry in 1898, back when scientific information was routinely discarded in order to obtain a more beautiful-looking specimen.
This is the specimen that I’ll be presenting at SVPCA this year — though only as a poster, unfortunately: there’s no talk for me, Matt or Darren this year. We’ve posted our abstract (including the illustration above) to the nascent PeerJ collection for SVPCA 2017, and we’re looking forward to seeing more of the materials from that conference — abstracts, then manuscripts, then papers — appearing in the collection.
So far as we know, there’s no other sauropod specimen with biconcave posterior dorsal vertebrae. (And, no, Amphicoelias is not an exception, despite its name.) But have we missed any?
Sauropod Vertebra Picture of the Week 
August 16, 2017 at 1:39 am
“So far as we know, there’s no other sauropod specimen with biconcave posterior dorsal vertebrae. (And, no, Amphicoelias is not an exception, despite its name.) But have we missed any?”
Going down my cladogram on the Database…
Antetonitrus
Leonerasaurus
Sanpasaurus
Tazoudasaurus
Dashanpusaurus
Barapasaurus
Cetiosaurus
Eomamenchisaurus
Tonganosaurus
Limaysaurus
Apatosaurus (Upchurch et al., 2004)
August 16, 2017 at 10:49 am
Ha! Very interesting — thanks, Mickey! I’ll look into the more derived ones.
August 16, 2017 at 10:56 am
What’s your source for Limaysaurus? Re-scanning Calvo and Salgado (1995), I read “Anterior dorsals are strongly opisthocoelous … in posterior dorsals, the centra are platycoelous” (pp. 20-22) — and the only dorsal vertebra figured in lateral view is the unspecified “anterior dorsal” of figure 8D, which is indeed notably convex in its anterior articulation.
Reference
Calvo, Jorge O., and Leonardo Salgado. 1995. Rebbachisaurus tessonei sp. nov. a new Sauropoda from the Albian-Cenomanian of Argentina; new evidence on the origin of the Diplodocidae. Gaia 11:13-33.
August 16, 2017 at 11:03 am
Excellent catch on Tonganosaurus: “Cervical and anterior dorsal centra are opisthocoelous, middle dorsal centra are platycoelous, posterior dorsal and anterior caudal centra are amphicoelous” (Li et al. 2010:198) and figures 2-3 seem to corroborate that.
Reference
Li, Kui, Chun-Yan Yang; Jian Liu and Zheng-Xin Wang. 2010. A new sauropod dinosaur from the Lower Jurassic of Huili, Sichuan, China. Vertebrata PalAsiatica 48(3):185–202.
August 16, 2017 at 10:53 pm
For Limaysaurus, Salgado et al. (2004) state “A posterior dorsal centrum (Pv-6756-MOZ) (Fig. 3E) is platycoelous, with the anterior articular surface slightly more concave than the posterior, which is virtually flat.”
So despite their label, they describe both sides as at least slightly concave. Importantly, the more concave surface is the anterior one, since in this post we’re contrasting your verts with opisthocoelous ones. Of course this also illustrates the issue of differentiating amphi- and platycoelous centra, since very few studies actually quantify the degree of concavity. In theropod analyses, they’re usually lumped together as the same state. Also note a platycoely like that described in Limaysaurus isn’t homologous with the normal saurischian presacral platycoely, where the anterior surface is the flat one.
In any case, from my review, basically all non-neosauropods, rebbachisaurids and dicraeosaurids have amphi- to platycoeous posterior dorsals. This is true of some diplodocids too, though most have a condition like Amphicoelias where part of the anterior surface is concave and part convex. Non-macronarians with opisthocoelous posterior dorsals are exceptions like Omeisaurus, Mamenchisaurus and Supersaurus.
Reference- Salgado et al., 2004. LOWER CRETACEOUS REBBACHISAURID SAUROPODS FROM CERRO AGUADA DEL LEON (LOHAN CURA FORMATION), NEUQUEN PROVINCE, NORTHWESTERN PATAGONIA, ARGENTINA. Journal of Vertebrate Paleontology 24(4):903–912.
August 16, 2017 at 11:18 pm
Thanks for all of the information, Mickey, this is extremely useful stuff.
Of course this also illustrates the issue of differentiating amphi- and platycoelous centra, since very few studies actually quantify the degree of concavity. In theropod analyses, they’re usually lumped together as the same state.
Yes on both counts. I haven’t personally examined most of the sauropod taxa you listed above, but in Cetiosaurus and Apatosaurus at least, the degree of concavity is so slight that it would not have occurred to me to describe them as amphicoelous rather than amphiplatyan. I have the sense that Biconcavoposeidon is doing something different, but it would be nice to quantify that.
August 17, 2017 at 11:40 am
Yeah. You know what would be good? If those two morons who have seen this material twice had thought to measure the depth of the concavities.
Sheesh. You know our problem? We have to work with idiots.
September 8, 2017 at 10:38 pm
[…] up next week. My poster is about a weird specimen that Matt and I have been informally calling “Biconcavoposeidon” (which I remind you is not a formal taxonomic […]
October 2, 2017 at 7:42 am
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