Mysterious, never-yet-outed titanosaur caudals

October 22, 2007

Welcome to another SV-POW! world first: the first ever outing (to my knowledge) of a photo of BMNH R5333, an articulated set of two-and-a-bit titanosaur caudal vertebrae. These vertebrae come from the famous Wessex Formation of the Isle of Wight: they are from the Lower Cretaceous, and specifically from the Barremian. The specimen is shown here in left lateral view: contrary to what you might expect, the bulbous, convex condyle on these vertebrae is located on the posterior articular surface, while the concave cotyle is located on the anterior articular surface (see Tutorial 2 if you need help with these terms). Vertebrae that have their concave articular faces positioned anteriorly are termed procoelous, and many (but not all) titanosaurs are characterised by procoelous caudal vertebrae. Why titanosaurs had procoelous caudal vertebrae is a good question. Some dinosaur workers have suggested that the ball-in-socket articulations present here might have given their owners a particularly strong or flexible tail that they might have used as a prehensile organ, or as mobile ‘fifth limb’ used when the animals were rearing up to eat from trees.

For those of you that care, BMNH R5333 was figured (but not discussed or mentioned) by Blows (1998): other than that I don’t think it’s ever been covered in the literature. For shame!

10 Responses to “Mysterious, never-yet-outed titanosaur caudals”

  1. Mike from Ottawa Says:

    Is there a specific point where they suddenly change or do they make a transition from postcoelous (?) to procoelous?

  2. Terry Hunt Says:

    Thanks, Mike. I now have this image of a mid-transition titanosaur, with planar condyles *and* cotyles on all vertebrae, suddenly falling apart like a sliced loaf!

    Presumably the transition must have proceeded (through the generations) one vertebra at a time up or down the tail? (I mean, alternate vertebrae would work, but seems developmentally unlikely.) Or could a gene have switched expression mid-way down the tail to reverse the anterior articulations ‘in one go’? (Hope I’m making some sense here.)

  3. Mike from Ottawa Says:

    I hadn’t even thought of “where” as referring to where in the animal’s evolution it went from ‘postcoelus’ to precoelus, but that’s certainly a good question. Probably a lot harder to answer than mine.

  4. Randy Says:

    Rather than “postcoelous”, the term you are looking for is “opisthocoelous”, where the convex articular surface is on the anterior face of the vertebra.

  5. Mike from Ottawa Says:

    I knew that ‘postcoelus’ to go with ‘procoelus’ would be too easy. :-)

  6. […] are crazy pneumatic. In fact, the only non-pneumatic vertebrae we’ve shown so far are these, and you can see big obvious pneumatic foramina in the vertebrae shown here and here and here and […]

  7. Matt Wedel Says:

    Hi all. Sorry I’ve been out of touch for a while. As vertebrae develop you get little balls of proto-cartilage between each one, and how those balls of cells get divvied up and and what they fuse to (the vert ahead or behind) determines the shape of the articulation. Sauropod cervicals are opisthocoelous (ball in front, socket behind), dorsals are opisthocoelous or amphiplatyan (flat on front and back, like your vertebrae), and caudals may be procoelous (socket in front, ball behind), amphiplatyan, opisthocoelous, or just about any combination of the above. In fact, the titanosaur Rinconsaurus caudamira has all of those types of articulation in one tail!

  8. […] articular surfaces, no matter what their morphology. When talking about crocodile cervicals or titanosaur caudals, we’re even likely to say ridiculous things like “the condyle is concave and the cotyle […]

  9. bricksmashtv Says:

    Would it be okay if I use this image for my paper I’m going to write about (hopefully) this specimen? I’ll give full credit to you for photographing and providing the image.

  10. Mike Taylor Says:

    As far as we are concerned, yes, absolutely. But remember that the NHM holds copyright on all photographs of their material, so you will need to acknowledge that as well.

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