What’s up with your irregular ventral ridges, diplodocines?

May 17, 2016

UPDATE 19 May 2016

I belatedly realized that I caused some confusion in the original version of this post. This will hopefully sort things out:

NAMAL Barosaurus cervical with features labeled

The ventrolateral processes (1) are nothing new. As Ken Carpenter pointed out in a comment, Hatcher noted them back in 1901 in his monograph on Diplodocus carnegii. These are the features I describe below as being, “huge in Barosaurus, big in Diplodocus, small in Apatosaurus, and nonexistent in Haplocanthosaurus, Camarasaurus, and the brachiosaurids, at least from what I’ve seen.” To clarify: occasionally in camarasaurs and frequently in brachiosaurs you can trace a ridge along the ventrolateral margin of the centrum from the parapophysis to the cotyle. But these ridges are basically just the ‘corners’ of the centrum, leftover by the lateral and ventral waisting of the centrum – they do not project beyond the margin of the cotyle. In contrast, what I’ve been calling the ventrolateral flanges in diplodocids do project beyond the margins of the cotyle – they are additive structures, not just architectural leftovers. They also don’t vary much, other than to be more pronounced in more posterior cervicals.

The irregular ventral ridges (2) are a totally different thing. They’re on or near the sagittal midline of the centrum, usually restricted to the anteroposterior middle of the ventral centrum (so, about halfway between the condyle and the cotyle), and as my preferred term implies, highly variable among individuals and even among vertebrae in a series.

Hope that helps! (Original post starts below.)

– – – – – – – – – – – – – – – – – – – – –

2005-07-29 BYU 16918 Diplodocus left lateral

Back in 2005 I visited BYU while I was working on my dissertation. Back then I noted ventral ridges in a few diplodocine cervical vertebrae. (I hesitate to call such flimsy things ‘keels’.)

Up above is BYU 16918, a mid-to-posterior cervical vertebra of Diplodocus from the famous Dry Mesa Quarry. Here it is again in posterior view:

2005-07-29 BYU 16918 Diplodocus posterior view labeled

The things I have labeled VLF here are ventrolateral flanges, which are huge in Barosaurus, big in Diplodocus, small in Apatosaurus, and nonexistent in Haplocanthosaurus, Camarasaurus, and the brachiosaurids, at least from what I’ve seen. See this post for details. I know that the left VLF here looks like a second ridge, but the cotyle is broken off in such a way that we’re seeing the fossa just dorsal to the VLF margin. The ridge itself is skewed to the right, which could be natural or a result of taphonomy – as you can see from the photo at the top of the post, this vert has seen better days.

Here’s another Dry Mesa vert, BYU 11617, this time an anterior cervical of Barosaurus and in left lateral view:

2005-07-29 BYU 11617 Barosaurus left lateral

Again in right lateral view – on this side you can see the fossa in the VLF more clearly:

2005-07-29 BYU 11617 Barosaurus right lateral

And here’s the ventral view showing the ridge:

2005-07-29 BYU 11617 Barosaurus ventral view labeled

I noted these things in my notebook back when, filed them under, “Huh. How about that?” and went on with life.

Then last week Mike and I were at the North American Museum of Ancient Life in Lehi, Utah, and we saw this super-nice Barosaurus cervical on display in the prep lab (left ventro-lateral view). Check out the monster ventrolateral flanges, and the ridges between them at about mid-centrum.

IMG_4605

Here’s another view, a more square-on ventral this time:

IMG_4604

We owe a big thank you to Rick Hunter, who let us into the prep lab at the North American Museum of Ancient Life to see the Barosaurus material up close.

So what’s the deal with these ridges? I assume that they’re caused by pneumatic diverticula remodeling the ventral surface of the centrum. We know that such diverticula were down there because there are actual foramina on the ventral centrum in Supersaurus, many apatosaurines (Lovelace et al., 2008), many brachiosaurids, and probably loads of other things that haven’t been checked. Oddly enough, I’ve never seen the ridges in any of those other taxa. It seems that you get foramina or ridges, but not both. I have no idea what’s up with that – to paraphrase Neal Stephenson, Barosaurus cervicals are confections of air and marketing, and you’d think that if any sauropod would have straight-up foramina down there, it would be Barosaurus. But Barosaurus gets ridges and clunky old Apatosaurus gets foramina (sometimes, not all the time).

It’s a sick world, I tell you.

Reference

  • Lovelace, D. M., Hartman, S. A., & Wahl, W. R. (2007). Morphology of a specimen of Supersaurus (Dinosauria, Sauropoda) from the Morrison Formation of Wyoming, and a re-evaluation of diplodocid phylogeny. Arquivos do Museu Nacional, Rio de Janeiro 65(4):527-544.
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7 Responses to “What’s up with your irregular ventral ridges, diplodocines?”

  1. Ken Carpenter Says:

    Hatcher (1901) has you beat. He states: “The infracentral cavity is very pronounced in this and the succeeding cervicals and the centra in these vertebra) are much constricted medially and expanded at their extremities.” And : “The two lateral lamina projecting inferiorly and externally from the posterior portions of the cervical centra are wanting in these … dorsals, and the inferior surface of that portion of the centra in these vertebrae is uniformly convex, there being no infracentral cavity.”

    He seems to consider the structures as due to the formation of the deep cavity on the ventral side of the cavity leaving what you call ridges (his lateral lamina that project ventrally and externally.

    In reality, the structure was developed by the Great Ankylosaur in the Sky so that the neck can be mounted onto a steel beam armature when the skeleton is mounted.

  2. Matt Wedel Says:

    Sorry, I wasn’t clear in the post. I’m not claiming that the ventrolateral processes – what Hatcher calls the “two lateral laminae projecting inferiorly and externally from the posterior portions of the cervical centra” – are in any way new observations. Just that they’re there. The structures I haven’t seen discussed before are the irregularly-developed ridges between the ventrolateral processes, closer to or even on the midline (although I should of course check Tschopp et al. 2015).

    In reality, the structure was developed by the Great Ankylosaur in the Sky so that the neck can be mounted onto a steel beam armature when the skeleton is mounted.

    Yeah, and the posterior centroparapophyseal laminae and ventrolateral processes even hide the beams for the most part.

    One striking thing about Barosaurus cervicals is that for much of their length, the centra basically do not exist. I think that deserves a whole post, though.

  3. Mike Taylor Says:

    Matt, you should consider revising the text of the post if Ken’s comment has persuaded you that it was unclear.

  4. Vishal Says:

    I have a question regarding the BYU 9024 specimen of Supersaurus. How big would the whole animal be with a vertebrae that size or are you going to do a seperate post on that

  5. Mike Taylor Says:

    We can’t really say how big the BYU 9024 individual was — or even, at this point, what it belonged to. But Matt has estimated (in his dissertation, pp. 195-197) that it probably came from a neck that was about 13.3-16.2 m in length:

  6. Mickey Mortimer Says:

    Yeah, I missed the whole irregular ridge angle until reading the comments. Flange is too close to ridge, though AFAIK many coelurosaurs have the flange but none have the ridge…

  7. Andrew Stuck Says:

    “Thunder Lizards” is almost as helpful as an actual scale bar. ;)


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