Brachiosaurus sp. BYU 12866 c5? in left lateral view with CT slices, some corrected for distortion.

Brachiosaurus sp. BYU 12866 c5? in left lateral view with CT slices, some corrected for distortion.

Last Tuesday Mike popped up in Gchat to ask me about sauropod neck masses.  We started throwing around some numbers, derived from volumetric estimates and some off-the-cuff guessing. Rather than tell you more about it, I should just paste our conversation, minimally edited for clarity and with a few hopefully helpful links thrown in.

Mike: Dud. Neck masses.
Matt: What about ’em?
Mike: Taylor (2009:803) measured the neck of Giraffatitan by GDI as 4117 liters.
Matt: k
Mike: I didn’t convert that to a mass, but I guess density of 0.5 is as good as any, which gives us (say) 2 tonnes.
Matt: That works for me.
Mike: That’s for an 8.5 m neck. So Supersaurus at 15 …
Matt: Yep. Almost twice as long, and not much more slender, and from what I’ve seen, ASP about the same.
Mike: Is 1.76 times as long. If it was isometric with the G. neck, it would be 5.5 times as heavy, which is 11 tonnes.
Matt: Oh.
Mike: So first: yeesh. Like, that is the mass of a whole freaking Diplo. Now we surely have to say isometry is unlikely.
Matt: Prolly.
Mike: But just multiplying out by length is unrealistic too. So maybe I should guess at mass =~ l^2? If I went with that, I’d get 6410 kg, which is elephant mass.
Matt: Something just occurred to me. Like, just now. For my 2006 poster, I calculated the mass of the cervical series in Giraffatitan, by summing over the CT slices from Brachiosaurus sp. BYU 12866 and multiplying by appropriate scale factors for the rest of the verts. We could “skin” that in muscle, and actually figure this out, for various muscle thicknesses, for one sauropod.
Mike: We should totally do that … if we had some idea how heavily muscled it was.
Matt: Well, obviously the thing to do is what Hutch et al. did for the tyrannosaurs, and put on several soft tissue envelopes. Crazy skinny, our best guess, markedly unfit, OMG, etc. It’s not that much more work. In fact, that could be my SVPCA talk this year.
Mike: Sure, but that’s just how to mitigate our ignorance. All we’d be doing at this point is taking n guesses instead of one. But, yeah, we should do it. Or you should if you prefer.
Matt: Let’s make it a Wedel and Taylor. I’ll crunch the numbers, but I want your input.
Mike: Works for me!
Matt: Good. Now let’s file it until April at least.
BYU 12613, a posterior cervical probably referable to Diplodocus, in dorsal (top), left lateral (left), and posterior (right) views. It compares most favourably with C14 of D. carnegii CM 84/94 (Hatcher 1901: plate 3) despite being less than half as large, with a centrum length of 270 mm compared to 642 mm for C14 of D. carnegii. From Wedel and Taylor (in press).

BYU 12613, a posterior cervical probably referable to Diplodocus, in dorsal (top), left lateral (left), and posterior (right) views. It most closely resembles C14 of D. carnegii CM 84/94 (Hatcher 1901: plate 3) despite being less than half as large, with a centrum length of 270 mm compared to 642 mm for C14 of D. carnegii. From Wedel and Taylor (in press).

Matt: Oh!
Matt: Also.
Matt: You know that little Diplo cervical from BYU that we figure in our in-press paper?
Mike: I think I know the one, yeah.
Matt: I am SUCH a moron. I have CT scans of the whole thing.
Mike: Good.
Matt: I forgot that Kent and I scanned it back in 2008. Even blogged about it, fer cryin’ out loud.  So I can do the sum-over-slices, scale-for-other-verts thing for Diplodocus, too. Which is at least closer to Supes than JANGO is.
Mike: Remind me, is it from a juvenile?
Matt: Maybe, maybe not. It IS tiny, but the neural spine is fused, the internal structure is crazy complex, and it doesn’t have any obvious juvenile characters other than just being small. The ASP is about as high as it gets in diplodocids. Which, as you may remember, is not nearly as high as it gets in titanosauriforms–that’s another paper that needs writing. Damn it. To know all this stuff and not have told it yet is killing me.
Mike: PeerJ!
Matt: I know!
Mike: Bottom line, it’s nuts that no-one has ever even tried to weigh a sauropod neck.* We should definitely do it, even if we do a really crappy job, if only so that others feel obliged to rebut.
Matt: Quite. Let’s do it. For reals.
Mike: In April. Done.

* R. McNeill Alexander (1985, 1989) did estimate the mass of the neck of Diplodocus, based on the old Invicta model and assuming a specific gravity of 1.0. Which was a start, and waaay better than no estimate at all. Still, let’s pretend that Mike meant “tried based on the actual fossils and what we know now about pneumaticity”.

The stuff about putting everything off until April is in there because we have a March 31 deadline to get a couple of major manuscripts submitted for an edited thingy. And we’ve made a pact to put off all other sciencing until we get those babies in. But I want to blog about this now, so I am.

Another thing Mike and I have been talking a lot about lately is the relation between blogging and paper-writing. The mode we’ve seen most often is to blog about something and then repurpose or rewrite the blog posts as a paper. Darren paved the way on this (at least in our scientific circle–people we don’t know probably did it earlier), with “Why azhdarchids were giant storks“, which became Witton and Naish (2008). Then last year our string of posts (starting here) on neural spine bifurcation in Morrison sauropods became the guts–and most of the muscles and skin, too–of our in-press paper on the same topic.

But there’s another way, which is to blog parts of the science as you’re doing them, which is what Mike was doing with Tutorial 20–that’s a piece of one of our papers due on March 31.

Along the way, we’ve talked about John Hawks’ model of using his blog as a place to keep his notes. We could, and should, do more of that, instead of mostly keeping our science out of the public eye until it’s ready to deploy (which I will always favor for certain projects, such as anything containing formal taxonomic acts).

And I’ve been thinking that maybe it’s time for me–for us–to take a step that others have already taken, and do the obvious thing. Which is not to write a series of blog posts and then decide later to turn it into a paper (I wasn’t certain that I’d be writing a paper on neural spine bifurcation until I had written the second post in that series), but to write the paper as a series of blog posts, deliberately and from the outset, and get community feedback along the way. And I think that the sauropod neck mass project is perfect for that.

Don’t expect this to become the most common topic of our posts, or even a frequent one. We still have to get those manuscripts done by the end of March, and we have no shortage of other projects waiting in the wings. And we’ll still post on goofy stuff, and on open access, and on sauropod stuff that has nothing to do with this–probably on that stuff a lot more often than on this. But every now and then there will be a post in this series, possibly written in my discretionary blogging time, that will hopefully move the paper along incrementally.

References