Here’s D10 and the sacrum of Diplodocus AMNH 516 in left lateral and ventral view, from Osborn (1904: fig. 3). Note how the big lateral pneumatic foramina, here labeled ‘pleurocoelia’, start out up at the top of the centrum in D10 and kind of pinch out up there, seemingly entirely absent by S3 (although there is a suspicious-looking shadowed spot above and behind the sacral rib stump labeled ‘r3’). Then on S4 and S5 the big foramina are back, but now they’re low on the centrum, ventral to the sacral ribs. In ventral view, the foramina on D10, S1, and S2 aren’t visible–they’re both over the curve of the centrum, and in the case of S1 and S2, obscured by the sacral ribs. But in S4 and S5, the big lateral foramina are visible in ventral view.

I’ve been interested in a while in this seeming hand-off in centrum pneumatization from dorsolateral, which prevails in the dorsal vertebrae, to ventrolateral, which prevails in the posterior sacral and caudal vertebrae. Almost all sauropod dorsals have the pneumatic foramina quite high on the centrum, sometimes even encroaching on the neural arch. But if sauropod caudals have pneumatic fossae or foramina on the centrum, they’re usually quite low, and almost always below the caudal rib or transverse process (there may also be pneumatic fossae on the neural arch and spine)–for evidence, see Wedel and Taylor (2013b). To me this implies two different sets of diverticula.

I think that in part because sometimes you get both sets of diverticula acting on a single vert. Here’s the centrum of sacral 4 of Haplocanthosaurus CM 879 in right dorsolateral view; anterior is to the right.

Here’s the same thing annotated (yeah, it does look a little like an Ent who is alarmed because his left eye has been overgrown by a huge nasal tumor). This vert has two sets of pneumatic features on the centrum: a big lateral fossa below the sacral rib articulation, presumably homologous with the same feature in S4 of the Diplodocus above; and a smaller dorsolateral fossa above and behind sacral rib articulation.

Unfortunately, CM 879 doesn’t tell us much about how these two sets of diverticula might have changed along the column. The centra of S1-S3 were not found, S5 lacks both sets of fossae, the first caudal has fossae both on the centrum, below the caudal rib, and low on the arch, and the second and subsequent caudals lack both sets of fossae. (I wrote a LOT more about pneumaticity in this individual in my 2009 air sacs paper, which is linked below.)

Working out how these diverticula change serially is a tractable problem. Someone just needs to sit down with a reasonably complete, well-preserved series that includes posterior dorsals, all the sacrals, and the proximal caudals–or ideally several such series–and trace out all of the pneumatic features. As far as I know, that’s never been done, but feel free to correct me if I’ve missed something. I’m neck deep in other stuff, so if someone wants that project, have at it. (If you happen to look into this, I’d be grateful for a heads up, so we don’t run over each other if I do get a yen to investigate further myself.)

References

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This is SUSA 515, a partial skeleton of Camarasaurus on display in the Museum of Moab. (SUSA stands for Southeastern Utah Society of Arts & Sciences.) It was described by John Foster in 2005.

I like this thing. The neural spines are blown off so you can see right down into the big pneumatic cavities in the dorsal vertebrae. And unlike the plastered, painted, and retouched-to-seeming-perfection mounted skeletons in most museums, this specimen reflects how most sauropod specimens look when they come out of the ground. With a few dorsal centra, a roadkilled sacrum, and some surprisingly interesting caudals, it puts me strongly in mind of MWC 8028, the Snowmass Haplocanthosaurus (another John Foster joint: see Foster and Wedel 2014).

Frankly, it doesn’t look like much: 17 centra and some odd bits of pelvis. Surely, with so many good Camarasaurus specimens in the world, this one couldn’t possibly have anything new to tell us about the anatomy of that genus. And yet, it has a couple of unusual features that make it worthy of attention. My colleagues and I are working on those things right now, and you’ll be hearing more about this specimen in the very near future.

References

In the first installment in this series (link), we looked at a couple of weird sauropod vertebrae with neurocentral joints that were situated either entirely dorsal or ventral to the neural canals. This post has more examples of what I am calling “offset” neurocentral synchondroses.

I decided it made more sense to refer to the synchondrosis as being offset, instead of referring to the neural canal as offset. Because the neural canal in all of these vertebrae is right where it pretty much always is, just dorsal to the articular surfaces of the centrum. In an adult, fused vertebra, there’d be no sign that anything unusual had ever happened. So I think it makes more sense to talk about the neurocentral joint having migrated dorsally or ventrally relative to the canal, rather than vice versa. If you know differently, or if these weirdos have been addressed before elsewhere and I’ve just missed it, please let me know in the comments!

Here’s a plate from Marsh (1896) showing caudal vertebrae of Camarasaurus (“Morosaurus” in O.C. Marsh parlance), which echo the Alamosaurus caudal from the first post in having the neurocentral joint almost entirely ventral to the neural canal. The neural arch here doesn’t just arch over the canal dorsally, it also cuts under it ventrally, at least in part.

This plate is also nice because it shows the relationships among the arch, centrum, and caudal ribs before they fuse. Here’s the caption, from Marsh (1896):

Here’s the preceding plate, Plate 33, with illustrations of an unfused Camarasaurus sacrum.

And its caption:

This plate not only shows how the sacral ribs fuse to the arch and spine medially, and to each other laterally (forming the sacrocostal yoke), it also shows a last sacral that is very similar to the aforementioned caudals in the position of the neurocentral joint. But interestingly that neurocentral joint offset only seems to be present in the last caudal sacral – the lower figure shows widely-separated neurocentral joint surfaces in the more anterior centra, indicating that the neural arches (not figured in this dorsal view) did not wrap around the neural canal to approach the midline. (I think we’re looking at S2 through S5 here, and missing a dorso-sacral.)

So now I’m freaked out, wondering if this neural arch wrap-around in the caudals is common to most sauropods and I just haven’t looked at enough juvenile caudals to have spotted it before. As always, feel free to ablate my ignorance in the comments, particularly if you know of more published examples. I’m a collector.

The neural canal of that last sacral also has a very interesting cross-sectional shape, like a numeral 8. I have some thoughts on that, but they’ll keep for a future post in this series.

jvp-fig-12

Fig. 14. Vertebrae of Pleurocoelus and other juvenile sauropods. in right lateral view. A-C. Cervical vertebrae. A. Pleurocoelus nanus (USNM 5678, redrawn fromLull1911b: pl. 15). B. Apatosaurus sp. (OMNH 1251, redrawn from Carpenter &McIntosh 1994: fig. 17.1). C. Camarasaurus sp. (CM 578, redrawn from Carpenter & McIntosh 1994: fig. 17.1). D-G. Dorsal vertebrae. D. Pleurocoelus nanus (USNM 4968, re- drawn from Lull 1911b: pl. 15). E. Eucamerotus foxi (BMNH R2524, redrawn from Blows 1995: fig. 2). F. Dorsal vertebra referred to Pleurocoelus sp. (UMNH VP900, redrawn from DeCourten 1991: fig. 6). G. Apatosaurus sp. (OMNH 1217, redrawn from Carpenter & McIntosh 1994: fig. 17.2). H-I. Sacral vertebrae. H. Pleurocoelus nanus (USNM 4946, redrawn from Lull 1911b: pl. 15). I. Camarasaurus sp. (CM 578, redrawn from Carpenter & McIntosh 1994: fig. 17.2). In general, vertebrae of juvenile sauropods are characterized by large pneumatic fossae, so this feature is not autapomorphic for Pleurocoelus and is not diagnostic at the genus, or even family, level. Scale bars are 10 cm. (Wedel et al. 2000b: fig. 14)

The question of whether sauropod cervicals got longer through ontogeny came up in the comment thread on Mike’s “How horrifying was the neck of Barosaurus?” post, and rather than bury this as a comment, I’m promoting it to a post of its own.

The short answer is, yeah, in most sauropods, and maybe all, the cervical vertebrae did lengthen over ontogeny. This is obvious from looking at the vertebrae of very young (dog-sized) sauropods and comparing them to those of adults. If you want it quantified for two well-known taxa, fortunately that work was published 16 years ago – I ran the numbers for Apatosaurus and Camarasaurus to see if it was plausible for Sauroposeidon to be synonymous with Pleurocoelus, which was a real concern back in the late ’90s (the answer is a resounding ‘no’). From Wedel et al. (2000b: pp. 368-369):

Despite the inadequacies of the type material of Pleurocoelus, and the uncertainties involved with referred material, the genus can be distinguished from Brachiosaurus and Sauroposeidon, even considering ontogenetic variation. The cervical vertebrae of Pleurocoelus are uniformly short, with a maximum EI of only 2.4 in all of the Arundel material (Table 4). For a juvenile cervical of these proportions to develop into an elongate cervical comparable to those of Sauroposeidon, the length of the centrum would have to increase by more than 100% relative to its diameter. Comparisons to taxa whose ontogenetic development can be estimated suggest much more modest increases in length.

Carpenter & McIntosh (1994) described cervical vertebrae from juvenile individuals of Apatosaurus and Camarasaurus. Measurements and proportions of cervical vertebrae from adults and juveniles of each genus are given in Table 4. The vertebrae from juvenile specimens of Apatosaurus have an average EI 2.0. Vertebrae from adult specimens of Apatosaurus excelsus and A. louisae show an average EI of 2.7, with an upper limit of 3.3. If the juvenile vertebrae are typical for Apatosaurus, they suggest that Apatosaurus vertebrae lengthened by 35 to 65% relative to centrum diameter in the course of development.

The vertebrae from juvenile specimens of Camarasaurus have an average EI of 1.8 and a maximum of 2.3. The relatively long-necked Camarasaurus lewisi is represented by a single skeleton, whereas the shorter-necked C. grandis, C. lentus, and C. supremus are each represented by several specimens (McIntosh, Miller, et al. 1996), and it is likely that the juvenile individuals of Camarasaurus belong to one of the latter species. In AMNH 5761, referred to C. supremus, the average EI of the cervical vertebrae is 2.4, with a maximum of 3.5. These ratios represent an increase in length relative to diameter of 30 to 50% over the juvenile Camarasaurus.

If the ontogenetic changes in EI observed in Apatosaurus and Camarasaurus are typical for sauropods, then it is very unlikely that Pleurocoelus could have achieved the distinctive vertebral proportions of either Brachiosaurus or Sauroposeidon.

apatosaurus-cm-555-c6-centrum-and-arch-united

C6 of Apatosaurus CM 555 – despite having an unfused neural arch and cervical ribs, the centrum proportions are about the same as in an adult.

A few things about this:

  1. From what I’ve seen, the elongation of the individual vertebrae over ontogeny seems to be complete by the time sauropods are 1/2 to 2/3 of adult size. I get this from looking at mid-sized subadults like CM 555 and the hordes of similar individuals at BYU, the Museum of Western Colorado, and other places. So to get to the question posed in the comment thread on Mike’s giant Baro post – from what I’ve seen (anecdata), a giant, Supersaurus-class Barosaurus would not necessarily have a proportionally longer neck than AMNH 6341. It might have a proportionally longer neck, I just haven’t seen anything yet that strongly suggests that. More work needed.
  2. Juvenile sauropod cervicals are not only shorter than those of adults, they also have less complex pneumatic morphology. That was the point of the figure at the top of the post. But that very simple generalization is about all we know so far – this is an area that could use a LOT more work.
  3. I’ve complained before about papers mostly being remember for one thing, even if they say many things. This is the canonical example – no-one ever seems to remember the vertebrae-elongating-over-ontogeny stuff from Wedel et al. (2000b). Maybe that’s an argument for breaking up long, kitchen-sink papers into two or more separate publications?

Reference

Wedel, M.J., Cifelli, R.L., and Sanders, R.K. 2000b. Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon. Acta Palaeontologica Polonica 45:343-388.

Wedel 2016 OMNH lecture flyer

Just a quick heads up for any SV-POW! readers within convenient striking distance of Norman, Oklahoma, this Wednesday, March 16. Like all of the lectures in the “Dinosaurs Past & Present” series at OMNH, this one is free to the public. I hope to see some of you there!

Back in 2012, when Matt and I were at the American Museum of Natural History to work on Apatosaurus” minimus, we also photographed some other sacra for comparative purposes. One of them you’ve already seen — that of the Camarasaurus supremus holotype AMNH 5761. Here is another:

diplodocus-sacrum-composite

(Click through for glorious 3983 x 4488 resolution.)

This is AMNH 3532, a diplodocid sacrum with the left ilium coalesced and the right ilium helpfully missing, so we can see the structure of the sacral ribs. Top row: dorsal view, with anterior to the left; middle row, left to right: anterior, left lateral and posterior views; bottom row: right lateral view.

As a matter of fact, we’ve seen this sacrum before, too, in a photo from Matt’s much earlier AMNH visit. But only from a left dorsolateral perspective.

When we first saw this, it didn’t even occur to us that it could be anything other than good old Diplodocus. And indeed it’s a pretty good match for the same area in the CM 84/94 cast in the Museum für Naturkunde Berlin (this image extracted from Heinrich Mallison’s beautiful giant composite):

img_4853-img_4886-v3-sm-sacrum

And the general narrowness of the AMNH sacrum says Diplodocus to me. But what is that expectation of narrowness based on? When I compared the AMNH specimen with Hatcher’s (1901) ventral-view illustration in his classic Diplodocus monograph, I had second thoughts:

Hatcher (1901: fig. 9). Inferior view of sacrum and ilia of Diplodocus carnegii (No. 94), one tenth natural size; bp, public peduncle; is, ischiadic peduncle; a, anterior end; p, posterior end.

Hatcher (1901: fig. 9). Inferior view of sacrum and ilia of Diplodocus carnegii (No. 94), one tenth natural size; pp, public peduncle; is, ischiadic peduncle; a, anterior end; p, posterior end.

That is a much wider sacrum than I’d expected from Diplodocus.

So what is going on here? Is Diplodocus a fatter-assed beast than I’d realised? I am guessing not, since my expectation of narrowness has been built up across years of looking at (if not necessarily paying much attention to) Diplodocus sacra.

So could it be that CM 94, the referred specimen that Hatcher used to make up some of the missing parts of the CM 84 mount, is not Diplodocus?

Well. That is certainly now how I expected to finish this post. Funny how blogging leads you down unexpected paths. It’s a big part of why I recommend blogging to pretty much everyone. It forces you to think down pathways that you wouldn’t otherwise wander.

References

  • Hatcher, Jonathan B. 1901. Diplodocus (Marsh): its osteology, taxonomy and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum 1:1-63 and plates I-XIII.

 

I’ve been taking a long-overdue look at some of the recently-described giant sauropods from China, trying to sort out just how big they were. Not a new pursuit for me, just one I hadn’t been back to in a while. Also, I’m not trying to debunk anything about this animal – as far as I know, there was no bunk to begin with – I’m just trying to get a handle on how big it might have been, for my own obscure purposes.

‘Huanghetitan’ ruyangensis was named by Lu et al. (2007) on the basis of a sacrum, the first 10 caudal vertebrae, some dorsal ribs and haemal arches, and a partial ischium. The holotype is 41HIII-0001 in the Henan Geological Museum. Lu et al. (2007) referred the new animal to the genus Huanghetitan, which was already known from the type species H. liujiaxiaensis (You et al., 2006). However, Mannion et al. (2013) found that the two species are not sister taxa and therefore ‘H.’ ruyangensis probably belongs to another genus, which has yet to be erected. Hence my use of scare quotes around the genus name.

Huanghetitan ruyangensis sacrum comparison

Here’s the sacrum of ‘H.’ ruyangensis from Lu et al. (2007: fig. 2). The original small scale bar is supposed to be 10cm. You know how I feel about scale bars (or maybe you don’t, in which case read this and this), but in this case the scale seems pretty legit based on limited measurements that are also given in the paper. I comped in the sacrum of Brachiosaurus altithorax FMNH P25107 from this post (many thanks to Phil Mannion for the photos!), and scaled it according to the max width across the second pair of sacral ribs, which Riggs (1904: p. 236) gives as 105 cm. The sacrum of ‘H.’ ruyangensis is a little bigger, but not vastly bigger. ‘H.’ ruyangensis had six sacrals to Brachiosaurus‘s five, so extra length is mostly illusory, whereas the extra width is mostly legit.

According to Lu et al. (2007), the anterior face of the first caudal vertebra in ‘H.’ ruyangensis measures 26.9 cm tall by 32 cm wide, and the centrum is 18.2 cm long. The same measurements in Brachiosaurus are 28 x 33 cm for the anterior face and 16 cm for the centrum length. It’s basically a tie.

What about the big rib? Lu et al. (2007) show a complete dorsal rib of ‘H.’ ruyangensis that is 293 cm long. That’s nothing to sniff at – the longest rib of Brachiosaurus, and the cause for the specific name altithorax (‘tall-bodied’), measures 274.5 cm, so the ‘H.’ ruyangensis rib is about 7% longer. But it’s not the longest rib known for any sauropod. As far as I know, that honor goes to a Supersaurus dorsal rib measuring 305 cm (Lovelace et al., 2008). The biggest Supersaurus caudal also blows away the caudals of both ‘H.’ ruyangensis and Brachiosaurus, with a anterior face 39 cm tall by 46 cm wide. But then diplodocids were all about that bass, so there’s not much point in comparing tail size with a titanosauriform if you’re trying to get a handle on overall body size. Still, the 35-40 ton Supersaurus shows that you can have 3-meter ribs without being anywhere near Argentinosaurus territory, mass-wise.

So what’s the verdict? ‘H.’ ruyangensis was a little bigger than the holotype of Brachiosaurus altithorax, but only by a few percent. It might have been about the same size as the XV2 specimen of Giraffatitan brancai. Or, who knows, it could have had completely different proportions and massed considerably more (or less). But on the current evidence, it doesn’t seem to have been one of the biggest sauropods of all time. I hope we get some more of it one of these days.

References