Look ma, no ventral bracing!
April 29, 2008
So, you’ll all recall the previous post where we looked at the absurdly broad neck base of the Upper Jurassic macronarian Camarasaurus. This time round we’re playing the same game, but looking up at the neck base of the diplodocoid Diplodocus, and again it is of course the Natural History Museum’s (London) mount of the Carnegie cast of D. carnegii (image © NHM). Note how elongate and narrow the centra are: the length-to-width ratio of sauropod cervical vertebrae has proved to be a useful character, and was formalised as the ‘EI’, or elongation index, by Paul Upchurch (1998). However, EI has also been used as centrum length-to-height by other sauropod workers (Wilson & Sereno 1998, Wedel et al. 2000), and this is the version we’re using here. The EI of Diplodocus is reasonable, ranging from 3.1 to 4.7 between C2 and C6, and with a maximum of 4.9 in C7, but it is exceeded by that of brachiosaurs (where it can be over 5.0 and even over 6.0), and – among diplodocoids – by those of Barosaurus, Australodocus and Supersaurus (where the EI ranges to an incredible 7.5). Erketu and a few other particularly long-necked taxa also have particularly high EIs. Note that the ventral surfaces of the centra are shallowly concave and lack any sort of midline ridge – these details are variable among sauropods, with some having flattened bases and some having low midline keels.
Finally for now, note also that the cervical ribs are not making contact with one another: a very basic observation which makes a mockery of the idea that the ribs somehow propped up the neck from underneath. Some sauropod workers have actually proposed this (Martin et al. 1998), in part because (I think) there seems to be an assumption among some scientists that bizarre products of evolution – like the incredible necks of sauropods – must have operated in bizarre and novel ways. That might sound like a reasonable position, but it is in fact countered by the evidence: so far as we can tell, sauropod necks worked much like those of other saurischian dinosaurs, and they were not off-the-scale whacky bizarre in terms of morphological innovation. More on this topic in the future, oh yes.
References
- Martin, J., Martin-Rolland, V. & Frey, E. 1998. Not cranes or masts, but beams: the biomechanics of sauropod necks. Oryctos 1, 113-120.
- Upchurch, P. 1998. The phylogenetic relationships of sauropod dinosaurs. Zoological Journal of the Linnean Society 124, 43-103.
- Wedel, M. J., Cifelli, R. L. & Sanders, R. K. 2000. Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon. Acta Palaeontologica Polonica 45, 343-388.
- Wilson, J. A. & Sereno, P. C. 1998. Early evolution and higher-level phylogeny of sauropod dinosaurs. Society of Vertebrate Paleontology Memoir 5, 68 pp.
Pleurocoelus: the birth of excellence
April 24, 2008
Othniel Charles Marsh, who was always careful to base all of his hundreds of new taxa on the best, most diagnostic material available (Alert: Sarcasm detected!), named Pleurocoelus nanus based on a handful of junenile sauropod vertebrae centra from the Arundel clays of Maryland (Marsh 1888). Here’s the dorsal. As you can see, it is loaded with unique features like big pneumatic fossae, which at the time were only known in all other sauropods (we have since found some with less pneumaticity in the dorsals, or none at all), and the absence of a neural arch, which is shared with any sufficiently immature vertebrate.
Here’s a cervical, which was not figured by Marsh (1888). These views are after Lull (1911:pl. 15), as modified by Wedel (2003:fig. 10); pfs stands for pneumatic fossa.
And a sacral, again from Marsh (1888).
To be fair, the criteria for “diagnosably distinct” in the 1880s were different than they are now. Wilson and Upchurch (2003) addressed this in their revision of Titanosaurus: as we find and describe more fossil taxa, characters that originally diagnosed small taxonomic groups (like species and genera) are often found to be more broadly distributed. For example, the original diagnosis of Titanosaurus ended up applying to almost everybody in the clade Titanosauria. It is conceivable that in the future we will discover an entire clade of xenoposeidonids with identical weird dorsals and all of their diagnostic characters elsewhere in the skeleton, and the longish list of weird characters that diagnose Xenoposeidon will turn out to be present in all xenoposeidonids. There’s not much we can do about this, other than to keep working, revisit old diagnoses from time to time and see if they need updating, and generally be nice about it.
I am cool with not being nice about Pleurocoelus, though, because of what happened later. But that’s a story for another post.
Note: In 2005 Carpenter and Tidwell sunk Pleurocoelus into Astrodon, which is totally cool by me, and which makes Astrodon the correct name for the poorly-known Arundel titanosauriform, just like Apatosaurus is the correct name for the Morrison diplodocine that is built like a brick outhouse. But in this series I am Telling a Tale about the Days of Yore, past tense, pre-2005, so I’m using Pleurocoelus.
References
- Carpenter, K., and Tidwell, V. 2005. Reassessment of the Early Cretaceous sauropod Astrodon johnsoni Leidy 1865 (Titanosauriformes). Pp. 78-114 in. Tidwell, V., and Carpenter, K. (ed.) Thunder-lizards: The Sauropodomorph Dinosaurs. Indiana University Press, Bloomington.
- Lull, R.S. 1911. Systematic paleontology of the Lower Cretaceous deposits of Maryland: Vertebrata. Lower Cretaceous Volume, Maryland Geological Survey, 183–211.
- Marsh, O.C. 1888. Notice of a new genus of Sauropoda and other new dinosaurs from the Potomac Formation. American Journal of Science, 3rd Series 35:89-94.
- Wedel, M.J. 2003. The evolution of vertebral pneumaticity in sauropod dinosaurs. Journal of Vertebrate Paleontology 23(2):344-357.
- Wilson, J.A., and Upchurch, P. 2003. A revision of Titanosaurus (Dinosauria – Sauropoda), the first ‘Gondwanan’ dinosaur genus. Journal of Systematic Palaeontology 1:125–160.
Off-topic: The Variety of Life
April 14, 2008
I’m going to exploit this site to post a (very rare) off-topic book recommendation. So here it is: The Variety of Life — a survey and a celebration of all the creatures that have ever lived, by Colin Tudge.
I’ve just finished reading this hefty book — 684 pages in the paperback edition — and I’ve found it fantastically invigorating. I’ve often bemoaned how stupidly over-specialised my zoological knowledge is: really, outside the realm of mid-to-posterior neosauropod dorsals, I am pretty darned hopeless, and Darren’s effortless mastery of pretty much every tetrapod group leaves me awestruck. Having come to the end of this whistle-stop tour of the whole of Biota — three domains, more kingdoms than you can shake a stick at, and hundreds of freakier lifestyles than I’d ever imagined — I’ve come to realise what a tiny and parochial corner of biology we inhabit here at SV-POW! towers.
The book is in two and a half sections. Part 1 consists of five chapters (90 pages or so) on the history and philosophy of biological classification, an outline of cladistic methodology and molecular biology techniques and a plea for a rather odd taxonomic approach that he terms “Neolinnaean Impressionism”, and which amounts to a PN-like naming of the nodes but with Linnean ranks arbitrarily imposed on some though not all of the nodes. While Tudge is not strongly attached to the idea that sister groups must have equal rank, he clearly has inclinations in that direction, resulting in several monogeneric “kingdoms” and some odd maneouvering towards the end of the book where he seems to consider Proboscidea and Coleoptera of equal importance for conservation purposes because they are both of rank “order”. *cough*. Well, let’s pass swiftly on.
Part 2 of the book, and by far its bulk, is the survey of all living creatures — 25 chapters covering Biota in 500-odd pages, broken down as follows: one chapter on how the old “two kingdoms” became “three domains”, one chapter briefly covering both Bacteria and Archaea, one on basal eukaryotes, one on fungi, a whopping eighteen on animals, and three on plants. Finally, part 3 is an “epilogue” concerning the need for conservation, the efficacy of various strategies and finally the reasons we should care.
Parts 1 and 3 have some interesting material, to be sure, but the survey is the heart of the book in every way. You can get some sense of how much ground it covers by reading the following paragraph from p. 430:
The Sauropodomorpha includes the Prosauropoda and the Sauropoda — the most famous examples of the latter being the huge herbivorous brachiosaurs of the Brachiosauridae, and Diplodocus of the Diplodocidae.
That’s it folks — that’s the entire coverage of sauropods. And it’s not that they get particularly short shrift, either: that’s how most groups are covered. Super-quick, very direct, bam, onto the next one. Because there is so much ground to cover.
So having read this, it’s not as though I particularly feel I have any real understanding of, say, cnidarians, “brown seaweeds” or sea-spiders. But at least I know they’re out there, and I know what it is that I don’t know. I feel richer and wiser (though also more aware of how stupendously ignorant I am) for having read it.
Obligatory Amazon links: UK and USA.
And finally, to keep the SV-POW! promise, here is a sauropod vertebra picture: but what is it? I’m not giving too much away if I say that it’s an NHM specimen (and therefore their copyright) — but who (apart from Matt and Darren) can tell me what it is?
The answer will follow in a week or two.
Your coccyx is contemptible
April 8, 2008
Those of you who have been paying attention to my recent posts will have pretty much known this was coming. I’d hate to disappoint you, so here it is:
What you’re looking at here is the first caudal vertebra (i.e. the first tail bone) of Apatosaurus ajax, the newish specimen NSMT-PV 20375 described by Upchurch et al. (2005). The drawings are all from the plates at the end of that lavishly illustrated paper: all I’ve done is composite them. The top row, from left to right, shows the vertebra in anterior, left lateral, posterior and right lateral views. Below the left lateral view is a dorsal view, with the front pointing to the left (as in the left lateral view).
Oddly, the size of this vertebra doesn’t seem to be stated in the paper, but two lines of evidence suggest that it’s about 65 cm in total height. First, measuring the caudal on the skeletal reconstruction that is the frontispiece, and comparing with that figure’s 1m scale-bar, yields a height of 64 cm; second, the neural spine’s height (measured from the ventral margin of the poztzygapophyses) is given in Table 9 as 392 mm, and that extrapolates, using the posterior view figure, to a total height of 665 mm. So about 65 cm, then.
The caudal vertebrae of diplodocids such as Apatosaurus, Diplodocus and Barosaurus are unusually complex for sauropods, having been somewhat “dorsalised”, i.e. taking on some of the complex morphology of posterior dorsals rather than being the rather dull round-centrum-with-a-flat-spine-on-top affairs you get hanging off the rear end of brachiosauruids. You’ll notice that the lateral processes, or “caudal ribs”, take the form of tall, broad plates, so that the middle part of the vertebra is trapezoidal in anterior view. This is as different as can be from the boring, stick-like caudal ribs of Brachiosaurus. (What actually are caudal ribs? So far as I can tell, amazingly, no-one really knows. They might be homologous with the diapophysis of dorsal vertebrae, or with the parapophysis, or perhaps both of them fused, or one or both fused with an actual rib.)
Oh, yes: also in the picture is your coccyx, that is, the four or five bones that make up your vestigial tail. It is, needless to say, contemptible. It’s surprisingly hard to find a reference for how big it should be, but by cross-scaling from illustrations of whole human skeleton and sacra, I’ve come up with a figure of about 2.5 cm, and that’s what I’ve used here. If you want to compare your tail with Apatosaurus‘s, remember that Apato had about eighty caudals: they diminish in size posteriorly, of course, but they do stay about the same anteroposterior length for much of the tail. In fact, diplodocids have tremendous tails, something like half the entire length of the entire animal. One of my long-standing bugbears is that the biomechanics of sauropod tails gets almost no attention (except for speculations about whip-cracking) compared with the love and care lavished on their necks. One day, one of us might do something about that.
That concludes our short but humiliating series of abuse directed at your frail human body. I’ll have to come up with something else next time it’s my turn. Hope you’ve enjoyed the ride.
Finally, good news for everyone who was intererested in Matt’s Aegyptosaurus post: he’s made a PDF of Stromer 1932 so you can see that mystery vertebra for yourselves.
Bibliography
- Upchurch, Paul, Yukimitsu Tomida, and Paul M. Barrett. 2005. A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurassic) of Wyoming, USA. National Science Museum Monographs No.26. Tokyo.
Aegyptosaurus lost
April 1, 2008
There seems to be some kind of bell curve associated with sauropods. We get lots of medium-sized ones, but very few babies, mostly disarticulated bits, and very few super-immense ones, which are also mostly disarticulated bits. Puertasaurus is known from two vertebrae. Sauroposeidon is known from 3.5. The holotype of Hudiesaurus is a single vertebra; the referred forelimb is not from the same individual or the same quarry, and there’s no particularly good reason to think it’s from the same taxon. Argentinosaurus is known from a handful of vertebrae and a smaller handful of limb bones.
Bruhathkayosaurus was evidently pretty big, but there’s only one paper on it so far, illustrated with very, um, simple line drawings of some bones and blurry non-orthogonal photos of others. More on that one later, maybe, although none of the preserved elements appear to be verts so it is a little outside our bounds. In any case, Bruhathkayosaurus may be the biggest sauropod known from remains that still exist (may be; by now you should know how much uncertainty that covers).
Then there are the really frustrating ones: the gigapods for which we have no remains left at all. What’s really frustrating is that these might be the biggest of all! The best known of our absent friends is Amphicoelias fragillimus, which Darren has discussed before and which we ought to cover here in the future. The genotype of Amphicoelias is the Diplodocus-sized A. altus, and it’s still around, or at least it was as of October 2006 because that’s when I took the photo above. No one knows what happened to the A. fragillimus vert. It might have gotten lost, or simply crumbled to dust since it was very fragile and it was excavated before the use of consolidant glues became widespread in paleontology (Carpenter 2006).
In the case of Aegyptosaurus, we know exactly what happened to the type material: it was blown to hell and gone, along with the original material of Spinosaurus and Carcharodontosaurus, when Allied bombs hit the museum in Munich in 1944. The type material of Aegyptosaurus baharijensis consisted of some caudal vertebrae and limb and girdle bones from an animal of unspectacular size. But in a curious parallel with Amphicoelias, there is–or rather was–a larger specimen, possibly one that represented a distinct species.
Near the end of the paper in which he described and figured A. baharijensis, Stromer (1932a) mentioned “ein Wirbel eines anderen noch größeren sauropod”, which he said would be described later. I’ll end the suspense right now: it wasn’t. Later that year Stromer published a short paper (1932b) on the sauropod fauna of Africa. That paper also did not describe any giant vertebrae in any detail, but it did include this photo (below).
The original caption reads “Professor Ernst Stromer neben einem Wirbel einer neuen Art von Aegyptosaurus“–Professor Ernst Stromer next to a vertebra of a new species of Aegyptosaurus. Presumably Stromer intended to provide a full description soon after, but it was not to be. The next summer at Bahariya Oasis he was attacked by a crocodile and nearly lost his left leg. In the end Stromer recovered, but only after repeated surgeries and many painful months spent learning to walk again. The wound effectively killed his professional career. Although he lived until 1952, his 1934 paper on Bahariasaurus was his last paleontological contribution. Almost all of the Bahariya Oasis collection was lost to science in 1944, but science lost Stromer himself almost a decade earlier.
So what about that vert? It’s clearly a posterior cervical. Stromer’s left hand is resting on the rib, which is awfully short and awfully high up on the centrum, which indicates that the vertebra is from near the base of the neck. There are other interesting features as well–note the hint of a keel on the bottom of the centrum, which is usually only found in fairly basal sauropods, and the ridges above the postzygapophyses, which put me in mind of Mamenchisaurus.
Also, I suppose you’ll have noticed that the vertebra is freakin’ immense. Frustratingly, neither Stromer nor the vert appear in their entirety, and neither are shown from an orthogonal angle (perils of using a portrait to try to do science, I know). Still, we know that Stromer was a tall man. Werner Janensch once playfully described him as “die bärtige Bohnenranke”–the bearded beanstalk. No one seems to have written down his exact height, and we’re missing his feet in this photo anyway, but from contemporary descriptions he seems to have been several inches over 6 feet. The diameter of the cotyle seems to be about the same as the distance between his shoulder and wrist, which is a good 2 feet in me and I’m only 6’2″. Assuming–well, you know–that would give a cotyle diameter of about 60 cm, which is just appallingly large. The cervico-dorsal vertebrae of the HM SII specimen of Brachiosaurus brancai are about 3/4 that big. Imagine B. brancai scaled up by a third.
It’s a cool thought, but that’s all it is. We don’t know exactly how tall Stromer was. We don’t know how much the vertebra might be foreshortened in this photo. It wouldn’t take much to get our imaginary monster sauropod downsized into being merely interesting instead of completely flabbergasting. And the specimen itself is literally history.
Farewell, Aegyptosaurus sp. We hardly knew you.
References
- Carpenter, K. 2006. Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus Cope, 1878. New Mexico Museum of Natural History and Science Bulletin 36, 131-137.
- Stromer, E. 1932a. Ergebnisse der Forschungsreisen Prof. E. Stromers in den Wüsten Ägyptens. II. Wirbeltierreste der Baharîje-Stufe (unterstes Cenoman). 11. Sauropoda. Abhandlungen der Bayerischen Akademie der Wissenschaften Mathematisch-naturwissenschaftliche Abteilung, Neue Folge 10:1-21.
- Stromer, E. 1932b. Die sauropod Fauna Afrikas und seine biogeographical Bedeutung. Monatsberichten der Deutschen Geologischen Gesellschaft 1932:85-91.
UPDATE
Okay, I’m pulling the plug on this one. It’s an April Fool’s Day post. Many of the biographical details about Stromer are just made up–he didn’t lose his leg in a crocodile attack, he did keep publishing after 1934, the giant Aegyptosaurus specimen is a Photoshopped cow vert. The ref for Stromer (1932b) is entirely fake–he never published a paper with that title. The fake paper was “supporting evidence” for the joke, and incorrect biographical details were tells that it was a sham. I’m telling all now because people are starting to look for the real Stromer (1932b), and although the joke had a good run, I hate wasting people’s time.
Sauropod Vertebra Picture of the Week 