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.

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Needless to say, one of the things I love most about Paco’s Brontomerus artwork is that it’s a rare and welcome example of the much neglected Sauropods Stomping Theropods school of palaeo-art.

When I reviewed the examples I know of, I was a bit disappointed to find that they number only five.  Here they are, in chronological order.

First, we have this gorgeous sketch by Mark Hallett, showing Jobaria (here credited as “unnamed camarasaurid”) quite literally stomping on Afrovenator:

To the best of my knowledge, this has never actually been published — I found it on Dave Hone’s Archosaur Musings, in the interview with Hallett.  Mark tells me that this was a concept sketch of possible main art for Paul Sereno’s North African dinosaur article, Africa’s Dinosaur Castaways in the June 1996 issue of National Geographic (Sereno 1996) — three years before Jobaria was described[1] (Sereno et al. 1999); but for some inexplicable reason, it wasn’t used.

It seems incredible to think that there was no published, or even completed but unpublished, sauropod-stomping-theropod art before the mid-1990s, but I’ve not yet found any.  I thought that Bakker might have come up with something in The Dinosaur Heresies (Bakker 1986) or The Bite of the Bronto (Bakker 1994); but I flipped through both and I don’t see anything relevant.  Anyone know of anything earlier?

The next entry on my list is Luis Rey’s striking Astrodon, carrying away a raptor that bit off more than it could chew.

This appeared in Tom Holtz’s outstanding encyclopedia (Holtz 2007), which I highly recommend for every interested layman, including but not limited to bright kids.  The image also turned up, with Luis’s permission, in the publicity for Xenoposeidon — notably in The Sun, one of Britain’s most downmarket, lowest-common-denominator tabloids, where it was a pleasant surprise indeed.

I just love the expression on the raptor’s face.  He’s going HOLY CRAP!, and his buddies are all like, Hey, dude, c’mon, we were only playing!  But Astrodon‘s all, Nuh-uh, you started this, I’m going to finish it.

Next up, and a year, later, we have this moody just-going-about-my-business Camamasaurus, squishing theropod eggs, nests and babies in a casual sort of way, as though he’s saying “Well, you should have got out of my way”:

As it happens, this one was done for me, by Mark Witton.  It was intended as an illustration for a “Fossils Explained” article that I was going to do for Geology Today on the subject of (get ready for a big surprise): sauropods.  In fact, I am still going to do it.  But since it’s been two and a bit years since I got the go-ahead from the editor, I’m hardly in a position to complain that Mark gave the image to Dave Martill and Darren when they suddenly needed artwork to publicise the findings of their Moroccan expedition.  (Since then, the Mail seems to have re-used this picture pretty much every time they have a story about dinosaurs — even when that story is complete and utter crap.)

I don’t mind too much about this Witton original being whisked away from me, because shortly afterwards Mark went on to provide me with a much better piece — the beautifully wistful Diplodocus herd scene that we used in the publicity for our neck-posture paper.

And, amazingly, that brings us up to date.  The next relevant artwork that I know of was Paco’s glorious Brontomerus life restoration, which you’ve already read all about.  Just to vary things a bit, this is the second of the two renders — the one that wasn’t in the paper itself:

So is that the end of the story for now?  Happily, not quite.  Emily Willoughby produced this alternative Brontomerus restoration on the very day the paper came out!

I’m not going to claim that this is close to the quality of the other four pieces in this article, but you have to admire the speed of the work.  Emily wrote most of the initial Wikipedia entry for Brontomerus, and produced this picture to illustrate it.  At first when I saw this, I thought Emily had misunderstood the paper as indicating powerful retractors, so that the drawing had Brontomerus kicking backwards like a horse. But when I looked closely I realised it’s kicking outwards, thanks to the enlarged abductors. Neat.

A question and a challenge

I’d like to end this post with a question and a challenge.  First, the question: what other pieces of palaeoart have I missed that feature sauropods handing theropods their arses?  There have to be others — right?

And the challenge: I’d love it if those of you who are artists were to fix this terrible hole in the fabric of reality?  I’d love to see new and awesome art on the timeless theme of sauropods stomping theropods.  How about it?  If any of you have influence with the Art Evolved people, you might try seeing whether you can get them to join in the challenge.  It would be awesome to see a whole new crop of these pieces!

References

  • Bakker, Robert T.  1986.  The Dinosaur Heresies: New Theories Unlocking The Mystery of the Dinosaurs and Their Extinction.  Morrow, New York.  481 pages.
  • Bakker, Robert T.  1994.  The Bite of the Bronto.  Earth 3 (6): 26-35.
  • Holtz, Thomas R., Jr., and Luis V. Rey.  2007.  Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House, New York.  432 pages.
  • Sereno, Paul C.  1996.  Africa’s dinosaur castaways.  National Geographic 189(6):106-119.
  • Sereno, Paul C., Allison L. Beck, Didier. B. Dutheil, Hans C. E. Larsson, Gabrielle. H. Lyon, Bourahima Moussa, Rudyard W. Sadleir, Christian A. Sidor, David J. Varricchio, Gregory P. Wilson and Jeffrey A. Wilson.  1999.  Cretaceous Sauropods from the Sahara and the Uneven Rate of Skeletal Evolution Among Dinosaurs.  Science 282:1342-1347.

Footnotes

[1] If you want to call it that.

Welcome to another episode of the ground-breaking and wonderful Sauropods of 2008 series. Yay! As I’m fond of pointing out, new dinosaurs do not only come from China, or South America: Europe continues to yield surprises. Tastavinsaurus sanzi Canudo et al., 2008 is from the Lower Cretaceous (Aptian) Xert Formation of Spain, and the holotype specimen is pretty good, including dorsal, sacral and caudal vertebrae, ribs, chevrons, and material from the pelvis and hindlimbs (we’ve previously mentioned it here, and figured some of it here). Evidently, only the hindquarters of the animal were preserved. But they’re in good shape, and preserve numerous unique characters: in fact 19 autapomorphies are identified, which is a pretty impressive number and indicates either that Tastavinsaurus was a highly disparate sauropod, or that the morphology of its close friends and relatives is but scrappily known (I have to say that the former possibility looks more likely).

Some of these autapomorphies are in the vertebrae. On the posterior surfaces of their neural spines, the antero-posteriorly short, opisthocoelous dorsal vertebrae sport two small accessory laminae that emerge from the base of a very wide, chunky looking postspinal process. Of more general interest (perhaps) is that the dorsal centra contain ‘big prismatic tubes linked together by slender walls [that exhibit] a honeycomb pattern in cross-section’ (Canudo et al. 2008, p. 713). The ‘honeycomb pattern’ sounds something like somphospondylous texture, but the authors note that the condition present in Tastavinsaurus is distinct, and perhaps represents a new type of pneumatic pattern. Frustratingly, they don’t illustrate the internal texture, so we’re left guessing.

Tastavinsaurus_fourth_caudal_vert

The caudal vertebrae of Tastavinsaurus are not all that different from those of macronarians like Camarasaurus and Brachiosaurus: in the proximal caudals, the centra are wider than they are long, the proximal vertebrae have slightly procoelous centra, and the neural spines are ‘club-shaped’ [proximal caudal above from Canudo et al. (2008), fig. 7]. The more distal vertebrae – those from the 15th position onwards – are slightly amphicoelous. One weird little feature on the distal caudals is a small, centrally placed convexity on both the anterior and posterior articular faces of the centra (see pics below). As Canudo et al. (2008) note, Cedarosaurus and Pleurocoelus nanus both have this as well (Tidwell et al. 1999) [distal caudal below from Canudo et al. (2008), fig. 8].

Tastavinsaurus_19th_caudal_vert

The rest of Tastavinsaurus suggests that it would perhaps have superficially resembled a cross between Camarasaurus and Brachiosaurus. Its ilium looks like a dorsally stretched version of the ilium of Brachiosaurus and, indeed, in general character the specimen would appear to be a brachiosaur-grade titanosauriform. With pneumatic ribs, a lateral bulge on the femur, and caudal vertebrae that have anteriorly positioned neural arches, the rest of Tastavinsaurus agrees with this classification, and in their phylogenetic analysis, Canudo et al. (2008) found Tastavinsaurus to fall within Somphospondyli within Titanosauriformes, and within this clade to be the sister-taxon of Venenosaurus from Utah. If this is correct it weakens the proposal that six sacral vertebrae are a synapomorphy of Somphospondyli (Wilson & Sereno 1998), for Tastavinsaurus only has five.

Well, yet again I’ve done my best to concentrate on CAUDAL vertebrae, given that we have an obvious (and understandable) bias towards cervicals and dorsals. Someone has to speak up for tails. For previous instalments in the Sauropods of 2008 series please see the articles on Eomamenchisaurus, Dongyangosaurus, and Malarguesaurus.

References

Canudo, J. I., Royo-Torres, R. & Cuenca-Bescós, G. 2008. A new sauropod: Tastavinsaurus sanzi gen. et sp. nov. from the Early Cretaceous (Aptian) of Spain. Journal of Vertebrate Paleontology 28, 712-731.

Tidwell, V., Carpenter, K. & Brooks, W. 1999. New sauropod from the Lower Cretaceous of Utah, USA. Oryctos 2, 21-37.

Wilson, J. A. & Sereno, P. C. 1998. Early evolution and higher-level phylogeny of sauropod dinosaurs. Society of Vertebrate Paleontology Memoir 5, 68 pp.

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

It is a strange fate that we should suffer so much fear and doubt over so small a thing.

Such a little thing….

Prepare yourselves, true believers. Pleurocoelus is coming!