Dinosaur farts and global warming – a crude analysis

Dinosaurs and farting. Two of mankind’s favourite things. Put them together, and apparently that warrants a scientific publication. A new study has attempted to forge a correlation between sauropod dinosaurs, their gassy output, and global warming during the Jurassic and Cretaceous periods. Naturally, being a bit obscure, it’s received great attention in the media. The less-than-two-page report, however, is pretty devoid of actual science, and is the kind of analysis that I’d expect from an undergraduate. A bad undergraduate.

The amount of times statements are preceded by ‘could have’ ‘suggests’, ‘estimates’, ‘likely’, etc. is an immediate trigger for concern. There’s nothing actually concrete in the paper. There is a hypothetical link between, er, biomethane production and global warming (it’s happening right now, actually – see cows), but there’s a way to approach this hypothesis: with scientific rigour.

The initial research concept is flawed. As most people know, dinosaurs consist of three major lineages: the herbivorous sauropodomorphs, the mostly-hypercarnivorous theropods, and the herbivorous ornithischians. So when looking at the methane output of herbivores, and you exclude a major group, just because they weren’t as big, you’re making a pretty big mistake. Especially when you consider the biological assumptions that were made regarding sauropods (they had digestive systems similar to modern ruminant herbivores) are actually more likely to have been applicable to ornithischians.

The methods applied were pretty naff too. The calculations are ridden with assumptions, and grossly oversimplify what intrinsically requires a more detailed study. Sauropod biomass is based on raw specimen estimates, based purely on the Upper Jurassic Morrison  Formation. Well known as a dinosaur ‘graveyard’, containing near-unparalleled quantities of dinosaur bones, this is pretty much the worst proxy that could have been used. Considering that sauropod diversity patterns are quite well established, this would have been a far more accurate proxy to use.

The next bit made me cringe. Sauropods were pretty frickin’ huge. So when estimating methane outputs based on modern organisms, you use at least something that’s vaguely comparable, right? Nope. You use guinea pigs, rabbits, and tortoises. I shit you not, these are the ecological analogues used in terms of fart-volume, or whatever you want to call it. The assumption is made that because the outputs are similar between these three, it holds true for every organism in the animal kingdom, ever. Methane emissions are assumed therefore to be insensitive to body mass, and also every other digestive parameter out there. As well as this theory of “evolution” (heard of it?).

There are a couple more terrible assumptions too. Vegetation area is assumed not just to be equivalent to land area, but also equivalent to sauropod number, globally, during the entire Jurassic and Cretaceous. No. I had expletives annotated all over the paper by this point; it was a bit too much.

I couldn’t resist making one of these..

So yeah, it wasn’t science. Sorry guys. It was a neat story, backed up by some pretty poor empirical analysis and speculative theory. Ten references just doesn’t cut it for a story of this magnitude, even if the mighty Marcus Clauss is reviewing it (I’m surprised such an awesome ecologist let his name be put anywhere near this). The lack of understanding of space and time is worrying, as well as a disregard for ornithischians (which are everyone’s favourite dinosaurs, right?), which are the more-likely culprits of mass-methanic expulsion, is somewhat worrying. How about getting a temperature curve for the Mesozoic, and attempting to correlate it with species diversity through time? Pretty sure a paper came out doing just that recently, without making such wild speculation.

If I haven’t gassed enough, here’s more slightly-less-critical analysis of the study:

New Scientist, PZ Myers, Science Daily, National Geographic [check out the URL for this one..]

A glitch in the [publishing] matrix?

Cretaceous Research is a journal published by the notorious for-profit publisher Elsevier (see articles on this blog). Tonight however, they have blessed us with a wealth of new research through their RSS feed (albeit, paywalled for the 99%), a lot including everyone’s favourite vertebrates, the dinosaurs. This is an inordinate amount of publications for K-Research (there were about 50 in total, and the same for Palaeo-3, also published through Lolsevier).

Could this be a glitch in the system? A way of attempting to appease those who most strongly oppose Elsevier’s business model? (Mike Taylor of SV-POW (amongst others) has been one of the strongest and most vocal opposers against Elsevier, and is a bona fide vertebrate palaeontologist [by day..]). A mystery indeed. Or, it could just be a chance to absorb some great palaeontology research!

Neo, the manifestation of Open Access

Either way, the latest published through Cretaceous Research includes: Alvarezsaurids and eggs from Patagonia, ceratopsids from Canada, marine reptiles from Chile, arthritis in birds, the world’s largest toothed pterosaur, another pterosaur from China, a Spanish sauropod, a new pliosaur from Utah, a new avian ichnotaxonanother Sauropod from Patagonia, a new ornithopod, and a tyrannosaurid from Uzbekistan! Wow. There’s more, including frogs, beetles, lizards, and rocks, but you can find them hanging around these bad boys.

Edit: Looking at the journals, it appears that what Elsevier have done is mistakenly allow access to both April and June’s editions through advanced online publication. Cheers!

Obviously *none* of these paywalled papers are available upon request.. (jon.tennant.2[at]gmail.com )

Evolution in the Reconstruction of Diplodocus

Diplodocus  has always held a significant position in the hearts of dinosaur palaeontologists, as it was one of the very first genera to ever be formally recognised and described. Following, are some images and attempted reconstructions from Hutchinson (1917), and by comparison some excellent recent research by Taylor et al. (2009) on posture in Diplodocus carnegiei (or carnegii). I just figured it would be cool to show how mechanical interpretations and life reconstructions had changed over the years, since from dinosaurs were first mounted to now where more complex biomechanical modelling procedures are being utilised.

Mounted skeleton model of Diplodocus carnegiei in the Reptile Gallery at the British Museum of Natural History, Hutchinson (1917) (click for larger image)

The following is a model reconstruction made from plaster based on the above skeleton. The tail rests on the ground, the neck is concave downwards and held-sub-horizontally, and the limbs are situated laterally to the trunk. Hutchinson (1917) explicitly says that despite this odd arrangement, Diplodocus did not crawl around on the ground like a lizard or crocodile.

Model of Diplodocus carnegiei, as restored by Hutchinson (1917). Try and ignore that it's head looks like a duck.. (click for larger image)

Following the above reconstruction, there is a simple reconstruction of the pelvic girdle and hind-limb provided. The femur and the tibia/fibula are perpendicular, with the pes also perpendicular to that to rest on a substrate. It pretty much looks like the ischium gouged a furrow whenever the animal tried to walk in this reconstruction.

Pelvic girdle and hindlimb of Diplodocus carnegiei in posterior (caudal) aspect, Hutchinson (1917) (click for larger image)

By comparison, more recent reconstructions are quite different. The following is just one of many illustrations by the talented Scott Hartman (follow @skeletaldrawing on Twitter). Note the distinct differences in posture: the legs are held vertically under (and slightly lateral) to the trunk, elevating the main body. Accordingly, the neck and tail both become more horizontal, acting as respective cantilevers with respect to the main body and the centre of gravity. Much more detail regarding stance and posture can be found on the wonderful SV-POW blog here, and in many formal publications.

Diplodocus carnegiei, based on specimen CM 84, Copyright: Scott Hartman (click for larger image)

Following on from reconstructions like above, the next step is to reconstruct the range of motion to discern possible ecological functions of various skeletal elements and domains. This has been done rather successfully by H. Mallison with Plateosaurus (Part 1 and Part 2). Hutchinson (1917) attempted a very rudimentary interpretation of this, as shown below.

Simplified illustration of the functional domains in Diplodocus carnegiei showing articulation points (above), and the range of humeral motion (below), Hutchinson (1917)

Yeah, ok, it’s pretty basic. Some progress has been made in this field with sauropods however, notably that from Taylor et al. (2009) with regards to Brachiosaurus brancai, as shown below (edit: the Tendaguru Brachiosaurus brancai is now regarded as Giraffatitan brancai, Taylor, 2009; see comment below). Obviously Brachiosaurus is not Diplodocus, but it illustrates the point nicely.

Reconstructions of Brachiosaurus brancai in a drinking (left) and browsing (right) posture (Taylor et al., 2009) (click for larger image) Edit: Note that these are not 'actual life poses', but examples of 'what if' deviations from a previously suggested 'neutral' model (see comment below).

Digital reconstruction is proving to be a pretty useful tool in imaging and interpreting life positions of dinosaurs and other extinct organisms. More recently, vertebrate palaeontologists, combined with mechanical modellers and zoologists have began to map muscles on to these digital skeletons using modern analogues and the ‘extant phylogenetic bracket‘ theory, to gain a significantly more detailed reconstruction and make more valid interpretations about extinct archosaur mechanics.

As computing technology has developed, palaeontologists have kept pace and are finding ever more elaborate methods to aid in understanding the mechanics, physiology, and ecology of extinct organisms. It’s an exciting field, with lots of promise for the future!

Note: I feel like a tit. Spent a whole year working/studying in the NHM London, and don’t have a single photo of the focal Diplodocus specimen there, Dippy. Oops.

Bates, K. T., Maidment, S. C., Allen, V. and Barrett, P. M. (2012) Computational modelling of locomotor muscle moment arms in the basal dinosaur Lesothosaurus diagnosticus: assessing convergence between birds and basal ornithischians, Journal of Anatomy, doi: 10.1111/j.1469-7580.2011.01469.x

Mallison, H. (2010) The digital Plateosaurus I: body mass, mass distribution and posture assessed using CAD and CAE on a digitally mounted complete skeleton, Palaeontologia Electronica, 13.2.8A

Mallison, H. (2010) The digital Plateosaurus II: an assessment of the range of motion of the limbs and vertebral column and of previous reconstructions using a digital skeletal mount, Acta Palaeontologica Polonica, 55(3), 433-458

Taylor, M. P., Wedel, M. J. and Naish, D. (2009) Head and neck posture in sauropod dinosaurs inferred from extant animals, Acta Palaeontologica Polonica, 54(2), 213-220