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..]