Thursday, 5 March 2009

How We Know

I used to listen to Radio 2 in the morning. The breakfast show was, and still is, presented by "national treasure" Terry Wogan. The 8:00am news bulletin was always where the big palaeontology discoveries were reported, usually in the "and finally" slot. Invariably, immediately following this, Terry would, with absolute incredulity, complain: "How do they know?".

And "How do they know?" is a question palaeontologists often have to deal with. You can explain the scientific method all you like, about testing hypotheses, observation, interpretation and conclusion, but knowledge is a weird concept, and philosophically we will never know about dinosaurs the way we know about pure mathematics.

But sometimes we can get a bit closer. Until a few years ago, most constructions of theropod dinosaurs showed them with palms facing downwards, or ventrally. A couple of studies of the wrist suggested that, in fact, theropods held their arms such that the palms of their "hands" faced towards each other - a palms-medial manual posture. Or think of it another way (as commonly quoted in the last few days): holding the basketball, not dribbling it.

With anything a little abstract (or at least abstract to the general public) like functional morphology, it's hard to avoid the "How do they know?" comments. So it's nice to have other evidence to back up one's conclusions. Which is where the really cool dinosaur above comes in.

The Dinosaur Discovery Site at Johnson Farm, St George, UT, is home to some of the most impressive dinosaur tracks I have ever seen (see a depressingly young-looking Ethical Palaeontologist at Johnson Farm back in 2005):

And the palaeontologists that work with and for the Site have made a whopping discovery. The trace of a crouching theropod at rest with its forelimbs on the substrate. Firstly this is awesome because it shows an Early Jurassic theropod in a bird-like squat. Secondly this is even more awesome because the forelimbs are resting pinkie-side down. This dinosaur is holding the imaginary basketball.

Spot the red outlines in the diagram above right, labelled "lm" for "left manus" and "rm" for "right manus". It also looks as though this is another example of Neffra Matthews' excellent work on digitising trackways with photogrammetry, but I confess I have only had time to scan the paper so far.

So we have prints made by an actual living dinosaur (at the time, obviously) confirming the functional morphology work already carried out. There is the caveat that the functional morphology work has only been done on Late Jurassic and Cretaceous theropods, and we could really do with some good Early Jurassic functional morphology, which would of course require some good Early Jurassic forelimbs. But I don't want to detract from just how exciting it is to find a resting trace of a dinosaur, not least one that can give us so much information. Nice work.

Milner, A.R.C., J.D. Harris, M.G. Lockley, J.I. Kirkland, N.A. Matthews. 2009. Bird-Like Anatomy, Posture, and Behavior Revealed by an Early Jurassic Theropod Dinosaur Resting Trace. PLoS ONE 4(3): e4591. doi:10.1371/journal.pone.0004591

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