One of the most pervasive but subtle errors of the Jurassic Park series LINK is the idea that theropod hands kind of fold forwards and down as if they are about to slap their thighs in some entertaining dinosaurian Bavarian dancing routine. In fact the palms of the hands should face inwards as if about to give a nice round of applause. Theropods were clappers, not slappers.
This is pretty pervasive in the minds of the pubic from the iconic moment of terror-inducement to children as a Velociraptor opens a door. It’s interesting to note that people seem to have accepted this position of the manus as more or less de-facto correct without even thinking about it. I have recently done a bit of work on a dinosaur book for kids and I think every single theropod that was sent to me had slappy hands. Every single one I sent back and told them to reorientate them, because they were wrong and that they didn’t look like that in pretty much any theropod and then a week later the next one would come in and well, you can guess where the hands were.
We actually have good evidence from two very different sources that theropods could not put their hands in this position (well a few derived ones may have been able to approach it). Most obviously when we have good 3-D skeletons we can simply articulate the bones to see A) what their natural position was, and B) how well they could pronate the arm (that is rotate the lower arm at the elbow towards a slapping position, something humans are exceptionally good at). Secondly we can see that even when actually wanting to do something like support the weight of themselves which you might think you’d really want to use the flat of your hand, rather than just the edge a theropod still does not (or more likely therefore cannot) pronate the hand. This comes from a recently reported fossilised print of a resting theropod with nice prints for the edges of the hand.
I should add that as ever this is biology and well probably they could we really can’t be sure exactly how they folded their arms. Doubtless some were better at this than others and could be proper slappers if you like and of course even those which you might call a ‘true’ clapper, could still pronate a bit, but as a general rule of thumb this is portrayal is accurate.
So the next time you see a slap-handed theropod remember to clap. Hmmm, that sounds awfully like the last ‘advice to kids’ line from the end of an 80’s cartoon. I think I’d probably better stop about there.
PS Thanks to Jerry Harris, Andrew Milner and Corwin Sullivan for discussions on this one, a bit out of my normal range.