A few more words on distortion

I wrote recently about the ways in which bones can be distorted and modified as fossils when compared to their original shape. And here is an example of that, a Pteranodon metacarpal photographed in the Oxford Museum. Two different things are clearly evident here and perhaps a third.

First off you can see the crushing that has taken place by all the little fragments and breaks along the middle of the bone. In particular there seems to be a crack running the whole length of the midline. Since pterosaur bones are generally hollow then the bone would expect to sort of fold in on itself and crack and break down the middle as it caved in under pressure. This certainly appears to be in evidence.

Secondly the bone seems to have twisted a little. The bone is seen at an angle somewhere between lateral and ventral view, but the condyles (the articulating bits at the ends) don’t seem to quite line up right. This could be supported by the fact that towards the ends, the broken parts are more concentrated in the upper right and lower left part of the bone. This has undergone a bit or torsion along the midline.

Finally, this might have been flattened a bit. Sure it’s crushed, but the shape might still be right, but I’m not sure. Based solely on eyeballing it, this looks wider than it should be for its length. This of course can be checked with a few simple measurements and proportions based on a good and uncrushed specimen, but if I was going to describe this bone that’s something I’d be looking to check.

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