I love it when this happens.
I made a mistake here earlier today, and within just a few hours, I am able to correct it. So what you are about to read here has been thoroughly rewritten to reflect the latest thinking.
Earlier I misidentified what looked like a too gracile mandible (relative to the other skull parts) on the pterosaur, Sercipterus (Figs. 1-3), as a tibia and fibula. Here is the illustration in which I made the mistake (Fig. 1). And made a further mistake by calling out the original interpretation as an error.
At the time I overlooked the left mandible. It’s easy to do. There’s not much that makes it look like a mandible. The back half is all that is preserved. The left mandible appears to be a little deeper, which it needs to be according to phylogenetic bracketing.
This is the key.
Allthough the fossil had been thoroughly stirred during preservation so that nothing is where it was in the living pterosaur, there are two bones that are indeed in their original configuration: the two posterior mandibles (Fig. 2, in pink). How can this be??
Restoration of the missing parts clears up all the confusion.
When you extend the lines of the posterior mandible, the anterior portion becomes plainly visible. Now we have a mandible that is the proper length for the skull parts (actually it elongates the earlier restoration of the skull and suggests a larger antorbital fenestra than in other dorygnathids, Fig. 3). And now the narrow mandible makes sense because it is not preserved in lateral view.
Colleague [name deleted] was kind enough to drop a note on this (see below) that prompted a review of the situation. Later Mike wrote, “Sometimes it is better to trust people who have spent many hours with the specimen in front of them and read the descriptions.”
That’s a common notion,
but that’s not the thought you should take-away from this exercise.
Science doesn’t work on trust.
It works on testing. Having never seen a mandible preserved edge-on in the matrix, without obvious alveoli and too gracile for the skull, I sought another explanation for the questionable portion of the fossil. The tibia/fibula seemed to be a good fit.
But I was wrong. The mandible was not preserved edge-on, but flattened along its widest dimensions, like most fossils are. Then the anterior half of the fused mandible was lost leaving the posterior parts edge-on. Now it makes sense.
It would have helped if the above restoration was made prior to publication. I’m sure you can see how well it illustrates the situation here. Making mistakes is one way to shed new light on a problem. I never would have arrived at this solution and explanation had I merely trusted the original authors.
When something doesn’t make sense, keep working on it until it does makes sense.
It’s a process. And I’m always glad to accept any help that is offered. Getting it right is the ultimate goal.
Andres B, Clark JM and Xing X 2010. A new rhamphorhynchid pterosaur from the Upper Jurassic of Xinjiang, China, and the phylogenetic relationships of basal pterosaurs, Journal of Vertebrate Paleontology 30: (1) 163-187.