Sometimes odd things pop out of fossils.
Here (Fig. 1) is a pterosaur foot (Rhamphorhynchus muensteri, JME-SOS 4009, no. 62 in the Wellnhofer 1975 catalog). Phalanx p4.1 is greatly expanded, yet no longer than it’s counterpart on the other foot.
Figure 1. Right pes of n62, Rhamphorhynchus muensteri. Note p4.1 is greatly expanded, like a balloon. The left foot is not so afflicted. There is still a claw on digit 4, off the edge of the photo. See if you can see a faint, very faint impression of a web. If you do, then look off to the right and you’ll see that geographical feature continuing beyond the bones.
Maybe you know what this is…
I don’t know what makes toe phalanges expand like this. It is no longer than the slender phalanx on the left pes, but it is greatly expanded, like a balloon. Is it due to disease or injury?
BTW
Very few Rhamphorhynchus have such a long pedal digit 4. I have only found one other specimen from about 20 or so that I have examined.
I thought you might find it as interesting as I did.
The Pterosaur Heresies 
What an odd pathology. Maybe an infection with a draining abscess? Closer looks would be useful. Very odd!