I've speculated about it all afternoon. It looks like a healed-over wound. I'm no wildlife biologist, obviously, but I wonder if it could have happened when the alligator was very small. Possibly a bird had him in its bill, but it got away? I see large birds eating baby alligators all the time when at Paynes Prairie, and the larger gators will eat the smaller ones if they are hungry enough, too. Since I didn't realize this alligator was "special" when I took the photo, i didn't pay much attention to it and took the picture as an afterthought. I don't usually see a ranger or member of the volunteer organization since I usually go during the week, but I will have to ask the next time I run into someone official.
That would be a good assumption, but there are no motor boats in the waters on Paynes Prairie. Just an occasional biologist's row boat is all I've ever seen. It may be that he was brought to the prairie by biologists, but I seriously doubt it.