I have had this greek desert tortoise for about 3 years now (got it from a friend who had it for about 10) and do not recall the bottom of his shell being wrinkled like this. The shell does not feel soft and I am unsure if he had it before (keep in mind I do not look at the bottom of his shell too often). What could cause this and do I need to be concerned? I can provide additional details or photos if needed.