I've been doing some research and it turns out he's an Eastern Box Turtle. Here's what I've learned:
- They're not aquatic (so he didn't come from the creek behind our neighborhood).
- They eats insects, mushrooms, berries, and other vegetation.
- Box turtles are some of the longest lived and slowest reproducing species in the world.
- They have natural homing instincts that causes them to return to the place of their birth (within 200 meters) if they're ever moved.
- It's fairly rare to find them in the Great Lakes region.
Speaking of reproduction, I'm pretty sure Thomas is a girl. Apparently female box turtles have "boxier" shells and orangish eyes while the male turtle has a flatter shell and red eyes. I looked at Thomas's eyes and they look reddish orange to me. But the shape of the shell seems to indicate female. Hopefully Thomas is laying lots of eggs this summer and we'll see some baby turtles in the fall.