It's hard to see one. Even a nice flat world with ample incentive and taking good "bearings" for granted, how can you evolve a wheel-organ that maintains a biological connection as well as being able to rotate an indefinite number of time?
A few difficult and grotesque endpoints:
* The wheel only rotates a fixed number of times before the creature must pivot and "unwind" in the opposite direction. This one seems most plausible, but it's not a real wheel.
* The main body builds replacement wheels internally (like tooth enamel) and periodically ejects a "dead" wheel which can be placed onto a spoke. This option would make it easier to generate very tough rim materials though.
* A biological quick-release/quick-connect system, where the wheel-organ disconnects to move, but then reconnects to flush waste and get more nutrients.
* A communal organism, where wheel-creatures are alive and semi-autonomous, with their own own way to acquire nutrients. Perhaps they would, er... suckle. Eeugh.