I don't know if any work has been done in this area (if anyone knows any updated findings on these tracks, let me know), but a friend pointed me to this interesting article
from the Smithsonian. Here's an excerpt:
The fossil tracks that MacDonald has collected include a number of what paleontologists like to call "problematica." On one trackway, for example, a three-toed creature apparently took a few steps, then disappeared--as though it took off and flew. "We don't know of any three-toed animals in the Permian," MacDonald points out. "And there aren't supposed to be any birds." He's got several tracks where creatures appear to be walking on their hind legs, others that look almost simian. On one pair of siltstone tablets, I notice some unusually large, deep and scary-looking footprints, each with five arched toe marks, like nails. I comment that they look just like bear tracks. "Yeah," MacDonald says reluctantly, "they sure do." Mammals evolved long after the Permian period [NOTE -- permian is at the end of the paleozoic -- jb], scientists agree, yet these tracks are clearly Permian.