Mechanism
Dead keratin wheel
Plausibility
72
Interactive museum exhibit
Biological wheels are physically possible: bacteria already use rotary motors. The hard part for Earth animals is anatomy, development, and evolutionary access: vascular supply, nerve connection, tissue repair, and terrain all constrain a true wheel-and-axle body plan.
Mechanism
Scores are heuristic, not claims of impossibility. They encode the visible constraints: terrain, size, tissue continuity, twisting risk, drive efficiency, and plausible evolutionary pathway.