"The Armadillo Lizard adopts a curious defensive posture when threatened by rolling itself up like an Armadillo, with its tail tightly held in its jaws, presenting a spiny ring to the predator and protecting the softer, vulnerable belly area."
Bonus: Plato described a self-eating, circular being as the first living thing in the universe — an immortal, perfectly constructed animal: the Ouroboros. (via reddit comments)
And there are more pictures of the Armadillo lizard here, with the benefit of scale.
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