Mean semicircular canal radius of curvature as a function of body mass was estimated for 18 fossil fish and 2 fossil labyrinthodont amphibians. The statistically significant regression for fossil fish is closely comparable to that of Recent teleosts, but both differ substantially from that of Recent mammals. Fossil labyrinthodont amphibian data points fall fairly close to those of Recent mammals, suggesting that all tetrapods are characterized by smaller semicircular canal dimensions than those of fish. No simple explanation of this dichotomy can be offered because several other important parameters which may affect semicircular canal sensitivity are presently poorly known, or cannot be measured in fossils.

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