Article: The braincase of the Middle Triassic shark Acronemus tuberculatus (Bassani, 1886)

The chondrocranium of the enigmatic Middle Triassic shark Acronemus tuberculatus is investigated using computerized tomography scanning and 3-D digital reconstitution techniques. The braincase reveals some autapomorphies, plus other features that suggest a phylogenetic relationship to both hybodontiform and neoselachian elasmobranchs, including evidence of features implicated in low-frequency semi-directional phonoreception. Acronemus can no longer be classified as a ‘ctenacanthiform’, although its relationships remain elusive and it presents supposedly hybodontiform and neoselachian features that have not previously been found in combination.