Pseudosphaerodon antiquus is a taxonomically uncertain acanthomorph known principally from jaws and rounded teeth. The dentition is very different from the sharp grasping teeth of the London Clay pursuit predators: the broad crowns indicate a feeding apparatus capable of crushing or bruising resistant food. Hard-shelled invertebrates are therefore plausible prey, although no direct gut contents are known.

Its exact family relationships remain debated, so the animal should not be reconstructed as a specific modern type of durophagous fish. The robust marginal teeth nevertheless provide direct evidence that crushing-based feeding niches were occupied by several unrelated teleosts in the London Clay ecosystem.