The Historia animalium is Gessner’s most influential work. The fourth volume of this natural history treatise deals with fish and aquatic creatures. It contains an illustration of a fossilised shark’s tooth, which Gessner took from André Thevet’s Cosmographie de Levant (1554). He identifies it as the ‘tongue stone’ mentioned in Pliny the Elder’s Natural History. The view that ‘tongue stones’ were fossilised shark teeth only became widely accepted in the 17th century.