One of the most distinctive features of Casieria casieri is the unusual shape of its teeth. Each has a tall central point flanked by two long, sharp side points, giving it the appearance of a miniature three-pronged crown. The side points can reach about half the height of the main one, while strong folds run up both faces of the tooth. These are small fossils, but an intact example is quite unlike the simple pointed teeth of many other sharks.

The species was first described from the London Clay of Essex in 1976, under the name Scyliorhinus casieri. Its fossil record also has a less familiar connection with the Netherlands. In 1985, scientists examining shark and ray teeth recovered from boreholes through the buried Dongen Formation recorded specimens under that earlier name. Unlike the London Clay exposures of the British coast, these Dutch Eocene deposits are hidden beneath the surface and can only be studied through drilling.

The shape of the teeth also became important in later research. When scientists described Casieria maghrebiana from Morocco in 1997, they recognised it as a different species partly because its side points were proportionally shorter. Such small differences can be enough to separate extinct sharks whose skeletons are otherwise unknown.

There is still much we cannot say about C. casieri. Its adult size, exact diet and appearance remain uncertain. But its teeth provide a particularly useful reminder for fossil collectors: a broken or heavily worn specimen may have lost precisely the small details that distinguish one species from another. In this shark’s case, those two sharp side points can make all the difference.