[7][8] Ptychodus teeth have long been identified as palates of diodon, or porcupinefish (Osteichthyes, Diodontidae), well-known for their ability to inflate their bodies in defense.

At the beginning of the 19th century, several authors including Swiss paleontologist Louis Agassiz eventually demonstrated the affinities of Ptychodus teeth with those of elasmobranchs (rays and sharks).

[3] The fact that so many fossils of Ptychodus have been found in different regions of the world provides evidence of a distribution of species during the Albian-Turonian time.

A 2016 publication found that Ptychodus are likely true sharks belonging to Selachimorpha, rather than hybodonts or batoids as previously thought.

[2] Ptychodus was a large shark, previously estimated at 10 meters (33 feet) long based on extrapolation from teeth.

[6] Many authors have suggested that Ptychodus fed on bottom dwelling (benthic) prey like bivalves (particularly inoceramids) and crustaceans, while also consuming some hard bodied organisms that lived in open water (pelagic).