Many species are known, primarily from the Cretaceous of England and the midwestern United States.

[2] Pachyrhizodus fossils were first collected from Cambridgeshire, England in the 1840s and were very fragmentary, only a partial maxilla (SMB.9097) and were described as a species of Raphiosaurus in 1842 by Richard Owen.

The type remains of Pachyrhizodus consisted of a maxilla (BMNH 49014) from the Lower Cretaceous of Sussex, England and was originally thought to be a mandible that Louis Agassiz dubbed Pachyrhizodus in 1850,[3] with Frederick Dixon creating the species name basalis for the specimen.

[4] During the 19th century, several complete and partial skeletons of Pachyrhizodus were collected from England, many of which belonging to P. basalis and P.

[7][8] P. caninus specifically has been discovered in the United States, Mexico, and New Zealand.