It was a member of the extinct order Multituberculata within the suborder Cimolodonta and superfamily Taeniolabidoidea.

The genus was named by William Diller Matthew and Walter Granger in 1925, and is based on a single species P.lucifer.

For example, they all share a short wide snout and a blocky head[2] so it is probably instructive to look at a close and more commonly occurring relative, Lambdopsalis bulla, a likely burrower.

[3][4] Matthew and Granger noted in their discovery that P.lucifer had a robust lower incisor, supportive of this similarity.

Prionessus fossils range from 59-55 million years ago, through the Thanetian age of the late Paleocene.