Agassizilia is an extinct genus of both freshwater and marine pycnodont fishes from the mid-late Cretaceous (late Albian/early Cenomanian-Campanian).

[1][2] The genus contains two species: A. erfoudina from freshwater deposits of the Kem Kem Group in south-east Morocco and A. barberi from marine deposits of the US (Marlbrook Marl of Arkansas, Eutaw Formation of Alabama, and possibly the Smoky Hill Chalk of Kansas).

[2][3][4] It was described in 2020 from an isolated prearticular bone (lower jaw) with a unique tooth arrangement on its dental pavement which differentiates it from all other known pycnodont genera.

Although the rest of its skeleton is unknown, the pavement of blunt delicate teeth on the holotype suggests that it fed of soft shelled invertebrates such as shrimp or ostracods.

It was found alongside several other typically marine pycnodont genera in a freshwater river system, suggesting a possibly amphidromous lifestyle.