Bonnerichthys is a genus of fossil fishes within the family Pachycormidae that lived during the Late Cretaceous Period  Fossil remains of this taxon are known from the Smoky Hill Member of the Niobrara Chalk Formation of Kansas (Late Coniacian-Early Campanian, about 87-81 million years ago). It grew to around 20 feet in length, though not quite as large as the related Leedsichthys from the Jurassic of Europe which likely grew up to 30 feet.
One of the most significant features of Bonnerichthys is the recognition that it was a filter feeder, living on plankton. This recognition that many large-bodied fish from the Mesozoic in the Pachycormidae were filter feeders shows that this niche was filled for at least 100 million years before previously known. The modern niche is filled by several species of sharks and the baleen whales.