Woodward initially assigned "Leedsichthys" to the Acipenseroidea, considering it related to the sturgeon, having the large gill rakers and branching finrays in common. In 1905, he changed this to the Pachycormidae. The Pachycormidae have a somewhat uncertain position. Often they are considered very basal Teleostei — if so, "Leedsichthys" would be the largest known teleost — others see them as members of a Pachycormiformes forming the sister group of the Teleostei, and sometimes they are seen as even more basal Amiiformes. In the latter case the extant bowfin, "Amia calva", would be the closest living relative of "Leedsichthys".