 It was long believed that several similar Cretaceous species known from fragmentary remains, including "Ambiortus", "Apatornis", "Iaceornis" and "Guildavis", were members of the Ichthyornithes in addition to the group's namesake, "Ichthyornis".However, these seem to have been more closely related to modern birds than to "Ichthyornis dispar".In Julia Clarke's 2004 review of "Ichthyornis"-like fossils, the former order Ichthyornithiformes and the family Ichthyornithidae were considered synonyms of the clade Ichthyornithes, which in that paper was defined according to phylogenetic taxonomy as all descendants of the most recent common ancestor of "Ichthyornis dispar" and modern birds.