The phylogenetic uncertainties surrounding them do not allow to infer whether the bony-toothed birds had a throat sac similar to pelicans. If they did, it was probably red or orange, and may have been used in mating displays. Sexual dimorphism was probably almost nonexistent, as it typically is among the basal Anseriformes and the "higher waterbirds". The name "pseudodontorns" refers to the genus "Pseudodontornis", which for some time served as the family's namesake. However, the presently used name Pelagornithidae pre-dates Pseudodontornithidae, and thus modern authors generally prefer "pelagornithids" over "pseudodontorns". The latter name is generally found in mid-20th-century literature however. Historically, the disparate bones of the pseudotooth birds were spread across six groups: a number of genera described from leg bones was placed in a family Cyphornithidae, and considered close allies of the pelican family (Pelecanidae). They were united with the latter in a superfamily Pelecanides in suborder Pelecanae, or later on (after the endings of taxonomic ranks were fixed to today's standard) Pelecanoidea in suborder Pelecani. Subsequently, some allied them with the entirely spurious "family" "Cladornithidae" in a "pelecaniform" suborder "Cladornithes". Those genera known from skull material were typically assigned to one or two families (Odontopterygidae and sometimes also Pseudodontornithidae) in a "pelecaniform" suborder Odontopteryges or Odontopterygia. "Pelagornis" meanwhile, described from wing bones, was traditionally placed in a monotypic "pelecaniform" family Pelagornithidae. This was often assigned either to the gannet and cormorant suborder Sulae (which was formerly treated as superfamily Sulides in suborder Pelecanae), or to the Odontopterygia. The sternum of "Gigantornis" was placed in the albatross family (Diomedeidae) in the order of tube-nosed seabirds (Procellariiformes). The most extensive taxonomic and systematic confusion affected "Dasornis". That genus was established based on a huge skull piece, which for long was placed in the Gastornithidae merely due to its size.