 Footbone traits are notoriously prone to selection forces in birds, with convergent evolution known to inhibit or even invalidate cladistic analyses; however, the apparent autapomorphies of the lower arm and hand bones are hard to explain by anything else than an actual relationship.The location of the salt glands inside the eye sockets of "Osteodontornis", "Pelagornis" (and probably others) shows that whatever their relationships were, the pelagornithids adapted to an oceanic habitat independently from penguins and tubenoses, which instead have supraorbital salt glands.Their missing or vestigial hallux – like in ducks but unlike in pelicans which have all four toes fully developed and webbed – was held against a close relationship with pelicans.