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. But as is known today, pelicans are closer to storks (which have a hallux but no webbing) than to pseudotooth birds and evolved their fully webbed toes independently.
The location of the salt glands in Osteodontornis, Pelagornis (and possibly others) suggests that these birds developed an oceanic lifestyle independently from penguins and tubenoses, which possess a distinct salt gland system. In contrast, penguins and tubenoses have a different salt gland arrangement.