The Pelagornithidae or pseudo-tooth birds were a family of large seabirds from the order Pelecaniformes, which were common worldwide from the Late Paleocene to the Late Pliocene; undetermined species even occurring in Middle Eocene Antarctica.
They had wingspans up to 6m (20ft) and were somewhat similar to albatrosses, although they had a large bill with tooth-like projections that enabled them to pick up slippery prey like fish or squids more easily. Their similarities with the Procellariiformes go so far that some paleontologists see them as possibly proving the common origin of pelicans and the tubenoses; others are more reserved and regard them far less close to these groups.
The oldest specimens are the Late Paleocene Pseudodontornis tenuirostris of Herne Bay and Odontopteryx tschulensis of Kazakhstan. 50 million years later, a Pelagornis from Morocco which lived just a few millions of years ago, ends the known reign of pseudo-tooth birds. As it seems, humans missed encountering these birds by a hair's-breadth of evolutionary time.
Neptuniavis from the London Clay, Early Eocene of England seems somewhat intermediate but is not known from much material, and Argilliornis from the same deposits may belong here too. The most well-known genus in the family is Osteodontornis, which lived in the Northern Hemisphere from the Early Oligocene to the Pliocene and was one of the largest birds of its time.