Quickly becoming one of the most famous of all birds
because of its great size and teeth, Pelagornis is, evidently, still a bird of mystery in the world of paleo-taxonomy.
Figure 1. Pelagornis skeletal elements.
Wikipedia reports,
“Pelagornis [was] probably rather close relatives of either pelicans and storks, or of waterfowl, and are here placed in the order Odontopterygiformes to account for this uncertainty. Like many pseudotooth birds, it was initially believed to be related to the albatrosses in the tube-nosed seabirds (Procellariiformes), but subsequently placed in the Pelecaniformes where it was either placed in the cormorant and gannet suborder (Sulae) or united with other pseudotooth birds in a suborder Odontopterygia.
Figure 2. Skull of Morus bassanus the Northern gannet. This taxon is most similar to Pelagornis in the LRT.
If experts can’t nest Pelagornis with certainty
based on rather complete morphology, then we have a problem. With the addition of the Northern gannet, Morus bassanus, Pelagornis nests with it with certainty in the large reptile tree (LRT, 1032 taxa).
Figure 3. Skeleton of Morus bassanus, the Northern gannet.
Pelagornis chilensis (Lartet 1857, Mayr and Rubilar-Rogers 2010; Miocene; MNHN SGO.PV 1061) is an extinct giant soaring bird related to the gannet Macronectes. Bony, not true teeth, developed along the jaw margins. The external naris was divided by bone. Mayr and Rubilar-Rogers reported, “We finally note that the phylogenetic affinities of bony-toothed birds still have not been convincingly resolved.”
Figure 4. The gannet (genus: Morus) in vivo. Note the diving pose below.
Morus bassanus (Linneaus 1758, extant; 100cm long) is the Northern gannet. Here the nasal has extended over the external naris to prevent water from entering the nose of this plunge diver. Secondary nostrils appear inside the mouth. The keratin at the jaw rims appears to form tiny teeth (Fig. 2). Compare to the much larger Pelagornis (Fig. 1).
Earlier we looked at the plunge diving possibility of the outwardly similar Late Jurassic pterosaur, Germanodactylus.
References
Lartet E 1857. Note sur un hum´erus fossile d’oiseau, attribu ´e `a un tr `es-grand palmip`ede de la section des Longipennes. Comptes rendus hebdomadaires des S´eances de l’Acad´emie des Sciences (Paris) 44:736–741.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Mayr G and Rubilar-Rogers D 2010. Osteology of a new giant bony-toothed bird from the Miocene of Chile, with a revision of the taxonomy of Neogene Pelagornithidae. Journal of Vertebrate Paleontology 30(5):1313-1340.
The Pterosaur Heresies 
Hey, David. This is unrelated to the post but I read it today and thought you might find it interesting:
“Galapagos finches caught in act of becoming new species”
http://www.bbc.com/news/science-environment-42103058
From what we all have learned about nature, the lumping and splitting is not always clear cut. Thank you!