Are pseudo-toothed seabirds actually toothed seabirds?
“An in-depth analysis of the affinities of pelagornithids is beyond the scope of this study,but we consider it likely that some of the putatively galloanserine features of these birds are plesiomorphic for neornithine birds. This is especially true for the morphology of the articular end of the mandible, which is strikingly similar to that of the Ichthyornithidae (compare Mayr & Rubilar-Rogers 2010: fig. 2B with Fieldet al.2018: extended datafig. 5). A better understanding of the affinities of pelagornithids would certainly be fostered by an improved knowledge of their cranial morphology, and in particular it remains to be hoped that future studies will reveal more details of the poorly known palate of these birds.”
- Mayr et al 2019
Ultimately, this study recovers pelagornithids in a polytomy with the neognath groups Galloanserae and Neognathae, but as noted above this result was provisory.
Since then, studies on Ichthyornis‘ palate show that it and other Cretaceous ornithurines actually had a neognath-like condition (Torres 2021), so even a complete pelagornithid palate showing neognath-like features over palaeognath ones wouldn’t dim this interesting alternative for their placement in the bird phylogenetic tree.
While this is the first study to imply a radical revision of Pelagornithidae’s supposed crown bird status, it’s been considered for a while that their tooth-like projections actually are genetically homologous to true teeth (Mayr 2012); for this to work, either tooth loss happened independently among crown birds, the split between all three neognath groups and paleognaths was nigh instantaneous after tooth loss, or pelagornithids simply aren’t within Aves. I find the latter scenario more plausible than the first two, especially the second since it would require a rather fast adaptive radiation.
Should pelagornithids be non-avian birds, this would be rather significant, as showing an additional lineage surviving after the KT event until recently. It would also explain why square pegging them as either waterfowl or “higher waterbirds” hasn’t worked since well they’re not related to either.
Ultimately, a revision of their phylogenetic placement with the new anatomical information on Ichthyornis and other Cretaceous ornithurines should confirm or deny this.
G. Mayr, V. L. De Pietri, L. Love, A. Mannering, and R. P. Scofield. 2019. Oldest, smallest, and phylogenetically most basal pelagornithid, from the early Paleocene of New Zealand, sheds light on the evolutionary history of the largest flying birds. Papers in Palaeontology
Torres, C.R. et al. (2021) Bird neurocranial and body mass evolution across the end-Cretaceous mass extinction: The avian brain shape left other dinosaurs behind. Science Advances, Vol. 7, no. 31, eabg7099. DOI: 10.1126/sciadv.abg7099
Mayr G., Zvonok E. (2012). “A new genus and species of Pelagornithidae with well-preserved pseudodentition and further avian remains from the middle Eocene of the Ukraine”. Journal of Vertebrate Paleontology. 32 (4): 914–925. doi:10.1080/02724634.2012.676114. S2CID 86572964.