Vegaviidae

Vegaviidae is an extinct basal family of anserimorph birds which existed from the Late Cretaceous to the Early Paleogene periods with fossils found in Canada, Chile, New Zealand, and Antarctica.

Previously the genera Neogaeornis and Polarornis were classified as stem-loons based on the similarities in the anatomy of the leg structure. However there were some criticism to these assertions as the material are from incomplete specimens from Antarctica lacking several important loon characteristics.

In 2017 Agnolín and colleagues perform a phylogenetic analysis of these genera in addition to the newly discovered Australornis and Vegavis, the latter genus of which a more complete specimen has been found. This allowed the team to do anatomical comparisons between these genera. They have found support of them making up a family of birds showing specializations to diving, classfied as the sister taxon to the crowned-order Anseriformes. This is evidence that some families of modern birds have crossed the K–Pg boundary unaffected by the extinction event that occurred. The authors also stated this is further evidence of Gondwana having an important role for the evolution of modern birds.

Another 2017 paper by Worthy et al. that focuses on the evolution and phylogenetic relationships of giant fowl has found weak support in finding the vegaviids to be the sister taxon to Gastornithiformes (which the authors included Gastornithidae and mihirungs in the order).

In the description and phylogenetic placement of Maaqwi from Sandy et al. (2017) found an alternative position for vegaviids where the data supported placing them as stem-birds in the more exclusive clade Ornithurae. If so this would significantly imply vegaviids were the only group of stem-birds to have survived the Cretaceous–Paleogene extinction event alongside modern or crowned birds.

In 2018 Mayr and colleagues did a review of the vegaviids systematics stating that while Vegavis and Polarornis are sister genera based on overall similarities in their femur and tibiotarsal bones, the inclusion of the other species is poorly supported and may not be vegaviids at all. Furthermore comparison of the plesiomorphic traits of the pterygoid and the mandible does not seem to firmly established anseriform or galloanserine affinities for Vegaviidae. Mayr et al. (2018) commented to try and classify all southern hemisphere birds into a single clade is premature as it may not illustrate the complex relationships and the convergent evolution birds have undergone.