|Mounted skeletons of Gastornis giganteus (top photo) and Dromornis stirtoni (bottom photo)|
Gastornithiformes were an extinct order of giant flightless fowl with fossils found in North America, Eurasia, and possibly Australia. Members of Gastornithidae were long considered to be a part of the order Gruiformes. However, the traditional concept of Gruiformes has since been shown to be an unnatural grouping.
Beginning in the late 1980s and the first phylogenetic analysis of gastornithid relationships, consensus began to grow that they were close relatives of the lineage that includes waterfowl and screamers, the Anseriformes. Recognizing the apparent close relationship between gastornis and waterfowl, some researchers even classify them within the anseriform group itself. Others restrict the name Anseriformes only to the crown group formed by all modern species, and label the larger group including extinct relatives of anseriformes in the clade Anserimorphae (which this article and related pages have adopted). While the order is generally considered to be monotypic, a 2017 paper concerning the evolution and phylogeny of giant fowl by Worthy and colleagues have found phylogenetic support in finding the mihirungs (Dromornithidae) to be the sister taxon to the gastornis.
The mihirungs are also another family of giant flightless birds that have been classified as anserimorphs either as crown anseriforms closely related to the screamers (Anhimidae) or the sister taxon to Anseriformes. Worthy et al. (2017) incorporated several new taxa and character traits into existing matrices of Galloanserae resulted in several of their phylogenies to support this grouping. The authors did note the bootstrap support is weakly supported and one of their phylogenies even found gastornithiforms to be stem galliforms instead. These were also weakly supported. Below is a simplified phylogeny showing their one phylogeny supporting gastornithiforms as anserimorphs.
- Worthy, T.H.; Degrange, F.J.; Handley, W.D.; Lee, M.S.Y. (2017). "The evolution of giant flightless birds and novel phylogenetic relationships for extinct fowl (Aves, Galloanseres)". Royal Society Open Science. 11 (10): 170975. doi:10.1098/rsos.170975. PMC 5666277. PMID 29134094.
- Mustoe, G.E.; Tucker, D.S.; Kemplin, K.L. (2012). "Giant Eocene bird footprints from northwest Washington, USA". Palaeontology. 55 (6): 1293–1305. doi:10.1111/j.1475-4983.2012.01195.x.
- Agnolín, F. (2007). "Brontornis burmeisteri Moreno & Mercerat, un Anseriformes (Aves) gigante del Mioceno Medio de Patagonia, Argentina". Revista del Museo Argentino de Ciencias Naturales. 9: 15–25. doi:10.22179/revmacn.9.361.
- Andors, A. (1992). "Reappraisal of the Eocene groundbird Diatryma (Aves: Anserimorphae)". Science Series Natural History Museum of Los Angeles County. 36: 109–125.
- Murrary, P.F; Vickers-Rich, P. (2004). Magnificent Mihirungs: The Colossal Flightless Birds of the Australian Dreamtime. Indiana University Press.