Temporal range: Late Paleocene - Middle Eocene, 56–45Ma
|Mounted skeleton of a Gastornis|
Gastornithiformes are an order of prehistoric birds. The birds from this group lived from the Paleocene to the Eocene and were spread out across Asia, Europe, and North America. All the birds were very large birds that were flightless, similar to an ostrich but more heavily built and with a huge beak. They are now thought to be omnivores or herbivores, but were once thought to be carnivores.
There is no agreement on the relationships of the Gastornithiformes. They were long and still are sometimes placed with the Gruiformes as a family Gastornithidae. The Gruiformes seem paraphyletic though, with some lineages that are exclusively Gondwanan but apparently not closely related to cranes, rails and allies which are common in Eurasia and Africa but far less so in the Americas. Some others, probably unrelated to either group, were very diverse in the Americas but prehistorically also occurred in Europe. Nothing is known of the ancestry of the Gastornithiformes; judging from biogeography, a relationship with either the true Gruiformes or the "Americas" lineage (which might include the seriemas and the phorusrhacids) is possible.
However, the early occurrence of the Gastornithiformes in the fossil record poses problems. These animals were highly apomorphic and thus the lineage must have evolved for significant time after diverging from their closest known relatives. Most purported relatives are not known nor suspected to have been so highly distinct at the time when the Gastornithiformes lived.
More recently, most consider the closest living relatives of the Gastornithiformes to be the Anseriformes (waterfowl and screamers). The present birds would thus be members of the fowl clade, Galloanserae. The clade name Anserimorphae has been proposed for the Gastornithiformes and the Anseriformes, as opposed to birds closer to Galliformes. As Galloanserae are known to have reached some diversity in the Late Cretaceous already, this scenario very plausibly explains the extreme adaptations of the Gastornithiformes: they would have evolved for some 15-25 million years at least after diverging from the ancestors of the Anseriformes.
Moreover, in this case the Neogene mihirungs would have recapitulated the gigantism of the Gastornithiformes, though based on a more advanced anseriform (i.e., more "gooselike" with regard to details of their osteology) ancestor. This would be an outstanding example of convergent evolution which was very close to being homologous phylogenetically but still a true convergence of phenes in most aspects.
List of genera
Apart from the genera listed above, there are some indeterminate gastornithiform fossils:
- Gastornithidae gen. et sp. indet. (Paleocene of Walbeck, Germany) - possibly Gastornis
- Gasthornithidae gen. et sp. indet. YPM PU 13258 (Willwood Early Eocene of Park County, USA) - possibly juvenile Gastornis giganteus
- "Diatryma" cotei (middle-Late Eocene of France)
- Witmer, L. & Rose, K. (1991)
- Mustoe, G. et al. (2012)
- "Parly" in Wetmore (1933) is a misprint.
- Wetmore (1933)
- Mlíkovský (2002)
- Mustoe, G. Tucker, D. & Kemplin, K. (2012) Giant Eocene bird footprints from northwest Washington, USA. Palaeontology 55(6):1293-1305.
- Mlíkovský, J. (2002) Birds of the World, Part 1: Europe. Ninox Press, Prague.
- Witmer, L. & Rose, K. (1991) Biomechanics of the jaw apparatus of the gigantic Eocene bird Diatryma; implications for diet and mode of life. Paleobiology 17(2):95-120.
- Brodkorb, P. (1967) Catalogue of Fossil Birds: Part 3 (Ralliformes, Ichthyornithiformes, Charadriiformes). Bulletin of the Florida State Museum 11(3).
- Wetmore, A. (1933) Bird Remains from the Eocene of Wyoming. Condor 35(3):115-118.