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'''Gastornis''' is an extinct genus of large flightless birds that lived during the late Paleocene and Eocene periods of the Cenozoic.
''Gastornis'' means "Gaston's bird"; it is named after Gaston Planté, who discovered the first fossils at Geiseltal, Germany in 1855. In 1876, Edward Drinker Cope discovered another set of fossils in North America, and named them ''Diatryma'' (DIE-a-TREE-ma) (from Ancient Greek ''diatrêma'' "canoe"). This is an extremely close relative; the North American bird is often called 'Diatryma', but experts now believe they both belong into ''Gastornis''. It is perhaps best to use the more familiar name of Cope as the common name, so that one might for example say "''Gastornis'' (the diatrymas)...".

Contents

Description and ecology

Systematics

''Gastornis'' in popular culture

References

External links

Description and ecology

''Gastornis parisiensis'' measured on average 1.75 metres tall, while ''G. edwardsi'' was 2 metres tall. It had a remarkably huge beak with a hook, which was taken as evidence suggests that it was carnivorous. ''Gastornis'' had large powerful legs, with large, taloned feet, which also were considered in support of the theory that it was a predator. At its time, the environment in which ''Gastornis'' lived in had large portions of dense forest and a moist to semiarid subtropical or even tropical climate. North America and Europe were still rather close, and especially since Greenland probably was covered with lush woodland and grassland then, only narrow straits of a few 100 km at most would have blocked entirely landbound dispersal of the diatrymas' ancestors. While there were large contiguous areas of land in their North American range after the Western Interior Seaway had receded, their European range was an archipelago due to the Alpide orogeny and the high sea levels of the Paleocene-Eocene Thermal Maximum; geographically (but not geologically), it was perhaps roughly similar to today's Indonesia.
Classically, the diatrymas have been depicted as predatory. However, with the size of ''Gastornis'''s legs, the bird would have had to have been more agile to catch fast-moving prey than the fossils suggest it to have been. Consequently, it has been suspected that ''Gastornis'' was an ambush hunter and/or used pack hunting techniques to pursue or ambush prey; if ''Gastornis'' was a predator, it would have certainly needed some other means of hunting prey through the dense forest.
Alternatively, they may have been predominantly scavengers, omnivores or even herbivores. Indeed, ''Gastornis'''s large beak would have been as well suited for crushing seeds and tearing off vegetation. Alternatively, the beak may simply have been used for social display - its presence in all known fossils argues against a sexual display role. These contradicting hypotheses , equivocally supported by the data, make the dietary paleobiology of ''Gastornis'' impossible to pinpoint.
Similar gigantic birds of the Cenozoic were the South American terror birds (phorusrhacids) and the Australian mihirungs (Dromornithidae). The former were certainly carnivorous, and the latter are suspected of being predators, too. On the other hand, ratites, the flightless giant birds of our time, feed on plants and invertebrates.

The diatrymas were among the largest, if not ''the'' largest birds alive during the Paleogene. They had few natural enemies and serious competitors apart from other ''Gastornis'' or then-rare large mammals, such as the predatory bear-like ''Arctocyon'' of Europe. If these huge birds were active hunters, they must have been important apex predators that dominated the forest ecosystems of North America and Europe until the Middle Eocene. The Middle Eocene saw the rise of large creodont and mesonychid predators to ecological prominence in Eurasia and North America; the appearance of these new predators coincides with the decline of ''Gastornis'' and its relatives. This was possibly due to an increased tendency of mammalian predators to hunt together in packs (prevalent especially in hyaenodont creodonts). The fact that no birds appear to have ever weighed much more than half a metric ton suggests that they were restricted in their ability to evolve to larger and larger sizes, out-evolving apex predators in sheer bulk as mammals are often able to do (see Cope's "Rule").

Systematics

There is no agreement on the relationships of the diatrymas. They were long and still are sometimes placed with the Gruiformes. This group seems 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 ''Gastornis''; 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 diatrymas 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 diatrymas lived.
More recently, most consider the closest living relatives of ''Gastornis'' 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 diatrymas 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 diatrymas: they would have evolved for some 15-25 million years after diverging from the ancestors of the Anseriformes.
Moreover, in this case the mihirungs would have recapitulated the gigantism of the diatrymas, though based on a more advanced anseriform (i.e., more "gooselike" as regards 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.

''Gastornis'' in popular culture

★ ''Gastornis'' was featured on the BBC special, Walking With Beasts, as the apex predator of a European forest.

★ ''Gastornis'' (aka. Diatryma) was also featured in the Canadian National Film Board special Miracle Planet.

★ ''Gastornis'' (aka. Diatryma) was shown in the children's video "Mr. Know it Owl's Dinosaurs and Strange Creatures". In it, it attacked and ate a small Eohippus, a primitive horse now named Hyracotherium.

★ ''Gastornis'' (aka. Diatryma) was featured in Carnivores: Ice Age

References

★ (1876): On a gigantic bird from the Eocene of New Mexico. Proc.Acad.Nat.Sc.Philadelphia, 10-11.

★ (1855): Note sur le tibia du ''Gastornis parisiensis''. ''C. R. Acad. Sci. Paris'' '40': 579-582. [Article in French]

External links

★ BBC Science and Nature

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