Gastornis

Gastornis is an extinct genus of large flightless birds that lived during the late Paleocene and Eocene epochs of the Cenozoic era. The genus is currently thought to contain three or four distinct species, known from incomplete fossil remains, found in western-central Europe (England, Belgium, France and Germany). More complete specimens are known from a fourth, North American species, which had previously been classified in the distinct genus Diatryma. Many scientists now consider Diatryma to be so similar to the other species of Gastornis that it should also be included in that genus. A fifth species, also previously classified in its own genus, is known from China.

Gastornis were very large birds, and have traditionally been considered to be predators of small mammals. However, several lines of evidence, including the lack of hooked claws in known Gastornis footprints and studies of their beak structure, have caused scientists to re-interpret these birds as herbivores which probably fed on tough plant material and seeds.

Description
Gastornis is known from a large amount of fossil remains, but the clearest picture of the bird comes from a few nearly complete specimens of the species G. giganteus. These were generally very large birds, with huge beaks and massive skulls superficially similar to the carnivorous South American "terror birds" (phorusrhacids). The largest known species, G. giganteus, could grow to the size of the largest moas, and reached about 2 metres (6.6 ft) in maximum height.[1]

The skull of Gastornis giganteus was huge compared to the body and powerfully built. The beak was extremely tall and compressed (flattened from side to side). Unlike other species of Gastornis, G. giganteus lacked characteristic grooves and pits on the underlying bone. The 'lip' of the beak was straight, without a raptorial hook as found in the predatory phorusrhacids. The nostrils were small and positioned close to the front of the eyes about midway up the skull. The vertebrae were short and massive, even in the neck. The neck was relatively short, consisting of at least 13 massive vertebrae. The torso was relatively short. The wings were vestigial, with the upper wings bones small and highly reduced, similar in proportion to the wings of the Cassowary.

History
Gastornis was first described in 1855 from a fragmentary skeleton. It was named after Gaston Planté, described as a "studious young man full of zeal", who had discovered the first fossils in Argile Plastique formation deposits at Meudon near Paris (France).[3] The discovery was notable due to the large size of the specimens, and the fact that, at the time, Gastornis represented one of the oldest known birds.[4] Additional bones of the first known species, G. parisiensis, were found in the mid 1860s. Somewhat more complete specimens, this time referred to the new species G. eduardsii (now considered a synonym of G. parisiensis) were found a decade later. The specimens found in the 1870s formed the basis for a widely-circulated and reproduced skeletal restoration by Lemoine. The skulls of these original Gastornis fossils were unknown except for nondescript fragments, and several bones used in Lemoine's illustration turned out to be those of other animals.[5] Thus, the European bird was long reconstructed as a sort of gigantic crane-like bird.[6][7]

In the 1874, the American paleontologist Edward Drinker Cope discovered another fragmentary set of fossils in the Wasatch Formation of New Mexico. He considered them to belong to a distinct genus and species of giant ground bird, and in 1876 he named it Diatryma gigantea (/ˌdaɪ.əˈtraɪmə/ DY-ə-TRY-mə),[8] from Ancient Greek διάτρημα, diatrema, meaning “through a hole”, referring to the large foramina (perforations) that penetrate some of the foot bones.[9][10] A single gastornithid toe bone from New Jersey was described by Othniel Charles Marsh in 1894 and classified as the new genus and species Barornis regens, but in 1911 it was recognized that this, too, could be considered a junior synonym of Diatryma (and therefore later Gastornis).[2] Additional fragmentary specimens were found in Wyoming in 1911 and assigned in 1913 to the new species Diatryma ajax (also now considered a synonym of G. giganteus).[2] In 1916, an American Museum of Natural History expedition to the Bighorn Basin (Willwood Formation) of Wyoming found the first nearly complete skill and skeleton, which was described in 1917 and gave scientists their first clear picture of the bird.[2] Matthew, Granger, and Stein (1917) classified this nearly complete specimen as yet another new species, Diatryma steini.[2]

After the description of Diatryma, most new European specimens were referred to this genus instead of Gastornis. However, after the initial discovery of Diatryma, it soon became clear that it and Gastornis were so similar that the former could be considered a junior synonym of the latter. In fact, this similarity was recognized as early as 1884 by Elliott Coues, but this was debated by researchers throughout the 20th century. Meaningful comparisons between Gastornis and Diatryma were made more difficult by Lemoine's incorrect skeletal illustration, the composite nature of which was not discovered until the early 1980s. Following this, several authors began to recognize a greater degree of similarity between the European and North American birds, often placing both in the same order (Gastornithiformes) or even family (Gastornithidae). This newly recognized degree of similarity caused many scientists to tentatively accepted their synonymy, pending a comprehensive review of the anatomy of these birds.[4] Consequently, the correct scientific name of the genus is Gastornis.