Gastornis

Julius T. Csotonyi Artwork

***Gastornis*** or *Diatryma* (Gaston's bird) was a giant bird as tall as a man and lived in the Paleocene and Eocene periods in the early Cenozoic where its fossils have been found in Europe and North America. *Gastornis* was related to waterfowl such as ducks, and not to phorusrhacids (terror birds) as commonly believed. At first, it was thought to be a carnivore, but now we know it is more likely to have been either a herbivore or an omnivore mainly due to the fact that it did not have a hooked beak, a feature that predatory birds have to help rip flesh.

## 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. The discovery was notable due to the large size of the specimens, and because, at the time, *Gastornis* represented one of the oldest known birds. 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. Thus, the European bird was long reconstructed as a sort of gigantic crane-like bird.

In 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, which, in 1876, he named *Diatryma gigantea* (/ˌdaɪ.əˈtraɪmə/ *DY-ə-TRY-mə*), from Ancient Greek διάτρημα, *diatrema*, meaning “through a hole”, referring to the large foramina (perforations) that penetrate some of the foot bones. 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*). 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. gigantea*). In 1916, an American Museum of Natural History expedition to the Bighorn Basin (Willwood Formation) of Wyoming found the first nearly complete skull and skeleton, which was described in 1917 and gave scientists their first clear picture of the bird. Matthew, Granger, and Stein (1917) classified this nearly complete specimen as yet another new species, *Diatryma steini*.

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 accept their synonymy, pending a comprehensive review of the anatomy of these birds. Consequently, the correct scientific name of the genus is *Gastornis*.

## 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. gigantea*. 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. gigantea* could grow to the size of the largest moas, and reached about 2 m (6 ft 7 in) in maximum height.

The skull of *G. gigantea* 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. gigantea* 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 wing-bones small and highly reduced, similar in proportion to the wings of the cassowary.

## Classification

*Gastornis* and its close relatives are classified together in the family Gastornithidae, and were long considered to be members of the order Gruiformes. However, the traditional concept of Gruiformes has since been shown to be an unnatural grouping. Beginning in the late 1980s with 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. A 2007 study showed that gastornithids were a very early-branching group of anseriformes, and formed the sister group to all other members of that lineage.

Recognizing the apparent close relationship between gastornithids and waterfowl, some researchers classify gastornithids 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, like the gastornithids, with the name Anserimorphae. Gastornithids are therefore sometimes placed in their own order, Gastornithiformes.

Today, at least five species of *Gastornis* are generally accepted as valid. The type species, *Gastornis parisiensis*, was named and described by Hébert in two 1855 papers. It is known from fossils found in western and central Europe, dating from the late Paleocene to the early Eocene. Other species previously considered distinct, but which are now considered synonymous with *G. parisiensis*, include *G. edwardsii* (Lemoine, 1878) and *G. klaasseni* (Newton, 1885). Additional European species of *Gastornis* are *G. russeli* (Martin, 1992) from the late Paleocene of Berru, France, and *G. sarasini* (Schaub, 1929) from the early-middle Eocene. *G. geiselensis*, from the middle Eocene of Messel, Germany, has been considered a synonym of *G. sarasini*, however, other researchers have stated that there is currently insufficient evidence to synonymize the two, and that they should be kept separate at least pending a more detailed comparison of all gastornithids. The supposed small species *G. minor* is considered to be a *nomen dubium*.

*Gastornis gigantea* (Cope, 1876), formerly *Diatryma*, dates from the middle Eocene of western North America. Its junior synonyms include *Barornis regens* (Marsh, 1894) and *Omorhamphus storchii* (Sinclair, 1928). *O. storchii* was described based on fossils from lower Eocene rocks of Wyoming. The species was named in honor of T. C. von Storch, who found the fossils remains in Princeton 1927 Expedition. The fossil bones originally described as *Omorhamphus storchii* are now considered to be the remains of a juvenile *Gastornis gigantea*. Specimen YPM PU 13258 from lower Eocene Willwood Formation rocks of Park County, Wyoming also seems to be a juvenile – perhaps also of *G. gigantea*, in which case it would be an even younger individual.

*Gastornis xichuanensis*, from the early Eocene of Henan, China, is known only from a tibiotarsus (upper foot bone). It was originally described in 1980 as the only species in the distinct genus *Zhongyuanus*. However, a re-evaluation of the fossil published in 2013 concluded that the differences between this specimen and the same bone in *Gastornis* species were minor, and that it should be considered an asian species of *Gastornis*.

## Paleobiology

A long-standing debate surrounding *Gastornis* is the interpretation of its diet. It has often been depicted as a predator of contemporary small mammals, which famously included the early horse *Eohippus*. However, with the size of *Gastornis* 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, *Gastornis* has been suspected to have been 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, it could have used its strong beak for eating large or strong vegetation.

The skull of *Gastornis* is massive in comparison to those of living ratites of similar body size. Biomechanical analysis of the skull suggests that the jaw-closing musculature was enormous. The lower jaw is very deep, resulting in a lengthened moment arm of the jaw muscles. Both features strongly suggest that *Gastornis* could generate a powerful bite. Some scientists have proposed that the skull of *Gastornis* was ‘overbuilt’ for a herbivorous diet and support the traditional interpretation of *Gastornis* as a carnivore that used its powerfully constructed beak to subdue struggling prey and crack open bones to extract marrow. Others have noted the apparent lack of predatory features in the skull, such as a prominently hooked beak, as evidence that *Gastornis* was a specialized herbivore (or even an omnivore) of some sort, perhaps having used its large beak to crack hard foods like nuts and seeds. Footprints attributed to gastornithids (possibly a species of *Gastornis* itself), described in 2012, showed that these birds lacked strongly hooked talons on the hind legs, another line of evidence suggesting that they did not have a predatory lifestyle.

Recent evidence suggests that *Gastornis* was likely a true herbivore. Studies of the calcium isotopes in the bones of specimens of *Gastornis* by Thomas Tutken and colleagues showed no evidence that it had meat in its diet. The geochemical analysis further revealed that its dietary habits were similar to those of both herbivorous dinosaurs and mammals when it was compared to known fossil carnivores, such as *Tyrannosaurus rex*, leaving phorusrhacids as the only major carnivorous flightless birds.

## Distribution

*Gastornis* fossils are known from across western Europe, the western United States, and central China. The earliest (Paleocene) fossils all come from Europe, and it is likely that the genus originated there. Europe in this epoch was an island continent, and *Gastornis* was the largest terrestrial tetrapod of the landmass. This offers parallels with the malagasy elephant birds, herbivorous birds that were similarly the largest land animals in the isolated landmass of Madagascar, in spite of otherwise mammalian megafauna.

All other fossil remains are from the Eocene; however, it is not currently known how *Gastornis* dispersed out of Europe and into North America and Asia. Given the presence of *Gastornis* fossils in the early Eocene of western China, these birds may have spread east from Europe and crossed into North America via the Bering land bridge. *Gastornis* also may have spread both east and west, arriving separately in eastern Asia and in North America across the Turgai Strait. Direct landbridges with North America are also known.

European *Gastornis* survived somewhat longer than their North American and Asian counterparts. This seems to coincide with a period of increased isolation of the continent.

## Extinction

The reason for the extinction of *Gastornis* is currently unclear. Competition with mammals has often been cited as a possible factor, but *Gastornis* did occur in faunas dominated by mammals, and did co-exist with several megafaunal forms like pantodonts. Likewise, extreme climatic events like the Paleocene–Eocene Thermal Maximum (PETM) appear to have had little impact.

Nonetheless, the extended survival in Europe is thought to coincide with increased isolation of the landmass.

## Appearance in other media

### *Jurassic Park*

* *Gastornis* can be created in the Glacial Park of *Jurassic Park: Builder* as a carnivore, but recent evidence suggests it was actually herbivorous.
* *Gastornis* can be created in the Cenozoic Park as a tournament Savannah creature in *Jurassic World: The Game*. Like the other Ludia game it appears in, Jurassic Park: Builder, it is portrayed as a carnivore since it uses the same animations as Phorusrhacos, even though the fact that it is herbivorous is brought up in a trivia point.