Gastornis
Temporal range: Paleocene - Eocene, 56–45Ma
|
|---|
 |
| Mounted skeleton of G. giganteus |
Scientific classification |
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| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Anseriformes |
| Family: | †Gastornithidae |
| Genus: | †Gastornis
Hébert, 1855 (vide Prévost, 1855) |
| Type species |
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†Gastornis parisiensis
Hébert, 1855 |
| Species |
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- †G. parisiensis Hébert, 1855
- †G. giganteus (Cope, 1876)
- †G. sarasini Schaub, 1929
- †G. geiselensis Fischer, 1978
- †G. russeli Martin, 1992
- †G. xichuanensis (Hou, 1980)
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| Synonyms |
|---|
- Diatryma Cope, 1876
- Barornis Marsh, 1894
- Omorhamphus Sinclair, 1928
- Zhongyuanus (Hou, 1980)
|
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[edit]
Skeletal restoration of
Diatryma steini (now
G. giganteus).
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.
[2]
History[edit]
Lemoine's incorrect 1881 illustration of
G. eduardsii(now
G. parisiensis).
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 (
// 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.
[11]
Classification[edit]
Life restoration of
G. steini (now
G. giganteus), 1917.
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.
[13]
Recognizing the apparent close relationship between gastornithids and waterfowl, some researchers classify gastornithids within the anseriform group itself.
[13] 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.
[14] Gastornithids are therefore sometimes placed in their own
order,
Gastornithiformes.
[15]
A simplified version of the family tree found by Agnolin et al. in 2007 is reproduced below.
Skull and mandible of
G. giganteusspecimen AMNH 6169
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.
[16][17] 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,
[11] 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.
[18] The supposed small species
G. minor is considered to be a
nomen dubium.
[4]
Gastornis giganteus (
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.
[19] The species was named in honor of T. C. von Storch, who found the fossils remains in Princeton 1927 Expedition.
[20] The fossil bones originally described as
Omorhamphus storchii are now considered to be the remains of a juvenile
Gastornis giganteus.
[21]Specimen
YPM PU 13258 from lower Eocene
Willwood Formation rocks of
Park County, Wyoming also seems to be a juvenile – perhaps also of
G. giganteus, in which case it would be an even younger individual.
[22]
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.
[23] 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.
[24]
Biology[edit]
A long-standing debate surrounding
Gastornis is the interpretation of its diet.
Gastornis has often been depicted as a predator of contemporary small mammals, which famously included the early horse
Eohippus.
[2] 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, 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. It could have also 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 of these features strongly suggest that
Gastornis could generate a powerful bite.
[1]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, which utilized its powerfully constructed beak to subdue struggling prey and crack open bones to extract marrow.
[1] 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 of some sort, perhaps having instead used its large beak to crack hard foods like nuts and seeds.
[25] 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.
[26]
Recent evidence suggests that
Gastornis was likely a true herbivore.
[27] Studies of the calcium isotopes in the bones of specimens of Gastornis by Dr. Thomas Tutken and colleagues showed no evidence that
Gastornis had meat in its diet. The geochemical analysis further revealed 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.
[28]
In
Late Paleocene deposits of
Spain and early
Eocene deposits of France, shell fragments of huge
eggs have turned up, namely in the
Provence.
[29][30] These were described as the
ootaxon Ornitholithus and are presumably from
Gastornis. While no direct association exists between
Ornitholithus and
Gastornis fossils, no other birds of sufficient size are known from that time and place: while the large
Diogenornis and
Eremopezus are known from the Eocene, the former lived in
South America (still separated from North America by the
Tethys Ocean then) and the latter is only known from the Late Eocene of North Africa, which also was separated by an (albeit less wide) stretch of the Tethys Ocean from Europe.
[31]
Some of these fragments were complete enough to reconstruct a size of 24 by 10 cm (about 9.5 by 4 inches) with shells 2.3–2.5 mm (0.09–0.1 in) thick,
[29] roughly half again as large as an ostrich egg and very different in shape from the more rounded ratite eggs. If
Remiornis is indeed correctly identified as a ratite (which is quite doubtful however
[11]),
Gastornis remains as the only known animal that could have laid these eggs. It is also notable that at least one species of
Remiornis is known to have been smaller than the
Gastornis, and was initially described as
Gastornis minor by Mlíkovský in 2002. This would nicely match the remains of eggs a bit smaller than those of the living Ostrich which have also been found in
Paleogene deposits of Provence, were it not for the fact that these eggshell fossils also date from the Eocene but no
Remiornis bones are known from that time yet.
[30]
Several sets of fossil footprints are suspected to belong to
Gastornis. One set of footprints was reported from late
Eocene gypsumat
Montmorency and other locations of the
Paris Basin in the 19th century, from 1859 onwards. Described initially by
Jules Desnoyers and later on by
Alphonse Milne-Edwards, these trace fossils were celebrated among French geologists of the late 19th century. They were discussed by
Charles Lyell in his
Elements of Geology as an example of the incompleteness of the fossil record – no bones had been found associated with the footprints.
[32] Unfortunately, these fine specimens which sometimes preserved even details of the skin structure are now lost. They were brought to the
Muséum national d'histoire naturelle when Desnoyers started to work there, and the last documented record of them deals with their presence in the geology exhibition of the MNHN in 1912. The largest of these footprints, although only consisting of a single toe's impression, was 40 cm (16 in) long. The large footprints from the
Paris Basin could also be divided into huge and merely large examples, much like the eggshells from southern France which are 20 million years older.
[31]
Another footprint record consists of a single imprint which still exists, though it has proven to be even more controversial. It was found in late Eocene
Puget Group rocks in the
Green River valley near
Black Diamond, Washington. After its discovery, it raised considerable interest in the
Seattle area in May–July 1992, being subject of at least two longer articles in the
Seattle Times.
[33][34]Variously declared a
hoax or genuine, this apparent impression of a single bird foot measures about 27 cm wide by 32 cm long (11 by 13 in) and lacks a
hallux (hind toe); it was described as the
ichnotaxon Ornithoformipes controversus. Fourteen years after the initial discovery, the debate about the find's authenticity was still unresolved.
[35][36] The specimen is now at
Western Washington University.
[36][37]
The problem with these early trace fossils is that no fossil of
Gastornis has been found to be younger than about 45 million years. The enigmatic
"Diatryma" cotei is known from remains almost as old as the Paris basin footprints (whose date never could be accurately determined), but in North America the fossil record of unequivocal gastornithids seems to end even earlier than in Europe.
[31][37] However, in 2009 a landslide near
Bellingham, Washington exposed at least 18 tracks on 15 blocks in the Eocene
Chuckanut Formation. The anatomy and age (about 53.7 Ma old
[38]) of the tracks suggest the track maker was
Gastornis. Although these birds long been considered to be predators or scavengers, the absence of raptor-like claws supports earlier suggestions that they were herbivores. The Chuckanut tracks are named as the ichnotaxon
Rivavipes giantess, inferred to belong to the extinct family Gastornithidae. At least 10 of the tracks are on display at Western Washington University.
[26]
Feathers[edit]
Supposed
Gastornis feathers which turned out to be plant material
The
plumage of
Gastornis has generally been depicted in art as a hair-like covering similar to some
ratites. This has been based in part on some fibrous strands recovered from a
Green River Formation deposit at
Roan Creek, Colorado, which were initially believed to represent
Gastornis feathers and named
Diatryma filifera.
[39] Subsequent examination has shown that the supposed feathers were actually not feathers at all but
plant fibers.
[40]
However, a second possible
Gastornis feather has since been identified, also from the Green River Formation. Unlike the filamentous plant material, this single isolated feather resembles the body feathers of flighted birds, being broad and vaned. It was tentatively identified as a possible
Gastornis feather based on its size; the feather measured 240 millimetres (9.4 in) long and must have belonged to a gigantic bird.
[41]
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. 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, it is possible that these birds spread east from Europe and crossed into North America via the
Bering land bridge. It is also possible that
Gastornis spread both east and west, arriving separately in eastern Asia and in North America across the
Turgai Strait.
[24]
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