Gastornithiformes
Encyclopedia
Gastornithiformes are an order of prehistoric bird
s. 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 generally assumed to be predators, but this is conjectural. It is likely though that they included a considerable amount of meat in their diet, although they may have been scavengers rather than active hunters.
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 Gondwana
n but apparently not closely related to crane
s, 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 seriema
s 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 screamer
s). 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" 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 phene
s in most aspects.
Apart from the genera
listed above, there are some indeterminate gastornithiform fossils:
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s. The birds from this group lived from the Paleocene
Paleocene
The Paleocene or Palaeocene, the "early recent", is a geologic epoch that lasted from about . It is the first epoch of the Palaeogene Period in the modern Cenozoic Era...
to the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
and were spread out across Asia, Europe, and North America. All the birds were very large birds that were flightless, similar to an ostrich
Ostrich
The Ostrich is one or two species of large flightless birds native to Africa, the only living member of the genus Struthio. Some analyses indicate that the Somali Ostrich may be better considered a full species apart from the Common Ostrich, but most taxonomists consider it to be a...
but more heavily built and with a huge beak. They are generally assumed to be predators, but this is conjectural. It is likely though that they included a considerable amount of meat in their diet, although they may have been scavengers rather than active hunters.
There is no agreement on the relationships of the Gastornithiformes. They were long and still are sometimes placed with the Gruiformes
Gruiformes
The Gruiformes are an order containing a considerable number of living and extinct bird families, with a widespread geographical diversity. Gruiform means "crane-like"....
as a family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Gastornithidae. The Gruiformes seem paraphyletic though, with some lineages that are exclusively Gondwana
Gondwana
In paleogeography, Gondwana , originally Gondwanaland, was the southernmost of two supercontinents that later became parts of the Pangaea supercontinent. It existed from approximately 510 to 180 million years ago . Gondwana is believed to have sutured between ca. 570 and 510 Mya,...
n but apparently not closely related to crane
Crane (bird)
Cranes are a family, Gruidae, of large, long-legged and long-necked birds in the order Gruiformes. There are fifteen species of crane in four genera. Unlike the similar-looking but unrelated herons, cranes fly with necks outstretched, not pulled back...
s, rails and allies which are common in Eurasia and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
but far less so in the Americas. Some others, probably unrelated to either group, were very diverse in the Americas
Americas
The Americas, or America , are lands in the Western hemisphere, also known as the New World. In English, the plural form the Americas is often used to refer to the landmasses of North America and South America with their associated islands and regions, while the singular form America is primarily...
but prehistorically also occurred in Europe. Nothing is known of the ancestry of the Gastornithiformes; judging from biogeography
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
, a relationship with either the true Gruiformes or the "Americas" lineage (which might include the seriema
Seriema
The seriemas are the sole extant members of the small and ancient family Cariamidae, which is also the sole surviving family of the Cariamae. Once believed to be related to cranes, they have been placed by one recent study near the falcons, parrots and passerines, as well as the extinct terror birds...
s 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
Anseriformes
The order Anseriformes contains about 150 living species of birds in three extant families: the Anhimidae , Anseranatidae , and the Anatidae, which includes over 140 species of waterfowl, among them the ducks, geese, and swans.All species in the order are highly adapted for an aquatic existence at...
(waterfowl
Waterfowl
Waterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans....
and screamer
Screamer
The screamers are a small family of birds, the Anhimidae. For a long time they were thought to be related to the Galliformes because of similar bills, but they are truly related to ducks , most closely to the Magpie Goose...
s). The present birds would thus be members of the fowl clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
, Galloanserae. The clade name Anserimorphae has been proposed for the Gastornithiformes and the Anseriformes, as opposed to birds closer to Galliformes
Galliformes
Galliformes are an order of heavy-bodied ground-feeding domestic or game bird, containing turkey, grouse, chicken, New and Old World Quail, ptarmigan, partridge, pheasant, and the Cracidae. Common names are gamefowl or gamebirds, landfowl, gallinaceous birds or galliforms...
. As Galloanserae are known to have reached some diversity in the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
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
Neogene
The Neogene is a geologic period and system in the International Commission on Stratigraphy Geologic Timescale starting 23.03 ± 0.05 million years ago and ending 2.588 million years ago...
mihirungs would have recapitulated the gigantism of the Gastornithiformes, though based on a more advanced anseriform (i.e., more "gooselike" as regards details of their osteology
Osteology
Osteology is the scientific study of bones. A subdiscipline of anatomy, anthropology, and archeology, osteology is a detailed study of the structure of bones, skeletal elements, teeth, morphology, function, disease, pathology, the process of ossification , the resistance and hardness of bones , etc...
) ancestor. This would be an outstanding example of convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
which was very close to being homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
phylogenetically but still a true convergence of phene
Phene
A phene is an individual genetically determined characteristic or trait which can be possessed by an organism, such as eye colour, height, behavior, tooth shape or any other observable characteristic.-Phene - phenotype - phenome distinction:...
s in most aspects.
Apart from the genera
Genera
Genera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...
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)