Avisaurus
Encyclopedia
Avisaurus is a genus
of enantiornithine
bird
from the Late Cretaceous
of North America
.
Two species are known; the type species
A. archibaldi and A. gloriae. Both are known only from single fossilized bones of the foot — the tarsometatarsus
.
Both species of Avisaurus are known from the humid low-lying swamps, lakes, and river basins of the western shore of the Western Interior Seaway
, and from the much more arid uplands between that area and the Cordilleran Overthrust Belt which eventually formed the Rocky Mountains
.
This genus belongs to the enantiornithine family
Avisauridae
, which also contains similar animals from South America
such as Soroavisaurus
and Neuquenornis
In the Late Cretaceous the Americas
were still separated by a branch of the Tethys Ocean
.
The presence of reported Avisaurus remains in both North and South America has been put forward as evidence that faunal changes in the southern half of North America during the Lancian resulted from an immigration event of South American taxa moving north.
of North America (Maastrichtian
, from c.70.6-65.5 million years ago), making it one of the last enantiornithids. It was collected in 1975 in the UCMP locality V73097, in Garfield County, Montana, USA.
A. archibaldi is represented by a single fossil of a tarsometatarsus
in the collection of the University of California Museum of Paleontology. It has the catalog number UCMP 117600. It was initially described as the left tarsometatarsus of a non-avian theropod by Brett-Surman and Paul in 1985. It was later redescribed as the right tarsometatarsus of an enantiornithine bird by Chiappe in 1992.
The specimen has a maximum length of 73.9 mm, making it one of the largest known tarsometatarsi of an enantiornithine.
It is named after J. David Archibald, its discoverer, from The University of California, Berkeley.
Two Medicine Formation
(c. 77 - 71 mya). It was collected in the MOR locality TM-068, Glacier County, Montana, USA.
A. gloriae is represented by a single fossil of a right tarsometatarsus
in the collection of the Museum of the Rockies of Montana State University. It has catalog number MOR 553E/6.19.91.64. It was collected in 1991. It was described by Varrichio and Chiappe in 1995.
The specimen has a maximum length of 30.9mm.
It is named after Gloria Siebrecht, a Volunteer Preparator for the Museum of the Rockies.
" PVL 4690 from Argentina. The authors assigned this latter fossil to Avisaurus sp. From this they concluded that members of the genus Avisaurus existed in both North and South America in the Late Cretaceous. Moreover, the authors concluded that the length/width ratio and degree of metacarpal fusion of these bones were more like those of non — avian dinosaurs. A terrestrial dinosaur genus in both continents would then support Brett — Surman's theory that there had been a land connection between the two continents.
Further discoveries and further study by Chiappe showed that all of the material belonged to enantiornithine birds, and that PVL 4690 was actually a bird called Soroavisaurus
.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of enantiornithine
Enantiornithes
Enantiornithes is an extinct group of primitive birds. They were the most abundant and diverse avialans of the Mesozoic. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern birds externally. Over 50 species of Enantiornithines have been named, but some...
bird
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...
from 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...
of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
.
Two species are known; the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
A. archibaldi and A. gloriae. Both are known only from single fossilized bones of the foot — the tarsometatarsus
Tarsometatarsus
The tarsometatarsus is a bone that is found in the lower leg of certain tetrapods, namely birds.It is formed from the fusion of several bones found in other types of animals, and homologous to the mammalian tarsal and metatarsal bones...
.
Both species of Avisaurus are known from the humid low-lying swamps, lakes, and river basins of the western shore of the Western Interior Seaway
Western Interior Seaway
The Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves, Laramidia and Appalachia, during most of the mid- and late-Cretaceous Period...
, and from the much more arid uplands between that area and the Cordilleran Overthrust Belt which eventually formed the Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
.
This genus belongs to the enantiornithine family
Family
In human context, a family is a group of people affiliated by consanguinity, affinity, or co-residence. In most societies it is the principal institution for the socialization of children...
Avisauridae
Avisauridae
The Avisauridae are a family of extinct Enantiornithine birds known from Cretaceous North and South America. They are represented by eight genera.Avisauridae was erected by Brett-Surman and Paul in 1985...
, which also contains similar animals from South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
such as Soroavisaurus
Soroavisaurus
Soroavisaurus australis was an enantiornithine bird related to Avisaurus. It lived during the Late Cretaceous of Argentina.S. australis is known from fossils collected from the Lecho Formation of Estancia El Brete, in the southern tip of the province of Salta, Argentina...
and Neuquenornis
Neuquenornis
Neuquenornis volans was an enantiornithine bird which lived during the Late Cretaceous in today's Patagonia, Argentina. It is presently the only known species of the genus Neuquenornis. Its fossils were found in the Santonian Bajo de la Carpa Formation, dating from about 85-83 million years ago....
In the Late Cretaceous 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...
were still separated by a branch of the Tethys Ocean
Tethys Ocean
The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean.-Modern theory:...
.
The presence of reported Avisaurus remains in both North and South America has been put forward as evidence that faunal changes in the southern half of North America during the Lancian resulted from an immigration event of South American taxa moving north.
Avisaurus archibaldi
A. archibaldi was discovered in the Late Cretaceous Hell Creek FormationHell Creek Formation
The Hell Creek Formation is an intensely-studied division of Upper Cretaceous to lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana...
of North America (Maastrichtian
Maastrichtian
The Maastrichtian is, in the ICS' geologic timescale, the latest age or upper stage of the Late Cretaceous epoch or Upper Cretaceous series, the Cretaceous period or system, and of the Mesozoic era or erathem. It spanned from 70.6 ± 0.6 Ma to 65.5 ± 0.3 Ma...
, from c.70.6-65.5 million years ago), making it one of the last enantiornithids. It was collected in 1975 in the UCMP locality V73097, in Garfield County, Montana, USA.
A. archibaldi is represented by a single fossil of a tarsometatarsus
Tarsometatarsus
The tarsometatarsus is a bone that is found in the lower leg of certain tetrapods, namely birds.It is formed from the fusion of several bones found in other types of animals, and homologous to the mammalian tarsal and metatarsal bones...
in the collection of the University of California Museum of Paleontology. It has the catalog number UCMP 117600. It was initially described as the left tarsometatarsus of a non-avian theropod by Brett-Surman and Paul in 1985. It was later redescribed as the right tarsometatarsus of an enantiornithine bird by Chiappe in 1992.
The specimen has a maximum length of 73.9 mm, making it one of the largest known tarsometatarsi of an enantiornithine.
It is named after J. David Archibald, its discoverer, from The University of California, Berkeley.
Avisaurus gloriae
A. gloriae was discovered in the CampanianCampanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
Two Medicine Formation
Two Medicine Formation
The Two Medicine Formation is a geologic formation, or rock body, that was deposited between 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma , during Campanian time, and is located in northwestern Montana...
(c. 77 - 71 mya). It was collected in the MOR locality TM-068, Glacier County, Montana, USA.
A. gloriae is represented by a single fossil of a right tarsometatarsus
Tarsometatarsus
The tarsometatarsus is a bone that is found in the lower leg of certain tetrapods, namely birds.It is formed from the fusion of several bones found in other types of animals, and homologous to the mammalian tarsal and metatarsal bones...
in the collection of the Museum of the Rockies of Montana State University. It has catalog number MOR 553E/6.19.91.64. It was collected in 1991. It was described by Varrichio and Chiappe in 1995.
The specimen has a maximum length of 30.9mm.
It is named after Gloria Siebrecht, a Volunteer Preparator for the Museum of the Rockies.
The Brett-Surman Paper
The paper by Brett-Surman and Paul in 1985 explicitly considered the possibility that A. archibaldi was an enantiornithine. The authors described and named UCMP 117600 formally, but they looked at other enantiornithine material, including the "metatarsusMetatarsus
The metatarsus or metatarsal bones are a group of five long bones in the foot located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial side : the first, second, third, fourth, and fifth...
" PVL 4690 from Argentina. The authors assigned this latter fossil to Avisaurus sp. From this they concluded that members of the genus Avisaurus existed in both North and South America in the Late Cretaceous. Moreover, the authors concluded that the length/width ratio and degree of metacarpal fusion of these bones were more like those of non — avian dinosaurs. A terrestrial dinosaur genus in both continents would then support Brett — Surman's theory that there had been a land connection between the two continents.
Further discoveries and further study by Chiappe showed that all of the material belonged to enantiornithine birds, and that PVL 4690 was actually a bird called Soroavisaurus
Soroavisaurus
Soroavisaurus australis was an enantiornithine bird related to Avisaurus. It lived during the Late Cretaceous of Argentina.S. australis is known from fossils collected from the Lecho Formation of Estancia El Brete, in the southern tip of the province of Salta, Argentina...
.