Tawa (dinosaur)
Encyclopedia
Tawa is a genus
of theropod dinosaur
from the Late Triassic
period. It is estimated to have been 2 m (6.5 ft) long. In 2004, a partial skeleton was excavated, and in 2006 two nearly complete fossil
skeletons of Tawa and parts of six others were found close together in the Hayden Quarry at Ghost Ranch
in New Mexico
(part of the Petrified Forest Member of the Chinle Formation
) in strata dating to approximately 215-213 million years ago. The discovery is significant and suggests that the earliest dinosaurs arose in the ancient area of Gondwana
that is now South America
and spread from there. The type species
is T. hallae, described in 2009 by Nesbitt et al. The specific name honours Ruth Hall, founder of the Ghost Ranch Museum of Paleontology.
, cataloged GR
241, is a mostly complete skull and postcranial skeleton belonging to a juvenile individual. Fossils of at least seven other individuals were also discovered at the site. One of these specimens, cataloged GR 242, is also nearly complete. An isolated femur suggests that adults were at least 30% larger than the holotype. All of these specimens are from the Hayden Quarry and date to between 215 to 213 million years old. Tawa was formally described in 2009 by a group of six American researchers led by Sterling J. Nesbitt
of the American Museum of Natural History
. At the time of publication in the journal Science
, Nesbitt was a postdoctoral researcher at the University of Texas at Austin
's Jackson School of Geosciences
.
, an early theropod from the Late Triassic. Tawa is, however, more advanced than the earliest known theropod dinosaurs, Eoraptor
, Herrerasaurus
, and Staurikosaurus
. A cladistic analysis of Tawa and other early theropods indicate that the Coelophysoidea
, a group of early dinosaurs, may be an artificial grouping because Tawa combines classic coelophysoid features with features which appear to be ancestral to the neotheropods. Tawa is believed to be the sister taxon of Neotheropoda, a group of carnivorous dinosaurs which bore only three functional digits on their feet.
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 theropod dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the Late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period. It is estimated to have been 2 m (6.5 ft) long. In 2004, a partial skeleton was excavated, and in 2006 two nearly complete fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
skeletons of Tawa and parts of six others were found close together in the Hayden Quarry at Ghost Ranch
Ghost Ranch
Ghost Ranch is a retreat and education center located close to the village of Abiquiu in Rio Arriba County in north central New Mexico. The conference center and lodgings at Ghost Ranch are run by the Presbyterian Church but open to the general public.-History:Ghost Ranch is part of Piedra...
in New Mexico
New Mexico
New Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
(part of the Petrified Forest Member of the Chinle Formation
Chinle Formation
The Chinle is a geologic formation that is spread across the U.S. states of northern Arizona, Nevada, Utah, western New Mexico, and western Colorado. The Chinle is controversially considered to be synonymous to the Dockum Group in eastern Colorado, eastern New Mexico, southwestern Kansas, the...
) in strata dating to approximately 215-213 million years ago. The discovery is significant and suggests that the earliest dinosaurs arose in the ancient area of 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,...
that is now 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...
and spread from there. 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...
is T. hallae, described in 2009 by Nesbitt et al. The specific name honours Ruth Hall, founder of the Ghost Ranch Museum of Paleontology.
Discovery
Fossils now attributed to Tawa were first discovered in 2004. The holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
, cataloged GR
Ghost Ranch
Ghost Ranch is a retreat and education center located close to the village of Abiquiu in Rio Arriba County in north central New Mexico. The conference center and lodgings at Ghost Ranch are run by the Presbyterian Church but open to the general public.-History:Ghost Ranch is part of Piedra...
241, is a mostly complete skull and postcranial skeleton belonging to a juvenile individual. Fossils of at least seven other individuals were also discovered at the site. One of these specimens, cataloged GR 242, is also nearly complete. An isolated femur suggests that adults were at least 30% larger than the holotype. All of these specimens are from the Hayden Quarry and date to between 215 to 213 million years old. Tawa was formally described in 2009 by a group of six American researchers led by Sterling J. Nesbitt
Sterling Nesbitt
Sterling Nesbitt , is an American paleontologist.-Biography:Sterling Nesbitt received his B.A. in integrative biology with a minor in geology from University of California Berkeley in 2004. He received his Ph.D from Columbia University in 2009, completing the majority of his research at the...
of the American Museum of Natural History
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
. At the time of publication in the journal Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....
, Nesbitt was a postdoctoral researcher at the University of Texas at Austin
University of Texas at Austin
The University of Texas at Austin is a state research university located in Austin, Texas, USA, and is the flagship institution of the The University of Texas System. Founded in 1883, its campus is located approximately from the Texas State Capitol in Austin...
's Jackson School of Geosciences
Jackson School of Geosciences
The Jackson School of Geosciences at The University of Texas at Austin unites the Department of Geological Sciences with two research units, the Institute for Geophysics and the Bureau of Economic Geology....
.
Classification
The 2009 description of Tawa places this genus as more basal than CoelophysisCoelophysis
Coelophysis , meaning "hollow form" in reference to its hollow bones , is one of the earliest known genera of dinosaur...
, an early theropod from the Late Triassic. Tawa is, however, more advanced than the earliest known theropod dinosaurs, Eoraptor
Eoraptor
Eoraptor was one of the world's earliest dinosaurs. It was a two-legged saurischian, close to the ancestry of theropods and sauropodomorphs. It lived ca. 231.4 million years ago, in what is now the northwestern region of Argentina...
, Herrerasaurus
Herrerasaurus
Herrerasaurus was one of the earliest dinosaurs. All known specimens of this carnivore have been discovered in rocks of late Ladinian age in northwestern Argentina...
, and Staurikosaurus
Staurikosaurus
Staurikosaurus is a genus of herrerasaurid dinosaur from the Late Triassic of Brazil.-Discovery:The first known specimen of Staurikosaurus was recovered from the Paleontological Site Jazigo Cinco of the Santa Maria Formation in the geopark of paleorrota , Rio Grande do Sul, southern Brazil...
. A cladistic analysis of Tawa and other early theropods indicate that the Coelophysoidea
Coelophysoidea
Coelophysoids were common dinosaurs of the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivorous forms with a superficial similarity to the coelurosaurs, with which they were formerly...
, a group of early dinosaurs, may be an artificial grouping because Tawa combines classic coelophysoid features with features which appear to be ancestral to the neotheropods. Tawa is believed to be the sister taxon of Neotheropoda, a group of carnivorous dinosaurs which bore only three functional digits on their feet.
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External links
- National Science FoundationNational Science FoundationThe National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
special report on Tawa hallae