Tarchia
Encyclopedia
Tarchia is a genus
of ankylosaurid
dinosaur
from the late Cretaceous
of Mongolia
. It is currently the geologically youngest known of all the Asia
n ankylosaurid
dinosaurs and is represented by five or more specimens, including two complete skulls and one nearly complete postcranial skeleton. It was discovered in the Upper Cretaceous
(possibly Campanian
-Maastrichtian
) Barun Goyot Formation
(previously known as the 'Lower Nemegt Beds') of the Nemegt Basin
of Mongolia. It had a bony tail club, like many ankylosaurids.
Named for its massive skull (Mongolian
tarkhi meaning 'brain' and Latin
ia), Tarchia currently includes only the type species
, T. gigantea. The rocks in which they were found likely represent eolian dunes and interdune environments, with small intermittent lakes and seasonal streams. Hence, we know that Tarchia was a desert
animal. The morphology
of cranial sculpturing seen in Tarchia, an assortment of bulbous polygon
s, is reminiscent of that of Saichania
chulsanensis, another ankylosaurid from the Barun Goyot Formation.
Tarchia is distinguished from Saichania on the basis of its relatively larger basicranium, an unfused paroccipital process-quadrate contact and that the premaxilla
ry rostrum is wider than the maximum distance between the tooth rows in the maxillaries. In Tarchia, wear facet
s indicative of tooth-to-tooth occlusion
is present (Barret, 2001).
s of Late Cretaceous ankylosaurids are nested deep to Tarchia, one comprising North America
n taxa (Ankylosaurus
, Euoplocephalus
) and the other comprising Asian taxa (Pinacosaurus
spp., Saichania
, Tianzhenosaurus
, Talarurus
). Dyoplosaurus
giganteus is considered a synonym of Tarchia and a second proposed species of Tarchia, T. kielanae has been found to be the same as T. gigantea (Vickaryous et al., 2004).
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 ankylosaurid
Ankylosauridae
An ankylosaurid is a member of the Ankylosauridae family of armored dinosaurs that evolved 125 million years ago and became extinct 65 million years ago during the Cretaceous-Tertiary extinction event...
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 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 Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
. It is currently the geologically youngest known of all the Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
n ankylosaurid
Ankylosauria
Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. They are first known to have appeared in the early Jurassic Period of...
dinosaurs and is represented by five or more specimens, including two complete skulls and one nearly complete postcranial skeleton. It was discovered in the Upper Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
(possibly Campanian
Campanian
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 ...
-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...
) Barun Goyot Formation
Barun Goyot Formation
The Barun Goyot Formation , dating from the Late Cretaceous Period, is located within and is widely represented in the Gobi Desert basin, in the Ömnögovi Province of Mongolia....
(previously known as the 'Lower Nemegt Beds') of the Nemegt Basin
Nemegt Basin
The Nemegt Basin is situated in the northwestern part of the Gobi Desert, in the Ömnögovi Province in the southern part of Mongolia. It is known locally as the valley of the dragons, since it is a source of many fossil finds, including dinosaurs, dinosaur eggs and trace fossils.The main geological...
of Mongolia. It had a bony tail club, like many ankylosaurids.
Description
Tarchia is one of the largest known Asian ankylosaurs, with an estimated body length of 8 to 8.5 m (26.2 to 27.9 ft), a skull length of 40 centimetres (15.7 in), and skull width of 45 centimetres (17.7 in). Tarchia may have weighed as much as 4.5 tonnes (5 ST).Named for its massive skull (Mongolian
Mongolian language
The Mongolian language is the official language of Mongolia and the best-known member of the Mongolic language family. The number of speakers across all its dialects may be 5.2 million, including the vast majority of the residents of Mongolia and many of the Mongolian residents of the Inner...
tarkhi meaning 'brain' and Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
ia), Tarchia currently includes only 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...
, T. gigantea. The rocks in which they were found likely represent eolian dunes and interdune environments, with small intermittent lakes and seasonal streams. Hence, we know that Tarchia was a desert
Desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...
animal. The morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
of cranial sculpturing seen in Tarchia, an assortment of bulbous polygon
Polygon
In geometry a polygon is a flat shape consisting of straight lines that are joined to form a closed chain orcircuit.A polygon is traditionally a plane figure that is bounded by a closed path, composed of a finite sequence of straight line segments...
s, is reminiscent of that of Saichania
Saichania
Saichania is a genus of ankylosaurid dinosaur from the Late Cretaceous period. It was found in the Barun Goyot Formation at Khulsan in the Nemegt Basin, southern Mongolia. It lived during the Campanian. The type species is Saichania chulsanensis.Saichania was described by Teresa Maryańska in 1977,...
chulsanensis, another ankylosaurid from the Barun Goyot Formation.
Tarchia is distinguished from Saichania on the basis of its relatively larger basicranium, an unfused paroccipital process-quadrate contact and that the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
ry rostrum is wider than the maximum distance between the tooth rows in the maxillaries. In Tarchia, wear facet
Facet
Facets are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure...
s indicative of tooth-to-tooth occlusion
Occlusion (dentistry)
Occlusion, in a dental context, means simply the contact between teeth. More technically, it is the relationship between the maxillary and mandibular teeth when they approach each other, as occurs during chewing or at rest....
is present (Barret, 2001).
Taxonomy and phylogenetics
Vickaryous et al. (2004) state that two distinct cladeClade
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...
s of Late Cretaceous ankylosaurids are nested deep to Tarchia, one comprising 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...
n taxa (Ankylosaurus
Ankylosaurus
Ankylosaurus is a genus of ankylosaurid dinosaur, containing one species, A. magniventris...
, Euoplocephalus
Euoplocephalus
Euoplocephalus was one of the largest genera of ankylosaurian dinosaurs, at about the size of a small elephant. It is also the ankylosaurian with the best fossil record, so its extensive spiked armor, low-slung body and great club-like tail are well documented.-Description:Among the...
) and the other comprising Asian taxa (Pinacosaurus
Pinacosaurus
Pinacosaurus is a genus of medium-sized ankylosaur dinosaurs that lived from the late Santonian to the late Campanian stages of the late Cretaceous Period , in Mongolia and China...
spp., Saichania
Saichania
Saichania is a genus of ankylosaurid dinosaur from the Late Cretaceous period. It was found in the Barun Goyot Formation at Khulsan in the Nemegt Basin, southern Mongolia. It lived during the Campanian. The type species is Saichania chulsanensis.Saichania was described by Teresa Maryańska in 1977,...
, Tianzhenosaurus
Tianzhenosaurus
Tianzhenosaurus is a genus of ankylosaurid dinosaur discovered in Tianzhen County, at Kangdailiang near Zhaojiagou Village, in Shanxi Province, China, in the Late Cretaceous Huiquanpu Formation. Thus far, a virtually complete skull and postcranial skeleton have been assigned to the genus, which is...
, Talarurus
Talarurus
Talarurus is a genus of hippopotamus-sized ankylosaurid dinosaur with heavy armour and a club tail. It was named by Evgeny Maleev in 1952.-Age and location:...
). Dyoplosaurus
Dyoplosaurus
Dyoplosaurus is the name given to a genus of ankylosaurid dinosaur. It lived during the Late Cretaceous near what is now the Red Deer River in Alberta, Canada and was named by William Parks in 1924, based on holotype ROM 784, a partial skeleton including parts of the skull and lower jaws.The type...
giganteus is considered a synonym of Tarchia and a second proposed species of Tarchia, T. kielanae has been found to be the same as T. gigantea (Vickaryous et al., 2004).