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''Erketu'' (meaning "Erketü Tengri") is a genus of somphospondylan sauropod
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
that lived in
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...
during the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...
roughly between 96 million and 89 million years ago. Its fossils were found in Mongolia between 2002 and 2003 during a field expedition and first described in 2006; later on in 2010 due to some cervicals that were left behind in the expedition. ''Erketu'' represents one of the first sauropods described from the
Bayan Shireh Formation The Bayan Shireh Formation (also known as Baynshiree/Baynshire, Baynshirenskaya Svita or Baysheen Shireh) is a geological formation in Mongolia, that dates to the Cretaceous period. It was first described and established by Vasiliev et al. 1959. ...
. The elongated cervical vertebrae of ''Erketu'' indicates that it was the sauropod with the longest neck relative to its body size.


Discovery and naming

The first remains of ''Erketu'' were found back in 2002 by the American Museum of Natural History–Mongolian Academy of Sciences expedition conducted in
Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...
. The team discovered the outcrops of the new locality Bor Guvé, which overlies the Khara Kuthul locality and therefore is referable to the
Bayan Shireh Formation The Bayan Shireh Formation (also known as Baynshiree/Baynshire, Baynshirenskaya Svita or Baysheen Shireh) is a geological formation in Mongolia, that dates to the Cretaceous period. It was first described and established by Vasiliev et al. 1959. ...
. The unearthed specimen, IGM 100/1803, was found in exposure at the sediments of Bor Guvé, mainly composed by
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...
and
interbedded In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology. For example, sedimentary rocks may be interbedded if there were sea level variations in their sedim ...
grey
siltstones Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility.Blatt ''et al.'' 1980, p ...
, suggesting a fluvial environment that is consistent with the Bayan Shireh Formation. Collected elements are mainly represented by cervical vertebrae and postcranial remains, such as the partial right
sternum The sternum or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, lungs, and major blood vessels from injury. Sha ...
,
tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...
and
fibula The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity i ...
with
astragalus ''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...
and
calcaneum In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. ...
. The remains became the
holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...
for the new genus and species ''Erketu ellisoni'', first described in 2006 by Daniel Ksepka and
Mark Norell Mark Allen Norell (born July 26, 1957) is an American paleontologist, acknowledged as one of the most important living vertebrate paleontologists. He is currently the chairman of paleontology and a research associate at the American Museum of Na ...
of the American Museum of Natural History. The generic name of this particular sauropod species is named after the creator god (tengri) of the Mongolian shamanism, Erketü. The specific name, ''ellisoni'', is in honor to the American Museum of Natural History's senior principal
paleoartist Paleoart (also spelled palaeoart, paleo-art, or paleo art) is any original artistic work that attempts to depict prehistoric life according to scientific evidence. Works of paleoart may be representations of fossil remains or imagined depiction ...
, and close friend of Norell: Mick Ellison. In 2003 the team returned to the site and recovered three additional cervicals that were left behind during the first field expedition, and consequently described in 2010.


Description

''Erketu'' was a relatively large sauropod, with an estimated length of and a weight of . Its neck was estimated to be twice as long as its body, which may be a record for neck to body ratio. The exact ratio is unknown, because no
dorsal vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical ...
of ''E. ellisoni'' have been reported, although some hindlimb material suggests the approximate size of the body. The long neck of ''Erketu'' is the result of the individual vertebrae being greatly elongated; it is unknown if the number of cervical vertebrae was increased. ''Erketu'' is also diagnosed by bifurcate anterior cervical neural spines, another unusual trait for a titanosauriform. The preserved cervicals include the
atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geograp ...
,
axis An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to: Mathematics * Axis of rotation: see rotation around a fixed axis * Axis (mathematics), a designator for a Cartesian-coordinat ...
and C3 to C9, however, the sixth is missing, giving a total of eight preserved cervical vertebrae. The preserved sternum is rather thickened at some borders and shows a very deep lateral edge, it measures about long. The right hindlimb elements were nicely found in articulation and they resemble those of '' Gobititan''. The tibia is very straight, measuring in total length, it has slightly expanded ends and in comparison to that of ''
Opisthocoelicaudia ''Opisthocoelicaudia'' is a genus of sauropod dinosaur of the Late Cretaceous Period discovered in the Gobi Desert of Mongolia. The type species is ''Opisthocoelicaudia skarzynskii''. A well-preserved skeleton lacking only the head and neck wa ...
'', the anterior and distal expansions are not very developed. The fibula is longer than the tibia with a length of , however, it appears to be broken on the distal end of one of the trochanters.


Classification

The phylogenetic analysis of sauropods performed by its describers indicates that ''Erketu'' is a basal somphospondylian (the clade of all
macronarians Macronaria is a clade of sauropod dinosaurs. Macronarians are named after the large diameter of the nasal opening of their skull, known as the external naris, which exceeded the size of the orbit, the skull opening where the eye is located (hence ...
closer to
titanosaurs Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still th ...
than to brachiosaurids), and is most closely related to
Titanosauria Titanosaurs (or titanosaurians; members of the group Titanosauria) were a diverse group of sauropod dinosaurs, including genera from all seven continents. The titanosaurs were the last surviving group of long-necked sauropods, with taxa still thr ...
, being a close relative of ''
Euhelopus ''Euhelopus'' is a genus of sauropod dinosaur that lived between 145 and 133 million years ago during the Berriasian and Valanginian stages of the Early Cretaceous in what is now Shandong Province in China. It was a large quadrupedal herbivore. U ...
''. During the description of '' Europatitan'' in 2017, a new cladistic analysis was performed. Here, ''Erketu'' was recovered in a
polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tr ...
along ''
Chubutisaurus ''Chubutisaurus'' (meaning " Chubut lizard") is a genus of dinosaur from the Early Cretaceous Period. It lived in South America. It is classified as a sauropod, specifically one of the titanosaurs. The type species, ''Chubutisaurus insignis'', w ...
'' within the Somphospondyli:


Paleoecology

The remains of ''Erketu'' are attributed to the
Bayan Shireh Formation The Bayan Shireh Formation (also known as Baynshiree/Baynshire, Baynshirenskaya Svita or Baysheen Shireh) is a geological formation in Mongolia, that dates to the Cretaceous period. It was first described and established by Vasiliev et al. 1959. ...
, which is believed to have been dominated by fluvial and lacrustine environments, such as large
meanders A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank ( cut bank) and deposits sediments on an inner, convex bank ...
and lakes but also a notorious semi-arid climate. The age is estimated to be around 95.9 ± 6.0 million to 89.6 ± 4.0 million years ago, Cenomanian to
Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya (million years ago) and 83.6 ± 0.7 mya. ...
epochs. Here, ''Erketu'' lived alongside diverse dinosaur fauna, such as the predators ''
Achillobator ''Achillobator'' ( ; meaning "Achilles hero") is a genus of large dromaeosaurid dinosaurs that lived in Asia during the Late Cretaceous period about 96 million to 89 million years ago in what is now the Bayan Shireh Formation. The genus is curren ...
'' and potentially ''
Alectrosaurus ''Alectrosaurus'' (; meaning "alone lizard") is a genus of tyrannosauroid theropod dinosaur that lived in Asia during the Late Cretaceous period, about some 96 million years ago in what is now the Iren Dabasu Formation. It was a medium-sized, ...
'', the abundant hadrosauroid ''
Gobihadros ''Gobihadros'' is a genus of basal hadrosauroid dinosaur that lived in Asia during the Late Cretaceous period in what is now the Bayan Shireh Formation (Cenomanian-Santonian). It contains only the type species ''Gobihadros mongoliensis''. It has ...
'', heavy armored '' Talarurus'' and '' Tsagantegia'', and the well-known therizinosaurs ''
Erlikosaurus ''Erlikosaurus'' (meaning "Erlik's lizard") is a genus of therizinosaurid that lived in Asia during the Late Cretaceous period. The fossils, a skull and some post-cranial fragments, were found in the Bayan Shireh Formation of Mongolia in 1972, da ...
'' and ''
Segnosaurus ''Segnosaurus'' is a genus of therizinosaurid dinosaur that lived in what is now southeastern Mongolia during the Late Cretaceous, about 102–86 million years ago. Multiple incomplete but well-preserved specimens were discovered in the Go ...
''. The locality of ''Erketu'' has also yielded an indeterminate/unnamed titanosaur and very abundant fossilized fruits. Some ecological niches were filled by several dinosaurs, such as the
browsers Browse, browser or browsing may refer to: Programs * Web browser, a program used to access the World Wide Web *Code browser, a program for navigating source code * File browser or file manager, a program used to manage files and related objects * ...
''Erlikosaurus'', ''Segnosaurus'' and ''Tsagantegia''; in contrast, ''Talarurus'' was a
grazer Grazer may refer to: *grazer, an animal that grazes *Grazer, a native or inhabitant of Graz *GRAZER, the shoegaze band GRAZER Astronomy * Earth Grazer, Earth-grazing fireball that enters the Earth's atmosphere and leaves again * Mercury grazer, ...
. ''Erketu'' in the other hand, due to its very long neck, was likely a high browser.


See also

*
Mark Norell Mark Allen Norell (born July 26, 1957) is an American paleontologist, acknowledged as one of the most important living vertebrate paleontologists. He is currently the chairman of paleontology and a research associate at the American Museum of Na ...
*
Sauropod neck posture Sauropod neck posture is a subject occasionally debated among scientists, with some favoring postures closer to horizontal whilst others a more upright posture. Research has looked at various avenues of evidence and analysis including: attempting ...


References

{{Taxonbar, from=Q138872 Late Cretaceous dinosaurs of Asia Fossil taxa described in 2006 Fossils of Mongolia Macronarians Taxa named by Mark Norell