| Erketu | |
|---|---|
 | |
| Skeletal reconstruction of the holotype | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | †Sauropodomorpha |
| Clade: | †Sauropoda |
| Clade: | †Macronaria |
| Clade: | †Titanosauriformes |
| Clade: | †Somphospondyli |
| Genus: | †Erketu Ksepka & Norell, 2006 |
| Type species | |
| †Erketu ellisoni Ksepka & Norell, 2006 | |
Erketu (meaning "Erketü tengri") is a genus ofsomphospondylandinosaur that lived inAsia during theLate Cretaceous, roughly between 96 million and 89 million years ago. It is known from theBayanshiree Formation ofMongolia, and its fossils were found between 2002 and 2003 during field expeditions.Erketu was first described in 2006 and later on in 2010 due to some cervicals that were left behind in the expedition. This genus represents the first sauropod described from the Bayanshiree Formation. The elongated cervical vertebrae indicate that it probably had the longest neck relative to its body size of any sauropod.
The first remains ofErketu were found back in 2002 by the American Museum of Natural History–Mongolian Academy of Sciences expedition conducted inMongolia. The team discovered the outcrops of the new locality Bor Guvé, which overlies the Khara Kuthul locality and therefore is referable to theBayan Shireh Formation. The unearthed specimen,IGM 100/1803, was found in exposure at the sediments of Bor Guvé, mainly composed bysandstone andinterbedded greysiltstones, suggesting afluvial environment that is consistent with the Bayan Shireh Formation. Collected elements are mainly represented bycervical vertebrae and postcranial remains, such as the partial rightsternum,tibia andfibula withastragalus andcalcaneum.[1]
The remains became theholotype for the new genus and speciesErketu ellisoni, first described in2006 by Daniel Ksepka andMark Norell of theAmerican Museum of Natural History. The generic name of this particular sauropod species is named after the creator god (tengri) of the Mongolianshamanism,Erketü. The specific name,ellisoni, is in honor to the American Museum of Natural History's senior principalpaleoartist, and close friend of Norell: Mick Ellison.[1] 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 in2010.[2]
Erketu was a relatively large sauropod, with an estimated length of 15 m (49 ft) and a weight of 5 t (11,000 lb).[3] 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 nodorsal vertebrae ofE. ellisoni have been reported, although some hindlimb material suggests the approximate size of the body. The long neck ofErketu 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 theatlas,axis and C3 to C9, however, the sixth is missing, giving a total of eight preserved cervical vertebrae.[1][2]
The preserved sternum is rather thickened at some borders and shows a very deep lateral edge, it measures about 530 mm (53 cm) long. The right hindlimb elements were nicely found in articulation and they resemble those ofGobititan. The tibia is very straight, measuring 710 mm (71 cm) in total length, it has slightly expanded ends and in comparison to that ofOpisthocoelicaudia, the anterior and distal expansions are not very developed. The fibula is longer than the tibia with a length of 750 mm (75 cm), however, it appears to be broken on the distal end of one of thetrochanters.[1]
The phylogenetic analysis of sauropods performed by its describers indicates thatErketu is a basal somphospondylian (theclade of allmacronarians closer totitanosaurs than tobrachiosaurids), and is most closely related toTitanosauria, being a close relative ofEuhelopus.[1]
During the description ofEuropatitan in 2017, a new cladistic analysis was performed. Here,Erketu was recovered in apolytomy alongChubutisaurus within the Somphospondyli:[4]
The remains ofErketu are attributed to theBayan Shireh Formation,[2] which is believed to have been dominated by fluvial and lacustrine environments, such as largemeanders andlakes but also a notorious semi-arid climate.[5][6] The age is estimated to be around 95.9 ± 6.0 million to 89.6 ± 4.0 million years ago,Cenomanian toConiacian stages.[7][8] Here,Erketu lived alongside diverse dinosaur fauna, such as the theropodsAchillobator andKhankhuuluu,[9][10] the abundant hadrosauroidGobihadros,[11] heavy armored ankylosaursTalarurus andTsagantegia,[12] and the well-known therizinosaursErlikosaurus andSegnosaurus.[13] The locality ofErketu has also yielded an indeterminate/unnamed titanosaur and very abundant fossilizedfruits.[1][2] Some ecological niches were filled by several dinosaurs, such as thebrowsersErlikosaurus,Segnosaurus[13] andTsagantegia; in contrast,Talarurus was agrazer.[12]Erketu in the other hand, due to its very long neck, was likely a high browser.[3]
