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RE: Erketu ellisoni

Andrew Farke wrote:

The partial citation from the Nature site is   Ksepka D. T.& Norell M. A.
2006. AMNH Novitates, 3508.

The full citation is:

Ksepka D.T. and Norell M.A. (2006). _Erketu ellisoni_, a long-necked sauropod from Bor Guvé (Dornogov Aimag, Mongolia). American Museum Novitates 3508: 1-16.

Abstract: "The first specimen of the new sauropod _Erketu ellisoni_, from the Lower Cretaceous of the eastern Gobi of Dornogov, Mongolia, is described here. The specimen comprises a well-preserved articulated anterior cervical series, an articulated lower hindlimb, and a sternal plate. This sauropod displays a unique combination of features including low, bifid neural spines, elongate cervical centra, and crescent-shaped sternal plates. Computed tomography imaging reveals the vertebrae were extensively invaded with pneumatic camellae. The holotype individual of _Erketu_ was of modest mass relative to other neosauropods, but had an extremely elongate neck. Phylogenetic analysis indicates _Erketu_ is a member of the Somphospondyli and may belong to a more exclusive clade therein."

"Holotype: IGM 100/1803: articulated cervical series including complete first through fifth cervical vertebrae, partial sixth cervical vertebra, right sternal plate, articulated right tibia, fibula, astragalus, and calcaneum.

Etymology: _Erketu_: In Mongolian shamanistic tradition, there are 99 Tengri (deities). Erketu Tengri is the Mighty Tengri, a creator-god who called Yesugei, the father of Chingis Khan, into being. _ellisoni_: In honor of Mick Ellison, for his contributions to ongoing AMNH dinosaur research.

Diagnosis: Referable to Titanosauriformes based on elongate cervical vertebrae with camellae and referable within Titanosauriformes to Somphospondyli based on reduced neural arch lamination. Differentiated from all other Titanosauriformes in which cervical vertebrae are known by combination of extremely elongated (EI indices of anterior cervicals exceeding 5.0) cervical centra and bifurcate anterior cervical neural spines.

Type locality and horizon: Bor Guve: late Early Cretaceous. Stratigraphically, the beds at this locality lie below the Tsaagan Tsonch beds (a unit that contains _Iguanodon orientalis_) and above the Khara Khuutul beds, both believed to be of late Early Cretaceous age (Shuvalov, 2000). The lack of materials suitable for radiometric dating leaves the exact age of this locality uncertain."

Technically _Erketu_ is not a titanosaur, but a somphospondylian or a titanosauriform. Further material might show it to be a true titanosaur (see below). The phylogenetic analysis puts _Erketu_ in one of two positions: the sister taxon of _Euhelopus_ or the sister taxon of Titanosauria. Thus, there is a potential for a monophyletic Euhelopodidae (_Erketu_ + _Euhelopus_). However, although both _Erketu_ and _Euhelopus_ are characterized by having very long necks, in _Euhelopus_ individual cervical vertebrae show little elongation; instead, the total number of cervical vertebrae in _Euhelopus_ is increased to 17. In _Erketu_, individual cervicals are very long, but we don't know the vertebral count for the neck.

There is more undescribed material from the type locality that may belong to _Erketu_, including some sauropod teeth. These teeth have cylindrical and unexpanded crowns, and if they prove to belong to _Erketu_ it may push this taxon up into the Titanosauria.

The authors also discuss the axial musculature of _Erketu_, with some neat comments on neural spine bifurcation. Sauropods as a group show no correlation between the latter character in the cervical series and the length of the neck relative to the body, in spite of the notion that (as the authors put it) "[A]s elongation of the neck increases, the functional benefits of bifurcation should increase concomitantly."