Tsagantegia

Discovery and naming

The first, and only, discovery of Tsagantegia fossils occurred in 1983, when the Mesozoic team of the Joint Soviet-Mongolian Paleontological Expedition unearthed an ankylosaur skull from the Tsagan-Teg (or "White Mountain") locality near the town of Dzun-Bayan, Mongolia. This locality is one of many deriving from the Bayan Shireh Formation, an Upper Cretaceous (Cenomanian-Turonian)-aged geologic formation in the eastern Gobi Desert, Mongolia. This ankylosaur skull was then deposited at the Institute of Paleontology and Geology of the Mongolian Academy of Sciences (MPC) under specimen number MPC 700/17. This skull remained unresearched until it was described by Russian paleontologist Tatiana Tumanova in 1993. Tumanova described the skull as belonging to a new genus and species of ankylosaurine ankylosaurid, Tsagantegia longicranialis. The generic name, Tsagantegia, is in reference to the Tsagan-Teg locality where the skull was unearthed, and the specific name, longicranialis, comes from the Latin roots longus "long" and cranium "skull" in reference to its elongated skull. Due to being known solely from MPC 700/17, MPC 700/17 was chosen as the holotype (name-bearing) specimen for Tsagantegia longicranialis. Since its description, no additional remains of Tsagantegia longicranialis have been mentioned in scientific literature.

Description

Tsagantegia was a medium to large-sized ankyosaur, with an estimated length of 6 to and weighing about 1 to. The skull measures about 38 cm in length, with a near width of 25 cm, missing the lower jaws. Unlike other Asian ankylosaurs, in Tsagantegia the caputegulae (cranial ornamentation) are not subdivided into a mosaic of polygons but are amorphous and flattened; they show some degree of symmetry. The quadratojugal, squamosal and orbital horns are poorly preserved, in contrast with other ankylosaurs. The snout was long and flat with a pointed rostrum (beak); each maxilla preserves approximately 18 alveoli, no teeth were preserved. According to Arbour, Tsagantegia differs from Gobisaurus and Shamosaurus based on the more rounded, U-shaped premaxillary beak and the flat ornamentation.[[File:Tsagantegia Skeleton Reconstruction.jpg|left|thumb|Skeletal diagram of MPC 700/17]]

Classification

Although fragmentary, the phylogenetic position of Tsagantegia can be established. In 2012, Thompson et al. conducted an analysis of almost all known valid ankylosaurs and outgroup taxa at the time. They based their resulting phylogeny on characters representing cranial, post-cranial, and osteodermal anatomy, and details of synapomorphies for each recovered clade. Tsagantegia was found to be closely related to Pinacosaurus and Shamosaurus. In the performed phylogenetic analysis by Arbour and Currie in 2015, below are the results for the analysis:

Paleoecology

Caliche-based boundary indicates a semi-arid environment and climate, but also, the presence of fluvial and lacustrine sediments are indicators of large rivers and lakes. As interpreted by Hicks et al. 1999, during the times of the Bayan Shireh Formation, large rivers drained the eastern part of the Gobi Desert. Additional to this, fossil fruits remains have been recovered from the Bor Guvé and Khara Khutul localities (Upper and Lower Bayan Shireh, respectively), suggesting the presence of Angiosperm plants.

Tsagantegia shared its habitat with numerous animals from other localities of the formation, compromising dinosaur and non-dinosaur genera; such as the theropods Achillobator, Khankhuuluu, Erlikosaurus, Garudimimus and Segnosaurus; Marginocephalians: Amtocephale and Graciliceratops; the hadrosauroid Gobihadros, the crocodylomorph Paralligator, unnamed azhdarchids and the shark Hybodus.

References

References

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