Tsagantegia

Tsagantegia (/ˌsɑːɡɑːnˈteɪɡiə/; meaning Tsagan Teg) is a genus of medium-sized ankylosaur thyreophoran dinosaur that lived in Asia during the Late Cretaceous period. The genus is monotypic, including only the type species, T. longicranialis. The specimen consists of a very partial individual, compromising the skull and lacking postcranial remains. Since it only preserves the skull, Tsagantegia is mainly characterized by its elongated snout and the flattened facial osteoderms, greatly differing from other ankylosaurs.

Tsagantegia
Temporal range: Late Cretaceous, 102–86 Ma
Diagram of the holotype skull in dorsal and ventral views
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: †Ornithischia
Family: †Ankylosauridae
Subfamily: †Ankylosaurinae
Genus: †Tsagantegia
Tumanova, 1993
Type species
†Tsagantegia longicranialis
Tumanova, 1993

Discovery and naming

The holotype specimen, MPC 700/17, is a virtually complete skull that was recovered from the locality Tsagan-Teg (or "White Mountain") of the Bayan Shireh Formation in the southeastern Gobi Desert, Mongolia. It was formally described in 1993 by the Russian paleontologist Tatyana Alekseyevna Tumanova. The generic name, Tsagantegia, is in reference to Tsagan Teg, the locality of its discovery, and the specific name, longicranialis, is derived from the Latin words longus and crānium, in reference to its elongated skull.[1]

Description
Skeletal diagram of MPC 700/17

Tsagantegia was a medium to large-sized ankyosaur, with an estimated length of 6 to 7 m (20 to 23 ft)[2][3] and weighing about 1 to 4 t (2,200 to 8,800 lb).[3] The skull measures about 38 cm (380 mm) in length, with a near width of 25 cm (9.8 in), 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.[1][2][4] According to Arbour, Tsagantegia differs from Gobisaurus and Shamosaurus based on the more rounded, U-shaped premaxillary beak and the flat ornamentation.[5]

Classification

Although fragmentary, its position 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. Tsagategia was found to be closely related to Pinacosaurus and Shamosaurus.[6] In the performed phylogenetic analysis by Arbour and Currie in 2015, Tsagantegia seems to be more related to Pinacosaurus and Zhejiangosaurus; below are the results for the analysis:[4]

Ankylosaurinae
 

Crichtonpelta

 
 
 

Tsagantegia

 
 

Zhejiangosaurus

 
 

Pinacosaurus

 
 
 
 

Saichania

 
 
 

Tarchia

 
 

Zaraapelta

 
 
 
Ankylosaurini
 

Dyoplosaurus

 
 
 
 

Talarurus

 
 

Nodocephalosaurus

 
 
 
 
 

Ankylosaurus

 
 

Anodontosaurus

 
 
 

Euoplocephalus

 
 
 

Scolosaurus

 
 

Ziapelta

 
 
 
 
 
 
 
 

Paleoecology
Tsagantegia compared to the Dinosauria of the Bayan Shireh Formation (Tsagantegia in dark yellow, next to Garudimimus)

Tsagantegia was unearthed from the Tsagan Teg locality, which represents part of the Upper Bayan Shireh.[7] Calcite U–Pb analyses seem to confirm the age of the Bayan Shireh Formation from 102 million to 86 million years ago, Cenomanian-Santonian ages.[8] Based on comparisons between the snouts of Tsagantegia and the contemporary Talarurus, these taxa were divided by niche partitioning. In a palatal view, the rostra Talarurus have a broad-like, rectangular shape, while Tsagantegia have a more shovel-like shaped rostra. These morphological differences indicate that Tsagantegia filled the niche of a browser herbivore, while Talarurus was a grazer.[9]

The Bayan Shireh Formation could have looked like the Finke River
Fossil localities in Mongolia. Locality of Tsagantegia in Tsagan Teg, at Area D

Caliche-based boundary indicates a semi-arid environment and climate[10], but also, the presence of fluvial and lacustrine sediments are indicators of large rivers and lakes.[11][12] As interpreded by Hicks et al. 1999, during the times of the Bayan Shireh Formation, large rivers drained the estern part of the Gobi Desert.[13] 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.[14]

Tsagantegia shared its habitat with numerous animals from other localities of the formation, compromising dinosaur and non-dinosaur genera; such as the theropods Achillobator[15], Alectrosaurus[16], Erlikosaurus[17], Garudimimus[18] and Segnosaurus[17]; the fellow ankylosaur Talarurus[19]; Marginocephalians: Amtocephale[20] and Graciliceratops[21]; the hadrosauroid Gobihadros[7], and the large sauropod Erketu.[14] The turtle Lindholmemys[22], the crocodylomorph Paralligator[23], unnamed azhdarchids[24] and the shark Hybodus.[12]

See also

References
  1. Tumanova, T. A. (1993). "O novom pantsirnov dinozavre iz iugo-vostochnoy Gobi" [A new armored dinosaur from Southeastern Gobi]. Paleontologicheskii Zhurnal (in Russian). 27 (2): 92–98.
  2. Tumanova, T. A. (2000). "Armoured dinosaurs from the Cretaceous of Mongolia". The Age of Dinosaurs in Russia and Mongolia (PDF). Cambridge University Press. p. 517-532.
  3. Holtz, T. R.; Rey, L. V. (2007). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House. Genus List for Holtz 2012 Weight Information
  4. Arbour, V. M.; Currie, P. J. (2015). "Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs". Journal of Systematic Palaeontology. 14 (5): 385–444. doi:10.1080/14772019.2015.1059985.
  5. Arbour, V. M. (2014). Systematics, evolution, and biogeography of the ankylosaurid dinosaurs (PDF) (PhD thesis). p. 265.
  6. Thompson, R. S.; Parish, J. C.; Maidment, S. C. R.; Barrett, P. M. (2012). "Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora)". Journal of Systematic Palaeontology. 10 (2): 301–312. doi:10.1080/14772019.2011.569091. ISSN 1477-2019.
  7. Khishigjav Tsogtbaatar; David B. Weishampel; David C. Evans; Mahito Watabe (2019). "A new hadrosauroid (Dinosauria: Ornithopoda) from the Late Cretaceous Baynshire Formation of the Gobi Desert (Mongolia)". PLoS ONE. 14 (4): e0208480. Bibcode:2019PLoSO..1408480T. doi:10.1371/journal.pone.0208480. PMID 30995236.
  8. Kurumada, Y.; Aoki, S.; Aoki, K.; Kato, D.; Saneyoshi, M.; Tsogtbaatar, K.; Windley, B. F.; Ishigaki, S. (2020). "Calcite U–Pb age of the Cretaceous vertebrate‐bearing Bayn Shire Formation in the Eastern Gobi Desert of Mongolia: usefulness of caliche for age determination". Terra Nova. doi:10.1111/ter.12456.
  9. Park, J. Y.; Lee, Y. N.; Currie, P. J.; Kobayashi, Y.; Koppelhus, E.; Barsbold, R.; Mateus, O.; Lee, S.; Kim, S. H. (2019). "Additional skulls of Talarurus plicatospineus (Dinosauria: Ankylosauridae) and implications for paleobiogeography and paleoecology of armored dinosaurs". Cretaceous Research. doi:10.1016/j.cretres.2019.104340.
  10. Martinson, G. G. (1982). "The Upper Cretaceous mollusks of Mongolia". Sovmestnaya Sovetsko– Mongolskaya Paleontolog-icheskaya Ekspeditsia. 17: 5–76.
  11. Samoilov, V. S.; Benjamini, C. (1996). "Geochemical features of dinosaur remains from the Gobi Desert, South Mongolia". Palaios. 11: 519–531.
  12. Averianov, A.; Sues, H. (2012). "Correlation of Late Cretaceous continental vertebrate assemblages in Middle and Central Asia" (PDF). Journal of Stratigraphy. 36 (2): 462–485.
  13. Hicks, J. F.; Brinkman, D. L.; Nichols, D. J.; Watabe, M. (1999). "Paleomagnetic and palynologic analyses of Albian to Santonian strata at Bayn Shireh, Burkhant, and Khuren Dukh, eastern Gobi Desert, Mongolia". Cretaceous Research. 20 (6): 829–850. doi:10.1006/cres.1999.0188.
  14. Ksepka, D. T.; Norell, M. A. (2006). "Erketu ellisoni, a long-necked sauropod from Bor Guvé (Dornogov Aimag, Mongolia)" (PDF). American Museum Novitates (3508): 1–16.
  15. Perle, A.; Norell, M.A.; Clark, J. (1999). "A new maniraptoran Theropod−Achillobator giganticus (Dromaeosauridae)−from the Upper Cretaceous of Burkhant, Mongolia". Contributions from the Geology and Mineralogy Chair, National Museum of Mongolia (101): 1–105. OCLC 69865262.
  16. Perle, A. (1977). "O pervoy nakhodke Alektrozavra (Tyrannosauridae, Theropoda) iz pozdnego Mela Mongolii" [On the first discovery of Alectrosaurus (Tyrannosauridae, Theropoda) in the Late Cretaceous of Mongolia]. Shinzhlekh Ukhaany Akademi Geologiin Khureelen (in Russian). 3 (3): 104–113.
  17. Barsbold, R.; Perle, A. (1980). "Segnosauria, a new suborder of carnivorous dinosaurs" (PDF). Acta Palaeontologica Polonica. 25 (2): 190–192.
  18. Barsbold, R. (1981). "Toothless carnivorous dinosaurs of Mongolia" (PDF). Transactions, Joint Soviet–Mongolian Palaeontological Expedition. 15: 28–39.
  19. Maleev, E. A. (1952). "Новый анкилозавр из верхнего мела Монголии" [A new ankylosaur from the Upper Cretaceous of Mongolia] (PDF). Doklady Akademii Nauk SSSR (in Russian). 87 (2): 273–276.
  20. Watabe, M.; Tsogtbaatar, K.; Sullivan, R.M. (2011). "A new pachycephalosaurid from the Baynshire Formation (Cenomanian-late Santonian), Gobi Desert, Mongolia" (PDF). Fossil Record 3. New Mexico Museum of Natural History and Science, Bulletin. 53: 489–497.
  21. Sereno, P.C. (2000). "The fossil record, systematics and evolution of pachycephalosaurs and ceratopsians from Asia". The Age of Dinosaurs in Russia and Mongolia (PDF). Cambridge University Press. pp. 489–491.
  22. Sukhanov, V. B.; Danilov, I. G.; Syromyatnikova, E. V. (2008). "The Description and Phylogenetic Position of a New Nanhsiungchelyid Turtle from the Late Cretaceous of Mongolia". Acta Palaeontologica Polonica. 53 (4): 601–614. doi:10.4202/app.2008.0405.
  23. Turner, A. H. (2015). "A Review of Shamosuchus and Paralligator (Crocodyliformes, Neosuchia) from the Cretaceous of Asia". PLoS ONE. 10 (2): e0118116. doi:10.1371/journal.pone.0118116.
  24. Watabe, M.; Suzuki, D.; Tsogtbaatar, K. (2009). "The first discovery of pterosaurs from the Upper Cretaceous of Mongolia" (PDF). Acta Palaeontologica Polonica. 54 (2): 231–242.
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