Tarchia

Taxobox
name = "Tarchia"
fossil_range = Late Cretaceous


image_width = 200px
image_caption = Skull of "Tarchia gigantea".
regnum = Animalia
phylum = Chordata
classis = Sauropsida
superordo = Dinosauria
ordo = Ornithischia
subordo = Thyreophora
infraordo = Ankylosauria
familia = Ankylosauridae
genus = "Tarchia"
genus_authority=Maryanska, 1977
subdivision_ranks=Species
subdivision=
*"T. gigantea" Maryańska, 1977 (type)

"Tarchia" (meaning "brain") is a genus of ankylosaurid dinosaur from the late Cretaceous of Mongolia. It is currently the geologically youngest known of all the Asian ankylosaurid dinosaurs and is represented by five or more specimens, including two complete skulls and one nearly complete postcranial skeleton. This is also one of the largest known Asian ankylosaurs, with an estimated body length of 8-8.5 meters (26-28 ft), a skull length of 40 centimeters (16 in), and skull width of 45 centimeters (18 in). "Tarchia" may have weighed as much as 4,500 kilograms (9,900 lb). Named for its massive skull (Mongolian "tarkhi" meaning 'brain' and Latin "ia"), "Tarchia" currently includes only the type species, "T. gigantea". It was discovered in the Upper Cretaceous (possibly Campanian-Maastrichtian) Barun Goyot Formation (previously known as the 'Lower Nemegt Beds') of the Nemegt Basin of Mongolia. The rocks in which they were found likely represent eolian dunes and interdune environments, with small intermittent lakes and seasonal streams. Hence, we know that "Tarchia" was a desert animal. The morphology of cranial sculpturing seen in "Tarchia", an assortment of bulbous polygons, is reminiscent of that of "Saichania chulsanensis", another ankylosaurid from the Barun Goyot Formation. "Tarchia" is distinguished from "Saichania" on the basis of its relatively larger basicranium, an unfused paroccipital process-quadrate contact and that the premaxillary rostrum is wider than the maximum distance between the tooth rows in the maxillaries. In "Tarchia", wear facets indicative of tooth-to-tooth occlusion is present (Barret, 2001).

Taxonomy and phylogenetics

Vickaryous "et al". (2004) state that two distinct clades of Late Cretaceous ankylosaurids are nested deep to "Tarchia", one comprising North American taxa ("Ankylosaurus", "Euoplocephalus") and the other comprising Asian taxa ("Pinacosaurus" spp., "Saichania", "Tianzhenosaurus", "Talarurus"). "Dyoplosaurus giganteus" is considered a synonym of "Tarchia" and a second proposed species of "Tarchia", "T. kielanae" has been found to be the same as "T. gigantea" (Vickaryous "et al"., 2004).

References

*Barret, P. M. 2001. "Tooth wear and possible jaw action in "Scelidosaurus harrisonii" and a review of feeding mechanisms in other thyreophoran dinoaurs", in Carpenter, K. (ed.) "The Armored Dinosaurs". Indiana University Press, Bloomington. pp.25-52.
*Carpenter, K., Kirkland, J. I., Birge, D., and Bird, J. 2001. "Disarticulated skull of a new primitive anklyosaurid from the Lower Cretaceous of Utah", in Carpenter, K. (editor) 2001, "The Armored Dinosaurs". Indiana University Press
*Maryanska, T. 1977. "Ankylosauridae (Dinosauria) from Mongolia",. "Palaeontologia Polonica" 37:85-151
*Tumanova, T. A. 1978. "New data on the ankylosaur "Tarchia gigantea", "Paleontological Journal "11: 480-486.
*Vickaryous, Maryanska, and Weishampel 2004. "Chapter Seventeen: Ankylosauria", in "The Dinosauria" (2nd edition), Weishampel, D. B., Dodson, P., and Osmólska, H., editors. University of California Press.

Links

* [http://www.gondwanastudios.com/info/tarc.htm "Tarchia", Gondwana Studios]
* [http://www.nhm.ac.uk/jdsml/nature-online/dino-directory/detail.dsml?Genus=Tarchia "Tarchia" in the Dino Directory]