Tarchia
From Wikipedia, the free encyclopedia
 |
||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 Skull of Tarchia gigantea.
|
||||||||||||||||||||
|
|
||||||||||||||||||||
|
Extinct (fossil)
|
||||||||||||||||||||
| Scientific classification | ||||||||||||||||||||
|
||||||||||||||||||||
|
|
||||||||||||||||||||
| Tarchia giganteus Maryanska, 1977 |
Tarchia (Maryanska, 1977) 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, a skull length of 40 cm and width of 45 cm. Tarchia may have weighed as much as 4,500 kilograms. Named for its massive skull (Mongolian tarkhi meaning 'brain' and Latin ia), Tarchia currently includes only the type species, T. gigantea. Discovered in the Upper Cretaceous (possibly Campanian-Maastrichtian) Barun Goyot Formation (previously known as the 'Lower Nemegt Beds') of the Nemegt Basin of Mongolia, these fossils can be dated to approximately 110 mya. 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).
[edit] Taxonomy and phylogenetics
Vickaryous et. al. (2004) state that two distinct clades of Late Cretaceous ankylosaurids are nested deep to Tarchia, one comprised of North American taxa (Ankylosaurus, Euoplocephalus) and the other comprised of 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 conspecific with T. gigantea (Vickaryous et. al., 2004).
[edit] 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.
