Temporal range: Late Cretaceous
|Tarchia kielanae skull|
|Species:||† T. gigantea|
Tarchia (meaning "brainy one") 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. 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. It had a bony tail club, like many ankylosaurids.
Tarchia is one of the largest known Asian ankylosaurs, with an estimated body length of 8 to 8.5 metres (26 to 28 ft), a skull length of 40 centimetres (16 in), and skull width of 45 centimetres (18 in). Tarchia may have weighed as much as 4.5 tonnes (5.0 short tons).
Named for its massive skull (Mongolian tarkhi meaning 'brain' and Latin ia), Tarchia currently includes only the type species, T. gigantea. 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).
- 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.
- Arbour V.M. and Currie P.J., 2013, "Euoplocephalus tutus and the Diversity of Ankylosaurid Dinosaurs in the Late Cretaceous of Alberta, Canada, and Montana, USA", PLoS ONE 8(5): e62421. doi:10.1371/journal.pone.0062421