Tarchia (meaning "brainy one") is a genus of herbivorous ankylosaurid dinosaur from the late Cretaceous of Mongolia. Discovery and naming In 1970, a Polish-Mongolian expedition discovered an ankylosaurian skull near Khulsan. In 1977, Teresa Maryańska named and described the type species Tarchia kielanae. The generic name is derived from Mongolian тархи (tarkhi, "brain") and Latin ~ia, in reference to a brain size presumed larger than that of the related form Saichania. The specific name honours Professor Zofia Kielan-Jaworowska, the leader of the expedition. The holotype, ZPal MgD-I/111, 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 consists of a skull roof, braincase and rear skull elements. Maryańska referred three additional specimens: ZPAL MgDI/43, a large postcranial skeleton containing three "free" tail vertebrae, twelve tail vertebrae of the "handle" of the tail club and a scute; ZPAL MgDI/49, a right humerus; and PIN 3142/251, a skeleton with skull, that as yet remains undescribed. Tarchia is the geologically youngest of all known Asian ankylosaurid dinosaurs. In 1977, Tatyana Tumanova named a second species: Tarchia gigantea. This was a renaming of Dyoplosaurus giganteus Maleev 1956, which had been based on specimen PIN 551/29. In 1987, Tumanova concluded that both species were identical. This would make Dyoplosaurus giganteus the senior synonym of Tarchia kielanae. This was generally accepted and Tarchia gigantea became the usual species name, as a combinatio nova replacing Tarchia kielanae. However, recent study by Victoria Megan Arbour indicates that D. giganteus is indistinguishable from other ankylosaurs from the late Campanian-Maastrichtian of Mongolia, and hence a nomen dubium; the study revived the name Tarchia kielanae. A rump with tail and club, specimen ZPAL MgD I/113, once referred to Dyoplosaurus giganteus and subsequently to Tarchia gigantea, was by Arbour seen as different from the D. giganteus holotype. The study by Arbour also concluded that specimen PIN 3142/250, in 1977 referred to Tarchia by Tumanova, probably belonged to Saichania instead. This would radically change the common image of Tarchia as this exemplar had been by far the best preserved and most illustrations, museum mounts and indeed scientific research had been based on it. Arbour discovered that the holotype of Tarchia shared distinguishing traits with that of Minotaurasaurus Miles & Miles 2009, concluding that the latter is a junior synonym of Tarchia. Subsequently, in 2016, a study conducted by