Trierarchuncus prairiensis remains were discovered in Montana, in 1980, in the Hell Creek Formation, and had its name formally described in 2020. It is closely related to the Asian alvarezsaur Mononykus. It is estimated to be around 80-100 centimeters (31-39 inches) in length.
In Saurian[]
Trierarchuncus is portrayed with feathers on pretty much all of the body, including in the forearms and a fan on the tail. Its' color is tan, reddish-brown, white and black feathers to match its' habitat.
Various concept designs for Trierarchuncus, by Chris Masna
Trierarchuncus concept art, by Akeiron
The book Saurian: A Field Guide to Hell Creek, suggests that this alvarezsaurid will not be included in the game due to its fossils being found in Montana and not Bone Butte, in South Dakota. The book states ”Alvarezsaurid (right) remains are known from the Hell Creek Formation of Montana.” In the chapter “Introduction“, it states that the field guide will focus in South Dakota in the area known as Bone Butte, for which Trierarchuncus is absent.