Temporal range: Late Cretaceous
Hell creek alvarezsaurid by chrismasna-d8t5g7p
Trierarchuncus concept art from the game Saurian.
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
clade: Dinosauria
Superorder: Theropoda
Family: †Alvarezsauridae
Subfamily: †Parvicursorinae
Genus: Trierarchuncus
Fowler et al., 2020
Type species
Trierarchuncus prairiensis
Fowler et al., 2020

Trierarchuncus ("Triarch hook") is a genus of alvarezsaurid from the Late Cretaceous Hell Creek Formation of Montana. Its name originates from "Trierarch," meaning "triarch," the title given to the captain of a trireme in classical Greece, and the Latin word "uncus," meaning "hook," referring to its hook-like claws. It is the youngest known alvarezsaurid and one of the last non-avian dinosaurs, going extinct during the K-Pg Extinction 66 million years ago. It is also one of the few alvarezsaurids known from North America. Another Hell Creek alvarezsaurid, "Ornithomimus" minutus is known, but it has not been referred to Trierarchuncus as of now. Its remains were discovered in 1998, but were not officially named until 2020.

Discovery and naming

The first remains ware discovered in Montana in 1980 and it was informally known as the "Hell Creek alvarezsaur".[5] The then unnamed species was not mentioned again until it was mentioned briefly in the 2018 Society of Vertebrate Paleontology abstract book. The species and genus were scientifically described by Denver Fowler and colleagues in 2020 based on three claw phalanges from MD-I-2, including the holotype MOR 6622, the distal end of a radius and fragmentary metatarsal.


Trierarchuncus was described by Fowler based upon several differences, especially on the three phalanges, the radius and the metatarsals. Trierarchuncus is known from its arms, feet and toes. Like its relatives, Trierarchuncus would have been feathered, with short arms bearing one clawed digit, a bird-like head and long legs.[1]

Trierarchuncus is estimated to be around 30 centimeters (12 in) tall and 80-100 centimeters (31-39 inches) in length when fully grown.


Trierarchuncus represents one of the few known alvarezsaurids from North America.[5][2][1] At 66 million years old, it is the youngest known alvarezsaurid and is one of the youngest non-avian dinosaurs in general, like its contemporaries Tyrannosaurus and Triceratops. Additionally, another Hell Creek alvarezsaurid, called "Ornithomimusminutus, is known, but Fowler et al. did not refer it to Trierarchuncus.

In Popular Culture

  • Trierarchuncus is set to appear in the video game Saurian.