Trierarchuncus

What it was like

Trierarchuncus was a small alvarezsaur, a bird-like dinosaur with short, strong arms that each ended in a single large claw. It is known from parts of the hand, arm and leg.

Its relatives had similar arms, which may have been used to dig into insect nests, though that idea is still debated.

Its world

It lived about 72 to 66 million years ago, at the very end of the Late Cretaceous, in what is now Montana, in the United States. Its bones come from the Hell Creek Formation, where it shared the land with Tyrannosaurus, Triceratops, Ankylosaurus and Pachycephalosaurus.

How it was found

Fowler and colleagues named Trierarchuncus in 2020, from six finds. It is the youngest alvarezsaur known, one of the last dinosaurs of its kind before the extinction.