Trierarchuncus
"captain hook"
- Lived
- 72 to 66 million years ago, Late Cretaceous
- Diet
- Carnivore
- Group
- Theropods, Alvarezsauridae
- Found in
- United States
- Named by
- Fowler et al. 2020
Where its fossils were found
The evidence
Today
70 million years ago
Habitat
Rivers and ponds dotted a wooded floodplain with flowering plants, palms and conifers. Tyrannosaurus, Triceratops and Edmontosaurus lived in the Hell Creek Formation.
Field notes
About 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.
Field gallery
More views of Trierarchuncus
Scenes reconstructed from the available fossil evidence.
1 of 2
Lived alongside
Found in the same rock formations
A rock formation can hold fossils laid down millions of years apart, so not every animal here met Trierarchuncus.
The evidence
The science behind Trierarchuncus
Which parts of the picture come from its own bones, and which come from its relatives.
From its own fossils
- Isolated fossils include enlarged hand claws, part of a forearm bone and part of a foot bone.
- The best-preserved hand claw curves strongly, giving it a hooked outline.
Borrowed from relatives
- Shuvuuia provides a model for a light, elongated head, long hind legs and a tapering tail.
- Mononykus and Shuvuuia provide models for short, stout arms with a dominant claw and much smaller side fingers.
Still unknown
- The exact shape of its skull and the arrangement of its fingers and toes.
- Whether it used its claws to open insect nests.
- Its color and body covering.
Often drawn wrong
- A hand with several equally large grasping claws misses the specialized dominant claw of this kind of alvarezsaur.
Discovery timeline
- 2009Close relativeLongrich & Currie
- 2020Named itFowler et al.
- 2021Growing upFreimuth & Wilson
Key papers
The research behind what we know of Trierarchuncus
Close relative
Described Albertonykus and proposed that specialized alvarezsaur arms helped open insect nests, a possible feeding model for Trierarchuncus.
Albertonykus borealis, a new alvarezsaur (Dinosauria: Theropoda) from the Early Maastrichtian of Alberta, Canada: implications for the systematics and ecology of the Alvarezsauridae. Cretaceous Research 30: 239-252
Read the paper : Albertonykus borealis, a new alvarezsaur (Dinosauria: Theropoda) from the Early Maastrichtian of Alberta, Canada: implications for the systematics and ecology of the Alvarezsauridae (opens in a new tab)Named it
Named Trierarchuncus from isolated hand claws and limb bones, including a strongly curved claw.
Trierarchuncus prairiensis gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana. Cretaceous Research 116: 104560
Read the paper : Trierarchuncus prairiensis gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana (opens in a new tab)Growing up
Described additional hand claws and proposed that changes in their shape across a size series reflect growth.
New manual unguals of Trierarchuncus prairiensis from the Hell Creek Formation, Montana, and the ontogenetic development of the functional alvarezsaurid hand claw. Cretaceous Research 119: 104698
Read the paper : New manual unguals of Trierarchuncus prairiensis from the Hell Creek Formation, Montana, and the ontogenetic development of the functional alvarezsaurid hand claw (opens in a new tab)
Close relatives
Other members of Alvarezsauridae
Sources: Wikidata