Alvarezsaurids are among the strangest theropods known: long, slender hindlimbs built for speed, a lightweight birdlike skull, and forelimbs reduced almost to vestigial status, each ending in a single large, robust claw rather than the multi-fingered hands typical of theropods. That single-claw arrangement has led most researchers to interpret alvarezsaurids as specialized diggers, likely breaking into termite mounds or ant nests -- an insectivorous niche almost unique among non-avian dinosaurs.
The family spans from Late Cretaceous South America and Mongolia. Genera like Mononykus and Shuvuuia, both from Mongolia, and Alvarezsaurus, from Argentina (which names the family), share the same distinctive limb reduction despite being found on opposite sides of the former Gondwana-Laurasia divide, a pattern that has made the group's evolutionary origins an active area of research.