Alvarezsauridae

Alvarezsauridae is a family of small, long-legged running dinosaurs. Although originally thought to represent the earliest known flightless birds, a consensus of recent work suggests that they are primitive members of the Maniraptora. Other work found them to be the sister group to the Ornithomimosauria. Alvarezsaurs are highly specialized. They bear tiny but stoutly proportioned forelimbs with compact birdlike hands and their skeleton suggests they had massive breast and arm muscles, possibly adapted for digging or tearing. They have tubular snouts, elongate jaws, and minute teeth. They may have been adapted to prey on colonial insects such as termites.

Alvarezsaurus, and thus Alvarezsauroidea, Alvarezsauridae, and Alvarezsauria are named for the historian Gregorio Álvarez, not the more familiar physicist Luis Alvarez, who proposed that the Cretaceous–Paleogene extinction event was caused by an impact event.

Description

Alvarezsaurs range from 0.5–2 m (20–80 inches) in length, although some possible members may have been substantially larger, including the European Heptasteornis that may have reached 2.5 m (8 ft). Fossils attributed to alvarezsaurs have also been found in North and South America and Asia, and range in age from about 86 to 66 million years ago.