Adasaurus (/ˌɑːdəˈsɔːrəs/ AH-də-SOR-əs; meaning "evil lizard"[1]) is a genus of dromaeosaurid dinosaur that lived in Asia during the Late Cretaceous period about 70 million years ago.

Unlike other dromaeosaurids, Adasaurus developed a rather small and blunt sickle claw that likely had a reduced use, and a recurved lacrimal bone; this latter trait is also shared with Austroraptor.

Adasaurus was first figured in 1977 by the Mongolian paleontologist Rinchen Barsbold on a pelvic comparison with other theropods, but it would remain as an informally named taxon until a proper description.

[2] In 1983, Barsbold published a large comparative revision of the known Mongolian theropod taxa at the time where he formally named Adasaurus and the type species A. mongoliensis, which was based on two partial specimens.

[10] The comparatively larger pedal elements of the paratype indicate a gently bigger size in this latter specimen which is estimated around 3.5 m (11 ft) long and 87 kg (192 lb) in body mass.

[13] The presence of a rounded pit on the inner surface of the lower tibiotarsus is often documented in dromaeosaurids, however, this feature is not verifiable in Adasaurus since the astragalus region is covered with sediments.

When erected by Barsbold in 1983, Velociraptorinae was conceived as a group containing Velociraptor and closely related species that were characterized by their smaller size and long-narrow snouts.

[7] The traditional view of the Velociraptorinae commonly included Velociraptor, Tsaagan and Linheraptor, which are known from complete skulls, however, most analyses vary widely regarding which species are actually velociraptorines and which are dromaeosaurines.

[16] Traditionally, Adasaurus was assigned to the Dromaeosaurinae, which includes giant, heavily built animals such as Achillobator and Utahraptor[17] but several analyses have suggested that it belongs to the Velociraptorinae instead.

[4] Kubota and Barsbold in 2006 stated that the highly reduced sickle claw of Adasaurus may have been used with less frequency than other deinonychosaurs as the bottom surface of lower heel on the penultimate phalanx has no apparent asymmetrical ridges like other dromaeosaurids and troodontids.

This proposal is based primarily on comparisons between the morphology and proportions of the feet and legs of dromaeosaurids to several groups of extant birds of prey with fairly known predatory behaviors.

The arms were covered in long feathers and may have been used as flapping stabilizers for balance while atop a struggling prey, along with the stiff counter-balancing tail.

With the addition of mathematical models and equations, Bishop simulated the conditions that would provide maximum force at the tip of the sickle claw and therefore the most likely function.

These results are consistent with the Fighting Dinosaurs specimen, which preserves a Velociraptor and Protoceratops locked in combat, with the former gripping onto the other with its claws in a non-extended leg posture.

Much of the sedimentation also indicates that a rich habitat existed, offering extensive vegetation in abundant amounts that could sustain most herbivorous dinosaurs.

[24][25][26] Other dinosaurs found in this formation include the ornithomimosaurs Anserimimus, Gallimimus, and a taxon that remains unnamed;[27] diverse oviraptorosaurs such as Nemegtomaia, Elmisaurus and Gobiraptor;[25][24] and the troodontid Zanabazar.