Alxasaurus (/ˌɑːlʃəˈsɔːrəs/; meaning "Alxa lizard") is a genus of therizinosauroid theropod dinosaurs from the Early Cretaceous (Albian age) Bayin-Gobi Formation of Inner Mongolia.

While therizinosaurs had previously been tentatively seen as late-surviving basal sauropodomorphs, the description of Alxasaurus lent credence to the idea that they were instead highly derived coelurosaurs.

While outside of Therizinosauridae itself, Alxasaurus had many of the traits characteristic of derived therizinosaurs, such as an abbreviated tail, shortened metatarsals and broad feetconvergent with those of basal sauropodomorphs, and fairly long, recurved hand claws.

Alxa (or Alashan) is also the name of the league, or administrative division, of the Inner Mongolia (Nei Mongol Zizhiqu) region of the People's Republic of China.

The single known species, elesitaiensis, is named after Elesitai, a village found in this region, near which the fossil remains of Alxasaurus were located.

[1] Alxasaurus is among the earliest known members of the Therizinosauroidea, but it already possessed the body shape — including the long neck, short tail, and relatively large claws — of later therizinosauroids.

The cervical (neck) vertebrae of Alxasaurus' holotype are badly crushed, though as far as can be gathered, their centra were amphiplatyan, meaning that their surfaces were relatively flat at both ends.

From either side of the anterior (front) portion of the vertebral centra, alar processes extended, bearing capitular facets.

The zygapophyses of the dorsal vertebrae had planes of articulation that sloped medially, and the prezygapophyses were buttressed by the roof of the neural canal.

Dorsal to the posterodistal end of the ilium was a large crest, probably homologous to a rugose area found in the same position in Segnosaurus.

Specifically, the semilunate carpal bone of the wrist is found only in maniraptoran theropods, which also include oviraptorosaurs, dromaeosaurs, troodontids, and birds.

[1] Even more basal therizinosaurs such as the feathered Beipiaosaurus and primitive Falcarius have since been discovered with more theropod features and have helped to solidify this arrangement.

[7][8] Alxasaurus is now thought to occupy a position between the early Beipiaosaurus and later therizinosaurids such as Erlikosaurus, Segnosaurus, or Therizinosaurus.

In 2010, Lindsay E. Zanno noted that, while technically still valid, the group currently consists of only a single species and is thus of dubious utility.