Neimongosaurus (meaning "Nei Mongol lizard") is a genus of herbivorous therizinosaur theropod dinosaur that lived in China during the Late Cretaceous period.

In 1999, a team from the Ministry of Land and Resources, based in Hohhot, Inner Mongolia, was conducting field work at Sanhangobi, 12 mi (20 km) southwest of Erenhot.

In 2001, Zhang Xiaohong, Xu Xing, Paul Sereno, Kwang Xuewen and Tan Lin assigned them to a new genus and species of therizinosaurid dinosaur, Neimongosaurus yangi, designating LH V0001 as the holotype.

[6] The skull of Neimongosaurus is represented by only the posterior (rear) part of the braincase, and the anterior (front) half of the right dentary.

Similar to ornithomimids, oviraptorosaurs, and most troodontids, the symphyseal region (the area at the very front, where both hemimandibles connected) was U-shaped, rather than V-shaped as in other theropods.

This would mean that Neimongosaurus would have had one of the longest cervical columns of any non-avian theropod,[1] longer than that of taxa such as Nanshiungosaurus, which had twelve or fewer.

[1] The proximal half of Neimongosaurus' scapula was strap-shaped, with dorsal (upper) and ventral (lower) margins that were nearly parallel to one another.

Like other therizinosauroids, the medial tuberosity was greatly enlarged, and the deltopectoral crest was deflected at an angle of about ninety degrees.

The lateral condyle was displaced, causing the proximal end to have roughly the shape of an equilateral triangle.

The left metatarsus exhibits many of the features that characterise therizinosauroids, and especially derived taxa, such as the first metatarsal's participation in articulation with the tarsus.

[1] Subsequent cladistic analyses have indicated a position in the more derived Therizinosauridae,[10][11] with Clark et al. in 2004 recovering it as the sister taxon of Segnosaurus.

[9] However, in 2019, Scott Hartman et al. once again recovered Neimongosaurus as a therizinosaurid, forming a clade with Erliansaurus, Suzhousaurus and Therizinosaurus.

[12] The below cladogram depicts the results of Hartman et al. (2019):[12] Suzhousaurus Neimongosaurus Therizinosaurus Erliansaurus Nanchao embryos Nanshiungosaurus Segnosaurus

Erlikosaurus Nothronychus graffami Nothronychus mckinleyi In a 2006 conference abstract, Sara Burch presented the inferred range of motion in the arms of the therizinosaur Neimongosaurus and concluded the overall motion at the glenoid-humeral joint at the shoulder was roughly circular, and directed sideways and slightly downwards, which diverged from the more oval, backwards-and-downwards-directed ranges of other theropods.