Archaeornithomimus (meaning "ancient bird mimic") is a genus of ornithomimosaurian theropod dinosaur that lived in Asia during the Late Cretaceous period, around 96 million years ago in the Iren Dabasu Formation.

In 1923, during the American Museum of Natural History expedition by Roy Chapman Andrews to Inner Mongolia, Peter Kaisen discovered numerous theropod remains in three quarries.

The generic name combines that of Ornithomimus with a Greek ἀρχαῖος (archaios), "ancient", because Russell believed that the layers in which Archaeornithomimus was found dated to the Cenomanian-Turonian ages, about 95 million years ago, making it one of the oldest ornithomimids known at the time.

[10][11][12] In 1995, Nesov named a new species of ornithomimosaur from the Bissekty Formation (Turonian) of Uzbekistan as Archaeornithomimus bissektensis, based on the holotype N 479/12457, a femur of a juvenile, along with other referred specimens including the metatarsals.

Rativates Ornithomimus sedens Anserimimus Qiupalong Dromiceiomimus Struthiomimus Timimus Gallimimus The remains of Archaeornithomimus were found in the Iren Dabasu Formation, which dates back to the Cenomanian stage about 96 million years ago during the Late Cretaceous period.

[4] The environments present on the formation were mainly large floodplain terrains with braided rivers and meanders[25][26] that were connected to the ocean,[27] supporting extensive vegetation as seen on the palaeosol development and the numerous remains from herbivorous dinosaurs such as hadrosauroids.

[25] Like other members of the Ornithomimosauria, Archaeornithomimus was likely an omnivore equipped with a horny beak, eating everything from small mammals, to plants and fruit, to eggs, and even hatchlings of other Asian dinosaurs.