Avimimus (/ˌeɪvɪˈmaɪməs/ AY-vim-EYE-məs), meaning "bird mimic" (Latin avis = bird + mimus = mimic), is a genus of oviraptorosaurian theropod dinosaur, named for its bird-like characteristics, that lived in the late Cretaceous in what is now Mongolia, around 85 to 70 million years ago.
The remains of Avimimus were recovered by Russian paleontologists[1] and officially described by Dr. Sergei Kurzanov in 1981. The Avimimus fossils were initially described as having come from the Djadokta Formation by Kurzanov; however, in a 2006 description of a new specimen, Watabe and colleagues noted that Kurzanov was probably mistaken about the provenance, and it is more likely that Avimimus hailed from the more recent Nemegt Formation.[2] The type species is A. portentosus.[3] Because no tail was found with the original find, Kurzanov mistakenly concluded that Avimimus lacked a tail in life.[1] However, subsequent Avimimus finds containing caudal vertebrae have confirmed the presence of a tail.[1] A second nearly complete specimen of Avimimus was discovered in 1996 and described in 2000 by Watabe and colleagues. Additionally, these authors identified a number of small theropod footprints in the same area as belonging to Avimimus.[4]
A variety of isolated bones that have been attributed to Avimimus were considered to be distinct from A. portentosus, and were initially referred to as Avimimus sp.[5] In 2008, a team of Canadian, American, and Mongolian paleontologists headed by Phil Currie reported in 2006 an extensive bonebed of Avimimus sp. fossils. The bonebed is in the Nemegt Formation, 10.5 meters above the Barun Goyot Formation, in the Gobi Desert. The team reported finding abundant bones of at least ten individuals of Avimimus, but the deposit may hold more. All individuals were either adult or subadult, and the adults showed little variation in size, suggesting determinate growth. The team also suggests that the individuals were found together because they were gregarious in life, providing possible indications that Avimimus formed age-segregated groups for either lekking or flocking purposes. The adults showed a greater degree of skeletal fusion in the tarsometatarsus and tibiotarsus, and also more prominent muscle scars. The preservation of the bonebeds suggest that they were buried rapidly, uncovered by rapid flow of water, and then buried again a short distance away.[6][7] In 2018, Avimimus sp. was formally described as a new species, A. nemegtensis.[8]
Avimimus was a small, bird-like dinosaur with a length of 1.5 m (5 ft).[1] The skull was small compared to the body, though the brain[1] and eyes were large. The size of the bones which surrounded the brain and were dedicated to protecting it are large.[1] This is also consistent with the hypothesis that Avimimus had a proportionally large brain.[1]
The jaws of Avimimus were thought to form a parrot-like beak lacking teeth, and a thorough review of the holotype specimen's anatomy confirmed that no teeth were preserved, although a series of tooth-like projections along the tip of the premaxilla were.[9] However, subsequently discovered specimens have been reported to preserve small premaxillary teeth.[4] The small teeth or possible lack thereof in Avimimus suggests that it may have been an herbivore or omnivore. Kurzanov himself, however, believed that Avimimus was an insectivore.[1]
The foramen magnum, the hole allowing the spinal cord to connect with the brain, was proportionally large in Avimimus.[1] The occipital condyle, however, was small, further suggestive of the skull's relative lightness.[1] The neck itself was long and slender, and is composed of vertebrae that are much more elongate than in other oviraptorosaurs. Unlike oviraptorids and caenagnathids, the back vertebrae lack openings for air sacs, suggesting that Avimimus is more primitive than these animals.
