Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America.

[5] The earliest and most basal ("primitive") known oviraptorosaurs are Ningyuansaurus wangi, Protarchaeopteryx robusta and Incisivosaurus gauthieri, both from the lower Yixian Formation of China, dating to about 125 million years ago during the Aptian age of the early Cretaceous period.

A tiny neck vertebra reported from the Wadhurst Clay Formation of England shares some features in common with oviraptorosaurs, and may represent an earlier occurrence of this group (at about 140 million years ago).

Most directly, four species of primitive oviraptorosaurs (in the genera Caudipteryx, Protarchaeopteryx, and Similicaudipteryx) have been found with impressions of well developed feathers, most notably on the wings and tail, suggesting that they functioned at least partially for display.

[9][10] Similarly, quill knobs (anchor points for wing feathers on the ulna) have been reported in the oviraptorosaur species Avimimus portentosus.

[12] Notably, a study on flight feathers has concluded that Caudipteryx was secondarily flightless, implying an ancestral volant ancestor for oviraptorosaurs.

[13] The eating habits of these animals are not fully known: they have been suggested to have been either carnivorous, herbivorous, mollusk-eating or egg-eating (the evidence that originally supported the latter is no longer considered valid); these options are not necessarily incompatible.

Evidence for this comes from a lizard skeleton preserved in the body cavity of Oviraptor and two baby Troodontid skulls found in a Citipati nest.

The moderate jaw gape seen in oviraptorosaurs is indicative of herbivory in the majority of the group, but it is clear they were likely feeding on much tougher or more types of vegetation than other herbivorous theropods in their environment, such as ornithomimosaurs and therizinosaurs were able to.

[18] The presence of two shelled eggs within the birth canal shows that oviraptorosaurs were intermediate between the reproductive biology of crocodilians and modern birds.

Gregory S. Paul has written extensively on this possibility, and Teresa Maryańska and colleagues published a technical paper detailing this idea in 2002.

[3][19][20] Michael Benton, in his widely respected text Vertebrate Paleontology, wrote placement of oviraptorosaurs among birds is highly controversial .

[25] Incisivosaurus gauthieri Similicaudipteryx yixianensis Caudipteryx zoui Caudipteryx dongi Avimimus portentosus Microvenator celer Gigantoraptor erlianensis Caenagnathasia martinsoni Ojoraptorsaurus boerei Alberta dentary morph 3 Epichirostenotes curriei Elmisaurus rarus Hagryphus giganteus Chirostenotes pergracilis Leptorhynchos gaddisi Leptorhynchos elegans "Caenagnathus" sternbergi Anzu wyliei Caenagnathus collinsi Nankangia jiangxiensis Yulong mini Nomingia gobiensis Oviraptor philoceratops Rinchenia mongoliensis Zamyn Khondt oviraptorid Huanansaurus ganzhouensis Citipati osmolskae Citipati sp.

Wulatelong gobiensis Banji long Shixinggia oblita Jiangxisaurus ganzhouensis Ganzhousaurus nankangensis Nemegtomaia barsboldi Machairasaurus leptonychus Conchoraptor gracilis Khaan mckennai Ajancingenia yanshini Heyuannia huangi