Oviraptoridae

The most characteristic feature of this group is the skull structure. Oviraptorids had short snouts and very deep mandibles. Some taxa (such as Citipati, Corythoraptor, Rinchenia) had a midline crest on top of the skull, resembling that of a cassowary. Other distinguishing characteristics include a bony spike intruding on the mandibular fenestra, nostrils placed very high and far back on the snout, an extremely thin bony bar beneath the eye, and highly pneumatized skull bones. Like their relatives the caenagnathids, the jaws were edentulous (with no teeth), having instead two small bony projections on the roof of the mouth. ==Classification==

The classification of the oviraptorids has been controversial. Most studies divide oviraptorosaurs into two primary sub-groups, the Caenagnathidae and the Oviraptoridae. However, some phylogenetic studies have suggested that many traditional members of the Caenagnathidae may be more closely related to the crested oviraptorids. Because of this, and the fact that at least one study found that Caenagnathus itself may not have been part of the 'caenagnathid' group, Tom Holtz (2010) placed that group close to the Oviraptoridae and termed it the Elmisauridae, though this idea has not gained consensus among other researchers. The Oviraptoridae itself is traditionally divided into two "subfamilies": the small, short-armed, and mainly crestless subfamily Heyuanniinae and the larger, crested, long-armed Oviraptorinae (Oviraptor + Citipati). Some phylogenetic studies have shown that Oviraptor is the most primitive known oviraptorid, thus making Citipati a closer relative of the "ingeniines" and this traditional division into crestless and crested forms artificial. Other possible oviraptorids include Nomingia gobiensis, Gigantoraptor erlianensis, Jiangxisaurus ganzhouensis and Shixinggia oblita. All four have been suggested to be oviraptorids, caenagnathids, or more primitive than either group. In 2020, during their description of Oksoko, the cladogram recovered by Funston et al. is shown below. Because Oviraptor did not clade with Citipati and the other "oviraptorines", they named the latter's clade Citipatiinae, although they did not provide a formal definition. However, according to Mickey Mortimer, the clade can be considered valid because its describers explicitly name it as new, which satisfies ICZN Article 16.1. }} ==Paleobiology==

Diet The diet of oviraptorids is not fully understood. Though some appear to have been at least partially carnivorous, they were probably primarily herbivorous or omnivorous. Still, some scientists have suggested that oviraptorids may have fed on shelled food items like eggs or shellfish. However, animals specialized for eating shelled food typically have broad, crushing beaks or teeth. In contrast, the jaws of oviraptorids had thin, sharp edges probably supporting shearing beaks, ill-suited for cracking shells. Among other known animals, the beaks of oviraptorids most closely resemble those of herbivorous dicynodont synapsids, which are usually considered herbivorous.(This leads to the possibility that these animals are omnivorous). Evidence of partial carnivory among some oviraptorines comes from a lizard skeleton preserved in the body cavity of the type specimen of Oviraptor Some scientists have also suggested that some oviraptorids (especially the small-handed, weak-clawed "ingeniines") fed mainly on plant material. All of the nesting specimens are situated on top of egg clutches, with their limbs spread symmetrically on each side of the nest, front limbs covering the nest perimeter. This brooding posture is found today only in birds and supports a behavioral link between birds and theropod dinosaurs. The eggs of Citipati are the largest known definitive oviraptorid eggs, at 18 cm. In contrast, eggs associated with Oviraptor are only up to 14 cm long. It was not until 1993, when a Citipati embryo was discovered inside an egg of the type assigned to Protoceratops, that the error was corrected. It represents a late-stage embryo preserved in a position similar to those of extant birds, and is the first example of this to be found in a non-avian dinosaur. In birds, this behavior is known as "tucking", and is controlled by the central nervous system. This posture places the head below the body with the feet on either side of the head and the back curled, which aids in successful hatching. However, this interpretation of the specimen has been challenged, with some scientists suggesting that it cannot be directly compared to extant birds. The skeleton of Baby Yingliang is approximately from head to tail, and is preserved within the confines of a egg. The skeleton occupies most of the egg's internal space other than a space between the dorsal vertebrae and the blunt pole of the egg. This hollow is thought to be the remains of the egg's air cell, though this inference is unproven. The presence of two shelled eggs within the birth canal shows that oviraptorosaurs were intermediate between the reproductive biology of crocodilians and modern birds. Like crocodilians, they had two oviducts. However, crocodilians produce multiple shelled eggs per oviduct at a time, whereas oviraptorosaurs, like birds, produced only one egg per oviduct at a time. Metabolism A study by Robert Eagle et al. of the University of California-Los Angeles indicates that from specimens of eggs found in Mongolia and examination of the isotopes carbon-13 and oxygen 18 found within, Oviraptorids had body temperatures that could be elevated higher than that of the surrounding environment but lower than that of birds. This is very different from the isotope ratios of sauropod dinosaurs like Brachiosaurus, which had body temperatures of up to and were fully endothermic. Feathers depiction of a nesting Nemegtomaia, featuring feathers used to incubate eggs Oviraptorids were probably feathered, since some close relatives were found with feathers preserved (including species of Caudipteryx, Protarchaeopteryx and Similicaudipteryx). Another finding pointing to this is the discovery in Nomingia of a pygostyle, a bone that results from the fusion of the last tail vertebrae and is responsible in birds to hold a fan of feathers in the tail. Finally, the arm position of the brooding Citipati would have been far more effective if feathers were present to cover the eggs. Pathology The brooding oviraptorid specimen IGM 100/979 showed a callus and possible longitudinal groove left over from a healed fracture of the right ulna. Other oviraptorids have had pathological features reported in their phalanges but these have not been described in detail in the scientific literature. ==Paleoenvironment==

'' restoration with nest Almost all oviraptorids come from desert deposits of the Gobi Desert. Even in the late Cretaceous period, much of this area was desert, or at least very dry, habitat. In many of the localities where they are found, oviraptorids are among the most abundant dinosaurs present, second only to ankylosaurs and protoceratopsids. This is consistent with the idea that they were primarily herbivores, which tend to far outnumber carnivores in a given environment. Oviraptorids appear to have been far more abundant in arid habitats dominated mainly by small dinosaurs (such as those preserved in the Barun Goyot and Djadochta Formations) than in wetter ecosystems where large dinosaurs are common (such as the Nemegt Formation). The same pattern holds true for protoceratopsids, indicating that both groups preferred dry, desert-like habitat, and fed mainly on the types of tough, low-growing plant life that grows in arid climates. ==See also==