Oviraptoridae

Oviraptoridae is a group of bird-like maniraptoran dinosaurs. They are currently known from Mongolia and China, although there is an unpublished report from Montana. These animals were small, measuring up to 2 m long in most cases. Definitive oviraptorids first appeared in the Cenomanian stage of the late Cretaceous Period, although the possible oviraptorid Microvenator is known from the Aptian stage of the Early Cretaceous Period. The family became extinct at the end of the Maastrichtian stage.

Species
Oviraptoridae includes -


 * Gigantoraptor erlianensis, the largest oviraptorid, at 8 meters in length.
 * Oviraptor philoceratops, from the Late Cretaceous of Mongolia. Found in 1924, it has a longer snout and seemingly extensive crest on its head.  Most illustrations of it are actually based on Citipati sp..
 * Rinchenia mongoliensis was originally called Oviraptor mongoliensis. It had a very high crest on the center of its head, and is from the Late Cretaceous of Mongolia as well.
 * Nemegtomaia barsboldi, originally named Nemegtia and once assigned to "Ingenia", is probably a close relative of Citipati, known from excellent skull material.
 * Citipati osmolskae was named based on several well-known specimens, including nesting adults, eggs, and an embryo. It had an anteriorly-placed crest and lived at the same time and place as Oviraptor.
 * Citipati sp., a specimen recently referred to the genus Citipati, was found in the 1980s and previously thought to be Oviraptor. It had a forward-sloping cassowary-like crest.
 * Conchoraptor gracilis is a small crestless form with a slender second toe. Many specimens have been referred to it, but there have been no detailed studies showing exactly which ones are correctly referred.
 * Khaan mckennai is another taxon that closely resembles Conchoraptor, but has a reduced third finger. It lived alongside Citipati.
 * "Ingenia" yanshini has also had a lot of material referred to it that probably doesn't belong. It was contemporaneous with Conchoraptor, and work needs to be done separating their remains from each other.  "Ingenia"s hand is distinguished by a very large first finger and reduced second and third fingers. The name "Ingenia" is preoccupied and will be replaced in the near future.
 * Heyuannia huangi is the first named oviraptorid from China and resembles Ingenia closely, but is distinguished by having more hip vertebrae and the first finger fused with the wrist.

Other possible oviraptorids include Nomingia gobienisis, Shixinggia oblita, and the early Microvenator celer. All three have been suggested to be oviraptorids, caenagnathids, or more primitive than either group.

Taxonomy
Oviraptorosauria
 * Superfamily Caenagnathoidea
 * Family Oviraptoridae
 * Gigantoraptor
 * Microvenator
 * ?Nomingia
 * Shixinggia
 * Subfamily Oviraptorinae
 * Oviraptor
 * Rinchenia
 * Nemegtomaia
 * Citipati
 * Subfamily Ingeniinae
 * Heyuannia
 * "Ingenia"
 * Conchoraptor
 * Khaan

Description
The most characteristic feature of this group is the skull structure. Oviraptorids had short snouts and very deep mandibles. Some taxa (Oviraptor, Citipati, Rinchenia) had a midline crest on top of the skull, resembling that of a cassowary. Other distinguishing characters 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 top jaw.

The eating habits of these animals are not fully known, but some ate small vertebrates. 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. There are also arguments for the inclusion of plant material or mollusks in their diet. Originally they were thought to be egg raiders, based on a Mongolian find showing Oviraptor on top of a nest. Recent studies have shown that in fact the animal was on top of its own nest. Another finding shows a Citipati on top of a nest, while brooding the eggs with its arms. There are a few other oviraptorid specimens preserved on nests as well, and a Citipati embryo was discovered inside the same kind of egg preserved in these nests.

Oviraptorids were probably feathered, since some close relatives were found with feathers preserved (Caudipteryx and possibly Protarchaeopteryx). 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.