Oviraptor

Oviraptor Temporal range: Late Cretaceous, 75Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Restoration of known Oviraptor skeleton.
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Suborder:	Theropoda
Clade:	†Oviraptorosauria
Family:	†Oviraptoridae
Subfamily:	†Oviraptorinae Barsbold, 1976
Genus:	†Oviraptor Osborn, 1924
Type species
†Oviraptor philoceratops Osborn, 1924

Oviraptor is a genus of small Mongolian theropod dinosaurs, first discovered by the paleontologist Roy Chapman Andrews, and first described by Henry Fairfield Osborn, in 1924. Its name is Latin for 'egg taker' or "egg seizer", referring to the fact that the first fossil specimen was discovered atop a pile of what were thought to be Protoceratops eggs, and the specific name philoceratops means "lover of ceratopsians", also given as a result of this find. In his 1924 paper, Osborn explained that the name was given due to the close proximity of the skull of Oviraptor to the nest (it was separated from the eggs by only 4 inches or 10 centimetres of sand). However, Osborn also suggested that the name Oviraptor "may entirely mislead us as to its feeding habits and belie its character".^[1] In the 1990s, the discovery of nesting oviraptorids like Citipati proved that Osborn was correct in his caution regarding the name. These finds showed that the eggs in question probably belonged to Oviraptor itself, and that the specimen was actually brooding its eggs, when it died at the nest.

Oviraptor lived in the late Cretaceous period, during the late Campanian stage about 75 million years ago; only one definitive specimen is known (with associated eggs), from the Djadokhta Formation of Mongolia, though a possible second specimen (also with eggs) comes from the northeast region of Inner Mongolia, China, in an area called Bayan Mandahu.^[2]

Description

Artist's restoration

Size compared to a human

Oviraptor philoceratops is known from a single partial skeleton (specimen number AMNH 6517), as well as a nest of about fifteen eggs that have been referred to this species (AMNH 6508).

When living, Oviraptor was one of the most bird-like of the non-avian dinosaurs. Its rib cage, in particular, displayed several features that are typical of birds, including a set of processes on each rib that would have kept the rib cage rigid. A relative of Oviraptor called Nomingia was found with a pygostyle, which is a set of fused vertebrae that would later help support the tail feathers of birds. Skin impressions from more primitive oviraptorosaurs, like Caudipteryx and Protarchaeopteryx, clearly show an extensive covering of feathers on the body, feathered wings and feathered tail fans. A tail fan is also indicated by the presence of a pygostyle in Nomingia, suggesting that this feature was widespread among oviraptorosaurs. Additionally, the nesting position of the brooding Citipati specimens implies the use of feathered wings to cover the eggs.^[3] Given the close anatomical similarity between these species and Oviraptor, it is highly likely that Oviraptor had feathers as well. On the other hand, there is one problem with the use of feathers to "brood" eggs. Since feather is good insulation, heat cannot easily transfer between the body of an animal and the eggs, if there is feather in between them. That is why many birds have a featherless patch of bare skin, known as the brood patch, to allow heat to flow freely from the bird's body to the eggs. So, if Oviraptor and Citipati were to cover their eggs with feathers, the feathers can only function to shield the eggs from the elements, such as the sun, wind or rain, but the feathers will not warm the eggs, regardless of whether Oviraptor and Citipati are endothermic or ectothermic.

Oviraptor is traditionally depicted with a distinctive crest, similar to that of the cassowary. However, re-examination of several oviraptorids show that this well-known, tall-crested species may actually belong to the genus Citipati, a relative of Oviraptor.^[4] It is likely that Oviraptor did have a crest, but its exact size and shape are unknown due to crushing in the skull of the only recognized specimen.

Classification

Drawing of the left arm and both hands of type specimen AMNH 6517

Drawing of the skull, type specimen AMNH 6517

Oviraptor was originally allied with the ornithomimids by Osborn due to its toothless beak. Osborn also found similarities with Chirostenotes, which is still considered a close relative of Oviraptor.^[1] In 1976, Barsbold erected a new family to contain Oviraptor and its close kin, making Oviraptor the type genus of the Oviraptoridae.^[5]

While the original specimen of Oviraptor was poorly preserved, especially the crushed and deformed skull, new and more complete oviraptorid specimens were assigned to the genus in the 1970s and 1980s. In 1976, Barsbold referred six additional specimens to the genus Oviraptor (including IGM 100/20 and 100/21),^[5] but these were later reclassified in the new genus Conchoraptor.^[6] Another specimen, IGN 100/42, is perhaps the most famous, owing to its well-preserved complete skull and large size. This specimen was referred to the genus Oviraptor by Barsbold in 1981^[7] and came to represent Oviraptor in most popular depictions and in scientific studies of oviraptorids.^[8] However, this specimen, with its distinctive tall, cassowary-like crest, was re-examined by the scientists who described the nesting oviraptorids, and found to resemble them more closely than the original specimens of Oviraptor. For this reason, they removed IGN 100/42 from the genus Oviraptor, provisionally re-classifying it as a species of Citipati.^[4]

The cladogram below follows an analysis by Fanti et al., 2012.^[9]

Paleobiology

Fossilized nest, specimen AMNH FR 6508

As its name suggests, Oviraptor was originally presumed to have eaten eggs, based on its association with a fossilized nest (specimen number AMNH FR 6508) thought to belong to Protoceratops.^[1] The idea of a crushing jaw was first proposed by H. F. Osborn, who believed that the toothless beak of the original skull, together with an extension of several bones below the jaw from the palate, would have made an "egg-piercing" tool. In 1977, Barsbold argued that the strength of its beak would indicate that it was strong enough to break the shells of mollusks such as clams, which are found in the same geological formation as Oviraptor. These bones form part of the main upper jaw bone or maxilla, which converge in the middle to form a pair of prongs. The rest of the bony palate, unlike all other dinosaurs, is extended below the jaw line and would have pushed into the space between the toothless lower jaws. A beak (rhamphotheca) covered the edges of upper and lower jaws and probably the palate, as proposed by Barsbold and Osborn.

The discovery of nesting specimens of the related Citipati, with the same types of egg in the original Oviraptor specimen, showed that the eggs actually belonged to Oviraptor, not Protoceratops, and that the type specimen was likely brooding the eggs, not feeding on them. While this discovery did not rule out the possibility that Oviraptor included eggs in its diet, its exact feeding strategies remain unknown. The only Oviraptor philoceratops skeleton preserved the remains of a lizard in the region of its stomach cavity,^[10] implying that the species was at least partially carnivorous.^[11]

References