Citipati

Description

The largest Citipati were emu-sized animals and, at about 3 meters (10 ft) long, were the largest known oviraptorids until Gigantoraptor was described in 2007. Like other oviraptorids, Citipati had an unusually long neck and shortened tail, compared to most other theropods. Its skull was unusually short and highly pneumatized (riddled with openings in the bone structure), ending in a stout, toothless beak. Perhaps the most distinctive feature of Citipati was its tall crest, superficially similar to that of a modern cassowary. The crest was relatively low in the type species, C. osmolskae, with a nearly vertical front margin grading into the beak. In contrast, the crest of one referred specimen which has not yet been assigned a specific name (provisionally labeled C. sp.) was taller, with a prominent notch in the front margin, creating a squared appearance.

History of discovery

The type species of Citipati, C. osmolskae, was named by James M. Clark, Mark Norell, and Rinchen Barsbold in 2001, in honor of Halszka Osmólska, a noted paleontologist whose work has dealt extensively with oviraptorids and other Mongolian theropods. The name Citipati is formed from the Sanskrit words citi, meaning 'funeral pyre' and pati meaning 'lord' (चितिपति). In Tibetan Buddhist folklore, the Citipati were two monks who were beheaded by a thief, while deep in a meditative trance. The Citipati are often depicted as a pair of dancing skeletons surrounded by flame, hence the application of the name to the beautifully preserved oviraptorid skeletons.

Since the type skull of Oviraptor is so poorly preserved and crushed, another oviraptorid specimen (IGM or GIN 100/42) had become the quintessential depiction of that dinosaur, even appearing in scientific papers with the label Oviraptor philoceratops. However, this distinctive-looking, tall-crested species has more features of the skull in common with Citipati than it does with Oviraptor and it may represent a second species of Citipati or possibly an entirely new genus, pending further study. Additionally, the nesting oviraptorid specimens had gained widespread attention before they were actually referred to Citipati. While usually labeled simply "oviraptorids", they have on occasion been confused with Oviraptor itself. The fact that the first Oviraptor specimen was found on a nest as well confused the matter further. As it stands, most popular illustrations of Oviraptor actually depict Citipati and the present material available for Oviraptor itself is too fragmentary to be reliably reconstructed.

Classification

The cladogram below follows an analysis by Fanti et al., 2012.

Reproduction

At least four Citipati specimens have been found in brooding positions, the most famous of which, a large specimen nicknamed "Big Mamma", was first announced (but not named) in 1995, described in 1999, and referred to the genus Citipati in 2001. 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 nesting position of Citipati also supports the hypothesis that it and other oviraptorids had feathered forelimbs. With the 'arms' spread along the periphery of the nest, a majority of eggs would not be covered by the animal's body unless an extensive coat of feathers was present.

Although fossilized dinosaur eggs are rare, Citipati eggs and oviraptorid eggs in general, are relatively well known. Along with the four known nesting specimens, dozens of isolated oviraptorid nests have been uncovered in the Gobi Desert. Citipati eggs are shaped like elongated ovals (elongatoolithid) and resemble the eggs of ratites in texture and shell structure. In the nest, Citipati eggs are typically arranged in concentric circles of up to three layers, and a complete clutch may have consisted of as many of 22 eggs. 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.

Ironically, it was the association with eggs that gave oviraptorids their name (which means 'egg thieves'). The first oviraptorid eggs (of the genus Oviraptor) were found in close proximity to the remains of the ceratopsian dinosaur Protoceratops and it was assumed that the oviraptorids were preying upon the eggs of the ceratopsians. 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. Norell et al., who recognized the embryo as oviraptorid, assigned it to the genus Citipati in 2001, based on the vertical orientation of the premaxilla (a bone structure at the tip of the jaw), a feature found only in Citipati. The egg containing the embryo was smaller than most known Citipati eggs at only 12 cm, though it was partially eroded and broken into three pieces, making an accurate estimate of its original size difficult. The embryo-bearing egg was otherwise identical to other oviraptorid eggs in shell structure and was found in an isolated nest, again arranged in a circular pattern.

Two skulls belonging to very young or embryonic Byronosaurus were found associated with the same nest as the first Citipati embryo. It is possible that these tiny troodontids were preyed upon by the Citipati. Alternately, Mark Norell suggested that the juvenile troodonts were raiding the Citipati nest, or even that an adult Byronosaurus had laid eggs in a Citipati nest as an act of nest parasitism.