Citipati (; meaning "funeral pyre lord") is a genus of oviraptorid dinosaur from the Late Cretaceous of Asia, approximately 75 to 71 million years ago. It is primarily known from the Ukhaa Tolgod locality of the Djadochta Formation, where its remains were first collected during the 1990s. The genus and its type species, Citipati osmolskae were formally named and described in 2001. A second species may be represented by remains from the nearby Zamyn Khondt locality. Citipati is among the best-known oviraptorids, owing to several exceptionally preserved specimens, including individuals found in brooding positions over nests of eggs. Many of these fossils were initially assigned to the closely related genus Oviraptor. These nesting specimens have contributed to the understanding of the evolutionary relationship between non-avian dinosaurs and birds.
Citipati was among the largest oviraptorids; measuring an estimated in length and weighing . Its skull was short and highly pneumatized, with a prominent crest formed by the premaxilla and nasal bones. Both the upper and lower jaws were toothless and terminated in a horny beak. The tail ended in a pygostyle, a structure formed by the fusion of the final caudal vertebrae and associated with the support of large rectrices.
The taxon is classified as an oviraptorid, a group of feathered, bird-like dinosaurs characterized by robust, parrot-like jaws. It is among the oviraptorids known from specimens preserved in the proximity of nests. Citipati laid elongatoolithid eggs in circular, mound-shaped nests, where adults brooded them by sitting over the nest and extending their arms around its perimeter. The arms and tail were covered with long feathers, which may have provided protection for the eggs and young from exposure to the elements. Citipati may have been omnivorous, as the remains of two juvenile troodontid were discovered in a nest, suggesting that they may have been prey brought by an adult Citipati to feed its young..
History of discovery
In 1993, a small fossilized oviraptorid embryo, labelled as specimen IGM 100/971, was discovered in a nest at the Ukhaa Tolgod locality of the highly fossiliferous Djadokhta Formation, Gobi Desert, during the Mongolian Academy of Sciences-American Museum of Natural History paleontological project. The expedition also discovered numerous mammal, lizard, theropod, ceratopsian and ankylosaurid fossils remains at this locality, with the addition of at least five types of fossil eggs in nests. The oviraptorid embryo is composed of a nearly complete skeleton and was found in a badly weathered semi-circular nest, which also included two perinate (hatchlings or embryos close to hatching) skulls less than of an unknown dromaeosaurid taxon. One of these skulls was reported to preserve portions of an eggshell. Both embryonic oviraptorid and dromaeosaurid skulls were briefly described by the paleontologist Mark A. Norell and colleagues in 1993, who considered this oviraptorid embryo to be closely related to the early named Oviraptor, and also as an evidence supporting that oviraptorids were brooding animals. The two perinates would be later identified as individuals belonging to the troodontid Byronosaurus.
During the same year 1993, expeditions of the paleontological project of the Mongolian Academy of Sciences-American Museum of Natural History discovered a large adult oviraptorid specimen also from the Ukhaa Tolgod locality of the Djadokhta Formation, in a sublocality known as Ankylosaur Flats. This new specimen was labelled under the specimen number IGM 100/979 and includes a partial skeleton comprising some ribs and partial limbs but lacking the skull, neck and tail. It was found in a nesting pose, sitting atop a nest of elongatoolithid eggs with folded forelimbs and crouched hindlimbs. Similar to the embryonic specimen, IGM 100/979 was considered to be an indeterminate oviraptorid closely related to Oviraptor. The specimen shortly became famous and was nicknamed as "Big Mama" by The New York Times press. A larger and more complete specimen, catalogued as IGM 100/978, was found in 1994 also from the Ankylosaur Flats sublocality by the American Museum–Mongolian Academy of Sciences field expeditions. The specimen was unearthed as a single individual not associated with eggs, and it is represented by a nearly complete skeleton including the skull and much of the postcranial elements. However, it was initially identified as a specimen of Oviraptor.
In 1995, the Mongolian Academy of Sciences-American Museum of Natural History expedition discovered a second nesting oviraptorid specimen from the Ukhaa Tolgod locality, in a region called Camel's Humps, at the Death Row sublocality. This new specimen was labelled as IGM 100/1004 and nicknamed "Big Auntie". The excavation lasted several days of work and a filming crew registered some of the excavation progress through video-documentary and photography. The professional team had to remove some of the sediments surrounding the specimen as the terrain was irregular and it was too heavy to be safely transported to the escarpment. As most fossils of the Ukhaa Tolgod locality have a relatively good preservation and exposure, the lack of associated nests argues against the possibility for this sublocality to be an oviraptorid nesting site. IGM 100/1004 is slightly more complete than 100/979; it preserves the entire cervical series with the exception of the atlas and axis, dorsal vertebrae with thoracic ribs, partial limbs and some sacral vertebrae.
In 2001, the paleontologists James M. Clark, Mark A. Norell and Rinchen Barsbold named the new genus and type species Citipati osmolskae based on the now regarded holotype IGM 100/978, and referred specimens IGM 100/971 (embryo) with 100/979 ("Big Mama"). The generic name, Citipati, is formed from the Sanskrit words citi (meaning funeral pyre) and pati (meaning lord) in reference to the lord of cemeteries in the Tibetan Buddhism folklore, Citipati, which is often depicted as a humanoid skeleton. The specific name, osmolskae, is in honor to the noted Polish paleontologist Halszka Osmólska, whose work dealt extensively with Mongolian theropods.
Description of specimens
Though the first specimen of Citipati (IGM 100/971) was briefly reported and discussed, Norell and colleagues in 2001 provided an extensive description of this specimen. As the description was published prior to the formal naming of Citipati, Norell and team tentatively referred this small embryo to a "new large species from Ukhaa Tolgod"—in fact, later known as Citipati osmolskae—based on the shared tall premaxilla morphology among specimens. The more famous IGM 100/979 was extensively described by Clark and team in 1999, also prior to the naming of Citipati. They considered this specimen to be most similar and closely related to Oviraptor than to the other oviraptorids known at that time. Despite being discovered in 1995, the specimen IGM 100/1004 remained partially figured and largely undescribed for years until its formal referral to the taxon Citipati osmolskae in 2018 by Norell and team.
The largest and most complete specimen of Citipati is represented by the holotype IGM 100/978, however, it was preliminarily described and figured in 2001 during the naming of the taxon and during that time, the specimen had not been completely prepared. The skull anatomy of the specimen was later described by Clark and colleagues in 2002, the furcula morphology in 2009 by Sterling J. Nesbitt with team, and the caudal vertebrae by W. Scott Persons and colleagues in 2014 who noted the presence of a pygostyle. Subsequent descriptions have been published in 2018 by Norell and team describing and illustrating some cervical vertebrae and uncinate processes, and Amy M. Balanoff and colleagues describing the endocranium anatomy. In 2003 Amy Davidson described the process in which the holotype was prepared, later supplemental by Christina Bisulca and team in 2009 describing conservation treatments of broken bones.
Zamyn Khondt oviraptorid
The Zamyn Khondt oviraptorid is a well-known oviraptorid represented by a single and rather complete specimen (IGM 100/42) collected from the Zamyn Khondt (also spelled as Dzamin Khond) locality of the Djadokhta Formation. Since the type skull and body remains of Oviraptor are crushed and partially preserved, the Zamyn Khondt oviraptorid had become the quintessential depiction of the former, even appearing in scientific literature with the label Oviraptor philoceratops.
Clark with team have pointed out that this distinctive-looking, tall-crested oviraptorid has more features of the skull in common with Citipati than it does with Oviraptor. Though being different in the crest shape of the skull, the Zamyn Khondt oviraptorid is similar to Citipati in the shape of the narial region and premaxilla morphology. They considered this oviraptorid to belong to the genus, however, they could neither confirm nor disregard that this specimen represents a second species of Citipati. Lü Junchang and colleagues in 2004 found this specimen to be closely related to Oviraptor, Phil Senter with team in 2007 placed it close to neither genus, and in 2020 Gregory F. Funston and colleagues found it to be the sister taxon of Citipati.
Description
Citipati was a large-bodied oviraptorid, with the largest individuals being emu-sized animals; it has been estimated at in length with a weight between , and was one of the largest known oviraptorosaurs until the description of Gigantoraptor. Supplementary Information Based on their humeral lengths, IGM 100/1004 was about 11% larger than IGM 100/979. Like other oviraptorids, Citipati had an unusually long neck and shortened tail compared to most other theropods. The presence of a pygostyle and the brooding pose in specimens of Citipati indicate the presence of large wing and tail feathers, and plumage. Other oviraptorids and oviraptorosaurs are also known to have been feathered. The evidence of pisiform bone has also been reported in a specimen referred to Citipati cf. osmolskae (IGM 100/3621) along with the indeterminate troodontid specimen (IGM 100/3686), providing evidence of replacement of the ulnare by the pisiform before the origin of birds, and close to the origins of flight in theropods.
Skull
Its skull was unusually short and highly pneumatized (riddled with air-spaced openings), 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 C. osmolskae formed by the premaxilla and nasal bones of the skull, with a nearly vertical front margin grading into the beak. In contrast, the crest of IGM 100/42 was taller with a prominent notch in the front margin, creating a squared appearance.
Classification Citipati is often referred to the subfamily Oviraptorinae along with Oviraptor. However, in 2020, Gregory F. Funston and colleagues found Oviraptor to be more basal, so they named a new subfamily Citipatiinae. The cladogram below follows their analysis:
Paleobiology Feeding mechanics