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". 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
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, 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 and could represent a second species of Citipati'' of the 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. 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==