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Citipati
Temporal range: Late Cretaceous,
~75–71 Ma
↓
Nesting Citipati specimen nicknamed "Big Mama", at the American Museum of Natural History
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Oviraptoridae
Subfamily: †Oviraptorinae
Genus: †Citipati
Clark et al., 2001
Type species
†Citipati osmolskae
Clark et al., 2001

Citipati ([ˈtʃiːt̪ɪpət̪i]; meaning "funeral pyre lord") is a genus of oviraptorid dinosaur that lived in Asia during the Late Cretaceous period, about 75 million to 71 million years ago. It is mainly known from the Ukhaa Tolgod locality at the Djadochta Formation, where the first remains were collected during the 1990s. The genus and type species Citipati osmolskae were named and described in 2001. A second species from the adjacent Zamyn Khondt locality may also exist. Citipati is one of the best-known oviraptorids thanks to a number of well-preserved specimens, including individuals found in brooding positions atop nests of eggs, though most of them were initially referred to the related Oviraptor. These nesting specimens have helped to solidify the link between non-avian dinosaurs and birds.

Citipati was among the largest oviraptorids; it is estimated to have been around 2.5–2.9 m (8.2–9.5 ft) in length and to have weighed 75–110 kg (165–243 lb). Its skull was highly pneumatized, short, and had a characteristic crest formed by the premaxilla and nasal bones. Both upper and lower jaws were toothless and developed a horny beak. The tail ended in a pygostyle (the fusion of the last caudal vertebrae), which is known to support large rectrices.

The taxon is classified as an oviraptorid, a group of very bird-like feathered dinosaurs that had robust, parrot-like jaws. It is among the oviraptorid species that preserve nesting specimens. Citipati laid elongatoolithid eggs in a circular mound-shaped nest, where the parents brooded the eggs by sitting on the nest with their arms covering the nest perimeter. Both arms and tail were covered in long feathers, which likely protected both juveniles and eggs from weather. Citipati may have been an omnivorous oviraptorid, given that the remains of two young individuals of the contemporaneous troodontid were found in a nest, possibly preyed and brought by an adult Citipati to feed its hatchlings.

History of discovery

[edit]
Citipati embryo IGM 100/971

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 5 cm (50 mm) 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.[1] The two perinates would be later identified as individuals belonging to the troodontid Byronosaurus.[2]

Citipati specimen IGM 100/979, popularly known as "Big Mama"

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.[3] The specimen shortly became famous and was nicknamed as "Big Mama" by The New York Times press.[4] 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.[5]

Citipati specimen IGM 100/1004, also known as "Big Auntie"

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".[6][5] 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.[7]

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.[8]

Description of specimens

[edit]
Caudal vertebra from the holotype

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.[9] 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.[10] 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.[7]

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.[8] The skull anatomy of the specimen was later described by Clark and colleagues in 2002,[11] the furcula morphology in 2009 by Sterling J. Nesbitt with team,[12] and the caudal vertebrae by W. Scott Persons and colleagues in 2014 who noted the presence of a pygostyle.[13] Subsequent descriptions have been published in 2018 by Norell and team describing and illustrating some cervical vertebrae and uncinate processes,[7] and Amy M. Balanoff and colleagues describing the endocranium anatomy.[14] In 2003 Amy Davidson described the process in which the holotype was prepared,[15] later supplemental by Christina Bisulca and team in 2009 describing conservation treatments of broken bones.[16]

Zamyn Khondt oviraptorid

[edit]
Mounted IGM 100/42; this specimen has been largely used as a reference for Oviraptor and could represent a second species of Citipati
Life restoration 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.[17]

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.[8][11] Lü Junchang and colleagues in 2004 found this specimen to be closely related to Oviraptor,[18] Phil Senter with team in 2007 placed it close to neither genus,[19] and in 2020 Gregory F. Funston and colleagues found it to be the sister taxon of Citipati.[20]

Description

[edit]
Size comparison of three specimens of Citipati (holotype, Big Auntie and Big Mama)

Citipati was a large-bodied oviraptorid, with the largest individuals being emu-sized animals; it has been estimated at 2.5–2.9 m (8.2–9.5 ft) in length with a weight between 75–110 kg (165–243 lb),[21][22][23] and was one of the largest known oviraptorosaurs until the description of Gigantoraptor.[24] Based on their humeral lengths, IGM 100/1004 was about 11% larger than IGM 100/979.[7] 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.[13][7] 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.[25]

Skull

[edit]
Line drawing of the holotype skull
Life restoration

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.[11]

Classification

[edit]

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:[20]

Oviraptoridae
unnamed

Nankangia

unnamed

Oviraptor

unnamed

Yulong

unnamed
Citipatiinae

Wulatelong

unnamed
unnamed
unnamed

Ganzhousaurus

unnamed
unnamed

Citipati

Zamyn Khondt oviraptorid

unnamed
Heyuanninae

Shixinggia

unnamed

Khaan

unnamed

Conchoraptor

unnamed

Machairasaurus

unnamed
unnamed

Nemegtomaia

unnamed

Heyuannia huangi

Heyuannia yanshini

unnamed
unnamed

Paleobiology

[edit]

Feeding mechanics

[edit]
Reconstructed jaw musculature of Citipati
Optimal (left) and maximum (right) jaw gapes of Citipati

A 2022 study of the bite force of Citipati and comparisons with other oviraptorosaurs such as Incisivosaurus, Khaan, and Conchoraptor suggests that Citipati had a very strong bite force, scored between 349.3 N and 499.0 N. The moderate jaw gape seen in oviraptorosaurs is indicative of herbivory in the majority of the group, but it is clear they were likely feeding on much tougher vegetation than other herbivorous theropods in their environment, such as ornithomimosaurs and therizinosaurs were able to. The examinations suggest oviraptorosaurs may have been powerful-biting generalists or specialists that partook of niche partitioning both in body size and jaw function. Of the oviraptorids examined in this study, Citipati had one of the most powerful bites, but its biting mechanics were unique among the oviraptorosaurs investigated.[26]

Reproduction

[edit]
Labelled Citipati embryo IGM 100/971
Life restoration of IGM 100/971

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 (IGM 100/972 and IGM 100/974) that might belong 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 to feed its nest. 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.[1][2] However, Norell later informally suggested that these skulls were likely washed from one nest to another,[27] and other researchers have stated that the skulls probably do not belong to Byronosaurus based on the differences in morphology.[28]

Although fossilized dinosaur eggs are rare, Citipati eggs and oviraptorid eggs in general, are relatively well known. Along with the two known nesting specimens, dozens of isolated oviraptorid nests have been uncovered in the Gobi Desert. Citipati eggs are elongatoolithid, which are shaped like elongated ovals 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.[29] 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.[10]

The two nesting specimens of Citipati 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.[10] The nesting position of Citipati also supports the hypothesis that it and other oviraptorids had feathered forelimbs. Thomas P. Hopp and Mark J. Orsen in 2004 analyzed the brooding behavior of extinct and extant dinosaur species, including oviraptorids, in order to evaluate the reason for the elongation and development of wing and tail feathers. Given that IGM 100/979 was found in a very avian-like posture, with the forelimbs in a near-folded posture and the pectoral region, belly, and feet in contact with the eggs, Hopp and Orsen indicated that long pennaceous feathers and a feather covering were most likely present in life. The "wings" and tail of oviraptorids would have granted protection for the eggs and hatchlings against climate factors like the sunlight, wind, and rainfalls. However, the arms of this specimen were not extremely folded as in some modern birds, instead, they are more extended resembling the style of large flightless birds like the ostrich. The extended position of the arm is also similar to the brooding behavior of this bird, which is known to nest in large clutches like oviraptorids. Based on the forelimb position of nesting oviraptorids, Hopp and Orsen proposed brooding as the ancestral reason behind wing and tail feather elongation, as there was a greater need to provide optimal protection for eggs and juveniles.[30]

In 2014, W. Scott Persons and colleagues suggested that oviraptorosaurs were secondarily flightless and several of the traits in their tails may indicate a propensity for display behaviour, such as courtship display. The tail of several oviraptorosaurs and oviraptorids ended in pygostyles, a bony structure at the end of the tail that, at least in modern birds, is used to support a feather fan. Furthermore, the tail was notably muscular and had a pronounced flexibility, which may have aided in courtship movements.[13]

Paleopathology

[edit]

Clark and colleagues in 1999 during the description of "Big Mama" noted that the right ulna was badly broken but healed, leaving a prominent callus and possible elongated groove over the injury.[10] As the ulna features positive signs of healing, in 2019 Leas Hearn and team suggested that this individual managed to survive an injury that would have interfered with foraging for several weeks in order to lay and incubate its nest.[31]

In 2002 Clark with team reported a small notch preserved on the right jugal, just beneath the orbit, of the holotype skull of Citipati. This anomaly was likely produced by external damage, leaving a small injury.[11]

Paleoenvironment

[edit]

Citipati is vastly known from the Ukhaa Tolgod locality of the Djadokhta Formation, which is dated around 71 million to 75 million years ago (Late Cretaceous).[32] This formation is separated into a lower Bayn Dzak Member and upper Turgrugyin Member, of which the Ukhaa Tolgod locality belongs to the former. Characteristic lithology across the formation include reddish-orange and pale orange to light gray, medium to fine-grained sands and sandstones, and caliche, with better exposures represented at Ukhaa Tolgod. The settings in which Citipati and associated paleofauna lived are interpreted as large dune fields/sand dunes and several short-lived water bodies with arid to semiarid climates.[32][33] Other dinosaurs known from Ukhaa Tolgod include alvarezsaurids Kol and Shuvuuia;[34][35] ankylosaurid Minotaurasaurus;[36] birds Apsaravis and Gobipteryx;[37][38] dromaeosaurid Tsaagan;[39] fellow oviraptorid Khaan;[40] troodontids Almas and Byronosaurus;[41][42] and an undescribed protoceratopsid closely related to Protoceratops.[43]

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Citipati

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from Grokipedia
Citipati is a of oviraptorid theropod dinosaur known from the period of , renowned for its bird-like features and exceptional evidence of nesting behavior. The type and only , C. osmolskae, was formally named in 2001 by paleontologists James M. Clark, Mark A. Norell, and Rinchen Barsbold, honoring the contributions of Polish paleontologist Halszka Osmólska to oviraptorid ; the generic name derives from the citipati, meaning "lord of the funeral pyre," referencing Tibetan Buddhist skeletal guardian figures that resemble the dinosaur's brooding posture. Fossils, including multiple nearly complete skeletons, come primarily from the Djadokhta Formation at the Ukhaa Tolgod locality in the , dating to approximately 75 million years ago during the stage. Measuring up to 3 meters (10 feet) in length and weighing an estimated 75–110 kilograms, Citipati was among the larger members of the family. Its skull was short and deep, featuring a prominent triangular crest formed by the premaxillae and , large orbits suggesting keen vision, and a robust, toothless suited for crushing or tearing food. The postcranial included a long neck, robust forelimbs with three-fingered hands bearing curved claws—recent analysis (2025) of its wrist bones, including a pisiform, suggests advanced flexibility contributing to the evolution of —and a relatively short tail ending in pygostyle-like fusion, traits linking it closely to the avian lineage. Extensive pneumatization in the skull and vertebrae indicates lightweight construction, potentially aiding in agility despite its size. Citipati is particularly notable for its , with at least three adult specimens preserved in a brooding posture atop clutches of 15–22 eggs arranged in a ring, mirroring the seen in modern birds and providing key evidence for the of avian nesting behaviors in theropods. These nests, containing elongated eggs with blue-green pigmentation—possibly for or UV protection—suggest Citipati inhabited arid, dune-dominated environments with seasonal oases. Likely omnivorous, it probably consumed small vertebrates, eggs, seeds, and , using its and claws for . The brooding individuals may represent males, based on comparisons with in related taxa, implying a division of parental roles. Preservation of soft tissues, including in claw sheaths from one specimen, has yielded molecular insights into dinosaur and evolutionary links to birds.

Discovery and Naming

Initial Discovery

The first specimen of Citipati osmolskae was discovered in 1993 during a joint paleontological expedition conducted by the and the Mongolian Academy of Sciences at Ukhaa Tolgod in the of . This specimen, cataloged as IGM 100/979, consists of a partial preserved in a brooding posture atop a nest of eggs, which initially led to its identification as a specimen of the related oviraptorid philoceratops. The find provided early evidence of in non-avian dinosaurs and highlighted the site's importance for understanding oviraptorosaur behavior. Subsequent excavations yielded additional material, including the specimen IGM 100/978, a nearly complete articulated lacking the nesting association. In 2001, James M. Clark, Mark A. Norell, and Rinchen Barsbold formally described and named the Citipati osmolskae based on these specimens from the Djadokhta Formation at Ukhaa Tolgod. The generic name Citipati derives from the Tibetan Buddhist skeletal representing death and impermanence, evoking the "funeral pyre lord" in , while the specific epithet osmolskae honors Polish paleontologist Halszka Osmólska for her contributions to oviraptorosaur . These early finds established Citipati as a distinct separate from Oviraptor, based on unique cranial and skeletal features observed in the preserved material. The Djadokhta Formation, where the specimens were unearthed, dates to the late stage of the , approximately 75–71 million years ago.

Key Specimens and Taxonomy

The of Citipati osmolskae, specimen IGM 100/979, represents another brooding adult discovered at Ukhaa Tolgod in the Djadokhta Formation, exhibiting a similar arched posture over eggs and comparable size to the , approximately 2 meters in length. This specimen, like the IGM 100/978, provides key evidence for oviraptorid nesting behavior and reinforces the within due to shared cranial and postcranial features such as a prominent nasal crest and robust limb elements. A third notable specimen, IGM 100/1004, is a larger brooding adult (about 11% bigger than IGM 100/979 based on length) from the same Ukhaa Tolgod locality, preserving a near-complete in a protective posture atop a nest with eggs of identical microstructure to those associated with other C. osmolskae individuals. This referral to C. osmolskae is supported by matching cranial morphology, including the tall, vertically oriented premaxillary process and nasal recesses. Additional brooding specimens have since been discovered at the site, with at least four known in total. Specimens from the nearby Zamyn Khondt locality in the Djadokhta Formation, such as the partial skeleton IGM 100/42 (previously referred to Oviraptor philoceratops), have been associated with Citipati based on similarities in the narial region and premaxilla, though differences in crest shape initially suggested it might represent a distinct taxon. Subsequent analyses indicate these features fall within the variation of C. osmolskae, leading to its informal referral as Citipati sp. rather than a separate species. Taxonomic debates center on species-level distinctions, with C. osmolskae as the only formally recognized ; the Zamyn Khondt material, while sharing key autapomorphies like the nasal recess configuration, has been considered a potential junior or undescribed but is currently treated as congeneric without formal synonymy. Several partial skeletons of Citipati are known, predominantly from the Djadokhta Formation, enhancing understanding of oviraptorid diversity in Asia.

Description

Skull and Dentition

The skull of Citipati osmolskae measures approximately 25–30 cm in length and is characterized by a rectangular profile in lateral view, with a notably vertical premaxilla contributing to its distinctive proportions. A prominent, tall crest, reminiscent of that in cassowaries, is formed primarily by the fused premaxillae and nasals, rising dorsally and providing a robust superstructure to the cranium. This crest lacks the convex contribution from the frontals and parietals seen in some other oviraptorids, such as Oviraptor mongoliensis. The overall structure is highly pneumatized, with extensive air-filled recesses enhancing lightness while maintaining rigidity. Like other oviraptorids, Citipati is edentulous, possessing no teeth and instead featuring a robust, parrot-like beak suited for processing food through crushing or shearing. The upper jaw forms a U-shaped triturating surface on the fused premaxillae, armed with five denticles per side and parallel ridges that likely aided in gripping and manipulating prey or vegetation. The tip of the rostrum is downturned, emphasizing its mechanical strength. In comparison to Oviraptor philoceratops, Citipati exhibits a more elongated rostrum and a larger antorbital fenestra, reflecting subtle differences in cranial elongation and fenestral proportions that may indicate a more basal position within Oviraptoridae. The braincase of Citipati is co-ossified and extensively pneumatized, with large dorsal recesses connecting to the tympanic region and exceeding the size of the endocranial cavity. CT scans reveal prominent olfactory bulbs, suggesting a well-developed that would have been advantageous for locating resources in its environment. A partial sclerotic ring, composed of five preserved in the right , indicates the presence of a structured eyeball, consistent with diurnal typical of many coelurosaurs. The nasal openings are large and elliptical, positioned high on the and bordered by the and nasal bones, with associated pneumatic pockets that contributed to the overall lightweight construction of the cranium.

Postcranial Skeleton

Citipati osmolskae was a bipedal oviraptorid theropod characterized by an overall body length of approximately 2.5–3 meters and an estimated mass of 40–80 kilograms, with robust hindlimbs supporting its cursorial lifestyle. The postcranial skeleton, as preserved in the holotype (IGM 100/978) and referred specimens like the brooding individual IGM 100/979, reveals a build adapted for both terrestrial mobility and reproductive behaviors, including egg incubation. The forelimbs of Citipati were notably long, extending up to 1 meter in total length, and terminated in a three-fingered manus with curved, robust claws suitable for grasping. The featured a prominent deltopectoral crest, while the and were slender yet strong; the carpometacarpus was short and subquadrangular, with the alular digit (digit I) bearing a particularly robust ungual . A recent using high-resolution CT scans identified a small , the pisiform, in the of Citipati specimens, positioned to stabilize the carpus and facilitate enhanced mobility, representing an early evolutionary step toward avian configurations. Hindlimbs were robust and proportionately long relative to body size, with a strong exhibiting an undivided trochanteric crest and a that partially fused with the proximal tarsals, featuring dual cnemial crests for muscle attachment. These adaptations supported efficient bipedal locomotion, including running across the arid paleoenvironments of . The pes was tridactyl, with digits II–IV bearing weight and a large, elevated hallux (digit I) that retained a subungual . The pelvis was broad and featured a retroverted pubis and that formed a distal , structural traits consistent with the reproductive demands of egg-laying in oviraptorids. The comprised approximately 30 caudal vertebrae, stiffened by elongated chevrons (haemal spines) that provided counterbalance during movement and posture maintenance. The ribcage was expansive, with a wide, carinate articulating to the first several thoracic and free, ossified uncinate processes interlacing between to reinforce the thoracic basket. This configuration supported the brooding posture documented in multiple Citipati specimens preserved atop nests.

Classification

Taxonomic History

Citipati osmolskae was first described and named as a new and within Oviraptoridae by Clark, Norell, and Barsbold in 2001, based on the (IGM 100/978) from the Upper Djadokhta Formation of . The was distinguished from the of , O. philoceratops, primarily by differences in crest shape, with Citipati possessing a shorter and a crest formed mainly by the nasals that slopes more gently compared to the taller, more rounded crest involving premaxillae and nasals in . This placement highlighted Citipati's position as a derived oviraptorid with a robust, parrot-like suited for a potentially herbivorous or omnivorous diet. Subsequent studies reinforced the generic status of Citipati through detailed anatomical comparisons. In 2018, Balanoff and Norell analyzed endocranial casts from Citipati osmolskae and the closely related oviraptorid Khaan mckennai, revealing distinct differences in braincase morphology, such as variations in the size and shape of cerebral hemispheres and olfactory bulbs, which supported maintaining Citipati as a separate rather than synonymizing it with other oviraptorids. These endocranial distinctions underscored evolutionary divergences within , with Citipati exhibiting more expanded regions indicative of enhanced . Early taxonomic assignments of Citipati specimens faced confusion with smaller oviraptorids like Conchoraptor due to ontogenetic variation, as juvenile individuals of Citipati resemble the adult morphology of Conchoraptor in features such as reduced crest development and more gracile limbs. This led to initial referrals of brooding specimens, like the famous "Big Mamma" (IGM 100/979), to indeterminate oviraptorids before their attribution to Citipati based on shared adult traits such as nasal pneumatization patterns. No additional species beyond C. osmolskae have been formally recognized, though debates persist regarding the validity of assigning juvenile or fragmentary specimens to the genus, with some researchers advocating for Citipati sp. designations to account for growth-related variability.

Phylogenetic Position

Citipati is classified within the family , a of derived maniraptoran theropods characterized by toothless jaws and elaborate cranial crests, and is specifically placed in the subfamily Oviraptorinae alongside genera such as and Rinchenia. This subfamily is defined by synapomorphies including a pronounced pneumatic recess on the basisphenoid and a quadrate with a large pneumatic . Within Oviraptorinae, Citipati shares close phylogenetic ties with philoceratops and Rinchenia mongoliensis, forming a derived distinguished by features such as an anterodorsally sloping occiput and a circular supratemporal . Recent phylogenetic updates in , incorporating high-resolution CT scans of carpal elements, have confirmed the presence of a in Citipati cf. osmolskae (specimen IGM 100/3621), repositioning it as a derived theropod exhibiting early bird-like features that predate the . This , a that migrates to replace the ulnare, is now recognized as a synapomorphy of Pennaraptora, the broader encompassing oviraptorosaurs and paravians, and its identification in Citipati underscores the stepwise reorganization of the theropod during the . These findings refine Citipati's position by highlighting its role in the evolutionary transition toward avian locomotor adaptations, with the bone's development within a mirroring that in modern birds. Citipati exhibits several key synapomorphies shared with other oviraptorids, including extensively pneumatized cervical and dorsal vertebrae that enhance skeletal lightness, a (wishbone) for stabilizing the pectoral girdle during movement, and a pygostyle-like fusion of distal caudal vertebrae forming a stiffened terminus. These traits collectively support its placement within and reflect adaptations for a lifestyle with enhanced dexterity. In the broader context of maniraptoran phylogeny, Citipati occupies a position within , sister group to and thus basal to , emphasizing its paravian affinities through shared pennaraptoran features like the and quill knobs on the . Cladistic analyses from the and , utilizing expanded character matrices with up to 200 taxa and 500 characters, consistently recover Citipati as the taxon to in multiple parsimony-based trees, with high consistency indices (above 0.5) supporting this topology across datasets incorporating cranial, postcranial, and soft tissue inferences.

Paleobiology

Locomotion and Forelimb Function

Citipati was an biped, relying on its robust hindlimbs for locomotion in the arid, dune-dominated landscapes of the . Hindlimb proportions, including a relatively long and relative to body size, suggest adaptations for a stable, suited to traversing shifting sands, with estimated maximum speeds of 20–30 km/h based on comparative theropod limb ratios. This bipedal stance, combined with a wide pelvic girdle, provided the stability necessary for agile maneuvers in eolian environments characterized by wind-swept dunes and sparse vegetation. The tail served as a critical , enhancing balance during bipedal progression and rapid turns, as evidenced by its elongated structure with fused terminal vertebrae forming a . In oviraptorosaurs like Citipati, the tail's stiffness and length helped counteract forward momentum, preventing tipping in uneven sandy terrains. Citipati's forelimbs were elongated and robust, featuring three-fingered hands with curved claws suited for reaching, grasping, or manipulating objects, though not for powered flight. Recent analysis of bones in Citipati specimens reveals the presence of a pisiform, a small carpal that replaced the ulnare and enabled semi-pronated rotation, allowing greater flexibility in folding the —a key precursor to the avian apparatus. This likely facilitated non-aerial functions such as display behaviors with pennaceous feathers to flush hidden prey or brooding postures over nests, rather than aerial locomotion.

Diet and Feeding Mechanics

Citipati, as an oviraptorid theropod, is inferred to have followed an omnivorous to primarily herbivorous diet, incorporating tough materials such as stems, , nuts, and fruits, with possible supplementation from small vertebrates or eggs. This dietary reconstruction aligns with the group's toothless beaks and cranial adaptations for processing fibrous or hard foods, distinguishing them from more carnivorous theropods. The discovery of gastroliths—smooth, rounded stones—in the abdominal cavity of a closely related oviraptorid from the of provides direct evidence for mechanical grinding in the digestive system, supporting consumption of vegetation or other indigestible items that required pulverization. The of Citipati featured a robust construction with a deep and a specialized quadrate-pterygoid that facilitated powerful adduction, enabling effective cropping and crushing. Finite element modeling of cranial musculature indicates that Citipati could generate bite forces ranging from 349 N at the anterior tip to 499 N posteriorly, values significantly higher than those of basal oviraptorosaurs and sufficient for cracking hard seeds, nuts, or even small shelled prey. These mechanics suggest a feeding strategy optimized for high-stress resistance, with the short, tall distributing forces efficiently during to avoid structural failure. In terms of , Citipati likely relied on its toothless, U-shaped rostrum to scoop or strip from the ground or low shrubs in its arid , supplemented by a muscular for further breakdown of ingested material. The absence of teeth emphasized dependence on the keratinous for initial manipulation, while expanded jaw adductor muscles (such as the m. adductor mandibulae externus and internus) provided the leverage for precise, forceful actions suited to an opportunistic browser. This combination of anatomical traits underscores Citipati's adaptation for versatile feeding in a resource-variable environment.

Reproduction and Nesting Behavior

Citipati constructed ring-shaped nests containing clutches of 15–22 elliptical elongatoolithid eggs, each measuring approximately 18–20 cm in length. These nests were arranged in concentric circles with up to three layers, and the eggs within Citipati nests, as well as those of closely related oviraptorids, preserved embryos indicative of theropod development similar to other maniraptorans. Fossil evidence from two adult specimens demonstrates a brooding posture consistent with incubation behavior. The holotype specimen (IGM 100/978) preserves a nearly complete skeleton positioned atop a nest with arms extended outward, while another specimen (IGM 100/979, known as "Big Mama") shows the forelimbs spread over the clutch in a manner that would have shielded the eggs with feathered wings from environmental extremes. A third nesting adult (IGM 100/1004) further corroborates this posture, with the individual estimated at about 13 years old based on bone histology, suggesting reproductive maturity coincided with subadult growth stages. Possible in Citipati may have involved differences in cranial crest morphology, potentially serving as display structures during , though direct evidence remains limited to size variations among specimens. Juvenile Citipati exhibited rapid ontogenetic growth, with histological analysis of brooding adults indicating they reached reproductive size within 6–18 years, reflecting a fast developmental trajectory typical of large theropods. Recent syntheses of nesting , including 2025 reviews, support hypotheses of biparental care in oviraptorids like Citipati, inferred from nest preservation, pigmentation for , and multiple adult-clutch associations suggesting shared incubation and protection duties. The open or semi-exposed nature of these nests, combined with low , aligns with active brooding to maintain optimal humidity and temperature.

Paleopathology

The brooding specimen of Citipati osmolskae (IGM 100/979), preserved in an avian-like posture atop a nest of eggs from Ukhaa Tolgod, Mongolia, exhibits evidence of trauma in the form of a healed fracture on the right ulna. This injury features a prominent callus formation and an elongated groove, indicative of significant bone remodeling following damage that likely impaired foraging ability. Researchers have suggested that the individual survived this trauma for an extended period, demonstrating notable resilience, possibly after an encounter with a predator such as Velociraptor while defending the nest. In the specimen (IGM 100/978), also from Ukhaa Tolgod, a small notch is present on the right jugal beneath the , interpreted as resulting from external rather than a congenital anomaly. Such traumatic pathologies highlight the potential hazards faced by Citipati in its arid paleoenvironment, including predation or intraspecific conflict. The edentulous of Citipati, characterized by a sharp shearing edge, shows signs of abrasion consistent with processing tough, fibrous vegetation or other resistant food items, analogous to wear patterns observed in modern herbivorous birds. This suggests adaptive feeding mechanics that could lead to surface wear over time. Documented pathologies in Citipati are limited, with no evidence of chronic diseases such as tumors or systemic infections reported across known specimens. This scarcity likely stems from taphonomic biases, including poor preservation of soft tissues and juvenile individuals, which reduces the visibility of non-traumatic conditions in the fossil record. The presence of healed injuries nonetheless underscores the species' capacity for post-trauma recovery, informing interpretations of theropod survivorship.

Paleoenvironment

Geological Setting

Citipati fossils are primarily known from the in the of southern , with key localities including Ukhaa Tolgod and Bayn Dzak. This formation consists predominantly of eolian sandstones deposited in a vast dunefield environment, characterized by cross-bedded sands and wind-ripple laminations indicative of dune slip faces and wind-blown sediments. Interdune areas featured shallow and fluvial deposits, represented by lenses formed during intermittent wet phases. The dates to the late Campanian stage of the , approximately 75 to 71 million years ago, as determined by magnetostratigraphic analysis correlating the strata to polarity chrons after Chron 34n. While layers are present in some regional sequences, the precise dating of the Djadochta relies primarily on these magnetic reversals and biostratigraphic correlations with such as multituberculate mammals. Citipati remains are restricted to this formation and have not been reported from the overlying, more fluvial . Taphonomic suggests that Citipati specimens, including brooding adults over nests, were often preserved in articulated or near-life positions due to rapid in slumps or sand avalanches from collapsing faces. These structureless sandstones, interpreted as deposits from catastrophic sandslides, encased skeletons in fine-grained matrices that minimized , though some erosion affects exposed elements like skulls and limbs. The open, mound-shaped nests were buried suddenly by influx, preserving eggs and, in at least one case, an alongside the adults. The paleoclimate of the was arid to semi-arid, dominated by westerly winds that shaped the eolian dunes, with evidence of seasonal rains from the fluvial interdune deposits and formations. Sedimentological features, such as the prevalence of wind-oriented cross-stratification, underscore a landscape with episodic moisture supporting limited aquatic habitats.

Associated Fauna and Flora

The associated with Citipati in the includes a diverse array of vertebrates from arid dune and fluvial environments in southern . Contemporary theropods such as mongoliensis, Tsaagan mangas, rapax (a velociraptorine dromaeosaurid described in 2025), and other dromaeosaurids likely served as predators or competitors, with evidenced as an active hunter through the famous "" specimen showing it locked in combat with . Small theropods, including troodontids like Byronosaurus jaffei, interacted closely with oviraptorid nests, as multiple Byronosaurus juveniles have been found within Citipati egg clutches, suggesting possible predation, scavenging, or even on eggs or hatchlings. Birds, such as the enantiornithines Apsaravis ukhaana, Elsornis keni, and Gobipteryx minuta, were also present in the ecosystem. Herbivorous contemporaries like andrewsi represented rivals for resources in the dune-dwelling community, while ankylosaurs such as grangeri added to the mix of larger herbivores. Prey items for Citipati and similar oviraptorids encompassed small vertebrates and eggs, reflecting an omnivorous or opportunistic diet suited to the sparse ecosystem. Small mammals, including eutherians like Zalambdalestes lechei and multituberculates such as Kryptobaatar dashzevegi, were abundant and likely scavenged or hunted, alongside lizards (e.g., Carusia intermedia) and other small reptiles. Eggs from various dinosaurs, including those of other oviraptorids like Oviraptor philoceratops and Khaan mckennai, may have been targeted, contributing to competitive dynamics among oviraptorosaurs. Invertebrates were diverse within nesting sites, with fossil evidence of insects and possibly arachnids associated with preserved eggs, indicating a rich microfauna in nest structures. Crocodylians like Gobiosuchus kielanae were present but not ecologically dominant, limited to small, terrestrial forms adapted to the dry conditions. The of the was adapted to a semi-arid, eolian , with direct fossils rare but inferred from paleosols and (fossilized structures) in lenses and interdune deposits. These indicate the presence of drought-tolerant gymnosperms, including and possibly gnetophytes, which formed sparse vegetation patches around dune fields and seasonal water sources. Ferns and other pteridophytes likely occupied moister microhabitats near fluvial channels, supporting the community indirectly through growth, though records from correlative strata suggest overall low diversity dominated by arid-adapted . Ecosystem dynamics centered on a dune-dominated where burrowing and scavenging behaviors were common adaptations to the harsh, wind-swept environment with intermittent rainfall. Citipati and associates likely nested in depressions amid shifting sands, fostering interactions like nest predation or for limited prey and , while larger herbivores like grazed on scattered plant resources, maintaining a balanced but precarious .

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