The left premaxilla is disarticulated from the braincase of IGM 100/3006 and is present in the jacket of IGM 100/1203 (figs. 3, 4). Because the right element is not exposed, it is impossible to tell whether the paired elements were fused as in the oviraptorids Citipati, Tongtianlong, and the Zamyn Khondt oviraptorid (IGM 100/79) (Funston, 2019; fig. 4.13) or unfused as in the more basally diverging oviraptorosaurs Caudipteryx and Incisivosaurus. Although only the anteroventral margin of the external naris is visible, it was likely elliptical as defined by the nasal process of the premaxilla.

The nasal process of the premaxilla sweeps posterodorsally and likely would have contacted the premaxillary process of the nasal, which is missing in IGM 100/3006 (fig. 4). The angle of ascent of the nasal process is shallow and most closely approximates that of Khaan and Gobiraptor minutus (Lee et al., 2019) as opposed to the almost vertical orientation of the process in Citipati, Oksoko, Rinchenia, and the Zamyn Khondt oviraptorid. The maxillary process of the premaxilla extends posterodorsally at a lower angle (30°) and would have contacted the descending process of the nasal, thus delimiting both the posteroventral margin of the external naris and the anterodorsal margin of the antorbital fossa—effectively excluding the maxilla from participating in the margin of the external naris, as in most oviraptorids. A slight depression marks the lateral surface of this process as was described by Kundrát and Janáček (2007). The lateral surface of the premaxilla overall is pneumatized with several neurovascular foramina that occur dorsal to the lingual margin, as in most oviraptorids (e.g., Citipati, Khaan, and Corythoraptor jacobsi (Lü et al., 2017). These foramina would likely have transported sensory nerve fibers (CN V) and arterial branches to a keratinous beak in life. The occlusal margin of the “beak” is edentulous and, based on the exposed surface, likely would have been U-shaped in ventral view as in most oviraptorosaurs. The triturating surface is rugose due to taphonomic wear.

The frontal is most completely preserved on the right side of IGM 100/3006 (fig. 1A). In dorsal view the element is roughly rectangular and tapers slightly anteriorly (fig. 2A). The abbreviated length of the frontals in Conchoraptor and Khaan (∼1/4 the length of the parietal; table 2) differs from that seen in other oviraptorosaurs such as Incisivosaurus, Caudipteryx, and the oviraptorid Citipati, in which the frontals are at least half the length of the parietal. The midline contact between the opposing frontals is weakly fused, however, the left frontal is displaced slightly dorsally, revealing a minor degree of interdigitation. The parietal overlaps the frontal dorsally (fig. 7D) and forms a sinuous, saddle-shaped contact with the anteriormost margin of the suture at the midline (fig. 2A). This distinct suture shape is similar to that of Khaan but differs from that of Citipati, which has a straight, posterolaterally angled (starting at the midline) contact with the parietals (see Clark et al., 2002: fig. 5). The postorbital in IGM 100/3006 overlaps the dorsolateral surface of the frontal posterolaterally, and a small, circular articular surface for the postorbital is visible at the frontoparietal contact in line with the supraorbital margin (fig. 1A). The ventral edge of the frontal is excluded from the supratemporal fenestra by the anterior process of the postorbital (fig. 2A), as in Khaan. Incisivosaurus, Citipati, and Oksoko all have a frontal contribution to the anterior border of the supratemporal fenestra. Maniraptorans outside of Oviraptorosauria also typically possess a frontal contribution to the supratemporal fenestra (Clark et al., 1994; Norell et al., 2006, 2009).

The anteriormost region of the dorsal surface of the frontal in IGM 100/3006 is rugose and possesses the small, circular “fenestrae” (figs. 1C, 2A) described by Osmólska et al. (2004) as present in most oviraptorosaurs (although they are lacking in the basally diverging oviraptorosaur Incisivosaurus). These openings connect to the pneumatic frontal sinus described below, as indicated by CT data (fig. 7D). The same connections are visible in Khaan (IGM 100/973; IGM 100/1127), Citipati (IGM 100/978), and previously described specimens of Conchoraptor (ZPAL MgD-I/95; Kundrát and Janáček, 2007).

In lateral view the frontal is rectangular and dorsoventrally deep at the frontal-parietal suture, tapers slightly anteriorly, and expands again at its anterior edge (fig. 1A, B). The dorsoventral depth of the frontal does not reach the extent observed in Corythoraptor, Rinchenia, and Oksoko, wherein the element is integrated into a pronounced cranial crest. The dorsolateral edge of the frontal forms the majority of the supraorbital margin, and the dorsal and medial walls of the orbit are formed by the ventral extension of the frontal. The small, laterally abbreviated postorbital process is comprised of the posterolateralmost part of the frontal, the postorbital, and the laterosphenoid.

CT data are able to reveal some pertinent features of the internal morphology of the frontal of IGM 100/3006. A pneumatic frontal sinus runs anteroposteriorly along the midline of the element, similar to that observed in Citipati (IGM 100/978; Clark et al., 2002), Khaan (IGM 100/973; Balanoff and Norell, 2012), and a previously described specimen of Conchoraptor (ZPAL MgD-I/95, Kundrát and Janáček, 2007) (fig. 7D). Incisivosaurus, however, lacks this enlarged sinus. A medial septum divides the frontal sinus as it does ZPAL MgD-I/95 (Kundrát and Janáček, 2007) and Khaan. Although a septum was previously reported by Clark et al. (2002) as absent in Citipati, more recent CT data also show its presence (Balanoff, 2011). While the anterior extent of this paired pneumatic cavity cannot be determined in IGM 100/3006, it fails to penetrate the parietals. In ZPAL MgD-I/95 the cavity extends anteriorly into the nasals, also failing to enter the parietals (Kundrát and Janáček, 2007: fig. 3).

The paired parietals are fused at the midline into a single, anteroposteriorly elongate element. In dorsal view the element has an hourglass shape, expanding posterolaterally, tapering anteriorly to form the medial and posterior portion of the supratemporal fossa, and expanding again anterolaterally at the frontoparietal contact to contribute to the small postorbital process (fig. 2A). This morphology is present in both Incisivosaurus and Khaan. It diverges from the condition of Yulong, Citipati, and Rinchenia, which lack a postorbital expansion and exhibit a strongly tapered anterior process that contacts the posterior margin of the frontals. The posterolateral expansion of the parietal in is the lateralmost extent of the element, as in Citipati, Incisivosaurus, and Khaan.

No ornamentation is present on the dorsal surface of the parietal in IGM 100/3006 as there is in Rinchenia and possibly Oviraptor (Osborn, 1924; Barsbold, 1986; Clark et al., 2002). A weakly formed sagittal crest runs along the midline, expanding transversely at the posteriormost edge to form the transverse nuchal crest which, although weakly developed compared to other coelurosaurs, is well developed in comparison to other oviraptorosaurs such as Incisivosaurus, Khaan, and Citipati (fig. 2A).

The lateral surface of the parietal is obscured by the overlapping squamosal and laterosphenoid (fig. 1A, B). Nonetheless, it forms the majority of the medial surface of the supratemporal fossa, with a very minor contribution from the posterior margin of the laterosphenoid. Posterolaterally the parietal abuts the squamosal in a straight, posteroventrally oriented contact that extends onto the occipital surface. This condition is also present in Citipati, Incisivosaurus, and Khaan. The left laterosphenoid in IGM 100/3006 is displaced, so that its articular surface on the parietal—a large, roughened, anteroposteriorly elongate surface—is visible (fig. 1B). The ventral part of the parietal abuts the dorsal edge of the prootic, preserved on the left side of IGM 100/3006 (fig. 1B). This region of the parietal lacks the depression for the dorsal tympanic recess that is present in Incisivosaurus, Citipati, Khaan, as well as several maniraptorans outside of Oviraptorosauria (see Currie and Zhao, 1993; Xu et al., 2002; Norell et al., 2006). The frontal process of the postorbital overlies a small portion of the anterolateral margin of the parietal (fig. 1A, B). This condition is divergent from that of Citipati, Incisivosaurus, and Khaan, wherein there is no overlap.

The flat occipital surface of the parietal is featureless and surrounds the lateral margins of the supraoccipital (fig. 1D). Similar to other archosaurs, the junction of the parietal, supraoccipital, exoccipital, and squamosal forms the opening for the external occipital vein to exit the cranium. This foramen is large and the sulcus for the path of the vein can be observed on the internal surface of the parietal in the CT data (figs. 7A, 8B, C).

The jugal is preserved only on the right side of IGM 100/3006 (fig. 1A). The anterior (maxillary) process tapers anteriorly and forms the ventral margin of the orbit. The general morphology of the jugal falls between the dorsoventrally expanded, “straplike” condition of Incisivosaurus and Oksoko and the slender, more gracile condition observed in Citipati, Khaan, and Yulong. The ascending (postorbital) process contacts the postorbital and, similar to most other oviraptorids, both elements extend almost the entire dorsoventral height of the lateral temporal fenestra (Norell et al., 2006; Turner et al., 2012; fig. 1A). This is unlike the morphology of Incisivosaurus, Yulong, Banji long (Xu and Han, 2010), and Tongtianlong, however, wherein the jugal and postorbital contribute equally, each extending about one-half the height of the fenestra. The ascending process of the jugal in IGM 100/3006 is oriented almost vertically (making the anteroventral angle of the lateral temporal fenestra slightly less than 90°), as it is in most oviraptorosaurs. This angle differs from the plesiomorphic condition for Maniraptora in which the postorbital process of the jugal slants further posteriorly to form a more acute angle (see Currie, 1995; Burnham et al., 2000). The posterior (quadratojugal) process of the jugal sits in a shallow groove on the dorsal surface of the quadratojugal that, because of a slight medial displacement of the jugal, is visible in IGM 100/3006 (fig. 1A). These elements form the ventral margin of the lateral temporal fenestra. The posterior process of the jugal forms the anterior two-thirds of the fenestra and tapers posteriorly as in Khaan, but unlike Incisivosaurus, Citipati, Banji, Yulong, Tongtianlong, and Oksoko wherein this process extends only halfway along the margin. The mediolaterally compressed, tapering morphology of the posterior process differs from the more rodlike morphology in other oviraptorids such as Citipati, Rinchenia, and Khaan as well as the basal oviraptorosaur A. portentosus. CT imagery shows that the jugal is hollow, with a slender canal running the length of each process (fig. 9D); however, there is no pneumatic foramen in the jugal as in more basal coelurosaurs (see Brochu, 2003).

The triradiate postorbital is preserved on both sides of IGM 100/3006 (fig. 1A, B). The frontal (anterior) process of the postorbital is strongly dorsomedially curved, and overlaps the frontal, parietal, and laterosphenoid. Although this morphology is present in most oviraptorosaurian taxa including Banji, Yulong, Citipati, Khaan (Holtz, 1998), and Oksoko. The process in the basal oviraptorosaur Incisivosaurus differs substantially by following the contour of the orbit not curving dorsally. The other extreme can be seen in Rinchenia and Oksoko in which the frontal process forms a 90° angle with the squamosal process (Barsbold, 1986; Osmólska et al., 2004; Funston et al., 2020a; Funston, 2024).

As in all oviraptorosaurs, the ventral two-thirds of the ventral (jugal) process is grooved posteriorly for the reception of the jugal, and together these elements form the complete postorbital bar, which is present only on the right side of IGM 100/3006 (fig. 1A). Based on the articulation surface on the dorsal process of the jugal, the ventral process of the postorbital would have formed almost the entire posterior margin of the orbit. This condition has been proposed as a Conchoraptor autapomorphy (Funston et al., 2018) (see Discussion).

The posterior (squamosal) process of the postorbital is straight and overlies the squamosal, forming the lateral margin of the anteroposteriorly elongate supratemporal fossa (fig. 2A) and the dorsal margin of the lateral temporal fenestra (fig. 1A). This overlap is dorsal in Conchoraptor (IGM 100/3006 and IGM 100/20), Incisivosaurus, and Citipati (Barsbold, 1986), but in Rinchenia the squamosal process is positioned more laterally (Osmólska et al., 2004: fig. 8.1E). The postorbital extends almost the entire anteroposterior length of the supratemporal fossa as it does in most other oviraptorosaurs. The crested oviraptorids Citipati, Corythoraptor, Rinchenia, and Oksoko, however, possess a squamosal process that extends only half the length of the fenestra (Barsbold, 1986).

The squamosal of IGM 100/3006 is well preserved. It is a large, roughly triradiate element with an anterior and posterior process and an elongate, sheetlike descending process (figs. 1A, B). In dorsal view the anterior process of the squamosal contacts the postorbital to form approximately half the length of the lateral margin of the supratemporal fossa (fig. 2A). It is grooved laterally for the reception of the overlying postorbital. In lateral view, the anterior process extends the entire length of the lateral temporal fenestra, forming its dorsal margin (fig. 1A). This process is ventrally concave in lateral view and contacts the postorbital in a roughly horizontal orientation, similar to Citipati, Khaan, and Oksoko, but unlike Incisivosaurus, which exhibits a straight, anterodorsally oriented process.

The descending process of the squamosal is best seen in lateral view (fig. 1A, B). It is anteroposteriorly broad and divided into anterior and posterior rami. A connecting web of bone extends between the anterior and posterior rami and overlaps a large region of the quadrate, likely yielding the articulation between these elements akinetic. The quadratojugal contact with the squamosal lies along the posterior surface of the descending process, and these elements make up the posterior margin of the lateral temporal fenestra. The squamosal contribution extends about two-thirds of the height of the fenestra, as in Citipati and Khaan, but unlike Banji wherein the squamosal contribution is restricted by a long dorsal process of the quadratojugal. This condition is also unlike that of Yulong, wherein the descending process contributes to only one-third the structure's length. The anterior ramus overlies the lateral surface of the prootic just posterior to the trigeminal foramen (fig. 1A). This extension is not present in coelurosaurs outside of Oviraptorosauria nor in more basally diverging members like Incisivosaurus. In occipital view, the contact of the squamosal with the parietal begins approximately midway along the length of the squamosal and curves posteroventrally onto the paraoccipital process (fig. 1D). CT data indicate that the entire squamosal is highly pneumatized, but it is unclear if this pneumatization is via the dorsal tympanic recess as it is in living birds (Kundrát and Janáček, 2007; fig. 11B).

The roughly triangular supraoccipital forms the majority of the occipital surface of the skull (figs. 1D, 2A, 5). It is surrounded by the parietals laterally and the exoccipitals ventrally. These are the only contacts visible on the occipital surface, but CT data reveal that the endocranial surface of the supraoccipital also contacts the opisthotic at its ventrolateral margin (fig. 7A).

Based on the position of the left exoccipital, the ventral margin of the supraoccipital would have been excluded from the foramen magnum—the same configuration seen in Citipati. In Incisivosaurus, Epichirostenotes, Banji, Oksoko, the Zamyn Khondt oviraptorid, and likely Khaan the supraoccipital does contribute to this border. This relationship cannot be assessed in ZPAL MgD-I/95 as the supraoccipital is not preserved in this specimen (see Osmólska, 1976, and Kundrát, 2007).

The external surface of the supraoccipital is slightly convex with a small, longitudinal nuchal eminence running along the midline (fig. 1D). This prominence extends from the dorsalmost edge of the supraoccipital to about the midheight of the element. A longitudinal nuchal eminence is also present in Citipati and Khaan—although in the latter, the eminence terminates at the dorsal margin of the magnum foramen. The endocranial surface, which is visible in the CT imagery, is deeply recessed to receive the posterodorsal extent of the cerebellum (fig. 7A). This fossa is a relatively shallow, V-shaped indention dorsally that widens ventrally.

The exoccipital makes up a large portion of the occipital surface of the skull (figs. 1D, 5). The right element is slightly displaced, but the left one remains in place. In occipital view (fig. 1D) the dorsomedial edge of the exoccipital fits into the curved ventral edge of the supraoccipital (see supraoccipital description). The lateral part of the element curves ventrolaterally to form the majority of the paraoccipital process, as in Incisivosaursus, Citipati, Khaan, and Oksoko. The paraoccipital process as a whole is oriented ventrolaterally and is roughly pendant shape, a character distributed throughout Oviraptorosauria (e.g., Sues, 1997; Clark et al., 2002; Xu et al., 2003; Norell et al., 2006; Balanoff et al., 2009; Balanoff and Norell, 2012) and other maniraptoran taxa (Norell et al., 2006; Turner et al., 2012). The paraoccipital process of Conchoraptor, similar to that of Khaan and Incisivosaurus, is slender and lacks the dorsoventral expansion seen in Citipati and Epichirostenotes. The process is extensively pneumatized by the caudal tympanic recess as in most coelurosaurs. The opening to this recess cannot be observed externally but is visible in the CT data (fig. 12A). The medial edge of the exoccipital makes up the lateral and dorsal margins of the foramen magnum to the exclusion of the supraoccipital (figs. 1A, 5). Displacement of the exoccipitals makes estimation of the size of this structure difficult, but it is undoubtedly larger than the occipital condyle—the lateral edge of the foramen extending laterally past the lateral edge of the condyle (fig. 1D). The displacement of the right exoccipital medially complicates reconstruction of this opening. Its dorsoventral depth, however, is at least as tall as it is wide, implying that it was probably not a mediolaterally wide ovoid as in Khaan and likely appeared more circular as in Citipati. The exoccipital contributes to the neck of the occipital condyle but is largely excluded from the condyle itself—an arrangement that also presents in Citipati and Khaan. In taxa outside of Oviraptoridae, such as Incisivosaurus, A. portentotus, and Epichirostenotes, the exoccipitals contribute a large portion to the occipital condyle (Kurzanov, 1981; 1985).

A shallow fossa on the occipital surface of the exoccipital lateral to the occipital condyle houses several openings, including two small foramina for the transmission of the hypoglossal nerve (CN XII) (fig. 5). These foramina are separated from a larger vagal foramen by a narrow crista. CT imagery shows the vagal canal leading into the adult remnant of the metotic fissure (fig. 8C). This canal likely transmitted the glossopharyngeal, vagus, and accessory cranial nerves (CN IX–XI) as well as the jugular vein, similar to the configuration in other coelurosaurs (Bever et al., 2013). The recessus scala tymapanae extends anteriorly and opens onto the lateral surface of the braincase as the fenestra pseudocochlearis (fig. 11D).

The opisthotic is visible only in the CT slices (fig. 7A, D). These data show that it is fused to the exoccpital, forming an otoccipital, and shares contacts with the prootic anteriorly, epiotic anterodorsally, and exoccipital and supraoccipital posteriorly. The posterior and part of the horizontal semicircular canals run through the opisthotic.

The basioccipital comprises the majority of the occipital condyle, with a small lateral contribution from the exoccipitals (fig. 2B). The straight contact between these elements runs along the dorsolateral surface of the basioccipital, remaining unfused in IGM 100/3006 (fig. 11D) The occipital condyle is oval, and wider than tall as it is in all observed oviraptorosaurs (Osmólska et al., 2004).

On the ventral surface of the basioccipital, the basal tubera, separated by a large depression, are short but distinct and oriented ventrally similar to the condition in Khaan (figs. 5, 8B, 9A, B, 11C). In contrast, the basal tubera of Incisivosaurus, Epichirostenotes, Citipati, and Oksoko are short but directed more ventrolaterally (Xu et al., 2003). In IGM 100/3006 the basal tubera are formed entirely by the basioccipital with no contribution from the basisphenoid. The pterygoids overlap the lateral surface of the basal tubera, a contact that is not apparent in any other oviraptorosaurs and thus is likely a result of taphonomic displacement of the pterygoids (fig. 1D). The lateral surface of the basal tubera is flat (not concave as in Citipati) and possesses a large pneumatic vacuity, communicating with the subotic recess (fig. 11C) (Kundrát and Janáček, 2007). These bilateral openings suggest that those in this same region of Citipati might not be due to breakage as first interpreted by Clark et al. (2002). The anterior extent of the basioccipital along the ventral surface of the braincase cannot be determined superficially because the overlying pterygoids obscure the ventral surface. CT imagery, however, shows that the basioccipital abuts the basisphenoid just anterior to the basal tubera in a flat contact (fig. 11C). Unlike Citipati, this contact is not fused, although this may be due to the skeletal immaturity of IGM 100/3006. The fusion of this contact in other oviraptorosaurs is difficult to determine due to poor preservation.

The fused parasphenoid and basisphenoid in IGM 100/3006 is not visible externally because of the anterodorsal slant of the braincase floor and the extensive palatal coverage of the pterygoid—two features present in all oviraptorosaurs (Barsbold, 1981; 1986; Elzanowski, 1999; Clark et al., 2002; Osmólska et al., 2004; Balanoff et al., 2009; Balanoff and Norell, 2012). Structures of the parabasisphenoid therefore are described using only CT imagery. The element is mediolaterally compressed and dorsoventrally tall. The suture between the basisphenoid and parasphenoid is not distinguishable. The parasphenoid rostrum is visible in lateral and anterior view (fig. 1A, C) and as in Khaan lacks the pneumaticity present in troodontids (Norell et al., 2009).

The basipterygoid processes are not easily identified in the CT images because, as in all oviraptorosaurs, they are extremely abbreviated a relative to other maniraptorans (Osmólska et al., 2004). The contact between the parabasisphenoid and the pterygoids accordingly lies nearly at the main body of the former element (fig. 11E).

The dorsolateral contact of the parabasisphenoid with the prootic lies at the level of the basisphenoid-basioccipital suture. The sella turcica sits at the anterior margin of the dorsal surface of the parabasisphenoid (figs. 7A, 8A, 9D, 12A, B). As previously mentioned, this region of the braincase is not well ossified, and the anterior wall of the fossa remains open as it does in other observed oviraptorosaurs including Incisivosaurus, Citipati, and Khaan (Franzosa, 2004; Balanoff and Norell, 2012). At the posterior margin of the sella turcica the cranial carotid canals open into the dorsum sellae (figs. 8B, 12A). Their path through the parabasisphenoid can be traced through the CT images beginning just posterior to the base of the parasphenoid rostrum on the ventral surface of the braincase and traveling dorsomedially. These canals do not anastomose within the parabasisphenoid as they do in some birds (Baumel and Witmer, 1993). An anastomosis is present in almost all coelurosaurs (Holtz, 1998) but is taxonomically variable (Baumel and Gerchman, 1968). The parabasisphenoid is highly pneumatized by the basisphenoid recess (fig. 9D) as in Citipati, Oksoko, and other maniraptorans (Witmer, 1997; Kundrát and Janáček, 2007; Bever and Norell, 2009; Bever et al., 2011, 2013).

Only the right quadratojugal is preserved in IGM 100/3006. It is a roughly L-shaped element (fig. 1A) with a long ascending process, relatively short posteroventral (quadrate) process, and a mediolaterally thin jugal process that is approximately twice the length of the posteroventral process. This is a similar shape to all observed oviraptorids (e.g., Barsbold, 1986; Clark et al., 2002; Osmólska et al., 2004; Balanoff and Norell, 2012). The rounded quadrate process lies within the aforementioned groove on the lateral surface of the mandibular process of the quadrate. The length of the quadrate process varies considerably among oviraptorosaurs with Citipati, Rinchenia, Nemegtomaia, Oksoko, and Banji having a long, pronounced process (Barsbold, 1986; Osmólska et al., 2004). In IGM 100/3006 this process is shorter than that of the aforementioned taxa, not extending beyond the posterior margin of the mandibular process of the quadrate, but still longer and slenderer than that of Khaan (Balanoff and Norell, 2012: fig. 5A). In more basally diverging taxa such as A. portentosus and Incisivosaurus the quadratojugal and jugal are fused, thus obscuring the morphology of the quadrate process. Caudipteryx, however, has a relatively short process that closely resembles the size and shape of Khaan.

The combination of the ascending process of the quadratojugal and descending process of the squamosal make up the posterior border of the lateral temporal fenestra, as in all oviraptorids. Although somewhat displaced from its original position, the ascending ramus of the quadratojugal extends approximately two-thirds the length of the lateral temporal fenestra (fig. 1A). In posterior view, the quadrate and quadratojugal form the quadrate foramen (fig. 1D). Along with the posterior process of the jugal, the jugal process of the quadratojugal makes up the ventral margin of the lateral temporal fenestra with the jugal and extends almost its entire length (fig. 1A). It bears a dorsolateral groove for the reception of the jugal. This process is straplike relative to the gracile, rodlike condition observed in Incisivosaurus, Citipati, and Khaan. In this way it is more similar to the condition in Oksoko and in the aforementioned taxa. The articular region of the anterior process is dorsoventrally deep and facilitates the equally tall posterior process of the jugal.

The quadrate resembles the general morphology of other oviraptorosaurs, possessing distinct otic, orbital (pterygoid), and mandibular processes, similar to the condition in living birds (fig. 1A, B). The orientation of the otic process is vertical, with an otic head that is in line with the mandibular process as it is in the oviraptorids Citipati, Khaan, and previously illustrated specimens of Conchoraptor (IGM 100/20; Barsbold, 1986: fig. 3; Osmólska et al., 2004). The vertical orientation is opposed to the somewhat more posteriorly oriented head of Incisivosaurus. The otic process is concave posteriorly with some medial flexure, which also is apparent in oviraptorid quadrates identified as either H. yanshini or Conchoraptor by Maryanska and Osmólska (1997). The articulation surface on the otic process is undivided but articulates with the prootic medially and the squamosal laterally as it does in all known oviraptorosaurs (Maryanska and Osmólska, 1997; Balanoff et al., 2009), alvarezsaurids (Chiappe et al., 1998), troodontids, and crown birds (Baumel and Witmer, 1993). The quadrate-squamosal contact is broad and probably lacked a large degree of movement (described above). The medial contact with the prootic is simple with the quadrate head sitting in a depression on the lateral surface of the prootic. The posterolateral edge of the otic process of the quadrate contacts the medial aspect of the dorsal process of the quadratojugal. These elements also contact each other ventrally (described below), forming a small, dorsoventrally elongate quadrate foramen between these two contacts (fig. 1D, 5). This foramen is smaller than that observed in dromaeosaurids (Norell et al., 2006); however, its presence contrasts with the basal oviraptorosaurs A. portentosus and Incisivosaurus.

The mandibular process of the quadrate is ventrally oriented and widely expanded in an anteromedial-posterolateral direction (fig. 1D) as it is in the oviraptorids Citipati, Rinchenia, Khaan, and Nemegtomaia. In more basally diverging oviraptorosaurs like A. portentosus and Incisivosaurus, this process is relatively narrower compared with the overall height of the quadrate. Maniraptoran taxa outside of Oviraptorosauria also tend to lack an expanded mandibular process (see Clark et al., 1994; Chiappe, 1998; Norell et al., 2006, 2009; Zanno, 2010). The mandibular process extends ventrally well beyond the level of the floor of the braincase (fig. 1D), a characteristic present in all oviraptorosaurs, though most pronounced in Incisivosaurus (Xu et al., 2003; Osmólska et al., 2004). The lateral surface of this process is grooved for the reception of the quadratojugal (fig. 1B). The anteromedial surface is flat and, with part of the confluent orbital process, overlies the quadrate process of the pterygoid (fig. 1D).

The orbital process of the quadrate is sheetlike, overlaps the lateral surface of the pterygoid, and lies medial to the descending process of the squamosal (fig. 1A, B). The orbital process of oviraptorosaurs contributes to the aforementioned lateral flange that obscures the lateral surface of the braincase and forms the lateral wall of the cranioquadrate space (Clark et al., 2002; Osmólska et al., 2004; Balanoff et al., 2009).

The prootic of IGM 100/3006 is only partially exposed on the lateral surface of the braincase; the majority of this element is obscured by the orbital wing of the quadrate and overlying squamosal (fig. 1A, B). The exposed anterior edge of the prootic abuts the posterior edge of the laterosphenoid in a straight contact that lacks suturing, forming a single large oval opening for the exit of the trigeminal nerve (CN V), as in Khaan and Oksoko (fig. 1A). The trigeminal foramen is not completely divided as it is in crown birds (Baumel and Witmer, 1993) but rather is pinched in the middle similar to the morphology present in Incisivosaurus and Epichirostenotes (Xu et al., 2002). All other observed oviraptorids (Clark et al., 2002; Balanoff and Norell, 2012), deinonychosaurs (Currie and Zhao, 1993; Norell et al., 2006; Norell et al., 2009), and Archaeopteryx (Wellnhofer, 1974, 1993; Rauhut, 2014) retain a single large, circular trigeminal foramen. CT imagery shows that IGM 100/3006 houses a fossa within the prootic for the trigeminal ganglion (figs. 9C, 11B) similar to Epichirostenotes.

Although much of the remainder of the lateral wall of the braincase, including the external ear, is obscured, CT images reveal some of this obstructed morphology. These data show a relatively large facial foramen piercing (CN VII) the wall of the prootic exiting internally from the internal acoustic fossa (fig. 10D). The vestibular and cochlear branches of the vestibulocochlear nerve (CN VIII) also enter this fossa and exit into the vestibular and cochlear fossae, respectively (fig. 10B, C). The cochlear branch is located farthest posteriorly and is the smaller of the two branches.

The posterior surface of the prootic articulates with the opisthotic and the contact remains unfused. The inner ear is housed primarily within the prootic and opisthotic and is described in Balanoff et al. (2014). A large floccular recess invades the junction of the prootic with the opisthotic and parietal (fig. 9A, B) but does not reach the exoccipital. The path of the anterior semicircular canal limits the anterior and posterior walls of the floccular recess. The horizontal semicircular canal lies at the lateral extent of the recess (Balanoff et al., 2014).

Both left and right laterosphenoids are preserved in IGM 100/3006, but the left element is displaced medially from its original position (fig. 1B). The external surface possesses a vertically oriented crista that divides the anterior and lateral surfaces (fig. 1A). The anterior surface, which makes up the posterior wall of the orbit, is featureless except for a triangular articular facet at its ventromedial corner for the reception of the epipterygoid. This articulation is visible on the right side of IGM 100/3006 (fig. 1A). The ventromedial edge of the anterior surface is notched for the exit of the optic nerve (II) (fig. 1A). The optic foramen is a single opening formed by the midline contact of the paired laterosphenoids (Osmólska et al., 2004). It is possible that this single opening is the artifact of a missing or unossified orbitosphenoid, as is present in Citipati (IGM 100/978 and 100/42), Rinchenia, and Nemegtomaia (Barsbold, 1981; 1986). An orbitosphenoid is absent in all known specimens of Conchoraptor (Osmólska, 1976; Barsbold, 1986; Kundrát, 2007; Kundrát and Janáček, 2007) as well as Khaan. A long, slender postorbital process extends laterally from the dorsal margin of the element, marking the transition from the orbital to the lateral surface (fig. 1A). The postorbital process has a notable expansion at its distal end, making up the laterosphenoid contribution to the postorbital process as in most oviraptorosaurs. The contact with the frontal lies along the length of this postorbital process as well as along the dorsal edge of the orbital surface.

In lateral view, the posterior margin of the laterosphenoid abuts the prootic without any suturing, and these two elements form the foramen for the exit of the trigeminal nerve (CN V)—the majority of which is formed by the prootic (see Prootic description). Dorsal to the contact with the prootic, the laterosphenoid overlies much of the lateral surface of the parietal. The ventral contact with the parabasisphenoid is visible only in the CT slices and consists of a simple contact wherein the laterosphenoid sits on the dorsal surface the parabasisphenoid. The endocranial surface of the laterosphenoid, as viewed in CT data, forms part of the anterolateral wall of the braincase, which is concave to house the optic tectum (fig. 9D).

The anterior palatine wings of both the left and right pterygoid are missing, therefore only the posterior portions of this element are preserved in IGM 100/3006 (figs. 1, 2). The pterygoid contacts the epipterygoid dorsally, the parabasisphenoid medially, the quadrate laterally, and its opposite along the midline. Overall, the pterygoid is an elongate element as in most theropods, and as in most oviraptorosaurs, it obscures almost the entire ventral surface of the braincase outside of the basioccipital.

In IGM 100/3006 the dorsal (quadrate) process of the pterygoid is a thin, mediolaterally compressed wing that extends dorsally and lies deep to the otic process of the quadrate, contributing to the quadrate/pterygoid flange that is present in all oviraptorosaurs (see quadrate description). On the palatal surface, the posterior extremity of the pterygoid is forked. Laterally, a mediolaterally flattened posterolateral process contacts the medial surface of the mandibular process of the quadrate (fig. 1D). A posteromedial process expands dorsally and lies on the lateral surface of the parabasisphenoid (fig. 1D). Anterior to this contact, the opposing pterygoids converge along the midline as they do in Citipati (fig. 2B). This is unlike the condition in the basally diverging oviraptorosaur Incisivosaurus and the oviraptorids Citipati, Jianxisaurus, and Oksoko, wherein the pterygoids are separated by an interpterygoid vacuity that was likely bridged by soft tissue in life.

An ossified epipterygoid is found in most oviraptorids including another specimen of Conchoraptor (ZPAL MgD-I/95; Osmólska, 1976), Citipati, Nemegtomaia, Khaan, and Oksoko. The right epipterygoid in IGM 100/3006 is preserved as a small, triangular bone that is flattened anteroposteriorly (fig. 1C). Its dorsal extent overlaps the anterior surface of the laterosphenoid, and its ventral side contacts the quadrate wing of the pterygoid. The epipterygoid is relatively smaller than that of Citipati, and the dorsal tip does not twist dorsolaterally as it does in that taxon (Clark et al., 2002).

The anteriormost portion of the left dentary is preserved in IGM 100/3006 (in the jacket of IGM 100/1203), including part of the symphyseal region and the posteroventral process (figs. 3, 6). The posterodorsal process is also present; however, it has broken away and is lying in the matrix adjacent to the premaxilla (fig. 3). Overall, the dentary is consistent with that of most other oviraptorid taxa in being edentulous, marked by numerous small nervous colliculi concentrated on the external surface of the anterior beak, and in having a downturned symphyseal region. The posteroventral process of the dentary is narrower than the basal oviraptorosaurs Incisivosaurus and Caudipteryx as well as the oviraptorids H. huangi (Lü, 2003), Citipati, Rinchenia, Corythoraptor, and Khaan. The width of this process in IGM 100/3006, however, compares closely with that of Caenagnathus Spp. (CMN 8776) (Currie et al., 1993).

The surangular is represented by its anteroventral tip in the jacket of IGM 100/1203 (fig. 6) and by its posteriormost extent, which remains in articulation with the posterior mandible in IGM 100/3006 (figs, 1, 2B). It articulates with the angular ventrally, and with the angular posterodorsally, while extending posteroventrally to form the lateral surface of the retroarticular process as in other oviraptorids (e.g., Clark et al., 2002; Balanoff and Norell, 2012). The surangular does appear to have taken part in a surangular/articular/coronoid complex as in caenagnathids (Currie et al., 1993).

The angular is represented by an anterior fragment in the jacket of IGM 100/1203 (fig. 6) and by its posteriormost extent in articulation with the cranium of IGM 100/3006 (figs. 1, 2) The element's anterior contact with the posteroventral process of the dentary is not preserved, but its dorsal contact with the surangular remains. As in Khaan, Rinchenia, and Oksoko, the element tapers into a rounded termination that does not continue onto the retroarticular process as it does in Citipati and Gigantoraptor erlianensis (Xu et al., 2007).

The posterior end of the prearticular is the only portion of this element preserved (fig. 1A, D). It lies along the medial surface of the articular and extends posteroventrally onto the retroarticular process. It is in a similar position to other oviraptorids (see Clark et al., 2002: fig. 9B).

The articular is expanded anteroposteriorly and is the only mandibular element that makes contact with the quadrate, likely facilitating a sliding articulation (fig. 1A–C). In this way, the articular of Conchoraptor exhibits the classic oviraptorosaur morphology wherein the mandibular joint articulates via a cotyle that would not have permitted anterior-posterior movement. The retroarticular process of IGM 100/3006 is slender, as in all oviraptorids, and projects posteroventrally from the posterior extent of the articular surface (Holtz, 1998; fig. 1). The articular contacts the prearticular anteriorly along its ventral surface. Contact with the surangular is made laterally (only a thin splint of the posterior region of this element is preserved).

All vertebral counts are taken from IGM 100/1203 except for the sacral vertebrae, which are obscured by the overlying ilia and thus taken from IGM 100/3006. There are six preserved vertebrae in the cervical series of IGM 100/3006, including the atlas and axis (figs. 13–15). In IGM 100/1203, a total of nine articulated cervical vertebrae can be observed (fig. 3). Preservation of the cervical series in IGM 100/1203 deteriorates cranially, and so this count is unlikely to be reflective of the true number, which usually amounts to 12 or 13 in oviraptorosaurs (Osmólska et al., 2004). This number differs from most theropods, which typically possess no more than 10 cervical vertebrae.

The atlas is rarely preserved in oviraptorosaurs, and when present, is often obscured due to its close association with the occipital surface of the skull or with the cranial cervical series (e.g., Wei et al., 2013; Lü et al., 2015; Funston et al., 2018). The disarticulation of the atlas in IGM 100/3006 allows for a more comprehensive description of this element than in most other specimens. The atlas is anteroposteriorly compressed as in all theropods (Osmólska et al., 2004) and consists of an isolated, U-shaped intercentrum that is comparable in size to the axial intercentrum (fig. 13). The anterior surface of the atlantal intercentrum is concave for the reception of the occipital condyle (fig. 13E). The width of the atlantal intercentrum is approximately two times its height at the midline and has a V-shaped dorsal margin. Both left and right atlantal neurapophyses are present and ascend at a steep angle as mediolaterally thin plates (fig. 13A–D).

The axial vertebra is preserved, although the neural arch, centrum, and intercentrum are disarticulated (fig. 14). The odontoid process is present and fused with the centrum, a condition that is variable in oviraptorosaurs (Osmólska et al., 2004; fig. 14E, F). There is no evidence of pleurocoels in the lateral surfaces of the axial centrum contra the condition described for Conchoraptor by Osmólska et al. (2004), however, there is a pair of small foramina on the dorsal midline, suggesting that the element is pneumatized (fig. 14F). Pneumatization of the axial centrum typically is present in oviraptorosaurs (Osmólska et al., 2004) in which the second cervical vertebra is preserved (e.g., Citipati IGM 100/978; Clark et al., 2002) and in most theropods, excluding some basally diverging members (Benson et al., 2012). As in many of the vertebrae in IGM 100/3006, the centrum and neural arch of the axis are not yet fused. The anterior articular surface bears two ventral, parallel surfaces that received the axial intercentrum (fig. 14E). The neural arch of the axis is anteroposteriorly shorter than those in the remainder of the cervical series. In dorsal view the neural arch is triangular in shape, with the apex anteriorly positioned (fig. 14C). It bears a robust neural spine that is angled posteriorly in lateral view. The posterior surface of the neural spine base is excavated and contains two foramina that may be pneumatic (a pneumatized axial neural arch is not typically seen within Theropoda [Benson et al., 2012], but it is present in Khaan). Damage to the anterior portion of the axis prevents a description of the prezygapophyses. The postzygapophyses are strongly developed and comprise nearly half of the anteroposterior length of the neural arch. As in Khaan, there are weakly developed mammillary processes on the dorsal surface of the axial postzygapophyses. The presence of this feature in other oviraptorosaur taxa is unclear due to the susceptibility of this exposed region to erosion.

Description of the cervical centra is based exclusively on IGM 100/3006 because these surfaces are poorly exposed in the articulated specimen IGM 100/1203 (fig. 3). The anteriormost cervical centra have anterior articular faces that are at least twice as wide as the posterior faces as in other maniraptoriforms (Gauthier, 1986; Holtz, 1998; Maryanska et al., 2002; Zanno, 2010; Turner et al., 2012). Similar to the crown avian condition, the anterior face is saddle shaped (heterocoelous) (Baumel and Witmer, 1993), thus representing a convergently derived feature of the two groups (absent in all other maniraptorans; see Turner et al., 2012). In living birds, this morphology facilitates increased dexterity of the neck, and it likely served a similar function in oviraptorosaurs (Furet et al., 2022). The posterior articular face is square and amphiplatyan. The intercentral articulation of the postaxial cervical vertebrae is steeply inclined with the anterior surface facing anteroventrally and the posterior surface facing posterodorsally, a characteristic of all maniraptorans (Turner et al., 2012) that might be associated with sinusoidal neck curvature (Ostrom, 1969; Barsbold, 1983; Norell and Makovicky, 2004). As a result of this orientation, the posterior articular face of the cervical centra extends posteriorly beyond the margin of the neural arch of the succeeding vertebra. The dorsal surfaces of the centra are concave, forming the ventral wall of the neural canal. The ventral surfaces of the anterior cervical centra are flat and split anteriorly to form parapophyses for the unfused articulation of the cervical ribs. In all three complete postaxial cervical vertebrae, an anteroposteriorly elongate pleurocoel pierces the lateral surface of the centrum approximately midway along its length (fig. 14A, B).

Cervical neural arches are visible in both IGM 100/1203 and IGM 100/3006. Description of the lateral surfaces, however, is based on IGM 100/3006. The arches belonging to the anterior cervical vertebrae are roughly rectangular in dorsal view (fig. 15C), with the anterior end being slightly narrower than the posterior end. IGM 100/1203 shows that the dorsal surface becomes progressively more X-shaped posteriorly in the series (fig. 3). The neural spine is located centrally on the arch, similar to other oviraptorosaurs (Makovicky and Sues, 1998; Osmólska et al., 2004; Balanoff and Norell, 2012). The neural spines are rectangular in lateral view and are slightly longer anteroposteriorly as well as mediolaterally thinner proceeding from CV III–V (fig. 15A, B). Neural spines in the cervical series posterior to CV V are progressively reduced in height but remain centered on the neural arch (Makovicky and Sues, 1998; Osmólska et al., 2004). The pre- and postzygapophyses are robustly developed in all postaxial cervicals. The dorsal surface of the postzygapophysis is spherical and well defined, with moundlike epipophyses (fig. 15C). This condition is similar to that of A. portentosus and Khaan, but distinct from the linear morphology in Microvenator celer (Makovicky and Sues, 1998), Similicaudipteryx yixianensis (He et al., 2008), Nomingia gobiensis (Barsbold et al., 2000), and Citipati. As described previously for the axial vertebra, the neural arch is excavated anteriorly and posteriorly at the base of the neural spine. A small tubercle, or diapophysis, for the reception of the cervical rib is present at the anterior margin of the ventrolateral pneumatic opening, indicating that the cervical ribs in IGM 100/3006 are not fused, another indicator of skeletal immaturity. The cervical neural canal is wide, as dorsoventrally tall as the centra and as transversely wide, about the same size as the posterior articular face (fig. 15C).

No cervical ribs are preserved in IGM 100/3006 although two right elements can be seen articulating with the caudal cervical vertebrae in IGM 100/1203 (fig. 3). They do not deviate considerably from previously described oviraptorid taxa.

Three cervicodorsal vertebrae can be observed starting immediately caudal to the furcula in IGM 100/1203. As in Khaan and Oksoko, the neural arches are X-shaped in dorsal view, and associated ribs are proximodistally shorter than those of the dorsal series.

No dorsal vertebrae are preserved in IGM 100/3006; therefore, the description is taken exclusively from IGM 100/1203 (fig. 3). The posterior dorsal vertebrae are poorly preserved and tightly compressed, making it difficult to distinguish the position of the dorsosacral vertebra using morphology alone. Nonetheless, approximately 11 dorsal vertebrae are present, based on the number of elements that have associated ribs, a count that aligns with the usual range for oviraptorosaurs (Osmólska et al., 2004; Balanoff and Norell, 2012). Maniraptorans outside of Oviraptorosauria, however, range up to 12 dorsal vertebrae (Norell and Makovicky, 2004).

Similar to the cervicodorsal vertebrae, the anterior dorsal vertebrae have an X-shaped neural arch in dorsal view with a small neural spine centered on the arch. Proceeding posteriorly along the dorsal series the transverse processes trend toward a more purely lateral extension, become more rectangular, and anteroposteriorly longer. The presence or absence of pleurocoels on the dorsal centra cannot be confirmed as they are not exposed in IGM 100/1203 (fig. 3).

The dorsal ribs are preserved in articulation with their corresponding vertebrae, and several of the anteriormost elements on the right side are accompanied by ossified sternal ribs. The 3rd and 4th right and left dorsal ribs possess elongate uncinate processes that extend from the rib with which they originate posteriorly past the posterior margin of the succeeding rib. These have an expanded proximal articulation surface and narrow distally, with each successive element becoming smaller and more gracile. The processes are not fused to the ribs and overall bear a similar morphology to those in Caudipteryx (IVPP V 12430) and Citipati (IGM 100/979 and 100/1004; Clark et al., 1999: fig. 12; Norell et al., 2018). Due to the inaccessibility of the ventral extent of the dorsal ribs in IGM 100/1203, the “single ossified ventral rib segment,” a character shared by dromaeosaurs and oviraptorids (Clark et al., 1999), cannot be ascertained. The left 7th and right 7th, 9th, 10th, and 11th dorsal ribs have associated sternal ribs. They are anteroventrally narrow and straplike, as in oviraptorosaurs generally (e.g., Lü, 2005; Funston and Currie, 2016; Balanoff and Norell, 2012).

The sacral vertebral count of IGM 100/3006 of six (fig. 16) is consistent with the number found in other oviraptorosaurs, which can vary between six and seven (Osmólska et al., 2004). In IGM 100/1203 the overlying ilium obscures the view of the sacral vertebrae (fig. 16). In IGM 100/3006, exposure is limited primarily to the ventral surface, but the centra, neural arches, and sacral ribs are visible and remain unfused at this stage of skeletal maturity (see Discussion). Fusion of these elements occurs in most oviraptorosaurs, including Chirostenotes pergracilis (TMP 79.20.1; Currie and Russell, 1988; Funston and Currie, 2021) and Citipati (IGM 100/978). The first vertebra in the sacral series of IGM 100/3006 is missing its anterior half. Overall, the anterior centra are wider and more dorsoventrally compressed than those in the posterior region, and all the sacral centra have anterior articular faces that are wider than the posterior articular faces. The width of the anteriormost centrum is approximately 3× its height; the posteriormost sacral vertebral centrum is about 2× as wide as tall. Lateral pleurocoels on the sacral centra are single and anteroposteriorly elongate, as in H. huangi, Khaan, Oksoko, and Citipati. In the anterior sacral vertebrae these are positioned midway along the length of the centrum. They become smaller and slightly more posteriorly positioned toward the caudal portion of the series. Pleurocoels are present within the sacral centra of caenagnathids (TMP 79.20.1; Currie and Russell, 1988), oviraptorids, and most other maniraptorans but absent in the more basally diverging oviraptorosaur A. portentosus. Large parapophyses for the sacral ribs are situated at the anterolateral edge of the centrum. The articular surfaces gradually lengthen, expanding their posterior margin in the more posterior part of the series. A shallow, rounded groove runs down the midline of the ventral surface of sacrals II–V (fig. 16B). The sulcus cannot be assessed on sacral I because of the broken surface. A midline groove also is present in H. yanshini (IGM 100/30), but absent in Rinchenia and H. huangi.

Three anterior caudal vertebrae are preserved in articulation in IGM 100/3006, and of these only the posteriormost vertebra in the series has an associated centrum (fig. 17). An additional disarticulated centrum and associated transverse process is also present in IGM 100/3006 (fig. 18). As observed in other regions of the vertebral column, the caudal vertebrae lack fusion between the centrum and neural arch. IGM 100/1203 preserves 13 caudal vertebrae but lacks the distalmost portion of the tail (fig. 3). A full caudal series in other oviraptorosaurs ranges from 22 in Caudipteryx to 32 in Citipati (IGM 100/978). Overall, the oviraptorosaur caudal series is reduced compared with other nonavian coelurosaurs, which can reach up to 43 vertebrae in taxa such as Velociraptor (Norell and Makovicky, 1999; Osmólska et al., 2004).

The caudal centra are not visible in IGM 100/1203; therefore, the description is based on the four vertebrae from IGM 100/3006 (figs. 17, 18). These vertebrae resemble the posterior sacral vertebrae in that the centrum is wider than tall and the anterior articular surface is wider than the posterior surface. The lateral surface bears an oval pleurocoel that is approximately the same size as those in the posterior sacral vertebrae, a character that is unknown outside of oviraptorids and caenagnathids (Maryanska et al., 2002; Benson et al., 2012) (figs. 17A, B, 18). It is located dorsally on the centrum, near the base of the neural arches. Caudal pleurocoels appear to be absent in A. portentosus, but may be present at least in the proximal portion of the tail in another basal oviraptorosaur, Similicaudipteryx.

The neural arches from the caudal series are described using both IGM 100/3006 and 100/1203. The neural arches of the anterior caudal vertebrae are more extensively pneumatized than other regions of the vertebral column. Both the dorsal and ventral surfaces of the transverse processes are pneumatized in IGM 100/3006, and the dorsal surface is pneumatized by anterior and posterior foramina (figs. 17C, 18A). Only an anterior foramen is present in IGM 100/1203 (fig. 3). The distribution of these pneumatic foramina is variable within Oviraptorosauria. Citipati (IGM 100/978), Nomingia and A. portentosus all lack pneumatization in their caudal neural arches, but like Conchoraptor, foramina are present on the dorsal surface of the transverse process in H. huangi (Lü, 2003) and Khaan and the ventral surface in H. yanshini (IGM 100/30). The transverse processes are elongate, thin, and extend laterally and slightly posteriorly. IGM 100/1203 does not exhibit a distinct transition point within the caudal vertebrae series as the transverse processes gradually shorten their lateral extent as they progress posteriorly (fig. 3).

The posteriorly positioned neural spines of the anterior caudal vertebrae from IGM 100/3006 are dorsoventrally taller and anteroposteriorly thinner in lateral view than those of the cervical or dorsal vertebrae (fig. 17A, B). That of the subsequent vertebrae is oriented dorsally and slightly more anteriorly. In IGM 100/1203, caudal vertebrae III–IX have a dorsally oriented neural spine that is triangular in lateral view. The subsequent vertebrae (X–XIII) possess a slightly posteriorly oriented spine. The anterior and posterior surfaces at the base of the neural spines are not excavated as they are in the cervical and dorsal vertebrae. The transverse processes of all the caudal vertebrae extend slightly posterolaterally and become gradually shorter toward the end of the tail. The prezygapophyses are small and narrow. They do not extend far beyond the margin of the centrum. The postzygapophyses, however, are larger and overlap the succeeding vertebral centrum, but not to the extent observed in deinonychosaurs.

The forelimbs are preserved only in IGM 100/1203 (figs. 3, 19). The pectoral girdle preserves a partial furcula and both left and right scapulae. The coracoid is not visible in this specimen although its articulation surface on the scapula is visible. It therefore seems likely that the scapula and coracoid were not yet fused into a single element as they are in most oviraptorids. The left ramus of the furcula is largely complete (fig. 3). Although the right ramus cannot be identified, a wide U-shape can be deduced, a character that is also present in H. huangi, Khaan, Oksoko, H. yanshini, Yulong, and Tongtianlong. This morphology is discordant with the acute V-shape of Oviraptor or Citipati (Nesbitt et al., 2009). The sternum is not visible in IGM 100/1203.

The left scapula of IGM 100/1203 is preserved in its entirety (figs. 3, 19), but the right element consists only of the midportion of the scapula blade. The scapula blade is approximately the same width along most of its length but expands slightly at its rounded distal extremity, similar to the condition present in other oviraptorosaurs (Osmólska et al., 2004; Balanoff and Norell, 2012; Funston, 2024). At the proximal end of the scapula, the acromion process is directed anteriorly and is relatively small, as in Oksoko. This contrasts with the large winglike acromion process in H. yanshini (IGM 100/1004) and the larger bodied oviraptorid Citipati (IGM 100/1004). The contribution of the scapula to the glenoid fossa is damaged, so it is difficult to determine in which direction the fossa was originally oriented.

The left humerus and right ulna and radius are preserved in IGM 100/1203 (fig. 3). Fragmentary pieces of the midshaft region of the left ulna and radius are recovered, but little morphology can be obtained. The humerus is broken into two pieces midway along the shaft. The humeral head and deltopectoral crest have also suffered damage, although its basic length and proportions can be reconstructed (table 3). The deltopectoral crest makes up approximately 40% of the length of the humerus as in Nankangia, Tongtianlong H. yanshini, and H. huangi but unlike Citipati, Khaan, and Oksoko wherein the crest stretches one third or less of its length. This region denies an assessment of the degree to which the crest is developed, however its apex is located at the distalmost end, as it is in other oviraptorids, differing from more basally diverging oviraptorosaurs Microvenator and Gigantoraptor, which have less pronounced, more rounded deltopectoral crests (Makovicky and Sues, 1998). The distal end of the humerus is not fully exposed although it can be ascertained that the medial condyle extends distinctly further distally than the lateral condyle.

Little can be determined about the partial right ulna present in IGM 100/1203 because it is broken into three pieces, although it was approximately 40% shorter than the humerus and circular in cross section. The olecranon process is weakly developed as it is in most maniraptorans.

The hindlimb and pelvic girdle of Conchoraptor as determined from IGM 100/1203 is “dolichoiliac,” meaning that the pre- and postacetabular processes of the ilia are elongate and the pubes and ischia are gracile as in most theropods. This is in contrast with the condition in sauropodomorph saurischians, which exhibit rostrocaudally short ilia with squat, platelike pubes and ischia (Colbert, 1964). The left and right ilia were recovered for IGM 100/3006; however, the majority of the preacetabular process is missing from both sides (fig. 16). In this specimen, the left ilium is crushed inward, but the right element is undistorted. Conchoraptor resembles most other oviraptorosaurs, with the exception of Rinchenia and Caudipteryx (Osmólska et al., 2004), in that the dorsoventral depth of the postacetabular process is approximately the same as that of the preacetabular process, and the dorsal margin is straight (Osmólska et al., 2004). The iliac blades remain completely separated in IGM 100/1203 (fig. 3) but come together along the midline in IGM 100/3006 (fig. 16). The preacetabular process has a slightly expanded anteroventral margin that, if the dorsal margin is held horizontally, does not reach the level of the pubic peduncle. A similar morphology is found in most oviraptorosaurs, but the ventral margin of the process extends beyond this level in Caudipteryx. The postacetabular process of Conchoraptor tapers slightly posteriorly but ends in a blunt posterior margin as in Khaan, rather than being rounded as in Nomingia or tapered as in H. huangi and Nankangia jiangxiensis (Lü et al., 2013b). The postacetabular blades diverge from one another and are not parallel as they are in most nonavian maniraptorans. An oval and anteroposteriorly elongate scar is present on the lateral surface of the ilium just anterodorsal to the acetabulum, which likely was for the attachment of the iliotibialis muscle (fig. 16C) (Shufeldt, 1909; Hutchinson, 2001). The remainder of the lateral surface of the element is featureless.

The supraacetabular crest in Conchoraptor is weakly developed with a prominent antitrochanter at its posterior margin (fig. 16). The pubic peduncle is not visible in IGM 100/1203; however, IGM 100/3006 exhibits one that, with the dorsal margin held horizontally, is slightly longer proximodistally and more medially directed than the ischiadic peduncle. The brevis fossa in IGM 100/3006 is present not as a deep fossa, but rather as a broad, ventral shelf similar to other oviraptorids and caenagnathids (Hutchinson, 2001; Osmólska et al., 2004. More basally diverging oviraptorosaurs such as Caudipteryx and A. portentosus preserve a well-formed brevis fossa.

The pubis is observable only in IGM 100/3006 and consists of a proximal shaft still attached to the ilium (fig. 16) and the corresponding pubic shaft, preserved as a separate piece (fig. 20). When articulated, these pieces form a ventrally projecting pubis. The preserved portion of the shaft is relatively straight, similar to A. portentosus, Nomingia, and Citipati (IGM 100/978). A more anteriorly concave pubis, however, is observed in H. yanshini (IGM 100/30), Gigantoraptor, Khaan (IGM 100/974), Oksoko, Corythoraptor, Nankangia, and Wulatelong ganzhouensis (Xu et al., 2013). The pubic shaft of Conchoraptor is compressed mediolaterally and joins its opposite at the distal extremity of the pubic boot. This narrow symphysis is extensively fused yet restricted to the posteromedial extent. IGM 100/3006 displays the plesiomorphic coelurosaur condition of a pubic boot that extends both anteriorly and posteriorly to the same degree, as in Nomingia but unlike Khaan, Nankangia, and Corythoraptor in which the anterior half of the boot is considerably more developed than the posterior. The pubic apron extends medially starting approximately halfway along the length of the shaft to the broken end. It cannot be determined whether the pubic aprons come together as they do in H. yanshini (IGM 100/30) and Citipati (IGM 100/978).

In IGM 100/3006, the proximal end of the ischium is preserved in articulation with the ilium (fig. 16) and the distal section is preserved in isolation (fig. 21). The proximal shaft of the isolated piece is broken into two pieces on the right side, but the left side is relatively undistorted. Only the proximalmost part of the ischium can be seen in IGM 100/1203 because of the overlying ilium (fig. 3). Overall, this element in Conchoraptor is similar to that of other oviraptorosaurs in that it is short and triangular in shape due to an obturator process positioned approximately midway along the length of the shaft (fig. 21C) (Osmólska et al., 2004). The ventral margin of the ischium is straight with a slight dorsal curvature, tapering to a point as it extends posteriorly. The posterior margin, which can be variable in oviraptorosaurs, is relatively straight. The distal part of the ischium is platelike with a concave lateral surface, a derived feature of all known oviraptorosaurs (Norell et al., 2006). The paired ischia meet each other medially along the ventral margin. Although this may be a taphonomic feature, the same morphology has been reported for Citipati (Clark et al., 1999).

IGM 100/3006 and 100/1203 preserve both femora (figs. 22, 23), however, the distal half of the left side is missing in the former specimen. Only lateral and posterolateral views are observable in IGM 100/1203. The overall shape of the femur does not differ substantially from that of a typical theropod. The shaft is straight and roughly circular in cross section at its midlength. Only near the distal condyles does the shaft bow posteriorly and very slightly laterally. Proximally, the greater trochanter is prominent, and exhibits an excavated medial surface. The lesser trochanter extends as far dorsally as the greater trochanter, and is fingerlike, with only a shallow groove separating these structures as in most other oviraptorids. More basally diverging oviraptorosaurs, such as Caudipteryx and Microvenator, have a wider notch separating the femoral trochanters. Diverging from this pattern, Citipati (IGM 100/978) and Gigantoraptor share a continuous, arc-shaped trochanteric crest. As in Oksoko, there is no sign of a fourth trochanter, or a roughened surface as is present in troodontids (Makovicky and Norell, 2004) and Khaan. The femoral neck is not constricted, and the head is roughly hemispherical. At the distal end, the lateral condyle extends distally past the medial condyle as it does in all oviraptorosaurs (Osmólska et al., 2004). As in Oksoko, a deep popliteal fossa separates these two condyles, in contrast to the relatively shallow fossa apparent in Khaan. Similar to all oviraptorids, the circular crista tibiofibularis, which sits on the posteromedial surface of the lateral condyle, is large and extends well past the posterior margin of the femur (fig. 23B, C) (Osmólska et al., 2004). The size of this crista is closer to that of Khaan or H. yanshini than larger-bodied oviraptorosaurs such as Citipati or Gigantoraptor.

A complete right tibia is preserved in IGM 100/3006 (fig. 24), and both are preserved in 100/1203 (fig. 3). In IGM 100/1203, the left tibia is damaged at its proximal end, but the posterior surface of the right element is almost pristine. The tibia of Conchoraptor is approximately 25% longer than the femur and has a straight shaft (table 2) that is anteroposteriorly compressed. The proximal end possesses a weakly developed, anterolaterally directed cnemial crest, similar to the morphology found in Khaan, but contrasting with the more robust process present in Citipati, Nomingia, and H. yanshini. As in all observed oviraptorosaurs, the cnemial crest extends less than 1/5 of the length of the tibia (Balanoff and Norell, 2012). A fibular crista along the lateral surface extends about one-third of the length of the tibia in Conchoraptor (fig. 24A, B). Immediately posterior to the distal end of the fibular crista of the right tibia of IGM 100/3006 is a large nutrient foramen (fig. 24B), also present in Khaan but lacking in other observed oviraptorids. The presence of this opening cannot be confirmed in other specimens of Conchoraptor and may be intraspecifically variable as it is in Khaan. This feature is relatively common among caenagnathids (Funston and Currie, 2018).

A partial right fibula that is missing its proximal end is preserved in IGM 100/3006 (fig. 25). IGM 100/1203 preserves both complete fibulae in articulation, and they can be seen tapering distally as they wrap slightly anteriorly around the tibiae (fig. 3). Generally, they resemble the morphology present in other oviraptorosaurs, being compressed mediolaterally and extending the entire length of the tibia to articulate with the calcaneum. The proximal head of the fibula is concave medially with a distinct posterior crista, where it articulates with the lateral articular face of the tibia (fig. 25A). A pronounced tuberculum is present laterally, just distal to the proximal head for the attachment of the iliofibularis muscle.

The astragalocalcaneum is preserved in both hindlimbs of IGM 100/1203 (fig. 3), although it is largely obscured by the articulated foot. The element is clearly visible in articulation with the distal surface of the right tibia of IGM 100/3006 (fig. 24). As in Khaan, Oksoko, and Citipati, the astragalus spans the entire width of the distal tibia. The ascending process similarly matches the width of the distal tibia at the level of the condyles, although it tapers proximally, so that its height is greater than the maximum width of the astragalus as in all oviraptorosaurs (Balanoff and Norell, 2012). The medial and lateral condyles of the astragalus are equally well developed, although the medial condyle does extend further anteriorly as in Citipati, H. yanshini, Oksoko, and Gigantoraptor. The intercondylar fossa is shallow as in Khaan and H. yanshini, contrasting the deep condition in Citipati. The lateral condyle is excavated laterally by a shallow depression that houses the calcaneum (fig. 24D). As in all oviraptorosaurs, the calcaneum is a small, kidney-shaped tab of bone and is otherwise unremarkable.

Fragments of distal tarsals are visible on the proximal surfaces of both left and right metatarsi in IGM 100/3006 (fig. 26) but are obscured posteriorly by the articulated astragalocalcaneum in IGM 100/1203 (fig. 3). These fragments in IGM 100/3006 are likely attributable to distal tarsal III, being situated proximally to metatarsal II and slightly overlapping metatarsal III, as in Tongianlong and Oksoko. The fragments take the form of a roughly trapezoidal plate, but little more morphology can be ascertained. The loss of distal tarsal IV may indicate that these elements were not strongly fused to one another as in some skeletally mature oviraptorosaurs such as Elmisaurus (Currie et al., 2016; Funston et al., 2015) and Avimimus nemegtensis (Funston et al., 2018). There is no sign of advanced fusion between the distal tarsals and the proximal metatarsals as is present in Oksoko.

The feet are preserved in both specimens of Conchoraptor (figs. 3, 26, 27); although the right foot of IGM 100/3006 is the most completely preserved in articulation, missing only the 3rd ungual phalanx. The left foot is missing its 2nd and 4th ungual phalanges.

Metatarsals II–IV are preserved in both specimens. As is the case in all oviraptorids, Conchoraptor lacks a true arctometatarsalian condition (Osmólska et al., 2004), but MT III is slightly constricted at its proximal end (figs. 26A, 27D) similar to Citipati (IGM 100/978), Corythoraptor, Ganzhousaurus nankangensis (Wang et al., 2013), and Wulatelong. Other oviraptorid taxa such as Khaan, Gigantoraptor, Oksoko, and Yulong lack any constriction of MT III whereas more basal oviraptorosaurs such as Caudipteryx and Similicaudipteryx have a highly compressed metatarsal III (Ji et al., 1998). A. portentosus has an extreme condition in which the proximal end of metatarsal III is no longer present (Kurzanov, 1981, 1985). The metatarsals of Conchoraptor are not fused proximally as has been posited in other oviraptorid taxa (Osmólska et al., 2004; Lü, 2005), and this state in Oviraptor likely represents either taphonomic distortion or disease. Fusion of these elements is present in some caenagnathids such as Elmisaurus (Currie et al., 2016) and Citipes (Funston et al., 2016). In the foot of Conchoraptor, metatarsal III is longest, followed by IV and then II. The shafts of metatarsals III and IV are dorsoventrally (dorsopalmarly) compressed. On either side of the distal articular surfaces on the palmar surface is a flared process that likely served as an attachment point for extensor muscles in the foot. These processes are more pronounced in oviraptorids (especially Citipati) than other observed maniraptoran taxa (see Norell and Makovicky, 1999).

Although the first digit is not preserved in any of the specimens, the phalangeal formula is likely (2?)-3-4-5, preserving the plesiomorphic state of maniraptorans. Digit III is longest, followed by II and then IV. In digit III, the combined length of phalanges 1 and 2 is greater than that of phalanx 3, contra the derived condition for oviraptorids according to Osmólska et al. (2004). The ligamentary fossae on the lateral surfaces of the phalanges are deep and elongate similar to those observed in Citipati (IGM 100/978), not circular as in Khaan. The ungual phalanges are only weakly curved and are the longest phalangeal elements in the foot, with that of digit II the longest. All ungual phalanges possess a deep groove on the lateral surface extending from the distal edge approximately halfway along the length of the element.