IVPP V12615, a disarticulated partial skull and partial skeleton.

IVPP V12583, an incomplete, articulated postcranial skeleton.

PMOL-AD00102, a partial skull and mandibles missing only the rostral portions, and six articulated cervical vertebrae (Yin et al. 2018); IVPP V20378, a nearly complete skeleton (Yu et al. 2024); SDUST-V1062, a nearly complete, articulated postcranial skeleton (Figs 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14).

All reported specimens of Sinovenator are recovered from Lujiatun, Shangyuan, Beipiao City, western Liaoning, China. SDUST‑V1062 was discovered at the Duanjiagou site, Xidayingzi Village, Bisiyingzi Township, Ningcheng County, Chifeng City, Inner Mongolia, China, a new fossil site (Fig. 1). The absolute geological age has been constrained to 125.7 ± 1.5 Ma using U–Pb zircon dating analyzed by CA-ID-IRMS (Li et al. in press), and the lithological features of the fossil beds are also the same as those of the Lujiatun Unit of the Yixian Formation at Beipiao, western Liaoning, China (Zhang et al. 2022).

Cervical vertebrate. The cervical series is articulated and well exposed (Figs 2, 3). The cervicodorsal transition can be clearly distinguished by the marked length disparity between the posteriormost cervical rib and the anteriormost dorsal rib. Considering that coelurosaurs typically possess 10 cervical vertebrae (Pei et al. 2017a; Gianechini et al. 2018), it is inferred that no vertebrae are missing and that all 10 cervical vertebrae are preserved in this specimen. The proatlas and most of the cervical vertebrae are completely preserved. The eighth cervical vertebra preserves only its posterior portion (Figs 2, 3). The cervical vertebrae increase in length posteriorly, reaching their maximum length at the sixth vertebra, and then shorten posteriorly (Table 1). The neural arches and centra are completely fused.

The proatlas consists of two subtriangular, plate-like elements (Figs 2, 3). The left element taphonomically overlies the right element on its anterodorsal side. Both elements are unfused (Fig. 3), as in SinovenatorPMOL-AD00102 (Yin et al. 2018) and Tsaagan (Norell et al. 2006). The proatlas is dorsoventrally tall, similar to that in SinovenatorPMOL-AD00102 (Yin et al. 2018), Tsaagan (Norell et al. 2006), and Archaeopteryx (O’Connor et al. 2025), but the caudodorsal expansion present in Archaeopteryx is absent in SDUST-V1062. The proatlas is slightly deflected laterally. The medial surface of the proatlas is concave, as in SinovenatorPMOL-AD00102 (Yin et al. 2018), Tsaagan (Norell et al. 2006), and Archaeopteryx (O’Connor et al. 2025). Ventrally, the proatlas articulates with the atlantal intercentrum. Within Troodontidae, the proatlas has only been reported in Gobivenator (Tsuihiji et al. 2014) and Sinovenator (Yin et al. 2018).

The atlas comprises an intercentrum, a centrum, and two neural arches. The atlantal intercentrum is U-shaped in anterior view (Suppl. material 1), as in SinovenatorPMOL-AD00102 (Yin et al. 2018). The atlantal centrum, namely the odontoid, is co-ossified with the axis. The odontoid is oval and wider than tall in anterior view (Suppl. material 1). As in SinovenatorPMOL-AD00102 (Yin et al. 2018), the neural arch is triradiate in lateral view (Fig. 3). The postzygapophysis extends posteriorly and articulates with the axis (Fig. 3), as in Liaoningvenator (Shen et al. 2017a) and SinovenatorPMOL-AD00102 (Yin et al. 2018). No remains of atlantal ribs could be observed.

The axis is poorly preserved anteriorly. Preservation limitations preclude definitive confirmation of pneumatic foramina on the lateral surfaces of the centrum. The posterior articular facet of the centrum is slightly concave. The postzygapophysis is elongated. The epipophysis is blunt and extends posterolaterally, but not beyond the posterior margin of the postzygapophysis. This condition is similar to that of some troodontids, such as Gobivenator (Tsuihiji et al. 2014), Liaoningvenator (Shen et al. 2017a), and SinovenatorPMOL-AD00102 (Yin et al. 2018), and some dromaeosaurids, such as Mahakala (Turner et al. 2011) and Buitreraptor (Gianechini et al. 2018). In contrast, the epipophysis extends beyond the posterior margin of the postzygapophysis in some dromaeosaurids, such as Deinonychus (Ostrom 1969) and Tsaagan (Norell et al. 2006). The neural spine is high and plate-like, with its posterior edge being almost vertical (Fig. 3), as in Liaoningvenator (Shen et al. 2017a) and SinovenatorPMOL-AD00102 (Yin et al. 2018). Unlike in Gobivenator (Tsuihiji et al. 2014) and Jianianhualong (Xu et al. 2017), the posterodorsal portion of the neural spine does not extend posteriorly in SDUST-V1062. The neural spine is slightly expanded bilaterally along its dorsal margin (Fig. 3). A pair of spinopostzygapophyseal laminae are well developed, diverge posterolaterally from the base of the neural spine, and bound the spinopostzygapophyseal fossa.

The postaxial centra are generally rectangular in lateral view (Fig. 3). The neural arches display an X-shaped profile in dorsal view. This profile is a common feature in paravians and is formed by the prezygapophyses and postzygapophyses extending anterolaterally and posterolaterally, respectively. In lateral view, the centra of the axis and the third and fourth cervical vertebrae extend posteriorly beyond the posterior margin of the neural arches (Figs 3, 4). This condition differs from that of dromaeosaurids, in which the centrum is level with or ends anterior to the posterior margin of the neural arch (Turner et al. 2012).

The third cervical vertebra is well preserved (Figs 3, 4). The ventral surface of the centrum is smooth (Fig. 4D). The lateral surface of the centrum bears two oval pneumatic foramina (pleurocoels; Currie and Dong 2001; Gao et al. 2012; Yin et al. 2018) (Fig. 4A, B), as in SinovenatorPMOL-AD00102 (Yin et al. 2018). These foramina are posteroventral and posterior to the diapophysis, respectively. As in SinovenatorPMOL-AD00102 (Yin et al. 2018), a depression is present and positioned more posteroventrally than the pneumatic foramina (Fig. 4A, B). The parapophysis is short and thick and is located at the anteroventral corner of the centrum (Fig. 4A, B). The articular facet of the parapophysis is oval and concave. The anterior articular facet of the centrum is saddle-like and transversely concave in ventral view (Fig. 4D, E), as in Deinonychus (Ostrom 1969) and the troodontid LH PV39 (Wang et al. 2021). The posterior articular facet of the centrum is slightly concave and posteroventrally inclined (Fig. 4F). The prezygapophysis is large, and its articular facet slopes anteroventrally and articulates with the postzygapophysis of the axis (Figs 3, 4). The epipophysis is well developed and does not extend beyond the posterior margin of the postzygapophysis (Fig. 4B), as in the axis. The diapophysis is triangular in lateral view and located on the posteroventral side of the prezygapophysis (Fig. 4A, B). The neural spine is plate-like. Dorsally, the spine is damaged but has left a subrectangular impression in the matrix (Figs 3, 4). The area of the neural spine of the third cervical vertebra is smaller than that of the axis, as in other troodontids (Tsuihiji et al. 2014; Shen et al. 2017a; Xu et al. 2017). Spinopostzygapophyseal and spinoprezygapophyseal laminae are present and diverge posterolaterally and anterolaterally from the base of the neural spine, respectively (Fig. 4E, F). The area of the spinopostzygapophyseal fossa is larger than that of the spinoprezygapophyseal fossa (Fig. 4E, F).

The fourth cervical vertebra is well preserved (Figs 3, 4) and is clearly slightly longer than the third cervical vertebra (Table 1). Two oval pneumatic foramina and a depression occur on the lateral surface of the centrum, and their positions and morphologies are similar to those of the third cervical vertebra (Fig. 4G, H). The parapophysis is short, and its articular facet is subcircular (Fig. 4G). As in the third cervical vertebra, the anterior articular facet of the centrum is saddle-like, and the posterior articular facet is shallowly concave (Fig. 4K, L). The prezygapophysis and postzygapophysis show comparable lateral extension (Fig. 4I). The diapophysis is located on the lateral side of the neural arch and projects lateroventrally (Fig. 4G). Ventrally, the prezygapophysis bears a prezygodiapophyseal lamina that extends posteroventrally to connect with the diapophysis (Fig. 4G, H). A postzygodiapophyseal lamina is also developed between the postzygapophysis and the diapophysis. The epipophysis is slightly shorter than that of the third cervical vertebra. The neural spine is subrectangular in lateral view, and its anteroposterior length is greater than that of the third cervical vertebra. As in the third cervical vertebra, the spinopostzygapophyseal and spinoprezygapophyseal fossae are also developed (Fig. 4K, L).

The fifth cervical vertebra is poorly preserved, and its neural spine is heavily damaged (Fig. 3). This cervical vertebra is elongate and is 1.4 times the length of the fourth cervical vertebra (Table 1). The prezygapophysis is more developed than that of the fourth cervical vertebra, whereas the postzygapophysis is subequal in size to that of the fourth cervical vertebra.

The sixth cervical vertebra is the longest vertebra in the cervical series (Table 1). The anterior portion of the centrum is poorly preserved, and the parapophysis is missing (Fig. 3A, B). The ventral surface of the centrum is smooth, without the ventral keel seen in Sinornithoides (Russell and Dong 1993), Troodon (Makovicky and Norell 2004), Saurornithoides (Norell and Hwang 2004), and Mei (Gao et al. 2012; Wang et al. 2021). Posteriorly, the centrum exceeds the posterior end of the postzygapophysis (Fig. 3A, B). Owing to preservation limitations, only a suboval pneumatic foramen is visible on the lateral surface of the centrum (Fig. 3A, B). An oval depression is also present posteroventral to the pneumatic foramen (Fig. 3A, B), as in the third and fourth cervical vertebrae. The prezygapophyseal articular facet is ovoid, faces anterodorsally, and slopes slightly medially. The postzygapophysis is comparable to the prezygapophysis in size (Fig. 3A, B) and bears a weakly developed epipophysis dorsally. The diapophysis is located more anteriorly on the neural arch and extends laterally (Fig. 3A, B), as in Mei (Gao et al. 2012) and the troodontid LH PV39 (Wang et al. 2021). As in the fourth cervical vertebra, the pre- and postzygodiapophyseal laminae are also developed. The neural spine is damaged dorsally and is located between the pre- and postzygapophyses (Fig. 3A, B).

The seventh cervical vertebra is preserved in its entirety (Fig. 3A, B). This vertebra is slightly shorter than the sixth cervical vertebra. Ventrally, the centrum bears a pair of weakly developed carotid processes between the parapophyses, as in Sinornithoides (Currie and Dong 2001) and Troodon (Makovicky and Norell 2004). The shape and location of the pneumatic foramen and depression are similar to those of the sixth cervical vertebra, but the depression is slightly larger and deeper (Fig. 3A, B). The parapophysis is located at the anteroventral corner of the lateral side of the centrum and articulates with the cervical rib (Fig. 3A, B). The prezygapophysis is weakly developed and directed more dorsally than that of the sixth cervical vertebra, and the postzygapophysis extends posteriorly beyond the posterior margin of the centrum (Fig. 3A, B). The diapophysis is posterodorsal to the parapophysis. This diapophyseal location is comparable to that of the sixth cervical vertebra, but the process extends more ventrally than in the latter (Fig. 3A, B). The pre- and postzygodiapophyseal laminae are developed between the diapophysis and the pre- and postzygapophyses, respectively. The neural spine is plate-like, and its anterior margin slopes slightly anteroventrally in lateral view (Fig. 3A, B).

Only the posterior margin of the eighth cervical vertebra is preserved (Fig. 3C, D). A depression is present on the lateral surface of the centrum and is shallower than those of the preceding cervical vertebrae. The posterior articular facet of the centrum is exposed and relatively flat. The postzygapophysis extends beyond the posterior margin of the centrum.

The ninth cervical vertebra is exposed on its right side (Fig. 3C, D). In lateral view, the centrum is subrectangular and ventrally concave. The parapophysis is located on the anterior side of the centrum and articulates with the corresponding rib. The pneumatic foramen of the centrum is obscured by the associated rib. The anterior articular facet of the centrum is flat. The prezygapophysis is short, approximately half the anteroposterior length of the postzygapophysis. The diapophysis is stout and lies posterodorsal to the parapophysis (Fig. 3C, D), as in SinovenatorIVPP V12615 (Xu 2002) and Liaoningvenator (Shen et al. 2017a). The neural spine is reduced and much lower than those of the anterior cervical vertebrae (Fig. 3C, D).

The tenth cervical vertebra is subequal in length to the ninth cervical vertebra. The prezygapophysis is short, and the postzygapophysis is elongated (Fig. 3C, D). The diapophysis also lies posterodorsal to the parapophysis and extends laterally and slightly posteriorly. Its neural spine and centrum are comparable in morphology to those of the ninth cervical vertebra.

Dorsal vertebrae. The anterior four and the last five vertebrae of the dorsal series are preserved (Figs 2, 3, 5). The anterior four dorsal vertebrae articulate with the cervical series, and the third and fourth dorsal vertebrae are severely damaged (Fig. 3C, D). The last five dorsal vertebrae are exposed on the right side, and the last three dorsal vertebrae are relatively well preserved (Figs 2, 5). As in the cervical series, the neural arches are fully fused to their respective centra in the dorsal vertebrae.

The first dorsal vertebra is well exposed (Fig. 3C, D). The centrum is overlain by the first dorsal rib. The parapophysis is positioned at the anteroventral corner of the centrum, as in Microraptor (Hwang et al. 2002), Gobivenator (Tsuihiji et al. 2014), and Buitreraptor (Gianechini et al. 2018). Posterodorsal to the parapophysis, the diapophysis is well developed and extends posterolaterally (Fig. 3C, D). A lamina extends anteroventrally from the diapophysis to the centrum. Dorsally, the lamina borders a triangular prezygapophyseal-centrodiapophyseal fossa. As in the cervical series, the neural arch is X-shaped in dorsal view. The prezygapophysis is stout, with its articular facet directed anteromedially (Fig. 3C, D). The anteroposterior length of the postzygapophysis is approximately twice that of the prezygapophysis. The neural spine is weakly developed. Moreover, the anterior part of the second dorsal vertebra is also well exposed. Its morphology is similar to that of the first dorsal vertebra, except that the diapophysis is more developed.

The last five dorsal vertebrae are similar in morphology but decrease gradually in length. The antepenultimate dorsal vertebra is well exposed (Fig. 5). The centrum is dumbbell-shaped in lateral view (Fig. 5). Laterally, the centrum is not pneumatized. It is ventrally smooth and lacks a keel. In lateral view, the parapophysis is located anterodorsally on the centrum and projects laterally. The neural arch is formed by the anterodorsally directed prezygapophysis and the almost horizontally directed postzygapophysis (Fig. 5). Both are subequal in length. The postzygapophysis exceeds the posterior margin of the centrum. The transverse process is positioned more posteriorly on the neural arch relative to the parapophysis (Fig. 5). It is broadened and projects laterally. The neural spine is tall and rectangular in lateral view (Fig. 5). Its posterior edge is apparently smooth, and the scar for attachment of the interspinous ligament is absent.

Sacral vertebrae. The sacral vertebrae are poorly preserved and partially obscured by the right ilium and femur (Fig. 2). Virtually no anatomical details can be discerned.

Caudal vertebrae. In SDUST-V1062, an incomplete segment of the caudal series is preserved in articulation (Fig. 2). Sixteen caudal vertebrae are preserved, including the last three proximal caudal vertebrae and the first 13 distal caudal vertebrae. The well-defined transition point corresponds to the caudal region where the transverse processes terminate, represents the terminus of the M. caudofemoralis attachment (Hone et al. 2021), and demarcates the proximal from the distal caudal vertebrae (Fig. 6).

Only the posterior portion of the antepenultimate proximal caudal vertebra is preserved, whereas the last two proximal caudal vertebrae are nearly complete (Fig. 6A, B). The penultimate proximal caudal vertebra is short and approximately two-thirds the length of the longest distal caudal vertebra (Table 1). In lateral view, the centrum is concave ventrally. The transverse process is poorly preserved and anteroposteriorly elongated, showing marked lateral extension (Fig. 6A, B). The pre- and postzygapophyses extend anterodorsally and posterodorsally, respectively. The postzygapophysis is short and does not extend posteriorly beyond the posterior border of the centrum (Fig. 6A, B). The last proximal caudal vertebra is slightly elongated relative to the preceding proximal caudal vertebrae. The transverse process is weakly developed, leaving a low, anteroposteriorly extended ridge (Fig. 6A, B). The postzygapophysis is shorter than the prezygapophysis and does not extend beyond the posterior margin of the centrum.

The first 13 distal caudal vertebrae are well preserved. The transverse process of the first distal caudal vertebra is absent (Fig. 6A, B). Along the series, the distal caudal vertebrae gradually elongate posteriorly, reaching their maximum length at the sixth distal caudal vertebra (Table 1). The distal caudal vertebrae are similar in morphology. In lateral view, the centra are rectangular, and the lateral surfaces bear a longitudinal depression (Fig. 6C, D). The prezygapophyses are elongated on the first six distal caudal vertebrae and then become gradually more slender and shorter posteriorly. In contrast, all postzygapophyses of the distal caudal vertebrae are strongly reduced. As in other troodontids (Makovicky and Norell 2004), the distal caudal vertebrae are sulcate along the dorsal midline, and neural spines are absent.

The anterior chevrons are poorly preserved, but the posterior chevrons are well preserved. The posterior chevrons are flattened dorsoventrally and elongated anteroposteriorly; this is a feature of derived coelurosaurians, such as dromaeosaurids, other troodontids, and basal birds (Xu 2002). These posterior chevrons are incomplete, except for the one between the tenth and eleventh distal caudal vertebrae. The anterior and posterior processes of this chevron are subequal in length (~10.5 mm; Fig. 6C, D). The anterior processes are slightly bifurcated, and the posterior processes are relatively blunt-ended in SDUST-V1062, as in Mei (Pei 2015), unlike in Jianianhualong, which has relatively blunt-ended anterior processes and slightly bifurcated posterior processes (Xu et al. 2017). Moreover, in Sinornithoides (Currie and Dong 2001), Jinfengopteryx (Ji et al. 2005), and Gobivenator (Pei 2015), the chevrons of the distal caudal vertebrae are bifurcated on both the anterior and posterior processes. These chevrons are separated from each other (Fig. 6C, D), as in Mei (Gao et al. 2012), Gobivenator (Tsuihiji et al. 2014), and Jianianhualong (Li et al. 2021), but unlike Sinusonasus (Xu and Wang 2004), whose chevrons contact each other and form a ventral band under the caudal centra.

Ribs. Cervical and dorsal ribs are partially preserved in SDUST-V1062 (Fig. 2). Some fragments of the cervical ribs are located near the third and seventh centra. The ninth and tenth cervical ribs are well exposed. They are double-headed, with a capitulum and tuberculum, and broad proximally (Fig. 3C, D). The capitulum of the ninth cervical rib is short and closely articulated with the centrum. The tuberculum is broad and subrectangular in lateral view. The notch separating the tuberculum from the capitulum is shallow. Distally, the rib shaft narrows. The tenth cervical rib is nearly completely preserved (Fig. 3C, D). The capitulum is elongated and tapers slightly anteriorly. The tuberculum is also subrectangular and is subequal to the capitulum in length but transversely wider than the latter (Fig. 3C, D). The notch is deeper than that of the ninth cervical rib. The shaft is slender and elongated posteriorly, exceeding the posterior margin of the tenth cervical centrum (Fig. 3C, D).

As with the cervical ribs, the first dorsal rib is also double-headed. However, the first dorsal rib is distinctly longer than the tenth cervical rib. The capitulum of the first dorsal rib is elongate, with a slightly expanded end, and the tuberculum is stout (Fig. 3C, D). The notch is deeper than those of the cervical ribs. The proximal end of the second dorsal rib is preserved. As in the first dorsal rib, the capitulum is slender and elongate, and the tuberculum is short and broad. Six other dorsal ribs are identified; they are similar in morphology, and all are extremely elongate (Fig. 2). Their proximal ends are preserved underlying the femur, and their shafts are bowed and taper distally. As in Archaeopteryx (Wellnhofer 2009), Microraptor (Hwang et al. 2002; Pei et al. 2014), and Anchiornis (Pei et al. 2017a), a longitudinal groove is present along the proximal shaft of these dorsal ribs. The groove is restricted to the proximal segment of each dorsal rib, tapers distally, and exhibits natural morphology. The cross-section of the mid-shaft is elliptical. As in other troodontids (Xu et al. 2017), the uncinate processes are not preserved. No attachment scars for uncinate processes have been identified on the dorsal ribs (Fig. 2).

Pectoral girdle. The pectoral girdle of SDUST-V1062 is preserved in articulation and is composed of the scapula and coracoid (Fig. 2). The scapula and coracoid are unfused, with a distinct suture between them. The glenoid fossa is not exposed, and its orientation is unclear.

Both scapulae are exposed in SDUST-V1062 (Fig. 2). The right scapular blade is missing, and the acromion process of the left scapula is damaged. The complete scapular length was estimated based on the relatively well-preserved left scapula. The estimated length of the scapula is approximately 82% of the humeral length (Table 2). This ratio is smaller than that in other Jehol troodontids, such as Mei (107%, Xu and Norell 2004; 100%, Gao et al. 2012), Jinfengopteryx (96%; Ji et al. 2005), Jianianhualong (98%; Xu et al. 2017), and Liaoningvenator (91%; Shen et al. 2017a). The left scapula is exposed medially and is elongate and slender (Fig. 2). The scapular blade is strap-like and mediolaterally compressed. It is nearly straight in medial view, unlike the bowed shape in Buitreraptor (Gianechini et al. 2018). A shallow groove is present on the medial surface near the proximal end and is subparallel to the ventral margin.

The left coracoid is exposed in posterior view (Fig. 2). It is rectangular, with an extensive ventral blade, as in Sinornithoides (Currie and Dong 2001) and SinovenatorIVPP V12615 (Xu 2002). In posterior view, the coracoid is thickened dorsally and gradually thins ventrally. A circular coracoid foramen is present and located on the medioventral side of the glenoid fossa.

Forelimb. The right humerus is well preserved (Fig. 7). The humerus is 68% of the femoral length (Table 2), much like that of some troodontids, such as SinovenatorIVPP V12583 (68%; Xu 2002), Jinfengopteryx (70%; Ji et al. 2005), and Jianianhualong (70%; Xu et al. 2017). In contrast, the humerus is proportionally short in Linhevenator (approximately 40% of the femoral length; Xu et al. 2011). Proximally, the deltopectoral crest is short, making up approximately 30% of the length of the humerus (Fig. 7). This condition of a short deltopectoral crest is also present in some other troodontids, such as Sinornithoides (23%; Russell and Dong 1993), Mei (22%; Gao et al. 2012), and Gobivenator (30%; Tsuihiji et al. 2014), but the proportion is greater than 50% in Linhevenator (Xu et al. 2011). An internal tuberosity is developed and projects transversely from the proximal margin of the humerus (Fig. 7). There is no obvious groove between the humeral head and the internal tuberosity, unlike in Liaoningvenator, in which a groove is developed (Shen et al. 2017a). The humeral shaft is twisted approximately 90° (Fig. 7). In posterior view, a longitudinally extending, groove-like olecranon fossa is present on the distal end of the humerus (Fig. 7).

Both ulnae and both radii are preserved (Fig. 2). The left ulna and radius are nearly complete, whereas the distal ends of the right ulna and radius are missing. The shaft of the ulna is bowed posteriorly (Fig. 2), as in many other maniraptorans (Xu 2002). In contrast, Anchiornis (Pei et al. 2017a) possesses a straight ulna. The cross-section of the mid-shaft is subcircular. The distal end of the ulna is transversely expanded, and its articular facet is flat.

The radius is straight (Fig. 2). It is approximately 65% of the humeral length (Table 2), whereas in Mei (Xu and Norell 2004), the radius is approximately 90% of the humeral length. Its mid-shaft is subcircular in cross-section and has a constant diameter. The shaft of the radius is more slender than the ulnar shaft. The diameter of the mid-shaft is 2.9 mm in the left radius and approximately half that of the left ulna (5.9 mm), whereas the diameter is 3.3 mm in the right radius and only slightly less than that of the right ulna (3.8 mm), which may be an artifact of taphonomic distortion or ontogenetic variation (Figs 2, 7). Distally, the left radius is slightly curved and articulates with the radiale.

Two left carpals are preserved in SDUST-V1062: the semilunate and radiale (Fig. 2). The semilunate is larger and crescent-shaped in dorsal view, with its proximal surface being convex. Distally, it covers the proximal ends of metacarpals I and II, as in most maniraptorans (Ostrom 1969; Xu et al. 2014; Pei 2015; Napoli et al. 2025). It is closely associated with the metacarpals. The radiale is smaller and lies between the semilunate and radius.

Metacarpals I, II, and III; manual phalanges I-1, II-1, III-1, and III-2; and the proximal portion of phalanx II-2 are preserved (Figs 2, 8). Metacarpal I is the shortest of the preserved manual elements and is approximately 43% of the length of metacarpal II (Table 2). Metacarpal I is relatively robust and has a diameter of approximately 3.5 mm at the mid-shaft. Proximally, metacarpal I is closely associated with metacarpal II. The distal end of metacarpal I expands dorsoventrally and appears to be ginglymoid, as in Mei (Gao et al. 2012).

Metacarpals II and III are exposed in dorsal view, except that their proximal ends are obscured by the tibia (Fig. 8). They are subequal in length. The shaft of metacarpal II has a mediolateral width of approximately 2.1 mm, similar to that of metacarpal III. Metacarpal III extends distally to the level of metacarpal II (Fig. 8). However, metacarpal III extends farther distally than metacarpal II in Mei (Gao et al. 2012).

Manual phalanx I-1 is long and robust. The cross-section of the mid-shaft is subcircular and has a diameter of 3.3 mm, which is greater than those of metacarpals II and III (Fig. 8B, D). The combined length of manual phalanx I-1 and metacarpal I is greater than that of metacarpal II, as in Mei (Gao et al. 2012) and Jianianhualong (Xu et al. 2017). This condition differs from that of some dromaeosaurs, such as Microraptor (Xu et al. 2003; Pei et al. 2014), in which the combined length of phalanx I-1 and metacarpal I is shorter than that of metacarpal II. Proximally, phalanx I-1 bears a prominent ventral intercondylar tuberosity. The shaft of phalanx I-1 is slightly dorsally bowed in lateral view. The distal end is apparently ginglymoid. A collateral ligament pit is exposed on the medial surface of phalanx I-1 (Fig. 8). This ligament pit is deep and dorsally shifted on the medial face of the distal articular end. A partially preserved ungual, tentatively identified as phalanx I-2, lies on the dorsal side of the distal end of phalanx I-1, and the blood groove is visible (Fig. 8). A fragmented bony element lies isolated near the distal end of phalanx I-1, and it cannot be confidently attributed to any element of the manus (Fig. 8).

The shaft and distal end of phalanx II-1 are partially exposed (Fig. 8). The shaft is slender, with a diameter of approximately 2.3 mm. Medially, the distal end is sculptured by a deep ligament pit that is positioned centrally (Fig. 8), whereas the medial ligament pit is absent in phalanx II-1 of the unnamed troodontid SDUST-V1042 (Yu et al. 2022). Phalanx II-2 is partially preserved, and its proximal part is well exposed. Proximally, phalanx II-2 bears well-developed ventral and dorsal intercondylar tuberosities (Fig. 8A, C), as in the unnamed troodontid SDUST-V1042 (Yu et al. 2022). The ventral tuberosity is larger than the dorsal one (Fig. 8A, C). The phalanges of digit III are comparable in diameter to those of digit II (Fig. 8B, D). Manual phalanx III-1 is subequal to phalanx III-2 in length (Table 2), as in some troodontids, such as Jianianhualong (Xu et al. 2017), Hypnovenator (Kubota et al. 2024), and the unnamed troodontids IGM 100/1126 (Pei 2015) and SDUST-V1042 (Yu et al. 2022).

Pelvic girdle. The right ilium is laterally exposed in SDUST-V1062, and the postacetabular process is missing (Fig. 9). The ilium is anteroposteriorly elongated. The preacetabular process has a convex anterior margin (Figs 5, 9), but this is possibly a taphonomic artifact. In contrast, the ilium of other troodontids, such as SinovenatorIVPP V12615 (Xu et al. 2002), Mei (Gao et al. 2012), Jianianhualong (Xu et al. 2017), and Latenivenatrix (Van der Reest and Currie 2017; Rhodes et al. 2021), has a nearly straight anterior margin. The ventral margin of the preacetabular blade slopes slightly anteroventrally, and the anteroventral process is drastically reduced (Fig. 9). The dorsal margin of the preacetabular process is roughly straight. The pubic peduncle is rectangular in lateral view and bears an articular facet that extends nearly horizontally (Fig. 9), which differs from the wedge-like pubic peduncle of Mahakala (Turner et al. 2011) and the unnamed troodontid IGM 100/1126 (Pei 2015). A large, deep fossa is located on the lateral surface of the pubic peduncle (Fig. 9) for the attachment of the M. cuppedicus. Dorsally, a ridge defining the fossa is well developed. It terminates dorsal to the pubic peduncle and is not continuous with the acetabular rim.

The right pubis is well preserved (Fig. 9). The pubis is nearly vertically oriented, as in Gobivenator (Tsuihiji et al. 2014), unlike the posteroventrally oriented condition in some basal paravians, such as Archaeopteryx (Ostrom 1976; O’Connor et al. 2025), Sinornithosaurus (Xu et al. 1999), and SinovenatorIVPP V12615 (Xu et al. 2002), and the anteroventrally oriented condition in Saurornithoides (Norell et al. 2009) and the unnamed troodontid IGM 100/1126 (Pei 2015). Proximally, the pubis projects anteriorly, forming an ambiens process (Fig. 9). The ambiens process is moderately developed, and its anteroposterior length is less than that of the ischial peduncle of the pubis, differing from the elongated condition in Saurornithoides (Norell et al. 2009), Gobivenator (Tsuihiji et al. 2014), and Latenivenatrix (Van der Reest and Currie 2017; Rhodes et al. 2021), in which the anteroposterior length is far greater than that of the ischial peduncle of the pubis. The pubis articulates dorsally with the pubic peduncle of the ilium along a nearly horizontal articular facet (Fig. 9). Posteriorly, the ischial peduncle of the pubis is trapezoidal in lateral view and narrows posteriorly to articulate with the ischium (Fig. 9). Distally, the pubic shaft is elongate and nearly straight but curves slightly posteriorly. It is mediolaterally flat in the proximal portion and twisted at the mid-shaft (Fig. 9). The pubic apron is transversely expanded, a characteristic of troodontids (Xu et al. 2017). The pubic apron is greater than half the length of the pubic shaft, as in SinovenatorIVPP V12615 (Xu 2002), but unlike in Talos (Zanno et al. 2011), Gobivenator (Tsuihiji et al. 2014), Troodon, and IGM 100/1126 (Pei 2015), in which the pubic apron is less than half the length of the pubis. The pubic boot is expanded posteriorly and has a slight anterior expansion (Fig. 9), as in Gobivenator (Tsuihiji et al. 2014) and Almas (Pei et al. 2017b).

Only the pubic peduncle of the right ischium is preserved (Fig. 9). The pubic peduncle is quadrangular in lateral view and articulates with the ischial peduncle of the pubis along an inclined articular facet.

Hindlimb. Both femora are preserved in SDUST-V1062 (Fig. 2). As in most theropods (Norell and Makovicky 1999; Xu et al. 2017), the femoral shaft is anteriorly bowed. The femoral head projects medially at approximately 90° relative to the long axis of the shaft. The greater trochanter is located on the lateral side of the femoral head (Fig. 10). Anteriorly, the proximal end of the femur is poorly preserved. Consequently, the morphology of the lesser trochanter is uncertain. The posterior trochanter lies on the posterolateral side of the femur, near the base of the greater trochanter (Fig. 10B). The posterior trochanter is developed as a large mound, as in SinovenatorIVPP V12615 (Xu et al. 2002) and Gobivenator (Tsuihiji et al. 2014), but in contrast to the ridge-like posterior trochanter seen in Saurornithoides (Norell et al. 2009), Linhevenator (Xu et al. 2011), Talos (Zanno et al. 2011), and Philovenator (Xu et al. 2012). The trochanteric shelf is a knob-like process on the lateral surface of the proximal portion of the shaft (Fig. 10A–C). Distally, the shelf gradually becomes a low lateral ridge extending along the long axis of the femur to the lateral condyle of the distal end (Fig. 10B, E). On the posterior surface of the proximal end of the shaft, a low ridge extends longitudinally and represents a reduced fourth trochanter, the insertion position of the M. caudofemoralis longus (Fig. 10B). The cross-section of the mid-shaft is subcircular, with a diameter of 11.3 mm. Distally, the lateral and medial condyles are comparable in size (Fig. 10D). As in SinovenatorIVPP V12615 (Xu 2002), the lateral condyle extends more distally than the medial condyle. In posterior view, the medial condyle clearly extends medially (Fig. 10D).

Both tibiotarsi are preserved. The right tibiotarsus is well exposed, with no taphonomic deformation (Fig. 2). The tibiotarsus is long and straight (Fig. 11). It is approximately 143% of the femoral length (Table 2), similar to that of SinovenatorIVPP V12583 (139%), IVPP V12615 (130%; Xu et al. 2002), and Mei (131%; Gao et al. 2012). Proximally, as in other troodontids, the tibiotarsus is anteroposteriorly expanded, unlike the more transversely expanded element in SinovenatorIVPP V12583 (Xu et al. 2002). The anterior cnemial crest is well developed, expands anteriorly, and curves slightly laterally (Fig. 11B, C), a feature common to many coelurosaurs (Norell and Makovicky 1999; Makovicky et al. 2003; Gianechini et al. 2018). The lateral and posterior condyles are well developed and separated by a shallow groove (Fig. 11A). In lateral view, the lateral condyle is rounded and contacts the proximal end of the fibula. In posterior view, the lateral condyle is slightly larger than the posterior condyle. In contrast to SinovenatorIVPP V12583 (Xu et al. 2002), the lateral cnemial crest is absent in SDUST-V1062 (Fig. 11C). The fibular crest is present on the lateral surface and is located approximately 25.0 mm from the proximal end of the tibia, which is approximately 12% of the total tibiotarsal length. It is slightly deflected anteriorly, bears a sharp edge, and gradually tapers distally into the shaft. The cross-section of the mid-shaft is subcircular. Distally, the tibiotarsus expands mediolaterally. The astragalus and calcaneum are fused (Fig. 11D, E). In posterior view, a shallow groove is present between the tibia and the proximal tarsals (Fig. 11A). The ascending process of the astragalus is broken; therefore, fine anatomical features of the astragalus cannot be observed (Fig. 11E).

The right fibula is exposed, and portions of the proximal end and shaft are missing in SDUST-V1062 (Fig. 11B). The fibula is a slender element extending along the lateral edge of the tibiotarsus. Proximally, the fibula is anteroposteriorly expanded and approximately 50% of the tibial width (Fig. 11B), as in SinovenatorIVPP V12615 (Xu 2002). In proximal view, the articular facet of the fibula is nearly flat. An iliofibularis tubercle is developed on the lateral surface of the proximal portion of the fibula (Fig. 11A, B), approximately 30.0 mm from the proximal end of the fibula. The cross-section of the mid-shaft is subcircular, and its diameter is 2.2 mm. The distal end of the fibula articulates with the calcaneum (Fig. 11B), as in many paravians, such as Archaeopteryx (Ostrom 1976; O’Connor et al. 2025), Sinornithoides (Currie and Dong 2001), and Microraptor (Hwang et al. 2002).

Both tarsometatarsi are well preserved (Fig. 2). The right distal tarsals are exposed (Fig. 12). The distal tarsals cover most of the posterior portions of the proximal ends of metatarsals III and IV and overhang the metatarsus posteriorly (Fig. 12B, C). In proximal view, the proximal surface of the distal tarsals is nearly horizontal (Fig. 12C). A small notch on the posterior border of this bone possibly represents the fusion of the distal tarsals.

The left metatarsus is nearly complete but slightly compressed medially (Figs 2, 13). The right metatarsus is not deformed, but its distal end is missing (Fig. 12). Metatarsals I–IV are exposed on the left side, and metatarsals II–V are exposed on the right side. The metatarsus of SDUST-V1062 is long, approximately 123.8 mm, based on the length of metatarsal III. It is approximately 86% of the length of the femur, unlike that of Philovenator (125%; Xu et al. 2012). Metatarsal II is narrower mediolaterally than metatarsal IV (Fig. 12). This condition is typically asymmetrical in troodontids (Turner et al. 2012).

Metatarsal I is short and narrow (Fig. 2), as in other coelurosaurians. Metatarsal I is roughly cone-shaped and narrows proximally (Fig. 13). Distally, it forms a single condyle (Fig. 14), as in some troodontids, such as Sinornithoides (Currie and Dong 2001), Talos (Zanno et al. 2011), and Troodon (Fowler et al. 2011). The distal end of metatarsal I is medially offset.

Metatarsal II is straight and approximately 89% of the length of metatarsal III, as in SinovenatorIVPP V12615 and IVPP V12583 (Xu 2002). In proximal view, the proximal end of metatarsal II is subrectangular, and its mediolateral width is approximately 8.0 mm (Fig. 12C). The mid-shaft of metatarsal II becomes subrhombic in cross-section, with a ridged posterior margin (Fig. 12B). Metatarsal II is only slightly narrower than metatarsal IV, as in SinovenatorIVPP V12583 (Xu et al. 2002), Mei (Xu and Norell 2004), and Jinfengopteryx (Ji et al. 2005). Distally, metatarsal II is closely associated with the medial surface of metatarsal III (Fig. 14). The distal end of metatarsal II is not ginglymoid, as in other troodontids (Xu et al. 2017). In medial view, the ligament pit is absent from the distal end (Fig. 14).

Metatarsal III is constricted between metatarsals II and IV. The proximal end of metatarsal III is not strongly constricted and is visible in anterior view (Fig. 12A), representing a subarctometatarsalian condition, as in SinovenatorIVPP V12583 (Xu et al. 2002), Mei (Xu and Norell 2004), and some dromaeosaurids, such as Sinornithosaurus (Xu et al. 1999) and Microraptor (Turner et al. 2012). Proximally, metatarsal III extends anteriorly to the same plane as metatarsals II and IV (Fig. 12A, C). In proximal view, the mediolateral width of metatarsal III is approximately 4.5 mm. The cross-section of the mid-shaft is subrectangular, and its mediolateral width is approximately 4.0 mm in anterior view. In posterior view, the shaft of metatarsal III does not extend posteriorly to the same plane as metatarsals II and IV (Figs 12, 13). Distally, metatarsal III extends beyond metatarsals II and IV, as in most troodontids, but in Tochisaurus (Kurzanov and Osmólska 1991) and Talos (Zanno et al. 2011), the distal end of metatarsal III is almost level with that of metatarsal IV. At the distal end of metatarsal III, a distinct extensor fossa is developed on the anterior surface (Fig. 14). A lateral bony tab proximal to the distal condyles is absent, as in SinovenatorIVPP V12583 (Xu et al. 2002) and Saurornithoides (Norell et al. 2009), whereas the tab is developed in the unnamed troodontid IGM 100/44 (Barsbold et al. 1987) and Talos (Zanno et al. 2011). A subcircular ligament pit is present on the medial side of the distal end (Fig. 14).

Metatarsal IV is the most robust element of the metatarsus (Fig. 12A, B), as in other troodontids (Xu et al. 2017). It is longer than metatarsal II but shorter than metatarsal III. In proximal view, metatarsal IV is mediolaterally widened (Fig. 12C). The anterior surface is flattened proximally and gradually becomes ridged distally (Fig. 12A). A flange is present posteriorly on metatarsal IV (Fig. 12B), as in most deinonychosaurians. The mid-shaft of metatarsal IV is subtriangular in cross-section. In posterior view, the shafts of metatarsals IV and II are nearly parallel and do not contact each other (Fig. 12B), unlike the condition in Mei (Xu and Norell 2004) and Late Cretaceous troodontids, such as Tochisaurus (Kurzanov and Osmólska 1991), Philovenator (Xu et al. 2012), and IGM 100/1126 (Pei 2015). The distal end of metatarsal IV reaches the level of the ligament pit of metatarsal III, as in SinovenatorIVPP V12583 (Xu et al. 2002) and Mei (Xu and Norell 2004).

The right metatarsal V is missing its distal margin (Fig. 12A, B). The preserved portion is a very slender bone. Proximally, metatarsal V is slightly expanded transversely and closely attached to the lateral surface of metatarsal IV (Fig. 12A, B). Distally, metatarsal V narrows gradually. It is oval in cross‑section and mediolaterally wider than anteroposteriorly tall.

All digits of the left pes are well preserved (Figs 2, 14). In contrast, the right pes preserves only part of pedal digit III. As in other coelurosaurians (Makovicky and Norell 2004), the pedal phalangeal formula is 2-3-4-5-0 in SDUST-V1062.

Pedal digit I is short and does not extend beyond the distal end of metatarsal III (Fig. 14), in contrast to Mei (Xu and Norell 2004) and Jianianhualong (Xu et al. 2017). Phalanx I-1 is slender and is the shortest phalanx (Table 2). The distal end of phalanx I-1 is ginglymoid (Fig. 14). Pedal ungual I is smaller than the other pedal unguals. The flexor tubercle is weakly developed. The blood groove is weakly developed and positioned relatively ventrally on the medial surface (Fig. 14).

Pedal digit II is more robust than the other pedal digits (Fig. 14). Phalanx II-2 is approximately 88% of the length of phalanx II-1 (Table 2). This ratio is larger than that in some early-diverging troodontids, such as SinovenatorIVPP V12615 (67%) and Jianianhualong (69%), indicating a relatively unreduced phalanx II-2. The distal end of phalanx II-1 is ginglymoid, with two asymmetrical condyles, and the lateral condyle is larger than the medial condyle. A circular ligament pit is exposed on the medial surface of the distal end of phalanx II-1 and is positioned near the center of the distal portion of the phalanx (Fig. 14). Phalanx II-2 bears a prominent ventral intercondylar tuberosity (Fig. 14), as in other deinonychosaurians (Turner et al. 2012; Xu et al. 2017). The shaft of phalanx II-2 is slightly constricted at its midlength, and its dorsoventral height is approximately 5.4 mm. The distal end of phalanx II-2 is subcircular in medial view, and the ligament pit is oval (Fig. 14). Pedal ungual II is damaged at the proximodorsal portion and distal tip. It is larger than the other unguals and strongly curved (Fig. 14), as in other deinonychosaurians (Turner et al. 2012). A flexor tubercle is strongly developed, implying the presence of flexor muscles (Ostrom 1969). The blood groove is distinct and tapers distally (Fig. 14).

Pedal digit III is the longest digit of the pes (Fig. 14). Phalanx III-1 is partially exposed. The ligament pit is well developed, circular, and centrally positioned on the medial surface of the distal end (Fig. 14). Proximally, the dorsoventral height of phalanx III-2 is 8.6 mm and gradually decreases distally. The distal articular end of phalanx III-2 is ginglymoid. The ligament pit is large and oval and is located in the center of the medial surface of the distal end (Fig. 14). Phalanx III-3 is shorter than phalanx III-2. The ligament pit is oval and dorsally shifted on the medial surface of the distal end (Fig. 14). Pedal ungual III is significantly smaller and less curved than pedal ungual II, as in other troodontids (Turner et al. 2012). The flexor tubercle is weakly developed, and the blood groove is positioned relatively ventrally along the medial surface. The proximodorsal lip, a raised bony flange, is developed (Fig. 14), as in Hypnovenator (Kubota et al. 2024).

Pedal digit IV includes five phalanges, and phalanx IV-1 is covered by digit II. Phalanges IV-2, IV-3, and IV-4 are similar in morphology, and the ligament pits are well developed at their distal ends (Fig. 14). The distal end of phalanx IV-4 is ginglymoid, with two symmetrical condyles. Pedal ungual IV is slightly larger than ungual I but smaller than ungual III (Fig. 14). The morphologies of the flexor tubercle and blood groove are similar to those of ungual III.