Introduction

Theropods were some of the first dinosaur fossils discovered from the Early Cretaceous locality of Öösh ( =  Ohshih or Oshih), but their described remains are limited to undiagnostic teeth of the large theropod “Prodeinodon” (Osborn, 1924a; but see Currie, 2000). Theropod remains are generally much more rare than the plentiful fossils of Psittacosaurus mongoliensis and sauropods at the locality (Osborn, 1923, 1924b). In some places, however, isolated theropod material of a range of sizes is encountered frequently—especially unguals, phalanges, and teeth.

The deposits at Öösh are considered to be Early Cretaceous (Berriasian–Barremian). This is roughly coeval with beds forming the Jehol group of northeastern China. The Jehol beds of the Yixian and Juifotang formations have produced abundant vertebrate fossil remains (reviewed in Zhou et al., 2003). These discoveries include the ubiquitous Psittacosaurus (also present in the Öösh beds) as well as avialan and nonavialan dinosaurs, including small feathered theropods (reviewed in Norell and Xu, 2005). Additionally, the Jehol beds contain a diverse mammalian fauna including one of the largest Mesozoic mammals, Repenomamus (Li et al., 2001). The Jehol flora is abundant, containing the putative earliest angiosperm Archaeofructus (Sun et al., 1998).

The Öösh locality lies in the Altai region of Central Mongolia (see Watabe and Suzuki, 2000; this paper, fig. 1). Fossils were first collected here by American Museum field parties in the 1922 (Andrews, 1932). New collections from the Öösh locality by field parties of the Mongolian Academy of Sciences and the American Museum of Natural History include a wide array of fossil materials, including gobiconodontids (Rougier et al., 2001), a pterosaur (Andres and Norell, 2005), lizards, large and small sauropods, and psittacosaurus ranging in size from hatchlings to senescent adults.

Figure 1

Map of Mongolia showing geographical relationship of the Öösh locality to other Gobi fossil localities.

The Jehol biota and Öösh locality contain some elements in common such as the primitive ceratopsian Psittacosaurus. Unfortunately, dates of the Jehol and Öösh faunas are poorly constrained. Despite an abundance of andesitic layers that allow for radiometric dating of rocks that produce Jehol fossils, several different ages have been published. Recent dating efforts agree with previous results (Swisher et al., 1999; Wang et al., 2001) in proposing a Barremian date for the feathered dinosaur beds in Sihetun and bracket the lowermost Yixian beds (one of the most fossiliferous formations in the Jehol group) as being between 128 m.y. and 139 m.y. (Swisher et al., 2002). Older dates have been published that would put much of the Yixian Formation in the Late Jurassic (Lo et al., 1999). These older dates, however, have been criticized on a number of grounds (Zhou et al., 2003).

Similarly, the stratigraphic and temporal divisions for the deposits at Öösh are poorly constrained (Jerzykiewicz and Russell, 1991). According to Shuvalov (2000), rocks that overlie the strata of the Öösh locality examined here have yielded dates of 141 ± 8 m.y. and 126 ± 9 m.y. This indicates a Berriasian–Hauterivian stage for these strata. Correlated exposures have been dated at around 130 m.y. (Samilov et al., 1988; Rougier et al., 2001), and are consistent with the results of Shuvalov (2000). A broader overview of the geology of Öösh is given by Andres and Norell (2005).

Components of the ÖÖsh Locality

Consistent with previous collecting, Mongolian Academy of Sciences–American Museum of Natural History Mongolian expeditions in 1997, 1999, 2001, and 2005 collected ubiquitous Psittacosaurus material and numerous undiagnostic large theropod teeth. In addition to this material, partial vertebrate material was recovered that is referable to varying levels of clade specificity. Isolated squamate vertebrae lacking zygophenes/zygantra, exhibiting an unconstricted precondylar region, and nonoblique condyles are insufficient for referral to a specific clade, but these characters do rule out varanoid, cordyliform, lacertiform, or snake affinities. Additional squamate material includes a probable nonvaranoid, nonsnake autarchoglossan (based on the presence of small dorsolateral zygosphenes) and a nonautarchoglossan caudal vertebra with a fracture plane that is on the transverse process. A nearly complete gekkonomorph skull is also known from Öösh (Conrad and Norell, 2006).

A large (~6 cm), heavily rugose postorbital was collected. Its straight frontal process precludes its referral to most coelurosaur clades except ornithomimosaurs or tyrannosauroids. Its size and rugose texture excludes it from ornithomimosaurs. It lacks an anterior process projecting into the orbit, like that in derived tyrannosaurids. In overall appearance it is similar to the postorbital of Sinraptor dongi (Currie and Zhao, 1993) and tentatively considered a noncoelurosaur (allosauroid?) or basal tyrannosauroid postorbital.

A partial pes along with other identified material pertaining to a small theropod was collected and is currently being prepared. Slightly weathered postcranial remains collected as float further indicated the presence of at least one small, derived theropod taxon. This material includes a proximal femur and tibia. The femoral head is weathered but preserves a prominent, moundlike lateral ridge and a well-developed posterior trochanter. The proximal tibia lacks a medial cnemial crest, unlike that seen in Mononykus olecranus (Perle et al., 1994) and other alvarezsaurids, and bears a well-developed fibular crest. Unfortunately, the dorsal surface of the femur is poorly preserved, so it is unclear if the lesser and greater trochanters were confluent as in derived avialans. Nonetheless, the moundlike lateral ridge and posterior trochanter indicate this material likely is referable to a small paravian theropod.

In 1999, the Mongolian Academy of Sciences–American Museum of Natural History Mongolian expedition recovered a partial skull of a small theropod dinosaur from Öösh in a coarse, well-sorted sand channel. Although incomplete, this skull (IGM 100/1119; fig. 2) is notable for its possession of several extremely derived coelurosaur characters, clearly distinguishing it as a small dromaeosaurid.

Figure 2

IGM 100/1119 in right lateral view. Anatomical labels in appendix 3.

Systematic Paleontology

Description

IGM 100/1119 consists of an almost complete right maxilla and dentary in articulation (fig. 2). The maxilla is eroded laterally, revealing details of its alveoli, pneumatic chambers, and fenestrae. Like most theropods, the maxilla of Shanag ashile can be divided into three parts: a posteriorly projecting subantorbital process that contacts the jugal, a dorsally projecting ascending ramus of the nasal process, and an anteriorly projecting ventral ramus of the nasal process (Witmer, 1990, 1997). The maxilla can be further divided into a medial lamina, or the portion of the maxilla that resides within the antorbital fossa, and a lateral lamina that forms the lateral surface of the maxilla outside the antorbital fossa. These laminae correspond to the lamina lateralis and lamina medialis of Witmer (1997). Nomenclature for the structures of the antorbital cavity follows that used by Witmer (1997).

The maxilla is triangular, tapering anteriorly as in Archaeopteryx lithographica (Wellnhofer, 1974: fig. 5; Mayr et al., 2005: fig. 2) and Sinornithosaurus millenii (Xu and Wu, 2001). The maxilla contributes to the narial border, as suggested by the slight depression on its dorsal margin near its anterior tip. This is unlike the condition in derived dromaeosaurids, but similar to the basal dromaeosaurids Microraptor zhaoianus (Xu et al., 2000) and Sinornithosaurus millenii (Xu et al., 1999) and derived troodontids such as Troodon formosus (Makovicky and Norell, 2004), Saurornithoides junior (IGM 100/1) and Byronosaurus jaffei (IGM 100/983). The articulation with the premaxilla is complex. Anteromedially, a thin projection of bone, the surface of which is slightly depressed, extends rostrally past the limit of the dentigerous portion of the maxilla. A complementary groove separates this process from the lateral lamina of the maxilla. In articulation, a portion of the posterior ramus of the premaxilla would have fit into this groove. A similar construction is present in a disarticulated maxilla of Velociraptor mongoliensis (IGM 100/976). Neurovascular foramina are present on the labial surface with each foramen generally corresponds to a single tooth position.

The antorbital fossa is large and occupies much of the lateral surface of the maxilla. Anterior to the fossa, a small triangular lateral lamina is present below the external nares. This is similar to the condition in Sinornithosaurus millenii (Xu and Wu, 2001), Microraptor zhaoianus (Xu et al., 1999), and Archaeopteryx lithographica (Wellnhofer, 1974: fig. 5; Mayr et al., 2005: fig. 2). The rostral boundary of the antorbital fossa is situated approximately 7 mm caudal to the premaxillary contact, above the 3rd maxillary tooth position. The caudal margin of the naris overlaps the rostral border of the antorbital fossa as in Archaeopteryx lithographica (Wellnhofer, 1974: fig. 5; Mayr et al., 2005: fig. 2) but unlike dromaeosaurids (Norell and Makovicky, 2004) and troodontids (Makovicky and Norell, 2004). The antorbital fossa is defined shallowly anteriorly, but the dorsal and posteroventral posterior margins are sharply bounded by thin, laterally projecting shelves of bone. Although the proportions of the antorbital fossa and general shape of the maxilla are similar to that of Archaeopteryx, the raised dorsal rim of the antorbital fossa differs from the recessed antorbital fossa seen in Archaeopteryx (Witmer, 1990). In almost all avialans, the ascending ramus of the maxilla is lost, and as a result, the nasal forms the majority of the dorsal border of the internal antorbital fenestra and antorbital fossa (Cracraft, 1986). Archaeopteryx lithographica is the only avialan that retains an extensive ascending ramus of the maxilla, but the ramus is recessed medially so that the nasal forms the dorsal border of the antorbital fossa as in other basal avialans (Witmer, 1990), but not the internal antorbital fenestra unlike other avialans. IGM 100/1119 retains the typical theropod condition in which maxilla excludes the nasal from the internal antorbital fenestra. Furthermore, there is no indication that the maxilla was recessed medially from the nasal and thus it is unlikely that the nasal formed the dorsal boundary of the antorbital fossa.

The antorbital cavity contains two fenestrae, the antorbital and maxillary fenestrae. There is no sign of a promaxillary (tertiary antorbital) fenestra. Archaeopteryx lithographica, which possesses the most plesiomorphic antorbital cavity of any avialan (Witmer, 1997), has both a maxillary and promaxillary fenestra in its recessed antorbital cavity. Confuciusornis sanctus, a basal avialan phylogenetically intermediate between Archaeopteryx lithographica and Ornithothoraces (sensu Chiappe, 1995), has only a small, round accessory antorbital fenestra (Chiappe et al., 1999). Chiappe et al. (1999) tentatively homologized this fenestra with the maxillary fenestra. All other known avialans have complex diverticula extending medially, rostrally, and caudally from one large antorbital cavity (Witmer, 1990), but laterally, the antorbital opening is not subdivided into separate accessory fenestrae. Witmer (1997) suggested that the promaxillary fenestra characterizes Neotheropoda. The lack of a promaxillary fenestra is not, however, entirely unusual among nonavialan theropods. The troodontids Saurornithoides junior (Barsbold, 1974; Norell et al., in prep.) and Byronosaurus jaffei (IGM 100/983) lack a promaxillary fenestra, while the more basal troodontid Sinovenator changii (Xu et al., 2002) retains a promaxillary fenestra. Additionally, the oviraptorosaur Incisivosaurus gauthieri (Xu et al., 2002) and the therizinosauroid Erlikosaurus andrewsi (Clark et al., 1994) lack a promaxillary fenestra.

The internal antorbital fenestra is large and is defined anteriorly (and probably dorsally) by the ascending process of the maxilla. The antorbital fossa does not extend ventrally beyond the border of the internal antorbital fenestra, as in troodontids (Saurornithoides junior, IGM 100/1; Saurornithoides mongoliensis, AMNH FR 6515; Troodon formosus [Witmer, 1997]). The surface bone is missing from the anterior rim of the internal antorbital fenestra exposing a substantial rostral excavation. Anteriorly, the excavation extends to the root of the 6th maxillary tooth. The thin lamina of bone forming the anterior wall of the excavation wraps around the entire length of the root. This excavation may correspond to the deep fossa invading the pila postantralis (the strut of bone reinforcing the posteromedial wall of the maxillary antrum) noted by Witmer (1997: 43) in Ornitholestes hermanni, Allosaurus fragilis, Marshosaurus bicentesimus, and Deinonychus antirrhopus. The lateral surface of the medial wall of the excavation is not smooth, but crossed by ridges and sculptured with rounded depressions. Ventrally, the dorsal surfaces of the posterior alveoli protrude slighting into the fossa.

The maxillary fenestra in Shanag ashile is positioned high on the ascending ramus of the maxilla. This location more generally corresponds to the excavatio pneumatica of other theropods (Witmer, 1997: 43). The plesiomorphic position of the maxillary fenestra is more ventral, such that the center of the maxillary fenestra is aligned with the center of the internal antorbital fenestra. Our interpretation of the structure as the maxillary fenestra is supported, however, by the presence of a maxillary antrum medial to the opening, a similarly positioned maxillary fenestra in Deinonychus antirrhopus (Ostrom, 1969; Witmer, 1997), and a generally dorsally displaced maxillary fenestra in dromaeosaurids.

The maxillary fenestra is a relatively large, anteroventrally inclined oval structure with both an internal and external aperture, similar in structure to the well-developed antorbital cavities of Erlikosaurus andrewsi (Clark et al., 1994), Bambiraptor feinbergorum (AMNH FR 30554), and Saurornithoides mongoliensis (AMNH FR 6516). The external aperture is confluent with the lateral surface of the maxilla and defines a fairly deep fossa that is continuous with the maxillary antrum. The internal aperture is positioned at the rostroventral end of this fossa and perforates the maxilla. A somewhat similar arrangement is seen in taxa such as Marshosaurus bicentesimus (see Witmer, 1997), Deinonychus antirrhopus (Ostrom, 1969), and Velociraptor mongoliensis (AMNH FR 6515, IGM 100/982). In these taxa, the maxillary fenestra is contained within a shallow, caudally or caudodorsally open fossa, both of which are located within the antorbital fossa. The fossa containing the internal aperture of the maxillary fenestra of Shanag ashile, however, is much deeper and more sharply defined than those in the previously mentioned taxa. It is, therefore, more similar to Bambiraptor feinbergorum (AMNH FR 30554), which has a maxillary fenestra that is nearly continuous with the excavatio pneumatica. In Bambiraptor feinborgorum (AMNH FR 30554) both structures are contained within a caudodorsally opening fossa. Thus, it is possible that the oval structure in IGM 100/1119, considered here to be the maxillary fenestra, may in fact represent a maxillary fenestra confluent with an excavatio pneumatica.

Some unusual accessory cavities—interalveolar pneumatic cavities—are present between the pairs of adjacent alveoli separated by a diastema. The interalveolar chambers of IGM 100/1119 would have been closed off from the rest of the craniofacial air sac system in life, surrounded on all sides by a thin layer of bone, and are visible only because of the eroded labial surface of the maxilla. The roots of the teeth that bracket them define the boundaries of the chambers. Thin laminae of bone envelop the roots of the flanking teeth, defining the anterior and posterior limits of the chambers. In addition, the chambers extend dorsally no farther than the dorsal margin of the shorter bounding tooth, no farther ventrally than the crown–root junction of the teeth, and no farther medially than the medial limit of the teeth. The medial walls of the chambers have the same irregular surface as that of the internal antorbital fenestra. These are not the “recessi pneumatici interalveolares” described by Witmer (1997), which are ventrolateral invaginations of the maxillary antrum into the alveolar process. Structures possibly homologous to the pneumatic interalveolar recesses are present within the antorbital fenestra in IGM 100/1119 where the alveoli protrude into the fenestra.

At least nine widely and unevenly spaced alveoli, six of which contain teeth, are present in the maxilla. The number of maxillary teeth is similar to the eight in Archaeopteryx lithographica (Wellnhofer, 1988), the nine in Dromaeosaurus albertensis (AMNH FR 5356; Currie, 1995), and the 10 in Velociraptor mongoliensis (AMNH FR 6515). The tooth count in IGM 100/1119 is, however, different from the numerous maxillary teeth present in Jinfengopteryx elegans (Ji et al., 2005) and troodontids—even basal taxa such as Sinovenator changii (Xu et al., 2002) and Mei long (Xu and Norell, 2004). The lateral surface of the maxilla is missing from the central portion of the maxilla so that the roots of two teeth are exposed. Although there are several empty alveoli in the maxillary tooth row, some of the gaps are solid stretches of interdental bone separating adjacent alveoli. The maxillary teeth are laterally compressed, with the carinae positioned lingually. Posterior teeth have serrations on their posterior carinae (fig. 3). The three central maxillary teeth are unusual in that they have long roots constituting approximately 70% of the entire tooth length. Tooth root bulges of these teeth are visible on the medial face of the ascending ramus of the maxilla.

Figure 3

Detail of posterior tooth morphology in IGM 100/1119. Note serrations on posterior carinae and unconstricted root-crown transition.

The dentary is long and relatively dorsoventrally shallow, its height comprising only about 12% of its length, although it is broken posteriorly. The dentary is straight and does not curve medially at the symphysis as in derived troodontids like Troodon formosus (Currie, 1985) or Saurornithoides (Barsbold, 1974; Norell et al., in prep). It is relatively labiolingually thick, with the tooth row slightly inset from the labial margin and becoming more inset posteriorly. The ventral and dorsal margins of the dentary are subparallel, as in dromaeosaurids (Currie, 1995) and Archaeopteryx lithographica (Wellnhofer, 1992: fig. 6). Two rows of mental foramina are present on the labial surface, although a series of smaller anteriorly directed foramina cluster rostrally. The dorsal row contains a greater number of foramina that are anteroposteriorly elliptical and elongate. The dorsal row of mental foramina does not lie in a deep subalveolar groove as in troodontids (Makovicky et al., 2003) and Buitreraptor gonzalezorum (Makovicky et al., 2005). Posteriorly, the dorsal foramina lengthen to form a shallow groove similar to that present in Archaeopteryx lithographica (Wellnhofer, 1974: plate 22), the holotype of Velociraptor mongoliensis (AMNH FR 6515), and Tsaagan mangas (IGM 100/1015; Norell et al., 2006). There are fewer foramina in the lower row, although they are of the same general shape.

A relatively deep Meckelian groove runs along the medial surface of the dentary. Anteriorly, the groove begins just caudal to the rugose symphyseal tip of the dentary. A small fragment of the splenial covers the posterior end of the Meckelian groove, so the posterior extent of the groove cannot be determined. The posterior margin of the dentary is broken, so the posterior articulations are unknown.

There are at least 15 teeth in the dentary. Due to the overhanging maxilla and its teeth, it is difficult to determine the exact number of alveoli present. Like the maxillary tooth count, the dentary tooth count of Shanag ashile is comparable to that of some dromaeosaurids, such as the 16 in Deinonychus antirrhopus (Ostrom, 1969), 15–16 in Saurornitholestes langstoni (Sues, 1978), and 14–15 in Velociraptor mongoliensis (AMNH FR 6515; Currie, 1995). The dentary teeth, like the maxillary teeth, are interspersed with diastemata. The anterior teeth are quite small and especially closely packed like in troodontids (Makovicky and Norell, 2004) and Microraptor zhaoianus (Xu et al., 2000; this paper, fig. 4). Overall, the dentary teeth are smaller and more closely packed than the maxillary teeth (1.0 versus 1.4 mm basal crown widths and 0.37 versus 0.70 mm gaps between adjacent teeth not separated by a diastema). The anterior dentary teeth are devoid of serrations, while the posterior teeth have small serrations only on their posterior carinae (12.4 serrations per millimeter). This is the same pattern seen in Microraptor zhaoianus (Hwang et al., 2002). Unlike Microraptor zhaoianus teeth and the teeth of troodontids and early avialans, the teeth of IGM 100/1119 do not have constrictions between their roots and crowns. This unconstricted root/crown transition is present in Buitreraptor gonzalezorum (Makovicky et al., 2005), Sinornithosaurus millenii (Xu and Wu, 2001), and other dromaeosaurids.

Figure 4

Detail of the tooth morphology and size variation seen in the dentary of IGM 100/1119. Anatomical labels in appendix 3.

Figure 5

Phylogenetic placement of IGM 100/1119. A. Strict consensus of 552 most parsimonious reconstructions of coelurosaurian interrelationships found in our phylogenetic analysis of 251 characters and 56 coelurosaurian taxa. The new taxon is indicated in bold. B. Adams consensus topology of non-unenlagiine dromaeosaurids recovered in from this analysis.

Only a small sliver of the splenial protrudes past the posterior edge of the dentary, but the anterior portion is nearly intact. It cannot be determined if the splenial was laterally exposed at the contact of the dentary and postdentary bones as in deinonychosaurs, as this region of the mandible is not preserved. It overlaps the posterior third of the dentary, reaching to about the level of the 13th dentary alveolus. The preserved portion of the splenial is thin, long, and sharply triangular, much like the splenial of the dromaeosaurids (Norell and Makovicky, 2004), Archaeopteryx lithographica (Wellnhofer, 1993), and the troodontid Saurornithoides junior (Barsbold, 1974; Norell et al., in prep). A long, narrow notch at the posterior of the splenial fragment, corresponding perhaps to the mylohyoid foramen (see Currie, 1995: fig. 7E), is confluent with the Meckelian groove.

Discussion

The taxon preserves an interesting mosaic of avialan and dromaeosaurid characteristics. Like most avialans, Shanag ashile possesses a tapering, triangular shaped maxilla, which participates in the narial border and has a large antorbital fossa. Additionally, the caudal margin of the external nares overlaps the rostral border of the antorbital fossa, as in avialans. A number of dromaeosaurid synapomorphies, however, are preserved in IGM 100/1119. These include a straight, parallel-sided dentary and a dorsally displaced maxillary fenestra that is itself recessed in a caudodorsally directed depression.

To test the phylogenetic placement of Shanag ashile we have expanded the Norell et al. (2006) study by including the new taxon and 15 additional characters, several of which are novel and pertain to the maxilla morphology of dromaeosaurids and avialans. A total of 56 coelurosaurian taxa and 251 characters (19 ordered) were used in the analysis, with Allosaurus fragilis and Sinraptor dongi used to root the most parsimonious trees. The dataset was treated with equally weighted parsimony analysis implemented in TNT v. 1.0 (Goloboff et al., 2003). A heuristic tree search strategy was conducted performing 1000 replicates of Wagner trees (using random addition sequences) followed by TBR branch swapping (holding 10 trees per replicate). The best trees obtained at the end of the replicates were subjected to a final round of TBR branch swapping. Zero length branches were collapsed if they lack support under any of the most parsimonious reconstructions (i.e., rule 1 of Coddington and Scharff, 1994). This analysis resulted in 552 most parsimonious trees of 764 steps (CI  =  0.381, RI  =  0.709) found in 625 out of the 1000 replicates.

Shanag ashile was found to be a member of a dromaeosaurid clade less inclusive than Unenlagiinae (i.e., Buitreraptor gonzalezorum, Unenlagia comahuensis, and Rahonavis ostromi) in all of the most parsimonious reconstructions (fig. 5). This placement is supported by the presence in Shanag ashile of three of the clade's six unambiguous synapomorphies: a solid quadrate (char. 52.0—unknown in Shanag ashile); dentary with subparallel dorsal and ventral edges (char. 70.1); large maxillary and dentary teeth, less than 25 in dentary (char. 84.0); anterior cervical centra level with or shorter than posterior extent of neural arch (char. 96.0—unknown in Shanag ashile); extremely long extension of the prezygapophyses of the distal caudal vertebrae (char. 120.1—unknown in Shanag ashile); and dorsal displacement of maxillary fenestra (char. 237.1). Given the large percentage of missing data for IGM 100/1119, Shanag ashile was recovered in numerous placements within the large clade more derived than Unenlagiinae clade (i.e., Sinornithosaurus + Velociraptor), resulting in an unresolved strict consensus. The Adams consensus depicted in figure 5 shows this lack of resolution is due to the labile position of IGM 100/1119 and to a lesser extent, Saurornitholestes langstoni. The Adams consensus demonstrates that consistent structure exists within the large non-unenlagiine dromaeosaurid clade. This phylogenetic structure is nearly identical to that recovered in the analysis of Norell et al. (2006). In the present analysis, an Adams consensus shows the consistent presence of a Deinonychus + Velociraptor sister group relationship when the position of Saurornitholestes is not considered as well as the consistent presence of an Achillobator + Utahraptor clade. However, in the latter case, both Adasaurus and Dromaeosaurus are depicted closer to Achillobator than Utahraptor or closer to Utahraptor than Achillobator in some of the fundamental trees. The largely incomplete nature of Dromaeosarus albertensis and Adasaurus mongoliensis reduced the resolution within this subclade of large-bodied dromaeosaurids.

Although the exact sister taxon of Shanag ashile is currently ambiguous, it is most similar in general shape and morphology to Sinornithosaurus millenii (Xu et al., 1999). Both taxa possess a triangle-shaped, anteriorly tapering maxilla as well as maxillary participation in the external nares. In the most parsimonious trees that recover Shanag ashile closely related to Sinornithosaurus millenii, the topology is supported by a single synapomorphy—the lateral lamina of the ventral ramus of the maxilla reduced to a small triangular exposure (char. 244.1). Shanag ashile remains distinguishable from Sinornithosaurus millenii due to its lack of a promaxillary fenestra.

Prior to the discovery of IGM 100/1119, the only theropod material from the Early Cretaceous Öösh deposits were undiagnostic. Shanag ashile marks the first theropod taxon from the deposits referable to a specific theropod clade—the Dromaeosauridae. The discovery of IGM 100/1119 is important as it extends our knowledge of Early Cretaceous dromaeosaurids. The best known Early Cretaceous dromaeosaurids—Sinornithosaurus and Microraptor—are known from the Jehol beds of China. The presence Shanag ashile in the Jehol–contemporaneous Öösh deposits of Mongolia suggests a wider diversity of Early Cretaceous dromaeosaurids that show a broader distribution of character states and avianlike cranial features.