Velociraptor mongoliensis, Osborn, 1924

Brownstein, Chase Doran, 2021, Dromaeosaurid crania demonstrate the progressive loss of facial pneumaticity in coelurosaurian dinosaurs, Zoological Journal of the Linnean Society 191 (1), pp. 87-112 : 92

Velociraptor mongoliensis

In the holotype skull of Velociraptor, AMNH FARB 6516, the promaxillary and maxillary fenestrae are both present and sit within the antorbital fossa of the maxilla ( Fig. 2A–B ). The promaxillary fenestra is ovoid, with its long axis running dorsoventrally. This fenestra is also placed anteriorly and medially bordered by a strongly developed wall of bone ( Fig. 2B ), and is mostly not visible in lateral view like the promaxillary fenestra of Deinonychus . The promaxillary fenestra is not as deepened as the maxillary fenestra, which is large, circular and clearly penetrates into the internal portion of the skull in lateral view. This represents the opposite of the condition in Deinonychus , where the promaxillary fenestra is deeper. Also, unlike Deinonychus , the maxillary fenestra is round, large and bordered by a somewhat developed crescentic wall of bone ( Fig. 2B ). Notably, another skull of Velociraptor, IGM 100/25, possesses a maxillary fenestra that is ovoid and similar to the one in Deinonychus (e.g. Norell et al., 2006: fig. 6), showing this feature is affected by intraspecific variation. Slightly posteroventral to the maxillary fenestra, there is a moderately-sized pneumatic recess that is reminiscent of the additional recess in Tsaagan (see next section). This structure appears variable in other skulls of Velociraptor , and is more pronounced in the holotype AMNH FR 6516 and IGM 100/25 than IGM 100/982 (fig. 6 in Norell et al., 2006; pers. obs.). The preantorbital body of the maxilla of Velociraptor is notably hollow. As a whole, the maxilla of Velociraptor is far more elongate than that of Deinonychus , and is also subtriangular rather than subrectangular. This suggests a more elongate, dorsoventrally shortened maxillary antrum was present compared to the condition in Deinonychus . The maxilla of Velociraptor is also more elongate than Tsaagan , indicating the maxillary antrum in this latter taxon was also widened dorsoventrally relative to Velociraptor mongoliensis . Similar elongate, triangular maxillae among dromaeosaurids are found in microraptorans like Sinornithosaurus (e.g. Turner et al., 2012). As in Tsaagan , the border of the antorbital fossa consists of a shelf undercut by a deeply invaginated bone surface.

Figures

Figure 2. Craniofacial pneumaticity of Velociraptor. Skull AMNH FARB 6515 in (A, C) lateral and (B, D) medial views, with the rostrum in (E) lateral and (F) medial views. Abbreviations: aofen, antorbital fenestra; aof, antorbital fossa; mf, maxillary fenestra; mx, maxilla; pmf, promaxillary fenestra; mi, maxilla interior;?pipf, premaxillary pneumatic foramina; pmx, premaxilla; pf, pneumatic foramina of the frontal; front, frontal; nf, neurovascular foramina; rugose, rugose bone surface; smooth, smooth bone surface. In (C) and (D), light blue are neurovascular foramina, light green is the maxillary fenestra, light red is the promaxillary fenestra, tan is an additional maxillary fenestra.