Neurocranium Due to the compression and articulation of the skull and–in the case of the lateral surface of the braincase–surface damage to the bone, the morphology and sutural relationships of the neurocranium are difficult to ascertain. The midline interfrontal suture is visible on the skull roof, as are the left and right frontoparietal sutures perpendicular to it (Fig. 3.4). The frontal participates in the dorsal rim of the orbit. The only suture discernible on the lateral surface of the braincase is that between the left exoccipital and the basioccipital (Fig. 3.3). The lateral wall of the braincase is pierced by five foramina: the fenestra ovalis, the metotic foramen, and the foramina for cranial nerves V, VII, and XII.
The left paroccipital process is preserved, and its distal portion can be detached from the rest of the skull (Fig. 3.3). The distal portion of the paroccipital process is pendant, with the straight pendant portion directed ventrally (Fig. 3.7A). The caudal aspect of the braincase is visible, although compression of the skull means that the sutures between the supraoccipital and the exoccipitals cannot be discerned. The ventral margin of the foramen magnum is formed exclusively by the left and right exoccipitals; the basioccipital is excluded (Fig. 3.7B). The occipital condyle is directed caudoventrally. The basioccipital bears a rostrocaudally oriented groove on its ventral surface.
Predentary Like the rest of the skull and mandible, the predentary has suffered marked transverse compression, rendering its true overall shape ambiguous (Fig. 3.8A, B); both of the lateral processes of the predentary appear to project caudally, but it cannot be determined whether they were divergent or parallel to each other. The lateral surfaces of the lateral processes are flat, whereas the medial surfaces are convex (Fig. 3.8C, D). The lateral processes taper at their caudal ends in all views (Fig. 3.8A–D). The ventral surface of each lateral process bears an elongated groove that narrows caudally, forming the contact surface for the rostral ramus of the dentary (Fig. 3.8B).
The dorsal margin of each lateral process bears a row of at least four marginal denticles; four intact denticles are present on the left lateral process, whereas all the denticles on the right lateral process are broken at their bases (Fig. 3.8A, C, D). The median denticle is not broken and is the tallest denticle on the predentary. The median denticle and the intact denticles on the left lateral process are rostrocaudally compressed, subtriangular prongs (Fig. 3.8C), as in Altirhinus (Norman, 1998) and Probactrosaurus gobiensis (Norman, 2002). Ventral to the denticles on each lateral process is a row of deep neurovascular foramina that extends along the lateral surface of the lateral process parallel to the denticle row and penetrates to the medial surface of the predentary (Fig. 3.8A, C, D). On the rostral surface of the predentary, ventrolateral to the median denticle, are two grooves that extend dorsomedially to ventrolaterally (Fig. 3.8C).
Although part of the ventromedial process is missing, it is clear that it was bifurcated into two ventrolaterally directed lobes, as indicated by the unbroken edges of the preserved left lobe (Fig. 3.8C); this is akin to the predentaries of Altirhinus (Norman, 2002) and Xuwulong (You et al., 2011), but differs from the non-bifurcated ventromedial process of Jinzhousaurus (Barrett et al., 2009). The left lobe of the ventromedial process is triangular with a rounded apex (Fig. 3.8C). The broken base of the dorsomedial process is visible between the lateral processes (Fig. 3.8A).
Dentary The left dentary of IVPP V 12534 is missing its rostral ramus, but the right dentary is complete, and its rostral ramus can be removed for closer inspection (Fig. 3.9A–C). At its rostral end, the dentary exhibits a shallow groove for articulation with the right lateral process of the predentary (Fig. 3.9A). There is a short and mediolaterally compressed diastema caudal to this predentary groove, forming a sharp margin between the predentary groove and the first alveolus (Fig. 3.9C). Medial to the predentary groove, the symphysis projects medially to form a rugose horizontal shelf (Fig. 3.9B, C). The symphysis is oriented rostrolaterally to caudomedially relative to the lateral surface of the dentary in dorsal view (Fig. 3.9C). Caudal to the symphysis is a shallow furrow, the Meckelian groove, which deepens caudally (Fig. 3.9B). The lateral surface of the dentary is pierced by several large neurovascular foramina, with two foramina on the ventrolateral surface of the dentary caudal to the symphysis and a row of irregularly spaced foramina that extends parallel to the tooth row (Fig. 3.9A, D).
The dorsal and ventral margins of the dentary are parallel in lateral view, with a ventrally inflected ventral margin that curves towards the symphyseal region (Fig. 3.9D), as in Iguanodon bernissartensis (Norman, 1980), Mantellisaurus (Norman, 1986), Altirhinus (Norman, 1998), Probactrosaurus gobiensis (Norman, 2002), and Eolambia (Kirkland, 1998). This differs from the straight dentaries of Penelopognathus (Godefroit et al., 2005), Lanzhousaurus (You et al., 2005), Jinzhousaurus (Barrett et al., 2009), and Xuwulong (You et al., 2011). The ventral margin also curves ventrally near the caudal end of the dentary, beginning approximately at the 11th dentary tooth position, and forms a ventrally convex bulge ventral to the base of the coronoid process (Fig. 3.9D). The coronoid process itself arises from another, laterally convex bulge on the lateral surface of the dentary, which begins approximately at the 13th tooth position (Fig. 3.9D). The coronoid process of the left dentary is better exposed than that of the right dentary due to breakage of the left jugal. The coronoid process projects vertically and is rostrocaudally expanded near