Lacrimal and Prefrontal The rostral ramus of the lacrimal tapers to a point, wedging between the maxilla and the ventrolateral process of the premaxilla (Figs. 3.3, 3.4); the rostral ramus also tapers in Dakotadon (SDSM 8656) and Xuwulong (You et al., 2011). The rostral ramus of the lacrimal is elongated in IVPP V 12534, extending along the dorsal margin of the maxilla to terminate rostral to the apex of the ascending process of the maxilla. This morphology has not been observed in other iguanodonts and is an autapomorphy of Equijubus; in other iguanodonts–such as Iguanodon (Norman, 1980), Altirhinus (Norman, 1998), Shuangmiaosaurus (You, Ji, et al., 2003), Jinzhousaurus (Barrett et al., 2009), and Xuwulong (You et al., 2011)–the rostral ramus of the lacrimal does not extend along the dorsal surface of the maxilla rostral to the apex of the ascending process. The ventral margin of the lacrimal is very slightly concave dorsally between its rostral end and the aforementioned finger-like process of the jugal. Caudal to the finger-like process of the jugal, the ventral margin of the lacrimal is convex ventrally (Figs. 3.3, 3.4). The caudal margin of the lacrimal is concave to form the rostral margin of the orbit. The caudal extension of the ventrolateral process of the premaxilla excludes the lacrimal from contact with the nasal.
3.6. Articulated right postorbital and squamosal of IVPP V 12534, holotype of Equijubus normani. (A) lateral view; (B) medial view. Abbreviations: gl, glenoid; jp, jugal process of postorbital; j/po, jugal-postorbital contact; ls, lateral shelf; lsf, laterosphenoid facet; orr, orbital rim; popj, postorbital process of jugal; pops, postorbital process of squamosal; poq, postquadrate process; po/sq, postorbital-squamosal contact; prq, prequadrate process; sqp, squamosal process of postorbital. Scale bar equals 10 cm.
Due to the articulated nature of the skull, damage to the right prefrontal, and severe deformation of the left prefrontal, little can be determined regarding the anatomy of this element. The prefrontal comprises the rostrodorsal margin of the orbit. Rostral to the orbital rim, the nasal process of the prefrontal is dorsoventrally expanded (Figs. 3.3, 3.4).
Postorbital and Squamosal The postorbital forms the caudodorsal margin of the orbit (Figs. 3.3, 3.4). The orbital rim is rugose (Fig. 3.6A). Rostromedial to the orbital rim, the postorbital meets the frontal along an almost straight suture (Figs. 3.3, 3.4). The jugal process of the postorbital projects rostroventrally to contact the postorbital process of the jugal (Figs. 3.3, 3.4, 3.6A). The squamosal process arches dorsally and projects caudally to meet the postorbital process of the squamosal (Figs. 3.4, 3.6A). The caudal end of the squamosal process is rounded and overlaps the lateral surface of the squamosal. The medial surface of the postorbital bears a shallow facet that would articulate with the rostral end of the laterosphenoid (Fig. 3.6B).
3.7. Braincase elements of IVPP V 12534, holotype of Equijubus normani. (A) distal portion of left paroccipital process in medial view; (B) braincase in caudal view. Abbreviations: boc, basioccipital; fm, foramen magnum; lexo, left exoccipital; ppoc, pendant portion of paroccipital process; rexo, right exoccipital. Scale bar equals 10 cm.
The postorbital process of the squamosal bears a rounded shelf on its lateral surface, forming the origin site for M. adductor mandibulae externus superficialis (Ostrom, 1961; Fig. 3.6A). Dorsal to this shelf, the lateral surface of the postorbital process is gently convex dorsally and slopes dorsomedially. Caudal to the postorbital process, two prongs, the prequadrate and postquadrate processes, project ventrally rostral and caudal to the glenoid that would receive the dorsal condyle of the quadrate (Figs. 3.4, 3.6A). The morphology of the caudomedial process of the squamosal cannot be ascertained due to crushing.
3.8. Predentary of IVPP V 12534, holotype of Equijubus normani. (A) predentary in dorsal view; (B) same in ventral view; (C) same in left lateral view; (D) same in right lateral view. Abbreviations: bdm, base of dorsomedial process; brl, broken base of right lobe of ventromedial process; dg, groove for contact with dentary; ll, left lobe of ventromedial process; md, marginal denticle; mmd, median marginal denticle; rg, groove on rostral surface. Scale bar equals 10 cm.
Quadratojugal and Quadrate The quadratojugal is a narrow sliver of bone wedged between the caudal end of the jugal and the lateral wing of the quadrate (Fig. 3.4). The quadratojugal does not overlap the notch in the lateral wing of the quadrate but instead forms the rostral margin of an open paraquadrate foramen.
The quadrate gradually curves caudally along its entire length in lateral view (Fig. 3.4). The ventral condyle of the quadrate is mediolaterally broad and rostrocaudally narrow, with an enlarged lateral condylar surface compared to the medial condyle surface. Approximately one-third of the way up of the quadrate from the ventral condyle is the semicircular quadratojugal notch in the lateral wing of the quadrate (Fig. 3.4); as stated above, the paraquadrate foramen is open, as in Iguanodon bernissartensis (Norman, 1980),