Hadrosaurs. David A. Eberth
to be present.
3.14. Representative caudal dorsal vertebrate of IVPP V 12534, holotype of Equijubus normani. (A) dorsal 13 in cranial view; (B) dorsal 13 in caudal view; (C) dorsal 13 in right lateral view; (D) dorsal 16 in cranial view; (E) dorsals 16 and 17 in right lateral view; (F) detail of neural spine of dorsal 13 in right lateral view showing hyposphene morphology. Abbreviations: cdd, caudal depression on hyposphene; crd, cranial depression on hyposphene; hsp, hyposphene; para, parapophysis; ri, vertical ridge on hyposphene. Scale bars equal 5 cm.
Only the centrum and lower part of the neural arch are preserved on dorsal 8. The centrum is unchanged from the morphology of the cranial dorsals, and the neurocentral suture is clearly visible. Once again the rib capitulum adheres to the left parapophysis, located caudodorsal to the prezygapophyses, which are broken. The hyposphene is again present, although the postzygapophyses are broken. Only the centra are preserved for dorsals 9 and 10, and the centrum and ventral part of the neural arch in dorsal 11. The morphology of these centra does not differ from that of the other dorsals.
3.15. Sacral vertebrae with associated ilia of IVPP V 12534, holotype of Equijubus normani, in (A) dorsal and (B) ventral view. Abbreviations: gr, groove; li, left ilium; ns, neural spine; ot, ossified tendons; ri, right ilium. Scale bar equals 10 cm.
The postzygapophyses of dorsal 11 are preserved in articulation with the prezygapophyses of dorsal 12. Immediately dorsal to the postzygapophyses, the base of the neural spine of dorsal 11 is preserved. It is rounded in cross section and transversely broad caudally, but extends cranially as a thin, plate-like sheet and is similar in morphology to that of Mantellisaurus (Norman, 1986) and Iguanodon bernissartensis (Norman, 1980). The prezygapophyses of dorsal 12 are separated by a groove ventrally, presumably for the hyposphene of dorsal 11. The parapophyses are oval and situated at the base of the transverse processes, which are broken and not preserved. The long axis of the parapophysis extends cranioventrally, and a ridge arises from the cranial margin and extends cranially to form the craniolateral margin of the neural canal in cranial view. The postzygapophyses of dorsal 12 are preserved in articulation with the prezygapophyses of dorsal 13. As in dorsal 11, the neural spine of dorsal 12 arises immediately dorsal to the postzygapophyses and is transversely relatively thickened in this area. Cranially, the neural spine becomes transversely thinner and plate-like. Cranial to the neural spine a deep prespinal fossa is present caudal to the prezygapophyses. A hyposphene is present.
Dorsal 13 is similar in morphology to dorsal 12 but the hyposphene is better preserved, allowing more details of the anatomy to be observed (Fig. 3.14). The hyposphene comprises a medially situated, transversely compressed plate of bone that arises dorsal to the neural canal and extends dorsally to the ventromedial margin of the postzygapophyses. Laterally, a depression on the hyposphene defines the caudal margin of the neural arch. A dorsoventral ridge extends up the hyposphene and separates this cranial depression from a second, caudal depression on its transverse surface. The transverse processes of dorsal 13 are broken, but at their bases they appear dorsoventrally compressed. The parapophysis, clearly preserved on the right, is located between the prezygapophysis and transverse process.
The centra of dorsals 14–17 become increasingly larger, moving caudally along the dorsal vertebral column; all bear irregular nutrient foramina on their lateral surfaces. Dorsal 14 is similar to dorsal 13 in morphology. Once again, the region of the hyposphene is well preserved, and features such as the two depressions separated by a dorsoventral ridge can also be observed on this vertebra. The centrum of dorsal 17 is preserved independently of its neural arch, which is articulated with the neural arches of dorsals 16 and 17. The postzygapophyses and hyposphene of dorsal 15 are well preserved and similar in morphology to those of dorsals 12 and 13. A portion of the lower part of the neural spine is preserved. It extends from dorsal to the postzygapophyses cranially, is angled slightly caudally, and is transversely compressed. Transverse processes are broken on this vertebra but they appear to be craniocaudally elongate and dorsoventrally compressed, at least at their bases.
Dorsals 16 and 17 are preserved in articulation, and only a portion of the centrum of dorsal 17 is present (Fig. 3.14E). The parapophyses are still located on the neural arch, and have not migrated onto the transverse process. This contrasts with the condition in Iguanodon bernissartensis, Mantellisaurus, and Jinzhousaurus, in which the parapophysis migrates along the transverse process, eventually forming a conjoined facet with the diapophysis in dorsal 17 (Norman, 1980, 1986; Wang et al., 2010). The transverse process of dorsal 17 is small, and has been crushed so that it now projects dorsally. It is relatively short and dorsoventrally flattened, being unsupported by buttresses or laminae, in contrast to more cranial transverse processes. A change in shape of the transverse processes along the dorsal series is also seen in Iguanodon bernissartensis (Norman, 1980) and Mantellisaurus (Norman, 1986). Small portions of the bases of the neural spines are preserved; these are strongly transversely compressed and angled slightly caudally.
3.16. Fragments of left scapula of IVPP V 12534, holotype of Equijubus normani, in lateral view. (A) proximal plate; (B) blade. Abbreviations: acr, acromion process; gle, glenoid; ri, ridge. Scale bar equals 10 cm.
Sacral Vertebrae Six vertebrae are fused together to form the sacrum. Eight vertebrae usually comprise the sacrum in Iguanodon bernissartensis (Norman, 1980), while seven co-ossified vertebrae form the sacrum in Mantellisaurus (Norman, 1986).
The sacrum is preserved with both ilia in natural articulation, and has been crushed transversely, so that details of the articulation between the sacrum and ilia are obscured (Fig. 3.15). The ventral portions of the first three sacrals and the caudal half of the sixth sacral have broken and are not preserved. Small foramina pierce the lateral surface of the centrum of sacral 4. A deep ventral groove is present on sacral 5, but was not present on sacral 4. The more caudal sacrals of Iguanodon bernissartensis also bear a groove ventrally (Norman, 1980), but this is not the case in Mantellisaurus (Norman, 1986) or Probactrosaurus (Norman, 2002). The neural spines, which are broken dorsal to the ilia, are craniocaudally broad and transversely compressed. Ossified tendons extend along the bases of the neural spines and are better preserved on the left-hand side. The total length of the sacral rod, as preserved, is 460 mm.
Appendicular Skeleton
The appendicular skeleton is in general very fragmentary and poorly preserved.
Scapula Two fragments represent the partial proximal plate and middle section of the left scapula blade, but could not be fitted together (Fig. 3.16). The partial plate includes the acromion process and dorsal part of the articulation for the coracoid, but lacks the glenoid. The lateral surface of the plate is strongly concave and is bounded dorsally by a low, rounded, striated swelling, which represents the acromion process. In the basal hadrosauroids Bactrosaurus (AMNH 6553), Gilmoreosaurus (AMNH 30725, 30727), and Jinzhousaurus (Wang et al., 2010), and in hadrosaurids, the acromion process projects laterally and the proximal plate is relatively small. Equijubus exhibits a condition more similar to that of more basal iguanodontians, in which the acromion process forms a distinct tubercle but is not folded strongly laterally (e.g., Camptosaurus dispar [USNM 4282, 5473]; Uteodon aphanoecetes [CM 11337]; Hypselospinus [NHMUK R1629; Norman, 2010]; Barilium [NHMUK R2848; Norman, 2011b]; Iguanodon bernissartensis [Norman,