Hadrosaurs. David A. Eberth
coracoid articulation is subtriangular in proximal view, with the apex of the triangle pointed medially. It is strongly rugose. The ventral part of the medial surface has a broad longitudinal ridge, which lies at the same level as the broadest part of the coracoid articular surface. The area dorsal to this is shallowly concave.
The central section of the scapula has a strongly concave ventral margin in lateral view and it appears that the proximal plate would have been expanded farther ventrally than dorsally with respect to the blade midline. In the majority of iguanodontians – such as Camptosaurus dispar (USNM 4282, 5473), Iguanodon bernissartensis (Norman, 1980), and Gilmoreosaurus (AMNH 30725, 30727) – the ventral margin of the scapula is dorsally concave; however, in Hypselospinus (NHMUK R1629) and Probactrosaurus (Norman, 2002) the ventral margin of the scapula blade is straight, allowing Equijubus to be distinguished from these taxa. A low ridge extends parallel to the ventral margin along the most strongly concave part of the ventral margin, forming a shallow ventrolaterally facing surface. The rest of the lateral blade surface is laterally bowed. The blade becomes more transversely compressed toward its distal end. Although the dorsal margin is incomplete, the curvature of the ventral margin suggests the presence of a distal expansion, as is present in the majority of iguanodontians (e.g., Dysalotosaurus, MB R.1707; Camptosaurus dispar, USNM 4282, 5473; Barilium, NHMUK R2848; Bactrosaurus, AMNH 6553), although the scapular blade is not distally expanded in Probactrosaurus (Norman, 2002) or in Iguanodon bernissartensis (Norman, 1980). In medial view, the blade is generally concave, with few surface features. Toward the distal end, there are a large number of prominent longitudinal striations. Again, a low ridge or swelling is present along the concave ventral margin, which fades out caudally and causes the ventral margin to be thicker than the dorsal margin.
3.17. Left sternal of IVPP V 12534, holotype of Equijubus normani. (A) ventral view; (B) dorsal view. Abbreviations: clp, caudolateral process; cmp, caudomedial process. Scale bar equals 10 cm.
3.18. Proximal end of left humerus of IVPP V 12534, holotype of Equijubus normani, in (A) cranial, (B) caudal and (C) proximal view. Abbreviations: dpc, deltopectoral crest; hd, humeral head; lt, lesser tuberosity. Scale bar equals 10 cm.
Sternals The left sternal is complete, whereas the otherwise well-preserved right sternal is broken along its caudomedial margin. At the craniolateral corner of the sternal, a concave facet, perhaps for a sternal rib, is present. The sternal is dorsoventrally thickened along its cranial margin, and the bone surface is rough and unfinished for the coracosternal cartilage. The main body of the sternal is slightly convex along its medial margin and straight along its lateral margin (Fig. 3.17). The rod-like caudolateral process of the sternal is directed caudolaterally, is oval in cross section, and is fringed by striations distally. The distal end of the caudolateral process is roughened. A small, hook-like, caudally directed caudomedial process is present (Fig. 3.17). The sternal of Equijubus is overall similar to that of Jinzhousaurus, except that the caudomedial process of the latter is more prominent and is directed caudomedially (Wang et al., 2010:fig. 6c, d). The sternal of Lanzhousaurus lacks the hook-like caudomedial process of Equijubus (You et al., 2005:fig. 3b).
Humerus Only the proximal portion of the left humerus is preserved (Fig. 3.18). In proximal view, the cranial surface is concave, with this concavity interrupted by a small swelling marking the cranial expansion of the humeral head. By contrast, the caudal margin of the humerus is divided into two concavities by the humeral head, which is strongly expanded caudally. Extending laterally from the humeral head, the proximal surface of the humerus expands slightly craniocaudally, before terminating in a narrow, rounded apex. Medial to the humeral head, the lesser tuberosity maintains the same width for its entire length, ending in a bluntly rounded process. In proximal view, the deltopectoral crest and tubercle are separated by an angle of approximately 120 degrees. In cranial view, the proximal margin of the humerus slopes slightly dorsally from the medial tubercle to the head, where the angle changes to slope ventrally to the top of the deltopectoral crest. In caudal view, a robust ridge extends ventrally from the ventral surface of the humeral head, dividing the caudal surface into two concave areas. The fragmentary nature of the humerus precludes detailed comparisons with other taxa, although the preserved portion appears similar to the proximal humerus in Iguanodon bernissartensis (Norman, 1980), Mantellisaurus (Norman, 1986), and Jinzhousaurus (Wang et al., 2010).
Ilium Parts of both ilia are preserved in natural articulation with the sacrum (Fig. 3.19). They have been transversely crushed against the sacral vertebrae, and as a result a series of gentle undulations on the lateral surface of the better-preserved left ilium correspond to the anatomy of the underlying vertebrae. The preacetabular process is not preserved on either side. The postacetabular process is entirely broken on the right and is not preserved; on the left it is broken at its distal end.
The dorsal margin of the ilium is gently convex, in contrast to the condition in most other hadrosauriforms, in which it is generally rather straight (e.g., Mantellisaurus, NHMUK R11521; Jinzhousaurus, Wang et al., 2010; Probactrosaurus, Norman, 2002), although it is also strongly convex in Barilium (NHMUK R802) and in NHMUK R3741, the famous “Mantel-piece” (Carpenter and Ishida, 2010). The dorsal margin is transversely thickened relative to the body of the ilium and fringed in a series of prominent striations. Just caudal to the ischial peduncle, the dorsal margin of the ilium becomes deeper dorsoventrally, thicker transversely, and is folded over into a laterally everted rim, possibly an incipient version of the supra-acetabular process of more derived iguanodontians; the striations continue under this surface. The development of the laterally everted rim appears to be comparable to that of Mantellisaurus (NHMUK R11521) and Probactrosaurus (Norman, 2002). The caudal end of the postacetabular process is broken on the left ilium, but the ventral margin of the process extends at a steep angle cranioventrally to the ischial peduncle, suggesting that the postacetabular process was relatively short and dorsoventrally deep. No brevis shelf is developed in Equijubus, similar to Probactrosaurus (Norman, 2002), but in contrast to the conditions in Iguanodon bernissartensis (Norman, 1980) – in which there is a relatively broad brevis shelf – and in Mantellisaurus (NHMUK R11521) and Jinzhousaurus (Wang et al., 2010).
3.19. Ilia of IVPP V 12534, holotype of Equijubus normani, in lateral view. (A) left ilium; (B) right ilium. Abbreviations: ace, acetabulum; ip, ischial peduncle; lev, laterally everted rim; poap, postacetabular process; pp, pubic peduncle. Scale bar equals 10 cm.
As in most neornithischians (Butler et al., 2008) the ischial peduncle is large, transversely thickened, and angled ventrolaterally. This contrasts with the situation in more basal iguanodontians (e.g., Camptosaurus dispar, USNM 4282) in which the ischial peduncle faces ventrally, but is similar to the condition in other hadrosauriforms (e.g., Mantellisaurus, NHMUK R11521; Probactrosaurus, Norman, 2002; Gilmoreosaurus, AMNH 30735). The pubic peduncle is broken distally, but is roughly triangular in cross section, with the flattened base of the triangle forming the internal surface of the acetabulum. This surface is prominently striated. The acetabulum is strongly dorsally concave in lateral view, similar to that of Mantellisaurus (NHMUK R11521) but in contrast to the condition in Probactrosaurus (Norman, 2002), Hypselospinus (NHMUK R1635), and Gilmoreosaurus (AMNH 30735), in which the concavity described by the acetabular margin is much weaker.
Femur