Hadrosaurs. David A. Eberth
that Richard Owen used in order to diagnose his new “sub-order” Dinosauria (Owen, 1842).
Sacral Vertebrae One specimen (Fig. 2.13) comprises a nearly complete sacrum (lacking the sixth true sacral) with portions of an attached ilium (NHMUK OR37685), which is attributable to this species. The sacrum comprises seven fused vertebrae in mature specimens (fusion is incomplete in immature individuals) and involves the incorporation of a posterior dorsal with a free (non-sacralized) rib. There is a narrow keel present, unlike I. bernissartensis, which exhibits a broad, longitudinal midline sulcus.
Girdles and Limbs The pectoral girdle and forelimb bones differ little from those described for previous taxa (and the contemporary I. bernissartensis) except that they tend to be smaller and less robust. The blade of the scapula tends to have a narrower shaft and the blade flares distally to a greater extent than in I. bernissartensis. The coracoid also exhibits a discrete foramen (cf) externally, which is different from the coracoid “notch” seen in I. bernissartensis.
The sternal bone (Fig. 2.14C) has the classic “styracosternan” hatchet-like shape. The humerus (Fig. 2.14A) is sinuous. The ulna and radius (Fig. 2.14B) are comparatively slender and bowed, thus suggesting the possibility of some axial rotation between these elements. The wrist and hand are worth mentioning because they are distinctive (Fig. 2.15). The carpals are sutured together, but they are neither as massive nor as tenaciously bound by ossified ligaments as is the case in previous examples (above; Norman, 2011a, in press) or in I. bernissartensis (below; Norman, 1980). The first metacarpal is fused to the carpals and forms an oblique, roller-like structure for articulation with the base of the pollex; the latter is relatively diminutive and, unlike the Barilium and Hypselospinus, is genuinely conical rather than transversely compressed or truncated. In its general shape the pollex of M. atherfieldensis echoes, on a smaller scale, the conical pollex of I. bernissartensis. The central bones of the hand (metacarpals II–IV) are slender and more elongate than those known in either Hypselospinus or Iguanodon.
The ilium (Fig. 2.16) has a long, slender, preacetabular process (prp) that is buttressed by a curved medial ridge. The main body of the iliac blade is vertical, but the dorsal edge is thickened and everted so that it overhangs the lateral surface. Farther posteriorly, the dorsal edge thickens and becomes more everted, forming a beveled structure (boss) posterodorsal to the ischiadic peduncle. The dorsal edge of the postacetabular process beyond the iliac boss is inflected downward before terminating in a short transverse bar. Beneath this bar there is a narrow, vaulted brevis fossa (br.f). In overall shape the ilium resembles that of Hypselospinus fittoni from the Valanginian of the Weald Sub-basin; however, the preacetabular process is more slender and transversely thicker, whereas the equivalent portion of H. fittoni is more strongly compressed laterally and considerably deeper; the central portion of the iliac blade is shallower than in H. fittoni; and the postacetabular process differs also in having a far less pronounced brevis fossa than in H. fittoni and, as a direct consequence, the posterior bar is also much narrower.
The pubis (Fig. 2.16) has a thin, deep, prepubic process that expands distally, whereas the pubic shaft is narrow and short; there is a massive iliac peduncle, and beneath this a broad cup-shaped depression forms the anterior part of the acetabulum. The proximal part of the pubic shaft has a finger-like dorsal process that nearly encircles the obturator foramen (obt.f); its posterior surface forms a flattened vertical surface for attachment of the adjacent part of the ischium and, when articulated, the obturator foramen is completely enclosed. The shaft of the ischium is long, slender, and only slightly arched along its length (the arching is perhaps exaggerated in Figure 2.16, and the distal boot is too large) and has a modest anterodistal expansion.
2.14. Mantellisaurus atherfieldensis, holotype of I. atherfieldensis Hooley, 1925, NHMUK R5764. (A) humerus, right in dorsal view; (B) radius and ulna, right lateral view; (C) right sternal bone in ventral view. Abbreviations: h, articular head of the humerus; ra, radius; ul, ulna (same as Norman, 2011b:fig. 27.43C–E).
The hindlimb (Fig. 2.17) is not particularly distinctive, as is true of most similar-sized iguanodonts. The femur (Fig. 2.17A, B) has a shaft that is more slender, less angular-sided, and less curved along its length than that seen in B. dawsoni and H. fittoni from the Weald Sub-basin (any remaining curvature of the shaft is present only below the fourth trochanter [4t]); and the anterior trochanter (at) is narrower, less robust, more laterally compressed, and more closely appressed to the lateral surface of the greater trochanter, when compared to the latter taxa. The lower leg elements (Fig. 2.16C, D) are not distinctive, except insofar as they are more slender and lightly built than in the contemporaneous taxon I. bernissartensis, and the proximal tarsals are firmly attached (but not fused) to the crus (Fig. 2.17: ast, cal).
The pes (Fig. 2.18A, B) is slender and functionally three toed. Neither the holotype (NHMUK R5764) nor the referred specimen (RBINS R57) have metatarsal I preserved. A well-preserved and articulated pes that is commensurate and that is the same stratigraphic age has been referred to M. atherfieldensis (Norman, 1986; NHMUK R1829) exhibits a narrow, splint-like metatarsal I. The sympatric contemporary I. bernissartensis has a small, laterally compressed metatarsal I (Norman, 1980).
2.15. Mantellisaurus atherfieldensis, holotype of I. atherfieldensis Hooley, 1925, NHMUK R5764. The associated elements of the right manus in dorsal view. Abbreviation: mc, metacarpal (from Norman, 1977).
Reconstruction of Mantellisaurus
The reconstruction in a bipedal pose (Fig. 2.19) is based primarily upon the proportions of the holotype skeleton (NHMUK R5764) and that of the referred skeleton (RBINS R57). The pectoral girdle and forelimb are notably less robust than those seen in either of the Valanginian taxa.
IGUANODON Mantell, 1825 IGUANODON BERNISSARTENSIS Boulenger (in Beneden, 1881)
Although extremely well known in mainland Europe, where more than 30 complete and partial skeletons have been recovered in Belgium, Germany, France, and Spain, Iguanodon bernissartensis is comparatively rare in Britain. The first occurrence of this morphotype was a hindlimb, pelvis, and some caudal vertebrae of large size collected in 1870 by John Whitaker Hulke at Brook Chine, Isle of Wight (late Barremian: NHMUK R2501-R2514; associated bones of an almost complete ilium and hindlimb that were given separate registered numbers). This material was eventually described and illustrated as Iguanodon seelyi Hulke, 1882 (Norman, 2012). Rather interestingly, from a purely historical perspective, this paper appeared shortly after Hulke had spent