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Craniodental Anatomy The dentary is robust and has parallel upper and lower edges and an elevated coronoid process that arises from a shelf lateral to the most posterior alveoli. The large, and visibly crushed, replacement dentary tooth crown preserved in NHMUK OR28660 generally resembles those seen in another referred specimen (NHMUK R2358) that comprises part of a robust dentary with three embedded teeth; these are of additional interest because they resemble the morphology seen in the lectotype tooth (I. anglicus: Norman, 2011b:fig. 27.23A).

Vertebrae Dorsal vertebrae are notable for having very tall, deep, and slightly inclined spines; anterior dorsals have slightly waisted, cylindrical vertebral centra; posterior dorsals become more axially compressed and develop everted edges. Sacrals are very poorly known, while the caudals are distinctive: those nearest the sacrum are squat, subrectangular in axial view, and somewhat inclined forward (Norman, 2011a:fig. 6); these are succeeded by deeper-bodied, hexagonal (more typical iguanodont) caudals, whereas the caudals toward the tip of the tail tend to have very angular sides and their articular faces tend to be deeply concave (Norman, 2011a:fig. 7).

Girdles and Limbs The pectoral (shoulder) girdle and forelimb are robust. The scapula (based upon the referred specimen NHMUK R2848) is long, curved, and expands towards its upper end. The coracoid is notably broad and dished, and has a prominent and completely enclosed coracoid foramen near the suture with the scapula (Norman, 2011a:fig. 17A). One specimen (NHMUK R2357) includes the “handle” portion of a hatchet-shaped sternal bone (Norman, 2011a:fig. 17B). The principal forearm bones (radius and ulna) are very robust; the carpals and metacarpal I cap the ends of the ulna and radius and are fused into a solid block that supports a fused, squat pollex. The form of the remaining bones of the hand is unknown. The hip (pelvic) bones include a very distinctive ilium, which has a long, robust, preacetabular process that is twisted along its length and bears a large rib facet near its base. The main body of the ilium is slab sided, thick along its dorsal edge with minimal lateral swelling and an inflection along its upper edge (posterodorsal to the ischiadic peduncle). The postacetabular process is deep and rounded in profile, and does not develop a ventrolateral ridge that delimits a vaulted brevis fossa; a well-developed brevis fossa is present in all other Wealden iguanodonts. The shape of the shaft of the ischium is unknown, but proximally the external surface of the shaft adjacent to the obturator process displays a pronounced vertical ridge that runs along the ischial shaft (NHMUK R2357) rather than forming a flat, rugose facet seen typically in this area in specimens attributable to H. fittoni; and the pubis appears to develop a thick, deep, and slightly upwardly curved prepubic process and the dorsoventrally compressed (strap-like) pubic shaft is unlikely to have extended to the end of the ischial shaft. The hindlimb is poorly known (Norman, 2011a).

2.4. Hypselospinus cf. fittoni, NHMUK R1831. Dentary (right) with teeth preserved in situ. (A) medial; (B) lateral; (C) dorsal views. Abbreviations: am, alveolar margin; br, badly broken portion of the dentary; cp, coronoid process; ds, dentary symphysis; m, matrix; mgr, Meckelian groove; pr, anterior lateral process of the dentary; sl, “slot-and-lip” portion of the dentary symphysis; tf, tooth fragments in alveolar bone; vc, vascular channel. Scale bar equals 10 cm (from Norman, in press).