DRYOSAURIDAE MILNER & NORMAN, 1984

Norman, David B., 2015, On the history, osteology, and systematic position of the Wealden (Hastings group) dinosaur Hypselospinus fittoni (Iguanodontia: Styracosterna), Zoological Journal of the Linnean Society 173 (1), pp. 92-189 : 163

DRYOSAURIDAE MILNER & NORMAN, 1984 ( JANENSCH, 1955; GALTON, 1981, 1983,

BUTLER ET AL., 2008)

Dryosaurids are small−medium-sized (3–5 m long) and generally lightly built (cursorial) animals that exhibit a range of distinct characters that have been used to differentiate the clade Dryomorpha from more basal ornithopods. Dryosaurids are first recognized in Callovian deposits and are also represented by unnamed material that is sympatric and contemporary with Hypselospinus . Taxa such as Valdosaurus demonstrate that they persisted into the Barremian−Lower Aptian (Norman, 2004, 2011b; Barrett et al., 2011).

Teeth and jaws

The dentition exemplifies the dryomorphan configuration. The lingual surface of the dentary crowns bear less prominent crown ridges with a more or less centrally positioned low primary ridge that is flanked on either side by a variable number of accessory ridges. Maxillary crowns, in marked contrast to more basal taxa, have a labially enamelled surface that is dominated by a prominent, distally offset, primary ridge. Such teeth are distinguishable in overall size and surface detail from those of Hy. fittoni . The lower jaw (dentary) differs significantly, being comparatively short and straight, tapering anteriorly, and bearing considerably fewer tooth positions than in Hy. fittoni .

Axial skeleton

The cervical vertebrae are low and lack the strong opisthocoely exhibited in Hypselospinus . The dorsa vertebrae are lower, more cylindrical, and exhibit relatively short neural spines compared with Hy. fittoni .

Appendicular skeleton

The pectoral girdle exhibits short, flared scapulae and the sternal bones are reniform, rather than hatchetlike. Details of the forelimb and manus structure (notably the phalangeal count) are not known. In the pelvis, the ilium and pubis are distinctive: the ilium has an elongate preacetabular process that is laterally compressed, curves gently laterally toward its anterior end and, in Valanginian forms, bears a longitudinal trough medially; the postacetabular process is shallow in lateral aspect and strongly expanded transversely, creating a broad, shallow brevis fossa. The pubic shaft is elongate and equal in length to that of the ischial shaft, which is distinct from the abbreviated shaft that is proposed for Hypselospinus ; the prepubic process is knife-like (comparatively narrow and laterally compressed) rather than deep, plate-like, and moderately distally expanded, as seen in Hypselospinus . The femur is bowed, slender, has a proximally positioned, pendant fourth trochanter and the extensor intercondylar groove is trough-shaped and open dorsally. The pes is functionally tridactyl, as in Hypselospinus , but the metatarsals and phalangeal digits are slender and the ungual phalanges are narrow and pointed.