Probactrosaurus (Norman, 2002)

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 : 158

PROBACTROSAURUS GOBIENSIS ROZHDESTVENSKY, 1952 (NORMAN, 2002)

Remains of this taxon indicate the presence of a medium-sized iguanodontian (attaining ∼ 6 m in length) collected from the Ulansuhai Formation (Turonian), Maortu, China ( Kobayashi & Lu, 2003).

Teeth and jaws

The dentary crowns of this taxon (Norman, 2002: figs 14–16) are narrower and less ornate than those described in Hy. fittoni ( Fig. 37 ). The marginal denticles support mammillations, but these are less numerous than in the case of Hy. fittoni and the denticles do not form a curved shelf as they do in Hy. fittoni . The roots of the teeth are also fluted for the compaction of adjacent functional and replacement crowns that form the dental magazine. There are at least two replacement crowns in each alveolus in the deeper portions of the dentary and the occlusal surface is broad because it comprises at least two dentary crowns, unlike Hy. fittoni . The dentary of Prob. gobiensis is comparatively shorter and deeper than that of Hy. fittoni with a larger and deeper area devoted to the dental magazine as well as a tall, perpendicular coronoid process (Norman, 2002: fig. 12).

Axial skeleton

What is known of the dorsal vertebral series (Norman, 2002: fig. 17) shows neither the thickening of the articular margins of the centra, nor any clear indication of the narrow and very tall neural spines that are displayed in Hy. fittoni (this is confirmed by reference to the shape of the anterior caudals – Norman, 2002: fig. 18).

Appendicular skeleton

Most of the postcranial anatomy of Prob. gobiensis (Norman, 2002: figs 20–33) appears to be gracile and generally comparable to that seen in M. atherfieldensis ( Norman, 1986) rather than Hy. fittoni . The forearm and manus are notably slender and lightly built in Prob. gobiensis, and the pollex ungual is small, narrow, and conical (Norman, 2002: figs 22–26), in marked contrast to these structures in Hy. fittoni . The ischial shaft is heavy, robust, and J-shaped (Norman, 2002: fig. 29) and resembles that seen in Hy. fittoni .

Figures

Figure 37. Hypselospinus cf. fittoni. NHMUK R1831. Teeth. A, dentary tooth in lingual view (isolated specimen on stub of matrix); B, maxillary tooth in labial view. C−E, dentary replacement crowns embedded in the alveolar bone of the dentary. Abbreviations: m, mammillae on the marginal denticles; p, primary ridge; r, minor ridges; st, strand-like ridges.