Altirhinus kurzanovi, Norman, 1998

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 : 155

ALTIRHINUS KURZANOVI NORMAN, 1998

Altirhinus includes the skull and partial skeleton of a medium-large sized ornithopod (∼ 8 m long) collect- ed from the lower Albian of Khuren Dhuk, Mongolia ( Norman, 1998; Hicks et al., 1999).

Teeth and jaws

The dentary teeth ( Norman, 1998: figs 21, 22) have broad, shield-like lingual surfaces divided by ridges. There is a distally offset primary ridge and a mesial secondary ridge, but there is a consistent additional pattern: distally positioned accessory (tertiary) ridges give the crown a more symmetrical appearance. None of the mesially placed strand-like accessory ridges, seen in the dentary crowns of Hy. fittoni , is present on the crowns of A. kurzanovi . At least three teeth (two replacement and one functional) appear to be present in each alveolus of the dentary. In some instances two crowns within the same alveolus contribute to the occlusal surface of the dentary ( Norman, 1998: fig. 22). The dentary has a generally similar form ( Norman, 1998: fig. 16) to that seen in Hy. fittoni . However, the anterior portion of the dentary of A. kurzanovi is longer and more strongly arched near the symphysis and the coronoid process is both taller and more obviously perpendicular to the long axis of the jaw.

Axial skeleton

This part of the skeleton is poorly represented in the original material. Short and broad neural spines are found on the anterior caudals ( Norman, 1998: fig. 24) and distinguish these from those seen in Hy. fittoni .

Appendicular skeleton

The forelimb resembles that which is seen in largebodied ornithopods, except that the radius and ulna are more slender and elongate ( Norman, 1998: fig. 28). The carpals are not co-ossified ( Norman, 1998: fig. 29) and the manus is notable for the elongation and close opposition of metacarpals II−IV. The pollex ungual ( Norman, 1998: fig. 31A, B) is large, pointed, lateral- ly compressed, and retains paired claw grooves; it has a narrower base than that seen in Hy. fittoni . The pelvis is distinct from the latter species in having an ilium with a well-developed medial ridge on the preacetabular process, a pronounced eversion along the dorsal margin in the region just posterior to the ischiadic peduncle, and no obvious development of a lateral ridge-brevis fossa complex along the ventrolateral edge of the postacetabular process. The prepubic process is bladelike, laterally compressed, expands distally, and is arched ventrally along its length and quite distinct from that seen in Hy. fittoni . The ischium has a narrow, straight shaft, quite distinct from that seen in Hy. fittoni , but the form of its distal end is unknown ( Norman, 1998: figs 32–34). The remainder of the hindlimb is poorly preserved ( Norman, 1998), but the femur is reported to have had a curved (rather than straight) shaft, and what is known of the remainder of the hindlimb differs in no obvious way from what is known in medium to large-sized iguanodontians.