Eolambia, Kirkland, 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 : 157

EOLAMBIA CAROLJONESA KIRKLAND, 1998 –

( MCDONALD ET AL., 2012A)

Eolambia is represented by several partial skulls and postcranial material collected from the Mussentuchit Member of the Cedar Mountain Formation (lower Cenomanian) of eastern Utah, USA ( Hunt et al., 2011). The material indicates a medium−large-sized ornithopod (∼ 7–8 m in length) .

Teeth and jaws

The dentary teeth are narrower, more lanceolate, and more nearly symmetrical in lingual view ( Kirkland, 1998: fig. 7B) than those described in Hy. fittoni . The primary ridge is dominant and only slightly distally offset on the crown surface and there is no obvious secondary ridge (although there is a slight thickening along the mesial edge that may represent a remnant of the secondary ridge; pers. observ. 1998). There is little evidence of strand-like accessory ridges. The dentary expands anteriorly and shows comparatively little evidence of a ventral arch ( Kirkland, 1998: figs 5H, J, 6A, B); the coronoid process is also very tall and perpendicular to the long axis of the dentary (compared with the short, oblique coronoid process in the dentary referred to Hy. fittoni ).

Axial skeleton

The vertebral column displays cervicals that resemble those of Hy. fittoni , but the dorsal series has comparatively short, plank-like neural spines and the centra do not have the expanded rims seen in Hy. fittoni .

Appendicular skeleton

The pectoral girdle displays a narrow-bladed, elongate scapula with a J-shaped acromial process. The coracoid has a fully enclosed coracoid foramen and the sternals are hatchet-shaped with an elongate, dorsoventrally flattened ‘handle’ that projects from the posterolateral edge and a comparative short ‘blade’. The humerus is sigmoid and resembles that of Mantellisaurus quite closely. Additionally, the radius and ulna are relatively slender and elongate com- pared with the short and robust morphology of Hy. fittoni . Carpal elements have not been described; nevertheless, many isolated manus elements are known ( McDonald et al., 2012a: figs 29, 30). These include what appears to be a large pollex ungual that is laterally flattened and bluntly truncated (broken?) and bears a remnant of the claw groove ( CEUM 5212; pers. observ. 1998). A smaller, conical pollex ungual was found by the author in the Mussentuchit Member of the Cedar Mountain Formation of Utah in 1998 ( CEUM 52962 – McDonald et al., 2012a: fig. 30A); this suggests that an abbreviated metacarpal 1 and ossified carpus may have been present. Individual manus elements (metacarpals) suggest that the manus was relatively slender and elongate: intermediate between the proportions of Mantellisaurus metacarpals ( Norman, 1986) and the more elongate metacarpals of Probactrosaurus (Norman, 2002) .

Unlike Hy. fittoni , the preacetabular process of the ilium is elongate and expands distally to form an enlarged flange; near its base this process has a pronounced medial ridge. The dorsal margin of the ilium ( Kirkland, 1998: fig. 10A; McDonald et al., 2012a: fig. 31A, B) bears an everted bevelled edge in the region posterodorsal to the ischiadic peduncle; this differs from the structure in this area in Hy. fittoni . There is no brevis fossa ( McDonald et al., 2012a: 30), in contrast to Hy. fittoni in which this structure is very well developed. The pubis has a deep, narrow prepubic process that is expanded distally and has a very different profile to that seen in Hy. fittoni . The ischium has a narrow and straight shaft that terminates in an anteriorly expanded ‘boot’ ( McDonald et al., 2012a: fig. 31E, F). The remainder of the postcranium has not been described in sufficient detail for further comparison. The femur has a shaft that is curved medially, but straight when viewed in lateral aspect, unlike the bowed femoral shaft of Hy. fittoni . The distal elements differ in no significant way from those seen in other large-bodied iguanodontians: there are three well-developed metatarsals, and the ungual phalanges have an arrowheadlike profile and prominent claw grooves when viewed dorsally.