Bolong yixianensis

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 : 152

BOLONG YIXIANENSIS WU, GODEFROIT & HU, 2010

This taxon is based on a partial skull and articulated skeleton of a medium-sized (3–4 m long) ornithopod that was collected at Bataigou, Toutai, Yixian County, western Liaoning Province, China (middle Yixian Formation: late Barremian−early Aptian). This specimen was first reported on the basis of its cranial remains ( Wu et al., 2010), but a more complete description has now been published ( Wu & Godefroit, 2012).

Teeth and jaws

The dentary teeth display a distally offset primary ridge and less prominent secondary ridge that divides the mesial sector of the crown; there are no multiple accessory ridges seen on these crown surfaces as are present in crowns of Hy. fittoni .

Axial and appendicular skeletons

The dorsal and caudal vertebrae display rectangular, slightly posteriorly inclined neural spines, but these are not narrow and elongate as in Hy. fittoni . The comparatively short and robust antebrachium resembles that seen in Hy. fittoni , but is capped distally by a group of six separate carpals, rather than a fused carpometacarpus. In the manus a flattened proximal phalanx is preserved at the base of the mobile, triangular, and laterally compressed pollex ungual. The metacarpals of digits II−IV are comparatively short and robust, and metacarpal II is typically shorter than the other two. The second and third digits have flattened, hoof-like unguals, the fourth digit has two small phalanges only, and the fifth digit seems to have been divergent. The pelvis is poorly preserved, but the postacetabular process of the ilium appears to form a narrow rectangular plate, unlike that seen in Hy. fittoni . In other respects what can be seen of the pelvic and hindlimb elements seems to resemble the morphology of Hy. fittoni .

Taxonomic note

Wu & Godefroit (2012) reported that the caudal ribs of this specimen are unfused to their centra, which led them to suspect that this specimen had not attained adult size. The lack of co-ossification of the carpal elements may therefore also be a reflection of ontogenetic immaturity. Nevertheless, the dental morphology, structure of the dorsal and caudal vertebrae, as well as the structure of the postacetabular process of the ilium serve to distinguish Bolong from Hypselospinus . It is noted that these taxa share a number of anatomical similarities, despite their apparent incongruent stratigraphical (Valanginian vs. late Barremian) and geographical (Europe vs. Asia) distributions. It should also be noted, in passing, that Jinzhousaurus and Bolong , although they differ in size are sympatric, very similar anatomically, and approximately coeval.