Huabeisaurus

''Huabeisaurus'' (, meaning "North China lizard") was a genus of dinosaur from the Late Cretaceous ( Cenomanian to Maastrichtian stages, around 99.7–70.6 million years ago). It was a sauropod which lived in what is present-day northern China. The type species, ''Huabeisaurus allocotus'', was first described by Pang Qiqing and Cheng Zhengwu in 2000. ''Huabeisaurus'' is known from numerous remains found in the 1990s, which include teeth, partial limbs and vertebrae. Due to its relative completeness, ''Huabeisaurus'' represents a significant taxon for understanding sauropod evolution in Asia. ''Huabeisaurus'' comes from Kangdailiang and Houyu, Zhaojiagou Town, Tianzhen County, Shanxi province, China. The holotype was found in the unnamed upper member of the Huiquanpu Formation, which is Late Cretaceous (?Cenomanian–?Campanian) in age based on ostracods, charophytes, and fission-track dating.

''Huabeisaurus'' measures long and high, as estimated by Pang and Cheng in 2000. It would have been a quadrupedal herbivore with a long neck and tail, like most other sauropods. The skeleton has been presumed to have belonged to an almost mature individual, because it lacks sutures on vertebrae, but not on pelvic material. A set of 12 characters were identified by D'Emic ''et al.'' in 2013 that differentiate ''Huabeisaurus'' from other sauropods.

An isolated humerus, designated the paratype by Pang and Cheng, comes from a locality over 200 meters away from the type locality of ''Huabeisaurus'', in a fluvially deposited sandy conglomeratic layer in the lower member of the Huiquanpu Formation. This layer is roughly 90 m lower stratigraphically than the type horizon of ''Huabeisaurus'', which comes from the upper member of the Huiquanpu Formation. The humerus thus comes from a stratum representing a different and likely older depositional environment than that of ''Huabeisaurus'', and does not overlap anatomically with the holotypic skeleton, and so cannot currently be referred it.

The discoverers erected a new family for the genus, Huabeisauridae, although this family name is not widely used amongst paleontologists. Recently, the family was again proposed, this time by D'Emic ''et al.'' because Euhelopodidae, which ''Huabeisaurus'' has been assigned to most recently, might have to be split into smaller clades throughout Somphospondyli because of all the taxa assigned to it.

Pang and Cheng tentatively suggested that "Titanosaurus" ''falloti'' be referred to ''Huabeisaurus''. One problem, however, is that the femora of ''Huabeisaurus'' and "T." ''falloti'' differ in the bevel of the distal end versus the long axis of the bone, so the two cannot represent the same genus.

Description

The Late Cretaceous titanosauriform sauropod ''Huabeisaurus'' is known from teeth and much of the postcranial skeleton. Its completeness makes it an important taxon for integrating and interpreting anatomical observations from more fragmentary Cretaceous East Asian sauropods and for understanding titanosauriform evolution in general.

Measuring in total length, ''Huabeisaurus'' is large when compared to most dinosaurs, but by sauropod standards, it was only midsized. It had a hip height of . Like other sauropods, it would have been a quadrupedal herbivore with a long neck and tail.Upchurch, Paul; Barrett, Paul M., and Dodson, Peter. (2004). "Sauropoda". In Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka. (eds.). The Dinosauria (2nd ed.). Berkeley: University of California Press. pp. 259–322.

The skeleton has been presumed to have belonged to an almost mature individual. The absence of sutures between the neural arches and centra of cervical, dorsal, and caudal vertebrae suggests that the specimen was nearing sexual maturity, but the open sutures between the scapula and coracoid, and the ilium and some sacral ribs suggest that it had not reached full maturity.

Discovery and naming

The sauropod ''Huabeisaurus'' was excavated from Upper Cretaceous sediments of the province of Shanxi, in northeast China. The skeleton was recovered in the 1990s. The holotype of ''Huabeisaurus'' is a partially articulated individual composed of teeth, cervical, dorsal, sacral, and caudal vertebrae, ribs, complete pectoral and pelvic girdles, and nearly complete limbs. Due to its relative completeness, ''Huabeisaurus'' represents a significant taxon for understanding sauropod evolution in Asia.

Material

Limb and girdle elements from the left and right sides of the body closely match each other in size and are the appropriate size to belong to the same individual as the vertebrae and ribs. The disposition of bones in the quarry is approximately as expected if the animal were lying on its left side in an opisthotonic pose, but nearly all bones show some disorientation and disarticulation: the cervical vertebrae are arranged along a curved line, and extending along this tight curve (approximately) sit two of the dorsal vertebrae followed by the sacrum and caudal vertebrae. The sacrum and first three caudal vertebrae were found in articulation and in line with the remaining articulated caudal vertebrae; others are present after a gap of about . Twenty-seven caudal vertebrae are shown on the quarry map, but 30 were found in the collection, and pre-restoration photos indicate that 32 were originally present. Many of the chevrons were found articulated with their respective caudal vertebrae. The left and right scapulae were recovered on the left and right sides of the body, respectively. The left radius was found about midway between the pectoral girdle elements. Left and right femora, pubes, and ilia were located close to one another and all of these were found near the sacrum. The sacrum is depicted with its left side facing upwards on the quarry map, but this might have been an error because the left side of the sacrum is damaged and the left ilium is missing. The elements of the left and right crura were found in close association. Dorsal rib fragments were scattered across the quarry area. In sum, some degree of dispositioning occurred to HBV-20001 before or during burial, resulting in loss and disarticulation of some elements, but the disposition, overall agreement in size, and lack of duplication of bones suggests the presence of a single sauropod individual at this locality.

Two teeth were preserved. One tooth was discovered in the quarry during excavation and a second was found as field jackets were opened during preparation of the specimen at Shijiazhuang University. The teeth are attributed to the holotype individual based on their close association with other bones and lack of evidence for transport from another site. Both teeth are well preserved, exhibiting wrinkled enamel. The crowns are subcylindrical