Hudiesaurus

Hudiesaurus (meaning "butterfly lizard") is an extinct genus of mamenchisaurid sauropod dinosaur that lived in present-day China during the Late Jurassic period. It was described by Chinese paleontologist Dong Zhiming in 1997. The genus contains a single species, Hudiesaurus sinojapanorum, named based on a single vertebra. However, he also assigned teeth and limb bones from a nearby locality to H. sinojapanorum. These fossils were unearthed by the Sino-Japanese Silk Road Expedition near Qiketai in Shanshan, Xinjiang province in rock layers coming from the Kalaza Formation. This formation dates to between the Late Kimmeridgian and Tithonian stages of the Late Jurassic, 154 to 143 million years ago. Dong believed that the vertebra was a dorsal (trunk) vertebra, but later analysis suggested that it is one of the last cervical (neck) vertebrae. In 2021, the limb bones were assigned to a distinct genus of sauropod, Rhomaleopakhus, and the teeth were classified as an indeterminate eusauropod.

Hudiesaurus is one of the largest dinosaurs known, possibly reaching 32 metres (105 ft) in length and 55 tonnes (61 short tons) in body mass. However, if the vertebra is a dorsal vertebra the length would be closer to 30.5 metres (100 ft) and the mass around 44 tonnes (49 short tons). Its vertebra is robust, large, and wide, with a width of 539 millimetres (21.2 in). The neural spine (the uppermost part of a vertebra) is bifurcated (split at the top), indicating that Hudiesaurus had strong lateral control over its neck. On the sides of the centrum (body of the vertebra) are pleurocoels (large cavities) which would store pneumatic air sacs.

Hudiesaurus is a member of the family Mamenchisauridae, though its exact relation to other members is uncertain. This is a group of sauropods with longer necks and shorter tails compared to other families like diplodocids and dicraeosaurids. Being a mamenchisaurid, Hudiesaurus was likely a low or medium-browsing, four-legged herbivore. Hudiesaurus coexisted with many other dinosaurs such as the sauropods Rhomaleopakhus and the dubious Chiayusaurus, the dubious theropod Szechuanosaurus, and an indeterminate megalosaurid theropod.