Tianzhenosaurus

Tianzhenosaurus, whose name means “Tianzhen lizard,” is a genus of ankylosaurid dinosaur from the Late Cretaceous Huiquanpu Formation in Shanxi Province, China. It includes one widely recognized species: the type species *T. youngi*. Some paleontologists have argued that *Tianzhenosaurus* may actually be a junior synonym of *Saichania*, an ankylosaurine known from the Barun Goyot and Nemegt formations.

The first fossils were found in 1983, when Pang Qiqing and Cheng Zhengwu uncovered articulated cervical vertebrae of an ankylosaurid in Shanxi. Later excavations at the site produced numerous specimens, including remains of sauropods, theropods, ornithopods, and other ankylosaurids. The holotype of *T. youngi*, HBV-10001, is a partial skull. Two paratypes were also assigned: HBV-10002 (an incomplete mandible) and HBV-10003 (a collection of vertebrae, a sacral complex, ilia, pectoral and pelvic girdles, limbs, a tail club, and osteoderms). All these specimens came from the Huiquanpu Formation and are housed at the Geoscience Museum, Hebei GEO University in Shijiazhuang. The genus name comes from Tianzhen County and the Greek word *sauros* (lizard). The species name *youngi* honors Professor Yang Zhongjian (C. C. Young), a key figure in Chinese vertebrate paleontology.

In 1999, Sullivan proposed that *Tianzhenosaurus* was a junior synonym of *Saichania*, based on the overall similarity of their skulls. He also suggested that *Shanxia* was a junior synonym of *Tianzhenosaurus*, because its only unique trait is known to vary within a single taxon like *Euoplocephalus*. Arbour and Currie (2015) agreed with Sullivan’s reasoning, but noted that if the humerus of *Tianzhenosaurus* later proves different from that of *Saichania*, it could be considered a distinct genus. In 2024, Pang, Li, and Guo described a new species, *T. chengi*, based on holotype HBV-10004 (a skull) and paratype HBV-10005 (a nearly complete skeleton), though this species is not widely recognized or described in peer-reviewed literature. The species name honors Chinese paleontologist Cheng Zhengwu for his work in Shanxi. They identified several cranial features that separate *Tianzhenosaurus* from other Asian ankylosaurids, including *Saichania*, *Talarurus*, and *Shanxia*. This new specimen was found in the same rock layers as *T. youngi*.