Fossil remains of Asiatyrannus xui (ZMNH M30360). From Zheng et al., 2024.

Tyrannosauroidea, the superfamily of carnivorous dinosaurs that includes the iconic Tyrannosaurus rex, originated in the Middle Jurassic, approximately 165 million years ago, and was a dominant component of the dinosaur faunas of the Northern Hemisphere. All tyrannosaurs were bipedal predators characterized by premaxillary teeth with a D-shaped cross section, deep snouts, extreme pneumaticity in the skull roof and lower jaws, a pronounced muscle attachment ridge on the ilium, and an elevated femoral head. For most of their evolutionary history, tyrannosauroids were mostly small-bodied animals and only reached gigantic size during the final 20 million years of the Cretaceous.

Their colosal body size and deep snouts were key features of tyrannosaurid species from the latest stages of the Mesozoic. In Asia, during the latest Cretaceous, existed a derived group of long-snouted tyrannosaurids called alioramins that includes Qianzhousaurus sinensis and Alioramus remotus. Asiatyrannus xui, from the Upper Cretaceous of Ganzhou City, southeastern China, is a small to medium-sized tyrannosaurine theropod. The new specimen reveals the coexistence of the long-snouted and deep-snouted tyrannosaurids in southeastern China.

Skull of Asiatyrannus xui. Adapted from Zheng et al., 2024. Scale bar = 5 centimeters.

The holotype (ZMNH M30360) comprises a nearly complete skull and partial disarticulated postcranial skeleton, including caudal vertebrae; right femur, tibia, and fibula; metatarsals, pedal phalanges, and a partial midshaft of the left tibia, fibula, and metatarsals (1). The generic name is derived from the word ‘Asia’ and the Latin word ‘tyrannus’ (meaning ‘king’ or ‘tyrant’). The specific name honors Dr. Xing Xu, a distinguished dinosaurologist who study several tyrannosaurs from China like Guanlong, Dilong, and Yutyrannus.

Asiatyrannus xui exhibits a skull length of 47.5 cm (18.7 inches) and an estimated total body length of 3.5-4 m (11.5-13.1 feet). The skull in lateral view is deeper than alioramins Alioramus and Qianzhousaurus, and is similar to other large-bodied tyrannosaurids like Tarbosaurus, Tyrannosaurus, and Gorgosaurus. Other features include two small, deep fossae located on the lateral surface of the premaxilla, and a large and sub-rectangular shaped maxillary fenestra. Histological and osteological evidence indicate that the new specimen  is not a fully growth adult. However, the different skull proportions and body sizes of Asiatyrannus and Qianzhousaurus, sugest that they occupied different ecological niches, with Qianzhousaurus as the apex predator.

References:

Zheng, W., Jin, X., Xie, J. et al. The first deep-snouted tyrannosaur from Upper Cretaceous Ganzhou City of southeastern China. Sci Rep 14, 16276 (2024). https://doi.org/10.1038/s41598-024-66278-5 (1)

Foster, W., Brusatte, S. L., Carr, T. D., Williamson, T. E., Yi, L., & Lü, J. (2021). The cranial anatomy of the long-snouted tyrannosaurid dinosaur Qianzhousaurus sinensis from the Upper Cretaceous of China. Journal of Vertebrate Paleontology, 41(4). https://doi.org/10.1080/02724634.2021.1999251