The generic name comes from Jiayuguan City (formerly called "Xiong Guan" or "grand pass") and the Mandarin word "long" which means dragon.

[2] Xiongguanlong was discovered in the upper member of the Xiagou Formation of the Xinminbao Group at a locality nicknamed the "White Ghost Castle" which is in the Yujingzi Basin of Gansu, China.

It was initially discovered in the early 2000s, but it was not described until 2009 when a paper was published in the Proceedings of the Royal Society by the paleontologists Daqing Li, Mark Norell, Ke-Qin Gao, Nathan D. Smith, and Peter J.

[2] In its initial description, and in numerous publications since, it has been remarked as a noteworthy transitional species between the basal tyrannosauroids of the Jurassic period and the derived tyrannosaurids of the Late Cretaceous.

They used a regression analysis based on the work of P. Christiansen and R.A. Fariña to estimate its mass at approximately 270 kilograms (600 lb).

[2] Autapomorphies of the genus given by the authors in its description include the following: a very elongate pre-orbital region, a basicranium that is wider than it is long, the absence of pneumatic foramina on the lateral edge of the nasal bone, a ridge on the middle of the premaxillary teeth, and lateral processes in the axial neural spines.

The parietal bones are fused and possess a short and concave sagittal crest, which served as attachment sites for the bite muscles.

The postorbital bone is much anteroposteriorally elongated and vertical in relation to the infratemporal fenestra, which resembles advanced tyrannosaurids.

[2] The preserved post-cranial bones of Xiongguanlong include the entire series of cervical and dorsal vertebrae, part of the ilium and a femur.

They also possess a pair of pneumatic foramina on the vertebrae, which is unlike the condition seen in Albertosaurus, Daspletosaurus, and Tyrannosaurus.

This clade was diagnosed, and Xiongguanlong was excluded from it, by the following synapomorphies: rugosities on the top of the nasal bone and subcondylar recesses in the brain case.

[14] Guanlong Proceratosaurus Dilong Eotyrannus Xiongguanlong Appalachiosaurus Tyrannosauridae In 2013, a team of scientists led by Mark Loewen, which included Philip J. Currie and Scott D. Sampson, published a description of the tyrannosaurid genus Lythronax which also contained a re-evaluation of the related taxon Teratophoneus.

The most recent comprehensive phylogenetic analysis of Tyrannosauroidea was conducted by Darren Naish and Andrea Cau in their monograph about the osteology and phylogeny of Eotyrannus in 2022.

Naish and Cau suggest that the uniqueness of this analysis is an artifact of the lack of extensive sampling of megaraptorans in previous analyses.

[6] Juratyrant Tugulusaurus Tanycolagreus Coelurus Proceratosauridae Xiongguanlong Megaraptora Information regarding the evolution of tyrannosauroids has been relatively obscure since the group's naming in the early 20th-century.

There are several basal taxa which are known from the Middle Jurassic (e.g. Guanlong, Kileskus, Proceratosaurus), a handful of more intermediate forms in the Early Cretaceous (e.g. Yutyrannus, Dilong, Eotyrannus), and numerous megafaunal hypercarnivorous genera from the Campanian and Maastrichtian (e.g. Tyrannosaurus, Albertosaurus, Daspletosaurus).

The landmass of Laurasia was in the process of breaking up during the Early Cretaceous, meaning the Atlantic Ocean was much more narrow.

This is corroborated by the emergence of animals in North America with an apparent recent Asian ancestry including Eolambia and Microvenator.

[9] However, some authors believe that the fossil record from this part of the Cretaceous is too poor to make any concrete inferences as to the nature of tyrannosauroid evolution or dispersal.

[2] Similar taxa like Suskityrannus are believed to have been mid-sized predators in their ecosystem, but no large carnivorous theropods have yet been found in the same area,[16] which may indicate that there was an evolutionary transition going on during the late Aptian of China.

Today, this region is part of the Gobi Desert, but during the Early Cretaceous, it was a much less arid environment, and it was probably on or near the coast of the Tethys Sea.

[17] The fauna present in the Xinminbao Group are hypothesized to be the ecological successors to the much more famous Jehol biota, which existed in China during the Barremian and the early Aptian.

[1] Xiongguanlong is known to have coexisted with the large ornithomimosaur, Beishanlong,[2] which was found at the same locality,[3] and some museum mounts depict a predator-prey relationship between these animals.