| Asiatyrannus | |
|---|---|
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| Skeletal diagram and fossil elements of theAsiatyrannus holotype | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Superfamily: | †Tyrannosauroidea |
| Family: | †Tyrannosauridae |
| Subfamily: | †Tyrannosaurinae |
| Genus: | †Asiatyrannus Zheng et al.,2024 |
| Species: | †A. xui |
| Binomial name | |
| †Asiatyrannus xui Zheng et al., 2024 | |
Asiatyrannus (meaning "Asian tyrant") is anextinct genus oftyrannosaurine theropod dinosaurs from theLate CretaceousNanxiong Formation of China. The genus contains asingle species,A. xui, known from a single specimen consisting of a skull and partial postcranial skeleton.Asiatyrannus is notable for its deep-snouted skull and small body size, in contrast to the gracile snout and larger size of the contemporaryQianzhousaurus. It represents the southernmost record of an Asian tyrannosaurid.[2]
TheAsiatyrannusholotype specimen,ZMNH M30360, was discovered in September 2017 in sediments of theNanxiong Formation nearShahe Town inNankang District ofGanzhou City,Jiangxi Province, China. The specimen consists of most of anarticulated skull in addition to disarticulated parts of the postcrania, comprising much of the right and left legs and several caudal vertebrae.[2]
In 2024, Zheng et al.describedAsiatyrannus xui as a new genus and species of tyrannosaurid based on these fossil remains. Thegeneric name,Asiatyrannus, combines "Asia", the continent of origin, with theLatinised Greek suffix "-tyrannus", meaning "tyrant" or "king". Thespecific name,xui, honors prominent dinosaur researcherXu Xing and his contributions to paleontological research in China.[2]
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Asiatyrannus is a small-medium-sized tyrannosaur. Its nearly complete skull measures 47.5 centimetres (18.7 in) long, and it has an estimated body length of 3.5–4 metres (11–13 ft).[2] In comparison, the mature skull of the closely relatedNanuqsaurus from thePrince Creek Formation of North America is estimated at 60–70 centimetres (24–28 in).[3] SinceNanuqsaurus likely had a body size similar toAlbertosaurus,Asiatyrannus may represent the only tyrannosaurine in this smaller size class.[4] TheAsiatyrannus holotype is about half the length of the contemporaryQianzhousaurus. However, the holotype ofAsiatyrannus with the estimated age of at least 13 years old did not belong to a skeletally mature individual, and as such, it would have been larger when fully grown. Nevertheless, it had probably passed through the life stages of most rapid growth, and other tyrannosaurines in similar growth stages are more than twice as large.[2]
In their 2025 description of the early-divergingtyrannosauroidKhankhuuluu, Voris and colleagues noted several problematic aspects of the original interpretations of theAsiatyrannus holotype. The researchers claimed that thehistology performed and lines of arrested growth (LAGs) identified by Zheng and colleagues the year prior did not support the specimen as having passed the rapid-growth phase, meaning it can not be regarded as mature. Voris et al. further noted six traits initially regarded as diagnostic toAsiatyrannus that it shares withTarbosaurus specimens or other tyrannosaurines (three of which are present only in immature specimens).[5]
Using a modified version of thephylogenetic dataset of Carr et al. (2017),[6] Zheng et al. recoveredAsiatyrannus as aderivedtyrannosaurine member of theTyrannosauridae, in apolytomy with the North AmericanNanuqsaurus. These results are displayed in thecladogram below:[2]
Voris et al. (2025) reidentifiedAsiatyrannus as a juvenile tyrannosaurine sharing at least foursynapomorphies with a late-diverging clade comprisingAlioramini andTyrannosaurini. They postulated that largeTyrannosaurus-like teeth previously identified from the Nanxiong Formation may in fact belong to a mature form of the same species asAsiatyrannus. The researchers concluded thatAsiatyrannus is most parsimoniously regarded as a juvenile member of the Tyrannosaurini that is difficult to distinguish—but is potentially distinct—fromTarbosaurus. The size and proportions of the skull are almost identical to those of juvenile specimens of this genus.[5]
Asiatyrannus is known from theNanxiong Formation, which dates to the end of theMaastrichtian age of the lateCretaceous period. Large teeth indicate the presence of a large tyrannosaurid in the ecosystem that may actually be a mature form ofAsiatyrannus.[7][5] Many other dinosaurs have been described from layers of the formation, including the fellow tyrannosauridQianzhousaurus.[2] Othertheropods includetherizinosaurids (Nanshiungosaurus)[8] and manyoviraptorids (Banji,Corythoraptor,Ganzhousaurus,Huanansaurus,Jiangxisaurus,Nankangia,Shixinggia, andTongtianlong).[9][10] Thesomphospondylan sauropodsGannansaurus andJiangxititan are also known from the formation.[11] The formation's non-dinosaurian fauna includescrocodilians (Jiangxisuchus),[12]lizards (Chianghsia andTianyusaurus),[13] and turtles (Jiangxichelys).[14]
The MongolianNemegt Formation contains a similar fauna, including the large tyrannosaurineTarbosaurus, two species of thealioraminAlioramus, and smallertyrannosauroids such asBagaraatan.[15]
We note that other Prince Creek Formation tyrannosaurid material in the UAMES collection do not support the assertion that Nanuqsaurus is a diminutive, small-bodied tyrannosaur. Rather, adult-sized teeth and isolated postcranial elements suggest an adult body size more closely comparable to other North American tyrannosaurid taxa, such as Albertosaurus sarcophagus.
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