| Qianzhousaurus | |
|---|---|
 | |
| Holotype skull | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Tyrannosauridae |
| Subfamily: | †Tyrannosaurinae |
| Tribe: | †Alioramini |
| Genus: | †Qianzhousaurus Lüet al.,2014 |
| Type species | |
| †Qianzhousaurus sinensis Lüet al., 2014 | |
Qianzhousaurus (meaning "Qianzhou lizard") is agenus oftyrannosauriddinosaur that lived inAsia during theMaastrichtian age of theLate Cretaceous period. There is currently only one species named, thetype speciesQianzhousaurus sinensis, which is a member of the tribeAlioramini and most closely related toAlioramus, the only other known alioramin.
The holotype specimen,GM F10004, was unearthed in southernChina,Ganzhou, at theNanxiong Formation in the summer of 2010 during the construction of an industrial park and it was first described bypaleontologistsJunchang Lü,Laiping Yi,Stephen L. Brusatte,Ling Yang,Hua Li andLiu Chen in the journalNature Communications in 2014. The genus is known from a partial sub-adult individual consisting of a nearly complete skull with the lower jaws missing allteeth (lost during fossilization), 9cervical vertebrae, 3dorsal vertebrae, 18 caudal vertebrae, bothscapulocoracoids, partialilia, and the left leg compromising thefemur,tibia,fibula,astragalus withcalcaneum, andmetatarsals III and IV. Thegeneric name,Qianzhousaurus, is in reference to Qianzhou (the older name of Ganzhou) where the remains were discovered, and thespecific name,sinensis, is derived from theGreek word Σῖναι (sin, sino, sinai) in reference to China.[1] Thefossil remains were discovered by workmen at a construction site near the city of Ganzhou, who then took them to a local museum.[2]
Lead authorLü Junchang from the Institute of Geology,Chinese Academy of Geological Sciences stated that "the new discovery is very important. Along withAlioramus from Mongolia, it shows that the long-snouted tyrannosaurids were widely distributed in Asia. Although we are only starting to learn about them, the long-snouted tyrannosaurs were apparently one of the main groups of predatory dinosaurs in Asia."[3] The existence of long-snouted tyrannosaurs was previously suspected due to other inconclusive fossil finds which could be explained as the juveniles of short-snouted species, but co-author Stephen L. Brusatte from theUniversity of Edinburgh reveals that the find "tells us pretty unequivocally that these long-snouted tyrannosaurs were a real thing. They were a different breed, living right at the end of the age of dinosaurs."[4]
Qianzhousaurus was a medium-sizedtyrannosaurid estimated at 6.3 m (20.7 ft) in length, 2 m (6.6 ft) in hip height and 750–757 kg (1,653–1,669 lb) in body mass.[1][5] Higher estimates suggest that it could have reached a maximum length between 7.5 and 9 metres (24.6 and 29.5 ft).[6] Thetaxon can be differentiated from other tyrannosaurids in having a highly narrowedpremaxilla, a pneumatic opening on the upper extension of themaxilla, and the lack of a vertical ridge-like structure on the lateral surface of theilium.[1]
Unlike more "traditional" tyrannosaurids, which had prominent deep-set jaws and thick teeth,Qianzhousaurus had a particularly elongated snout, with (when restored) narrow teeth. The holotype specimen is notably larger and more mature than the holotypes of both species ofAlioramus. However, since somesutures between the cervical and dorsal vertebrae are partially fused, the holotype seems to have come from an immature animal, likely a sub-adult.Qianzhousaurus was a long-legged animal with a 70 cm (28 in) longfemur and 76 cm (30 in) longtibia.[1]
The discovery ofQianzhousaurus led to a new branch of thetyrannosaur family being named, consisting of the long-snoutedQ. sinensis and the two known species ofAlioramus. This clade, named the tribeAlioramini, had an uncertain placement relative to other members of the tyrannosaur branch in the initial analysis that discovered it. The primaryphylogenetic analysis found Alioramini to be closer toTyrannosaurus than toAlbertosaurus, and therefore a member of the groupTyrannosaurinae. However, a second analysis in the same paper found it to be located outside of the clade includingAlbertosaurinae andTyrannosaurinae, and therefore the sister group ofTyrannosauridae. Below is the first analysis found by the authors:[1]
Thomas D. Carr with colleagues in 2017 regardedQianzhousaurus as a junior synonym ofAlioramus based on the reasoning that they were recovered assister species in their phylogenetic analysis. Despite their argument, they indicated that this synonymy does not necessarily constitute a taxonomic reevaluation of the Alioramini.[7] However, Foster and his colleagues conducted a detailed redescription of the holotype skull ofQianzhousaurus in 2022, finding several traits unique to this genus, hence supporting the separation ofAlioramus andQianzhousaurus.[8]
A 2022 study of the three known species of the two known alioramin genera,Qianzhousaurus andAlioramus (A. altai andA. remotus), respectively, suggests that the variation seen between the various species is consistent with the growth trends seen in other tyrannosaurid genera, though specimens that could constitute a full growth series from infant to adult for each species have not been recovered for any of these theropods. Of these,Qianzhousaurus represents the largest and most mature animal found within Alioramini thus far and represents the adult level of maturity. One part of the growth series across all specimens in this study was discovered to remain unique to alioramin tyrannosaurs, this being the rugose process of the jugal starts out small and conical, but becomes massive and indistinct as the animals grow. This same study also suggests Alioramins did not undergo a secondary metamorphosis from slender juveniles to robust adults like other tyrannosaurs, but maintained a unique physiology better suited to pursuit of fast prey.[8]
In 2022, Foster and his colleagues indicated thatQianzhousaurus and other alioramins, due to their slim and gracile build, may have been hunters of small, particularly fast and nimble prey, which would have allowed these tyrannosaurids to avoid competition with larger, robust relatives that specialized in killing larger animals. The long and delicate snouts of alioramins likeAlioramus andQianzhousaurus may have prevented them from killing the same prey that juvenile and adult tyrannosaurids likeTarbosaurus hunted, though these larger tyrannosaurs themselves may have hunted alioramins as prey on occasion. Alioramins may also have had a different feeding strategy than other tyrannosaurids, as their jaws seem to have been weaker than those of the larger genera and even juveniles of larger species have proportionately higher bite forces than alioramins of equivalent size. Furthermore, Alioramini seemingly remained confined to Asia, suggesting that some factor prevented them from colonizing the better-sampled fossil deposits from North America. What this may be remains a mystery at the present moment.[8]
Studies of the skulls of various tyrannosauroids in 2024 suggest thatQianzhousaurus and other alioramin tyrannosaurs experienced lower stresses when biting and feeding. Additional evidence in the same study suggests thatQianzhousaurus did not utilize the "puncture-and-pull" feeding method utilized by other, larger genera of tyrannosaurids.[9]
Qianzhousaurus is known from theNanxiong Formation, which has been dated to the latestMaastrichtian age of theLate Cretaceous period, about 66.7 ± 0.3million years ago based onargon–argon dating.[10] The mainlithology of this formation is composed by purplishmudstones andsiltstones, deposited in afloodplain environment under a relatively warm,humid subtropical climate.[11]Oviraptorideggs are particularly common across the formation with numerous well-preserved egg clutches or nests,[12] as well as nesting individuals.[13][14][15] The Nanxiong Formation has been noted for its abundantoviraptorosaur genera. It is most likely that, given the poorstratigraphic analysis of the formation, the extremely large oviraptorosaur diversity of this formation was temporally separated.[16] The presence of the smaller and more robustly built tyrannosaurineAsiatyrannus also suggests thatQianzhousaurus was filling the role of apex predator in the formation's ecosystem, withAsiatyrannus occupying a different niche and hunting different prey than its larger relative.[17]
Other vertebrates in the Nanxiong Formation include numerous oviraptorosaurs, such asBanji,Ganzhousaurus,Corythoraptor,Nankangia,Huanansaurus,Shixinggia, orTongtianlong;[16][18] the hadrosauridMicrohadrosaurus (may benomen dubium);[19] the sauropodGannansaurus;[20] the therizinosauridNanshiungosaurus;[21] the crocodilianJiangxisuchus;[22] the squamatesChianghsia andTianyusaurus;[23] and the turtlesJiangxichelys andNanhsiungchelys.[11]
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