Evrim Yazgin
Cosmos science journalist
Meet Asiatyrannus xui, the latest addition to the tyrannosaur family.
A. xui was discovered in 2017 at the Nanxiong Formation near Ganzhou City in southeastern China.
It lived about 69 million years ago, toward the end of the Cretaceous period (145 – 66 million years ago) only a few million years before the mass extinction event which saw the end of the age of dinosaurs.
The creature is a distant cousin of Tyrannosaurus rex in the Tyrannosaurine subgroup. Asiatyrannus, however, was unlike T. rex in one very obvious way: it was comparatively tiny.
While T. rex could reach sizes of up to 13 metres long and 9 tonnes (and possibly even bigger), A. xui would have reached only 3.5–4m in length. Even among Asian tyrannosaurs, it was a relative tiddler, with the largest, Tarbosaurus bataar, reaching about 10m in length and 5t.
The new species is known from a single specimen with a near-complete skull and other skeletal fragments. The skull fossil is 47.5cm long.
It is the southern-most tyrannosaur found in Asia.
The fossils are described, and the new species named, in a paper published in the journal Scientific Reports.
A. xui would have been about half the size of other tyrannosaurs such Qianzhousaurus sinensis which was also found in the Nanxiong Formation in Jiangxi province. Q. sinensis has a longer, more slender snout than that of Asiatyrannus which has a deep, robust snout
“The different skull proportions and body sizes suggest that Asiatyrannus and Qianzhousaurus likely had different feeding strategies and occupied different ecological niches,” the authors write.
Tyrannosaurs evolved about 165 million years ago in the middle of the Jurassic period (201–145 million years ago). The paper’s authors write: “They became the apex predators in their respective ecologies during the final 20 million years of the Cretaceous in Asia and western North America.”
More than 30 species of tyrannosaur are known from around the world.
The fossil record of Asia shows a “gap” in the Late Cretaceous between small, often omnivorous oviraptorids (bird-like dinosaurs with toothless beaks shaped like those of parrots), and the large-bodied tyrannosaurs.
Previously, palaeontologists suggested that “the ‘missing middle-sized’ niches” were filled “by juvenile and subadults of tyrannosaurid species,” the authors write.
“In southeastern China, the Qianzhousaurus undoubtedly occupied the apex predator, but Asiatyrannus might represent the small to medium-sized theropod [two-legged dinosaur] niche between the large-bodied Qianzhousaurus and the diversified small-bodied oviraptorosaurs.”
