The Early Cretaceous Jehol Biota sensu stricto contains numerous well-preserved fossils. The tyrannosauroid Sinotyrannus kazuoensis Ji, Ji & Zhang, 2009 (Fig. 1) is the largest-known theropod and likely apex predator within the Jehol Biota. S. kazuoensiswas originally interpreted as closely related to the Late Cretaceous Tyrannosauridae Osborn 1906, but later studies proposed it within theProceratosauridae Rauhut, Milner & Moore-Fay, 2010 as a basal tyrannosauroid. S. kazuoensis was unearthed from near the base of the Jiufotang Formation in the Huoguoshan outcrop of the Kazuo Basin. Clarifying its age aids understanding of the evolution of early-diverging tyrannosauroids in Laurasia and the spatiotemporal distribution of the late Jehol Biota in western Liaoning.
Recently, Professors Daran Zheng and Haichun Zhang at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, collaborating with Professor Lijun Zhang from the Hainan Tropical Ocean University, and researchers from the Beipiao Natural Resources Bureau, Institute of Geology, Chinese Academy of Geological Sciences, Kazuo Natural Resources Bureau, The University of Hong Kong, and National Taiwan University, conducted a detailed geological investigation of the Lower Cretaceous succession in the Huaguoshan outcrop. Two radioisotopic zircon U-Pb methods, LA-ICP-MS and SIMS, were conducted on a tuffaceous siltstone collected from the bone bed to provide a robust age for exploring the proceratosaurid evolution. By reviewing the ages and precious fossiliferous “beds” of the Jiufotang Formation, this study discusses the spatiotemporal distribution of the late Jehol Biota and potential drivers of its distribution (Fig. 2). The results were published online in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
Two zircon U-Pb dating methods consistently provide an age of ca. 124.0 Ma (lower Barremian) for the bone bed. This indicates thatS. kazuoensis represents the last appearance of the putative proceratosaurids, which were widespread across Laurasia from the Bathonian through the early Barremian. S. kazuoensis exceeds the body size of other putative proceratosaurids and suggests a trend toward larger size among some early-diverging tyrannosauroids (Fig. 3). This age provides the first lower constraint for the Jiufotang Formation in the Kazuo Basin, and is nearly coeval with the basal age (ca. 124.4 Ma) of the Jiufotang Formation in the Chaoyang Basin, but ca. 2 Myr older than that of the Yixian Basin (Fig. 4), indicating temporal asynchrony among basins. Compared with the distribution pattern of the late Jehol Biota concentrated in the western basins of western Liaoning, we propose that the late Jehol Biota dispersed eastward with a more restricted distribution in the eastern basins. The spatiotemporal pattern of the late Jehol Biota may have been at least partly triggered by the eastward retreat of the subducting paleo-Pacific plate.
Notably, several “beds” yield a cluster of ages near ca. 121 Ma: Shangheshou (121.258 ± 0.043 Ma), Xiyingzi (121.272 ± 0.040 Ma), and Xiaotaizi (121.539 ± 0.085 Ma) “beds”. These similar ages challenge the view that these beds belong to different members of the Jiufotang Formation, indicating that the late Jehol Biota may have peaked around ca. 121 Ma, when the majority of the late Jehol Biota (i.e., diverse dinosaurs, birds, mammals, pterosaurs, choristoderes, fish, invertebrates and plants) appeared. The peak time of the late Jehol Biota is at least 4 Myr younger than that (ca. 125.8 Ma for the Jianshangou Bed of the Yixian Formation) of the middle Jehol Biota.
This research was supported by the Application of the Chaoyang Jehol Biota Fossil Site for World Natural Heritage and the National Natural Science Foundation of China.
Reference: Zheng, D.R.*, Zhang, L.J.*, Qu, Z., Wu, B., Ji, S.A., Zhang, S.D., Xia, Y.Y., Fang, R., Zhang, H.C., Chang, S.-C., 2026. U-Pb calibrating the evolution of the tyrannosauroid theropod Sinotyrannus kazuoensis Ji, Ji & Zhang, 2009, with a review on the spatiotemporal distribution of the late Jehol Biota in western Liaoning, China. Palaeogeography, Palaeoclimatology, Palaeoecology, 704, 114323. DOI: 10.1016/j.palaeo.2026.114323
Fig. 1 Spatiotemporal distribution of the late Jehol Biota in western Liaoning.
Fig. 2 Skull of Sinotyrannus kazuoensis Ji, Ji & Zhang, 2009
Fig. 3 Cladogram and spatiotemporal distribution of the early-diverging tyrannosauroids
Fig. 4 Correlation of the Jiufotang Formation in western Liaoning
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