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The Yanliao Biota is notable for producing rare and well-preserved Jurassic vertebrate fossils. Many discoveries in the Bawanggou section, northern Hebei Province have greatly enhanced our knowledge of important vertebrate fossils from the Yanliao Biota, including an arboreal euharamiyidan mammal, maniraptoran theropods, salamanders and pterosaurs. However, lacking of precise dating for the sediments bearing these fossils in the Bawanggou section hampered further understanding of the evolution of this biota. Here we report a chronology based on secondary ion mass spectrometry (SIMS) U-Pb zircon analyses from the Tiaojishan Formation bearing the Yanliao Biota in the Bawanggou section. Three bentonite layers dated to 159.0 ± 1.1 Ma, 159.5 ± 0.8 Ma, and 159.8 ± 0.8 Ma, respectively, were found to be interstratified with the fossil-bearing layer in this area. These data place the Yanliao Biota from Qinglong in the Oxfordian Stage of the Upper Jurassic and provide stringent constraints on vertebrates discovered in the Bawanggou section. Previous biostratigraphic studies and our geochronology show that fossil assemblage in the Bawanggou section is coeval with the Linglongta Biota (late Yanliao Biota) preserved in the Daxishan section (western Liaoning Province). [ABSTRACT FROM AUTHOR]

The Lower Cretaceous Jiufotang Formation in western Liaoning Province, northeastern China contains important vertebrate fossils of the late Jehol Biota, e.g., the four-winged non-avian dinosaur Microraptor. This formation documents the late phase of the Jehol Biota, producing the most abundant fossil records of the Mesozoic birds. However, the precise age constraints on the fossiliferous layers of this formation remain scarce and chronological consensus of this formation has not been reached, limiting our understanding of the evolutionary history of the Jehol Biota and its time-spatial distribution. Here we present secondary ion mass spectrometry (SIMS) U-Pb zircon analysis results of four tuff samples interbedded within the Jehol fossil-bearing layers from the Jiufotang Formation outcrops at the Sanmendian and Xiaotaizi sections in the Jianchang Basin, western Liaoning. Stratigraphic correlation between two outcrop sections is achieved by combining lithostratigraphic, biostratigraphic, and SIMS U-Pb zircon dating results. One tuff bed SMD17-1 closed to the boundary of the Yixian/Jiufotang formations from the Sanmendian section yielded an age of 122.0 ± 0.9 Ma, and three tuff beds XTZ17-1, XTZ17-2, and XTZ17-3 from the Xiaotaizi section dated to 118.9 ± 0.8 Ma, 118.8 ± 0.6 Ma, and 118.6 ± 1.1 Ma, respectively. These ages suggest that the Jiufotang Formation in Jianchang Basin was deposited at ca. 122.0–118.9 Ma, the latest Barremian–Aptian stage of the Lower Cretaceous and provides stringent constraints on the Mesozoic vertebrates discovered in the Jianchang Basin. Furthermore, the late Jehol Biota documents in the Jiufotang Formation has been placed between ~123 and ~119 Ma based on our new chronology and previous radiometric dates. It is critical to evaluate the evolutionary history of various important Mesozoic taxa discovered from the Jehol Biota and explore the patterns and modes of major vertebrate lineages documented in this interval. • • We report a new chronology from the Jiufotang Formation in Jianchang Basin, NE China. • • The fossiliferous horizons have precisely constrained to 122.0–118.9 Ma. • • Age calibration for the diversification of mammals and birds of late Jehol Biota. • • Updated age of the Jiufortang Formation for Palaeobiology Database (paleodb.org /). [ABSTRACT FROM AUTHOR]