Vertebrate assemblages of the Jurassic Yanliao Biota and the Early Cretaceous Jehol Biota: Comparisons and implications

Abstract

Although both the Yanliao and Jehol vertebrate assemblages are known for exceptional preservation of feathered dinosaurs, mammals, pterosaurs, lizards, salamanders, and fish, the Early Cretaceous Jehol Biota also contains birds, choristoderes, frogs, and turtles that are currently lacking in the Jurassic Yanliao Biota. The vertebrate assemblages of the Yanliao and Jehol biotas are very distinct from each other, with the salamander Liaoxitriton being the sole unquestionably shared taxon on generic level. Both assemblages contain mainly stem relatives of major clades of extant vertebrates, with all genera and species extinct. Crown group taxa are restricted to some fishes, salamanders, frogs, and turtles.In addition to its much greater taxonomic diversity, the Jehol vertebrate assemblage also shows a greater body size variation among dinosaurs, pterosaurs, and mammals (three major vertebrate groups shared by the two biotas); however, members of these groups are generally small in the Yanliao Biota. The Jehol aquatic vertebrates also show a much greater diversity, characterized by many large-sized forms such as acipenseriforms and choristoderes, possibly indicating growing and more expanded ecological adaptations of the Jehol vertebrates.The relatively greater biodiversity of pterosaurs in the Yanliao Biota as compared to that in the Jehol Biota was due possibly to the lack of birds as a competitor then. Birds in the Jehol Biota had occupied much of the similar ecological niches (forest, lakes etc.) with more sophisticated and refined flight capability.The Yanliao dinosaurs that were dominated by maniraptorans are either paravians or closely related species, possibly indicating that northeastern China could be an origin center of the earliest birds, consistent with the previous hypothesis that this area was probably also the origin and diversification center for many other biological groups.The flourishing time of the Jehol Biota (125 Ma) appears to be coincident with the peak of the destruction of the North China Craton, and the flourishing time of the Yanliao Biota (160 Ma) is coincident with the initiation time of the destruction of the North China Craton or the beginning of the subduction of the Paleo-Pacific plate underneath the Asian continent that resulted a series of tectonic and palaeogeographic and palaeoenvironmental changes, confirming the co-evolution between the two biotas and their geological and palaeoenvironmental background. The frequent volcanic activities during the formation of both the Yanliao and Jehol biotas not only provided much nutrient to the lakes, but also were critical for the exceptional soft tissue preservation of the two lagerstätten.The cold temperature or the fluctuation of temperature during the Middle Jurassic–Late Jurassic transition might be related to the first appearance of feathered dinosaurs and haired pterosaurs. The cold interval during the Early Cretaceous Jehol Biota could possibly partially explain the presence of many feathered dinosaurs including some large-sized theropods.