Jehol Biota

The Jehol Biota (pinyin: Rèhé Qún) includes all the living organisms – the ecosystem – of northeastern China between 133 and 120 million years ago. This is the Lower Cretaceous ecosystem which left fossils in the Yixian Formation and Jiufotang Formation. It is also believed to have left fossils in the Sinuiju series of North Korea. The ecosystem in the Lower Cretaceous was dominated by wetlands and numerous lakes (not rivers, deltas, or marine habitats). Rainfall was seasonal, alternating between semiarid, and mesic conditions. The climate was temperate. The Jehol ecosystem was interrupted periodically by ash eruptions from volcanoes to the west. The word 'Jehol' now said to refer to a mythical land of the past in Chinese folklore, was the name given during the Japanese occupation of the former Rehe Province. The Jehol Biota (pinyin: Rèhé Qún) includes all the living organisms – the ecosystem – of northeastern China between 133 and 120 million years ago. This is the Lower Cretaceous ecosystem which left fossils in the Yixian Formation and Jiufotang Formation. It is also believed to have left fossils in the Sinuiju series of North Korea. The ecosystem in the Lower Cretaceous was dominated by wetlands and numerous lakes (not rivers, deltas, or marine habitats). Rainfall was seasonal, alternating between semiarid, and mesic conditions. The climate was temperate. The Jehol ecosystem was interrupted periodically by ash eruptions from volcanoes to the west. The word 'Jehol' now said to refer to a mythical land of the past in Chinese folklore, was the name given during the Japanese occupation of the former Rehe Province. Some scientists have argued that the Jehol Biota evolved directly from the preceding Daohugou Biota without any strongly defined division. However, the absolute dating of the Daohugou beds has been the subject of divergent opinion: in 2006, Wang et al. found an overall similarity between the fossil animals found in the Daohugou Beds and the 'Jehol Biota' from the Yixian Formation. Several other research teams, including Liu et al., have attempted to disprove this reasoning by using Zircon U-Pb dating on the volcanic rocks overlying and underlying salamander-bearing layers (salamanders are often used as index fossils). Liu et al. found that the Daohugou beds formed between 164–158 million years ago, in the Middle to Late Jurassic. Later, Ji et al. argued that the key indicator of the Jehol biota are the index fossil fishes Peipiaosteus and Lycoptera. Under this definition, the earliest evolutionary stage of the Jehol Biota is represented by the Huajiying Formation. The Yixian and Jiufotang Formations are called Lagerstätte, meaning that they have exceptionally good conditions for fossil preservation. The fossils are numerous, but also very well preserved – often including articulated skeletons, soft tissues, colour patterns, stomach contents, and twigs with leaves and flowers still attached. Zhonghe Zhou et al.. (2003) deduced two things from this. The first is that the land animals and plants were washed into the lakes very gently, or were already in the lakes when they died. They do not show the damage seen in fossils formed by large floods. Secondly, volcanic ash is commonly inter-bedded with lake sediments, and ashfalls seem to have quickly buried the fossilized organisms, creating anoxic conditions around them and preventing scavenging. Zhonghe Zhou et al. (2003) noted that, for the Early Cretaceous, the Jehol Biota includes a mixture of advanced and ancient species, and also of species found only in the Jehol and others found all around the world. It is possible that northeast Asia was isolated for part of the Jurassic by the 'Turgai Sea' which separated Europe from Asia at the time. The Jehol Biota includes many species that were previously known only from the Late Jurassic or earlier. These 'relict' species include the compsognathid dinosaur Sinosauropteryx and the anurognathid pterosaur Dendrorhynchoides. It also has the earliest and most primitive known members of groups that spread all around the world by the Late Cretaceous, including neoceratopsians, therizinosaurs, tyrannosaurs, and oviraptorids. Northeastern Asia may have been the center of diversification of these dinosaur groups. The Jehol Biota was not entirely isolated, however, because it also includes animals which were known from all around the world at the same time, including discoglossid frogs, paramacellodid lizards, multituberculate mammals, enantiornithine birds, ctenochasmatid pterosaurs, iguanodontian ornithopods, titanosauriform sauropods, nodosaurid ankylosaurs, and dromaeosaurid theropods.