The
Jehol Biota includes all the living organisms – the
ecosystem – of northeastern China between 133 to 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 Japanese occupation of the former
Rehe Province.