Jehol Biota

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The **Jehol biota**  includes all the living organisms – the ecosystem – of northeastern China between 133 to 120 million years ago (mya). This is the Lower Cretaceous ecosystem which left fossils in the **Yixian** Formation, some 125–121 mya, and the **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 semi-arid, and mesic conditions. The climate was temperate. The Jehol ecosystem was interrupted at times by ash eruptions from volcanoes to the west. The word *Jehol* was the name given during the Japanese occupation of North-East China, 1933–1946.

The Jehol biota is noteworthy for the many different fossils and the large numbers of individuals of each species that have been recovered.

## Diversity 
The biota includes many species that were previously known only from the Upper Jurassic or earlier. These include the dinosaur *Sinosauropteryx*, and the pterosaur *Dendrorhynchoides''. There was even a primitive protomammal – a tritylodont therapsid – from Lower Cretaceous Japan. Tritylodonts were previously thought to have gone extinct in the Middle Jurassic. The biota also has the earliest and most basal (primitive) known members of groups which spread all around the world by the Upper Cretaceous, including neoceratopsians, therizinosaurs, tyrannosaurs, and oviraptors.

The Jehol biota has produced fossils of plant mega- and microfossils, including the earliest angiosperms, charophytes and dinocysts, snails (gastropods), clams (bivalves), superabundant aquatic arthropods called conchostracans, ostracods, shrimps, insects, spiders, fish, frogs and salamanders, turtles, choristoderes, lizards (squamata), pterosaurs, and dinosaurs including dinobirds, the largest mammals known from the Mesozoic, and a great diversity of birds including the earliest advanced birds, and the smallest and largest birds known from the Mesozoic.

### Yixian Formation 
A geological formation in Liaoning, N.E. China. It has outstanding preservation. The deposits of siliclastic (SiO2) sediment alternate with basalt. It was first recognised by the Japanese when they occupied Manchuria ('Jehol'). The formation was laid down 125–121 million years ago. It contains the famous *Confuciusornis* beds.

*Sinodelphys*, the earliest metatherian mammal, was found in this formation.

### Jiufotang Formation 
The **Jiufotang Formation** is a Lower Cretaceous geological formation in Liaoning. It has yielded fossils of feathered dinosaurs, primitive birds, pterosaurs, and other organisms. 

The exact age of the Jiufotang has been debated for years, with estimates ranging from the Upper Jurassic to the Lower Cretaceous. Argon radiometry confirmed a Lower Cretaceous age for the site, 120.3 +/-0.7 million years ago. Fossils of *Microraptor* and *Jeholornis* are from the Jiufotang.

### Huajiying Formation 
Lower Cretaceous, but exact dates uncertain. This is probably the earliest of the Jehol biota lagerstätte sites. Contains sedimentary members interspersed with volcanic ash. Contains birds, dinosaurs and fish.

## References