Jehol Biota

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 and 158 million years ago, in the Middle to Late Jurassic.

[4] Later, Ji et al. argued that the key indicator of the Jehol biota are the index fossil fishes Peipiaosteus and Lycoptera.

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.

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.

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.

The Jehol Biota is particularly noteworthy for the very high diversity of fossils and the very large numbers of individuals of each species that have been recovered.

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

The leaves and needles of the trees show adaptations to a dry season, but some of the ferns and mosses are types that grow in very wet habitats.