Tiaojishan Formation
Using Argon–argon dating, Wang and colleagues in 2005 dated part of the Tiaojishan Formation to about 160 million years ago, the beginning of the Oxfordian stage, the first stage of the Upper Jurassic epoch. In 2006, a study by Liu and colleagues used U-Pb zircon dating to conclude that the Tiaojishan Formation correlates with the Daohugou Beds, and the complete chronological range of this shared biota dates to between 168 and 164/152 Ma ago. A subsequent study, published in 2008, refined the age range of the formation further, finding that the lower boundary of the Tiaojishan was formed 165 Ma ago, and the upper boundary somewhere between 156 and 153 Ma ago. Based on the plant life present in the Tiaojishan Formation, Wang Yongdong and colleagues determined that the climate in Liaoning during the mid Jurassic would have been subtropical to temperate, warm and humid. Beautifully preserved fossils of dinosaurs, pterosaurs, salamanders, insects, arachnids and other invertebrates, conifers, ginkgoes, cycads, horsetails, and ferns, and even the earliest known gliding mammal ("Volaticotherium") have been discovered in these rocks. These organisms were part of the Daohugou Biota, which formed the local ecosystem of that Jurassic time. The tuffaceous composition of some rock layers show that this was a volcanic area, occasionally experiencing heavy ashfalls from eruptions. The landscape then was dominated by mountain streams and deep lakes surrounded by forests of gymnosperm trees. Some authors have concluded that the Daohugou Biota is an early stage of the Jehol Biota, while recent work has demonstrated that the two are distinct. The forests of the Daohugou biota grew in a humid, warm - temperate climate and were dominated by gymnosperm trees. There were ginkgopsids like "Ginkoites", "Ginkgo", "Baiera", "Czekanowskia", and "Phoenicopsis". There were also conifers like "Pityophyllum", "Rhipidiocladus", "Elatocladus", "Schizolepis", and "Podozamites". Also, Lycopsids like "Lycopodites" and "Sellaginellities", horsetails (Sphenopsida) like "Equisetum", cycads like "Anomozamites", and ferns (Filicopsida) like "Todites" and "Coniopteris". The following orders are represented in the formation; Ephemeroptera, Odonata, Plecoptera, Blattodea, Orthoptera, Hemiptera, Neuroptera, Coleoptera, Hymenoptera, and Diptera.
An indeterminate aeshnoid (insect) species is known from Liaoning. Survey based on Wang "et al." 2006 unless otherwise noted. Cycad-like plants, the most abundant plant group in the formation. 27 species in 11 genera. Prehistoric ginkgo trees, common, with 11 species present in 6 genera. Conifers, 5 species present in 4 genera. Leptosporangiate ferns, represented by 17 species in 8 genera, are the second most abundant plant type in the formation. Cycads, fairly diverse, with 10 species present in 2 genera.
Fauna
It is known for its exceptionally preserved fossils, including those of plants, insects and vertebrates.