Daohugou Beds

The Daohugou layers (Chinese道 虎 沟 化石 层, Pinyin Dàohǔgōu huàshícéng ) are a very fossil -rich sedimentary sequence in the northeast of the People 's Republic of China to the south of Chifeng; they were named after the village Daohugou the community Shantou (山头 乡) in a circle Ningcheng the southeastern edge of Ningcheng Basin (宁 城 盆地). The layers consist mainly of gray, finely laminated sandy mudstones, are interposed in the tuffhaltige documents; the deposit occurred in lakes probably during the period of upper Dogger to lower Malm, ie in the period 168-152 Ma BP ( Bathonian - Kimmeridgian ).

Fossil content

The Daohugou layers contain well-preserved fossils of dinosaurs, pterodactyls, salamanders, insects and other invertebrates, as well as plant remains of conifers, ginkgo, cycads, horsetails and ferns - even the first known Gleitsäuger Volaticotherium and the aquatic primitive mammal Castorocauda were discovered here. All of these organisms together form the Daohugou biota (道 虎 沟 生物 群, Dàohǔgōu Shengwu Qun ), a specific law for the ecosystem of Northeast Asia. The Tuffgehalt individual layers suggests a volcanic area, went down into the volcanic eruptions sometimes quite violent rain of ashes. The former landscape seems to have been probably influenced by mountain streams and deep lakes, surrounded by Gymnospermienwäldern. Earlier it was believed that the Daohugou biota represent an early form of the Jehol biota; recent studies have shown, however, that the two biota are different.

Stratigraphy

The Daohugou layers have a sometimes quite complicated geological structure, they are folded and disrupted by volcanic activity in their layer bandage. According to Liu et al (2006 ) provides that the Daohugou biota but not only in the Daohugou layers, but also in the Tiaojishan and in the Lanqi lineup. They were also able to show that the Jiulongshan Formation is older ( Dogger ) and the Tuchengzi Formation (土城 子 组, Tǔchéngzǐ zǔ ) younger ( Malm ). In 2006, field investigations published long-range expansion of the layers illustrated - from western Liaoning up to the circle of Nincheng in Inner Mongolia ( Nei Mongol, Nei Měnggǔ ).

Dating

The exact age of the Daohugou layers is still controversial. There have already been applied several different dating methods, however, led to very conflicting results. So the fossil age was awarded the Dogger from up in the Lower Cretaceous ranges ( period 169-122 Ma BP).

Scientific dating methods

In their work, from 2004 He found, inter alia, for Daohugou layers under a crete zisches age, only a few million years older than the overlying Yixian Formation with the Jehol biota. The starting point here was the radiometric age determination of a Tufflage in the Daohugou layers. A subsequent work of Gao Ren & denied this result because in their opinion, erroneous operation. Instead, they advocate a (using index fossils ) biostratigraphically certain age from the Middle Jurassic.

One in 2006 by Wang et al published study came to the conclusion that the Tiaojishan formation age of 164 -159 Ma BP owns ( Callovian - Oxfordian ) and the Daohugou layers under and not superimposed. In contrast to the previous study by Gao and Ren, they recognized a broad agreement in the fossil content of the Daohugou layers with the Yixian Formation:

" Vertebrates such as Liaoxitriton, Jeholopterus and feathered Manoraptoria show a great similarity with their counterparts from the Yixian Formation Despite the lack of Lycoptera -. A the Jehol Group characterizing fish species - are the vertebrates the Daohugou layers in composition most likely with the biota of the Lower Cretaceous Jehol group comparable. "

Wang et al concluded that the Daohugou biota are likely to represent a very early development stage of the Jehol Biota and therefore " as the Yixian Formation are to be expected from the Jehol Group vulkanosedimentären the same cycle." In the same year published Liu et al their dating of Daohugou layers that had been carried out by means of the U-Pb method; examined here was embedded in a volcanic deposits Leitfossilhorizont with salamanders. Liu et al found for the two volcanogenic layers of an age of 164 and 158 Ma BP ( Callovian and Oxfordian ).

The Daohugou biota

The forests of the Daohugou biota grown under warm and humid to humid temperate climatic conditions and were dominated by gymnosperms. But among them were also found Ginkgophyta such as Ginkoites, ginkgo, Baiera, Czekanowskia and Phoenicopsis. The conifers were represented by Pityophyllum, Rhipidiocladus, Elatocladus, Schizolepis and Podozamites. In addition Bärlapppflanzen thrived as Lycopodites and Sellaginellities, horsetails ( Equisetopsida ) with Equisetum, cycads such as Anomozamites and ferns ( Filicopsida ) as Todites and Coniopteris.

Fauna

• Liaoxitriton

• Epidendrosaurus / Scansoriopteryx?
• Pedopenna

• Jeholopterus
• Pterorhynchus

• Ephemeroptera Mesoneta

• Castorocauda lutrasimilis

• Antiquum Volaticotherium