Daohugou Beds
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The Daohugou Beds are a series of fossil-bearing rock deposits located in northeastern China, south of Chifeng, around Daohugou village of Ningcheng county. The rocks are grey, finely bedded, lacustrine, sandy mudstones mixed with tuffaceous mudstones. The beds probably date from between the late Middle Jurassic (168 million years ago) and early Late Jurassic Period (164-152 million years ago).[1] Beautifully preserved fossils of dinosaurs, pterosaurs, salamanders, insects, other invertebrates, conifers, ginkgoes, cycads, horsetails, and ferns, and even the earliest known gliding mammal (Volaticotherium) and an aquatic protomammal (Castorocauda) have been discovered in these rocks. These organisms were part of the of the Daohugou Biota, which was the 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. [2] 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 geology of the Daohugou Beds is confusing because it is complex and does not conform; meaning that elements and layers of rock of different ages are mixed up together by folding and by volcanic activity. Liu et al. (2006) concluded that the rocks that bear the Daohugou Biota include the Tiaojishan, Lanqi, and Daohugou formations. They demonstrated that the Jiulongshan Formation is older (Middle Jurassic), and that the Tuchengzi Formation is younger (Late Jurassic). Fieldwork published in 2006 has also found that the beds are consistent over a large area; from western Liaoning into Ningcheng county of Inner Mongolia (Nei Mongol).[3] The age of the Daohugou Beds has been debated, and a number of studies, using different methodology, have reached conflicting conclusions. Various papers have placed the fossils here as being anywhere from the Middle Jurassic period (169 million years ago) to the Early Cretaceous period (122 ma) [4].
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[edit] Scientific Studies
A 2004 study by He et al. on the age of the Daohugou Beds found them to be Early Cretaceous, probably only a few million years older than the overlying Jehol beds of the Yixian Formation.[5] The 2004 study primarily used radiometric dating of a tuff within the Daohugou Beds to determine its age. However, a subsequent study by Gao & Ren took issue with the He et al. study. Gao and Ren criticize He et al. for not including enough specifics and detail in their paper, and also take issue with their radiometric dating of the Daohugou tuff. The tuff, Gao and Ren argue, contains crystals with a variety of diverse radiometric ages, some up to a billion years old, so using dates from only a few of these crystals cannot determine the overall age of the deposits. Gao and Ren go on to defend a Middle Jurassic age for the beds based on biostratigraphy (the use of index fossils) and the bed's relationship to a layer that is known to mark the Middle Jurassic-Late Jurassic boundary. [6]
Another study, published in 2006 by Wang et al., found that the Tiaojishan Formation (159-164 million years old, Middle-early Late Jurassic in age) underlies, rather than overlies, the Daohugou Beds. Unlike the earlier study by Gao and Ren, Wang et al. found an overall similarity between the fossil animals found in the Daohugou Beds and those from the Yixian Formation. The authors stated that
"vertebrate fossils such as Liaoxitriton, Jeholopterus and feathered maniraptorans show much resemblance to those of the Yixian Formation. In other words, despite the absence of Lycoptera, a typical fish of the Jehol Biota, the Daohugou vertebrate assemblage is closer to that of the Early Cretaceous Jehol Biota than to any other biota."
Wang et al. concluded that the Daohugou probably represents the earliest evolutionary stages of the Jehol Biota, and that it "belongs to the same cycle of volcanism and sedimentation as the Yixian Formation of the Jehol Group."[3] Later in 2006, Liu et al. published their own study of the age of the Daohugou beds, this time using Zircon U-Pb dtating on the volcanic rocks overlying and underlying salamander-bearing layers (salamanders are often used as index fossils). Liu et al. found that the beds formed between 164-158 million years ago, in the Middle to Late Jurassic.[7]
[edit] The Daohugou Biota
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.[8]
[edit] Fauna
[edit] Amphibians:
- Liaoxitriton
[edit] Dinosaurs:
[edit] Insects:
- Mesoneta
- Ephemeroptera
- Odonata
- Plecoptera
- Blattodea
- Orthoptera
- Heteroptera
- Homoptera
- Neuroptera
- Coleoptera
- Hymenoptera
- Diptera
[edit] Mammaliaformes:
[edit] Mammals:
[edit] Pterosaurs:
[edit] References
- ^ Liu, Yongqing, Liu, Yanxue, Ji, Shu'an, Yang, Zhiqing (2006) "U-Pb zircon age for the Daohugou Biota at Ningcheng of Inner Mongolia and comments on related issues" Chinese Science Bulletin Vol.51 no. 21, pp. 2634-2644. DOI 10.1007/s11434-006-2165-2
- ^ Tan, Jingjing, Ren, Dong, Shih, Chungkun "NEW CUPEDIDS FROM THE MIDDLE JURASSIC OF INNER MONGOLIA, CHINA (COLEOPTERA: ARCHOSTEMATA)" Annales Zoologici 2006, 56(1):1-6z
- ^ a b Wang, X., Zhou, Z., He, H., Jin, F., Wang, Y., Zhang, J., Wang, Y., Xu, X. & Zhang, F. (2005). "Stratigraphy and age of the Daohugou Bed in Ningcheng, Inner Mongolia." Chinese Science Bulletin, 50(20): 2369-2376.
- ^ Ren, D. et al. (2002). "On the biostratigraphy of the Jurassic fossil beds at Daohugou near Ningcheng, Inner Mongolia." Geol. Bull. China 21, 584-591.
- ^ He, H., Wang, X., Zhou, Z., Zhu, R., Jin, F., Wang, F., Ding, X. and Boven, A. (2004). "(^40)Ar/(^39)Ar dating of ignimbrite from Inner Mongolia, northeastern China, indicates a post-Middle Jurassic age for the overlying Daohugou Beds." Geophysical Research Letters 31, L20609.
- ^ Gao, K., and Ren, D. (2006). "Radiometric dating of ignimbrite from Inner Mongolia provides no indication of a post-Middle Jurassic age for the Daohugou Beds." Acta Geologica Sinica English Edition, 80(1): 42-45 (February 2006)
- ^ Liu, Y., Liu, Y., and Zhang, H. (2006). "LA-ICPMS zircon U-Pb dating in the Jurassic Daohugou Beds and correlative strata in Ningcheng of Inner Mongolia." Acta Geologica Sinica (English Edition), 80(5): 733-742.
- ^ Zhang, Kuiyan, Yang, Ding, Ren, Dong. (2006) "The first snipe fly (Diptera: Rhagionidae) from the Middle Jurassic of Inner Mongolia, China" Zootaxa 1134:51-57(2006)z
[edit] See also
- Yixian Formation
- Jehol Biota
- List of fossil sites (with link directory)
