Daohugou Beds

Daohugou Beds Stratigraphic range: Middle-Late Jurassic
Type	Geological formation
Unit of	Tiaojishan Formation?, Haifanggou Formation?
Underlies	Tuchengzi Formation
Overlies	Tiaojishan Formation?, Haifanggou Formation?
Lithology
Primary	Mudstone
Location
Region	Inner Mongolia & Liaoning
Country	China

The Daohugou Beds are a series of fossil-bearing rock deposits located in northeastern China, with the type locality around Daohugou village of Ningcheng County south of Chifeng, Inner Mongolia, but extending into southwest Liaoning. The rocks are grey, finely bedded, lacustrine, sandy mudstones mixed with tuffaceous mudstones formed from the intermittent ashfall of volcanic events. 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]

Geology

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 erosion and by volcanic activity. Liu et al. (2006) concluded that the rocks that bear the Daohugou Biota also include the Tiaojishan and Lanqi Formations. They demonstrated that the Jiulongshan Formation is older (Middle Jurassic), and that the Tuchengzi Formation is younger (Late Jurassic). However, many other researchers consider the Daohugou to be a part of the Jiulongshan Formation itself.^[2]

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 methodologies, 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]

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] However, a later study by Ji et al. argued that the key indicator of the Jehol biota are the index fossils Peipiaosteus and Lycoptera. Under this definition, the earliest evolutionary stage of the Jehol Biota is represented by the Huajiying Formation, and the Daohugou Formation is excluded due to the absence of Lycoptera fossils.^[7] Later in 2006, Liu et al. published their own study of the age of the Daohugou beds, this time 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 beds formed between 164-158 million years ago, in the Middle to Late Jurassic.^[8]

Fauna of the Daohugou Beds

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 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.^[9] 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.^[10]

Amphibians

Color key Taxon Reclassified taxon Taxon falsely reported as present Discredited taxon Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative data are in small text; crossed out data are discredited.

Amphibians of the Daohugou Beds
Genus	Species	State	Abundance	Notes
Jeholotriton	J. paradoxus			Wang, 2000
Chunerpeton	C. tianyiensis			Gao & Shubin, 2003
Liaoxitriton	L. daohugouensis			Wang, 2004
Pangerpeton	P. sinensis			Wang & Evans, 2006

Arthropods

The following orders are represented in the formation; Ephemeroptera, Odonata, Plecoptera, Blattodea, Orthoptera, Heteroptera, Homoptera, Neuroptera, Coleoptera, Hymenoptera, and Diptera.

Color key Taxon Reclassified taxon Taxon falsely reported as present Discredited taxon Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative data are in small text; crossed out data are discredited.

Arthropods of the Daohugou Beds
Genus	Species	State	Abundance	Notes
Ahirmoneura	A. neimengguensis[11]	Inner Mongolia		A tangle-veined fly
Archirhagio	A. striatus[12]			Archisargid flies
	A. zhangi[13]	Inner Mongolia
Archisargus	A. spurivenius[12]			Archisargid flies
	A. strigatus[12]
Calosargus	C. (Calosargus) antiquus[12]			Archisargid flies
	C. (C.) bellus[12]
	C. (C.) daohugouensis[12]
	C. (C.) hani[12]
	C. (C.) tenuicellulatus[12]
	C. (C.) validus[12]
	C. (Pterosargus) sinicus[12]	Inner Mongolia
Daohugocorixa	D. vulcanica[12]			A water boatman
Fuyous	F. gregarious[12]			A mayfly
Eoplectreurys	E. gertschi[14]		1 Specimen	A plectreurid spider
Jurassinemestrinus	J. orientalis[12]	Inner Mongolia		A Nemestrinoid fly
Meoslova	M. daohugouensis[12]			An archisargid fly
Mostovskisargus	M. portentosus[12]	Inner Mongolia		Archisargid flies
	M. signatus[12]	Inner Mongolia
Nephila	N. jurassica[2]		1 Specimen	A golden silk orb-weaver spider
Shantous	S. lacustris[12]			A mayfly

Dinosaurs

Color key Taxon Reclassified taxon Taxon falsely reported as present Discredited taxon Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative data are in small text; crossed out data are discredited.

Dinosaurs (including birds) of the Daohugou Beds
Genus	Species	State	Abundance	Notes	Images
Epidendrosaurus	E. ninchengensis	Inner Mongolia	One specimen	A scansoriopterygid probably synonymous with Scansoriopteryx heilmanni	Scansoriopteryx
Epidexipteryx	E. hui	Inner Mongolia	One specimen	A scansoriopterygid
Pedopenna	P. daohugouensis	Inner Mongolia	One specimen	A primitive paravian
Scansoriopteryx	S. heilmanni		One or two specimens	A scansoriopterygid. Exact provenance of type specimen unknown, most likely from the Daohugou Beds[3]

Lepidosaurs

Color key Taxon Reclassified taxon Taxon falsely reported as present Discredited taxon Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative data are in small text; crossed out data are discredited.

Lepidosaurs (lizards and relatives) of the Daohugou Beds
Genus	Species	State	Abundance	Notes	Images
Unnamed lizard[15]		Inner Mongolia	One specimen	A new lizard with relatively short forelimbs
Unnamed lizard[15]		Inner Mongolia	One specimen	A new lizard with long hind limbs and a narrow body

Pterosaurs

Pterosaurs of the Daohugou Beds
Genus	Species	State	Abundance	Notes	Images
Jeholopterus	J. ninchengensis	Inner Mongolia	Several specimens[16][17]	An anurognathid	Wukongopterus
Pterorhynchus	P. wellnhoferi	Inner Mongolia	One specimen[16]	A rhamphorhynchid
Wukongopterus	W. lii	Liaoning	One specimen[18]	A rhamphorhycnhoid

Synapsids

Synapsids of the Daohugou Beds
Genus	Species	State	Abundance	Notes	Images
Castorocauda	C. lutrasimilis	Inner Mongolia	One specimen[19]	Aquatic docodont	Castorocauda
Volaticotherium	V. antiquum	Inner Mongolia	One specimen	A gliding mammal

References

1. ^ Liu, Y., Liu, Y., Ji, S., and Yang, Z. (2006) "U-Pb zircon age for the Daohugou Biota at Ningcheng of Inner Mongolia and comments on related issues" Chinese Science Bulletin, 51(21): 2634-2644. doi:10.1007/s11434-006-2165-2
2. ^ ^{a b} Selden, P.A., Shih, C.-K. and Ren, D. (2011). "A golden orb-weaver spider (Araneae: Nephilidae: Nephila) from the Middle Jurassic of China." Biology Letters, doi:10.1098/rsbl.2011.0228
3. ^ ^{a b c} 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.
4. ^ 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.
5. ^ 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.
6. ^ 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)
7. ^ Jin, F., Zhang, F.C., Li, Z.H., Zhang, J.Y., Li, C. and Zhou, Z.H. (2008). "On the horizon of Protopteryx and the early vertebrate fossil assemblages of the Jehol Biota." Chinese Science Bulletin, 53(18): 2820-2827.
8. ^ 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.
9. ^ 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
10. ^ 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
11. ^ Zhang, K., Yang, D., Ren, D. and Ge, F. (2008). "New Middle Jurassic tangle−veined flies from Inner Mongolia, China." Acta Palaeontologica Polonica, 53(1): 161-164.
12. ^ ^{a b c d e f g h i j k l m n o p q} Zhang, J.F. (2010). "Records of bizarre Jurassic brachycerans in the Daohugou biota, China (Diptera, Brachycera, Archisargidae and Rhagionemestriidae)." Palaeontology, 53(2): 307–317. doi:10.1111/j.1475-4983.2010.00934.x
13. ^ Zhang, K., Li., J., Yang, D. and Ren, D. (2009). "A new species of Archirhagio Rohdendorf, 1938 from the Middle Jurassic of Inner Mongolia of China (Diptera: Archisargidae)." Zootaxa, 1984: 61–65.
14. ^ Selden, P.A. and Huang, D. (2010). "The oldest haplogyne spider (Araneae: Plectreuridae), from the Middle Jurassic of China." Naturwissenschaften, doi:10.1007/s00114-010-0649-z PMID 20140419
15. ^ ^{a b} Evans, S.E. and Wang, Y. (2010). "A new lizard (Reptilia: Squamata) with exquisite preservation of soft tissue from the Lower Cretaceous of Inner Mongolia, China." Journal of Systematic Palaeontology, 8(1), 81–95.
16. ^ ^{a b} Wang, X. and Zhou, Z. (2006). "Pterosaur assemblages of the Jehol Biota and their implication for the Early Cretaceous pterosaur radiation."Geological Journal, 41: 405-418.
17. ^ Lü, J. and Ji, Q. (2006). "Preliminary results of a phylogenetic analysis of the pterosaurs from western Liaoning and surrounding areas." J. Paleont. Soc. Korea, 22(1): 239-261.
18. ^ Wang, X., Kellner, A.W.A., Jiang, S. and Meng, X. (2009). "An unusual long-tailed pterosaur with elongated neck from western Liaoning of China." Annals of the Brazilian Academy of Sciences, 81(4): 793-812.
19. ^ Meng, J., Hu, Y., Li, C. and Wang, Y. (2006). "The mammal fauna in the Early Cretaceous Jehol Biota: implications for diversity and biology of Mesozoic mammals."Geological Journal, 41: 439-463.

See also

• Yixian Formation
• Jehol Biota
• List of fossil sites (with link directory)