Doushantuo Formation

The Doushantuo Formation (formerly transcribed as Toushantuo or Toushantou,<ref name="Lee1924"/> from Template:Lang-zh) is a geological formation in western Hubei, eastern Guizhou, southern Shaanxi, central Jiangxi, and other localities in China.<ref>Template:Cite journal</ref> It is known for the fossil Lagerstätten in Zigui in Hubei, Xiuning in Anhui, and Weng'an in Guizhou, as one of the oldest beds to contain minutely preserved microfossils, phosphatic fossils that are so characteristic <ref>Template:Cite journal</ref> they have given their name to "Doushantuo type preservation". The formation, whose deposits date back to the Early and Middle Ediacaran,<ref>Template:Cite journal</ref><ref name="Jiang2011" /> is of particular interest because it covers the poorly understood interval of time between the end of the Cryogenian geological period and the more familiar fauna of the Late Ediacaran Avalon explosion,<ref>Template:Cite journal</ref> as well as due to its microfossils' potential utility as biostratigraphical markers.<ref>Template:Cite journal</ref> Taken as a whole, the Doushantuo Formation ranges from about 635 Ma (million years ago) at its base to about 551 Ma at its top, with the most fossiliferous layer predating by perhaps five Ma the earliest of the 'classical' Ediacaran faunas from Mistaken Point on the Avalon Peninsula of Newfoundland, and recording conditions up to a good forty to fifty million years before the Cambrian explosion at the beginning of the Phanerozoic.

Sedimentology

The whole sequence sits on an unconformity with the underlying Liantuo formation, which is free of fossils, an unconformity usually being interpreted as a period of erosion. On that unconformity lie tillites of the Nantuo formation - cemented glacial till formed of glacial deposits of cobbles and gravel laid down at the end of the Marinoan glaciation (also known as Varangian glaciation, this is the second and last of a series of very extensive glaciations during a period called the Cryogenian—named because 'Snowball Earth' conditions at the time). This latest Cryogenian glacial level is tentatively dated ca 654 (660 ± 5) — 635 Ma (million years ago).

The Doushantuo formation itself has three layers representing aquatic sediments that formed as sea levels rose with the melting of worldwide glaciation. Biomarkers indicate highly saline conditions, such as might be found in a lagoon, low oxygen levels, and very little sediment that had been washed off land surfaces.

The richest finds (the Lagerstätte itself) lie at the bottom of the middle stratum, with a date about 570 Ma, thus from some time after the great Gaskiers glaciation of [585 ± 1 - 582.1 ± 0.4 Ma].

Fossils

Template:Further Doushantuo fossils are all aquatic, microscopic, and preserved to a great degree of detail. The latter two characteristics mean that the structure of the organisms that made them can be studied at the cellular level, and considerable insight has been gained into the embryonic and larval stages of many early creatures. One contentious claim is that many of the fossils show signs of bilateral symmetry, a common feature in many modern-day animals which is usually assumed to have evolved later, during the Cambrian Explosion. A nearly microscopic fossil animal, Vernanimalcula ("springtime micro-animal") was announced in October 2005, with the claim that it was the oldest known bilateral animal.<ref name=spring>Template:Cite journal</ref> However, the absence of adult forms of almost all animal types in the Doushantuo (there are microscopic adult sponges and corals) makes these claims difficult to prove: some argue that their lack suggests these finds are not larval and embryonic forms at all; supporters contend that some unidentified process "filtered out" all but the smallest forms from fossilization. An alternative interpretation suggests that it was created by non-biological rock-forming processes.<ref name="Bengtson2004">Template:Cite journal</ref> The team that discovered Vernanimalcula have defended their conclusion that it was an animal, pointing out that they found ten specimens (not illustrated) of the same size and configuration, and stating that non-biological processes would be very unlikely to produce so many specimens that were so alike.<ref name="ChenDefendVernanimalcula">Template:Cite journal</ref>

The discovery was made when the rich phosphate deposits were being mined, and was first reported in 1998. The finds offer direct evidence that confirms expectations that major evolutionary diversification of animals already had occurred before the onset of the Cambrian period, with its apparent 'explosion' of metazoan life-forms and, therefore, that more remote ancestral forms of the phyla recognizable in Cambrian macrofossils must have existed previously.Template:Citation needed

The documented biota now includes phosphatized microfossils of algae, multicellular thallophytes (seaweeds), acritarchs, ciliates,<ref>Template:The Rise and Fall of the Ediacaran Biota</ref> and cyanophytes, besides adult sponges and adult cnidarians (coelenterates; these may be early forms of tabulate corals (tetracorallians)).Template:Citation needed There also seem to be what scientists cautiously report as bilateral animal embryos, termed Parapandorina, and eggs (Megasphaera). Some of the possible animal embryos are in an early stage of cellular division (that was first interpreted as spores or algal cells), including eggs and embryos which are most probably of sponges or cnidarians, as well as adult sponges and a variety of adult cnidarians.

An alternative possibility is that the "embryos" and "eggs" are in fact fossils of giant sulfur bacteria resembling Thiomargarita, a bacterium so large that it is visible to the naked eye.<ref name=Bailey2007>Template:Cite journal</ref> The interpretation would also provide a mechanism for phosphatic fossilization through microbially mediated phosphate precipitation by the bacteria, which has been observed in modern environments. If dark spots in the fossil transpire to be fossilised nuclei - an unlikely claim<ref name="Schiffbauer2012">Template:Cite journal</ref> - this would refute the Thiomargarita hypothesis. That being said, recent comparisons of the Doushantuo fossils to modern decaying Thiomargarita and expired sea urchin embryos shows little similarity between the fossils and decaying bacterial cells.<ref>Template:Cite journal</ref>

Only about one-twentieth of the site's fossils have been excavated. The fossil beds are threatened by increasing intensity of phosphate mining operations in the area. A workshop led in protest by local paleontologists resulted in a temporary halt to the mining in 2017.<ref>Template:Cite news</ref>

Paleobiota

While here they are placed in the Doushantuo Formation, most of the algae are found in the Miaohe biota, which may instead belong to the lower part of the Dengying Formation.<ref>Template:Cite journal</ref>

Algae

Algae
Genus	Species	Higher taxon	Notes	Images
Anhuiphyton	A. lineatum	Eukaryota	Essentially identical to specimens from the Lantian Formation<ref name=algae/>
Anomalophyton	A. zhangzhongyingi	Eukaryota	Similar to Doushantuophyton, but branches less frequently<ref name=reassess/>
Baculiphyca	B. taeniata, B. brevistipitata	Eukaryota	Species differ in stipe length<ref name=miaohe/>
Beltanelliformis	B. brunsae	Cyanobacteria	Originally interpreted as a polypoid cnidarian<ref name=reassess/>	Beltanelliformis fossil from Ukraine
Crassitubus	C. costata	Cyanobacteria	Originally interpreted as a tubular animal,<ref name=tube/> before being reinterpreted as a cyanobacterium<ref name=not-meta/>
Cobios	C. rubro	Rhodophyta	Preserves evidence of multiple life stages<ref>Template:Cite journal</ref>
Doushantuophyton	D. lineare, D. rigidulum, D. quyuani, D. cometa, D. laticladus	Eukaryota	Relatively small and thin<ref name=miaohe/>
Enteromorphites	E. siniansis, E. magnus	Eukaryota	One of the larger "branching algae" from Doushantuo<ref name=miaohe/>
Gemmaphyton	G. taoyingensis	Eukaryota	Bears a very long stipe and round holdfast<ref name="algae">Template:Cite journal</ref>
Globusphyton	G. lineare	Eukaryota	Fairly unusual morphology suggests it likely crept along the seafloor<ref>Template:Cite journal</ref>
Glomulus	G. filamentum	Cyanobacteria	Resembles modern cyanobacteria like Microcoleus<ref name=miaohe/>
Gremiphyca	G. corymbiata	Rhodophyta	Likely a stem-rhodophyte,<ref>Template:Cite journal</ref> resembles coralline algae<ref name=mineralise/>
Grypania	G. spiralis	Eukaryota?	One of the most common large Proterozoic fossils<ref name=miaohe/>	Grypania fossils from the Negaunee Iron Formation in the USA
Jiuqunaoella	J. simplicis	Eukaryota	Resembles Grypania, but differs in presence of constrictions<ref name=miaohe/>
Jixiania	J. lineata	Eukaryota?	Also known from the Mesoproterozoic, probably a filamentous alga<ref name=micro/>
Konglingiphyton	K. erecta, K. laterale	Rhodophyta?	Likely a rhodophyte, a formerly separate genus ("Ramalga") was actually a specimen of this genus overlaid by one of Doushantuophyton<ref name=reassess/>
Latiortenuiphyton	L. robusta	Eukaryota	Has large vein-like structures in its thallus<ref name=algae/>
Liulingjitaenia	L. alloplecta	Eukaryota	Unusually consists of a set of braided filaments<ref name=miaohe/>
Longifuniculum	L. dissolutum	Eukaryota	Similar to Liulingjitaenia, but its filaments fray out at each end almost like a braided rope<ref name=miaohe/>
Maxiphyton	M. stipitatum	Eukaryota	Has an unusually thick stipe<ref name="miaohe">Template:Cite journal</ref>
Megaspirellus	M. houi	Eukaryota	Holotype reinterpreted as a coprolite due to sediment grains<ref name=miaohe/>
Miaohephyton	M. bifurcatum	Phaeophyta?	Fossils likely represent shed fragments from larger thalli<ref>Template:Cite journal</ref>
Paramecia	P. incognata	Corallinales?	Formerly interpreted as a marine lichen<ref name=mineralise/>
Paratetraphycus	P. gigantea	Bangiophyceae?	Resembles early developmental stages of the alga Porphyra<ref name=mineralise/>
Pseudodoushantuophyton	P. wenghuiensis	Eukaryota	Bears cluster-like filaments on its branches<ref name=algae/>
Quadratitubus	Q. orbigoniatus	Cyanobacteria	Originally interpreted as a tubular animal,<ref name=tube/> before being reinterpreted as a cyanobacterium<ref name=not-meta/>
Ramitubus	R. increscens, R. decrescens	Eukaryota	Originally interpreted as a tubular animal,<ref name="tube">Template:Cite journal</ref> then found to be an alga similar to Epiphyton<ref name=not-meta/>
Sinocylindra	S. linearis, S. yunnanensis	Eukaryota	Resembles the cyanobacteria Siphonophycus<ref name=miaohe/>	S. yunnanensis fossil from the Chengjiang biota
Sinocyclocyclicus	S. guizhouensis	Cyanobacteria	Formerly thought to be a larval or tube-dwelling metazoan alongside other tubular microfossils<ref name="not-meta">Template:Cite journal</ref><ref name="mineralise">Template:Cite journal</ref>
Siphonophycus	S. solidum, S. septatum, S. kestron, S. typicum, S. robustum<ref name=micro/>	Cyanobacteria	Relatively common cyanobacteria<ref name=reassess/>
Thallophyca	T. corrugata	Rhodophyta	Resembles the Solenoporaceae<ref name=mineralise/>
Thallophycoides	T. phloeatus	Eukaryota	May be a rhodophyte?<ref name=mineralise/>
Tongrenphyton	T. komma	Eukaryota	Has several filaments along its thallus, showing a clear eukaryotic affinity<ref name=algae/>
Vendotaenia	V. sp	Vendotaenid	Resembles specimens from the lower Cambrian<ref name=miaohe/>	Indeterminate vendotaenid fossil
Wengania	W. globosa, W. exquisita, W. minuta<ref>Template:Cite journal</ref>	Eukaryota	Resembles various algae in its parenchymatous structure, especially green algae<ref name=mineralise/>

Microorganisms

Microorganisms
Genus	Species	Higher taxon	Notes	Images
Aggregatosphaera	A. miaoheensis	Eukaryota?	Spheroidal cell clusters with similarities to algal cysts<ref name="reassess">Template:Cite journal</ref>
Annularidens	A. inconditus	Acritarch	Bears numerous hollow processes on its outer surface,<ref name="micro">Template:Cite journal</ref> giving it a gearwheel-like appearance in cross-section<ref name=spiky/>
Apodastoides	A. basileus	Acritarch	Bears processes with plugs at their base<ref name=mineralise/>
Appendisphaera	A. anguina, A. clava, A. grandis, A. fragilis, A. longispina, A. setosa, A. tabifica, A. tenuis, A. helicaea,<ref name=spiky/> A. brevispina, A. hemisphaerica<ref name=stego/>	Acritarch	Bears numerous long, flexible processes<ref name=micro/>
Archaeophycus	A. yunnanensis	Eukaryota?	Either a cyanobacteria or the early developmental stage of an alga<ref name=micro/>
Asterocapsoides	A. sinicus	Acritarch	Original holotype was damaged by the surrounding rock breaking<ref name=mineralise/>
Bacatisphaera	B. baokangensis	Acritarch	Bears large pimple-like processes<ref name="giant">Template:Cite journal</ref>
Baltisphaeridium	B. rigidum	Acritarch	Bears short, triangular processes<ref name="acritarch">Template:Cite journal</ref>
Bispinosphaera<ref name=stego/>	B. vacua	Acritarch	Bears two separate types of process; one is conical and hollow, the other is solid and hair-like<ref name=spiky/>
Botominella	B. lineata	Eukaryota?	Known from small trichome-like structures<ref name=micro/>
Castaneasphaera	C. speciosa	Acritarch	Resembles Phanerozoic "mazuelloids"<ref name=giant/>
Cavaspira	C. acuminata, C. basiconica	Acritarch	Bears short, conical processes<ref name=micro/>
Cerionopora	C. ordinata	Acritarch	May be a resting cyst of a multicellular alga<ref name=mineralise/>
Comasphaeridium	C. magnum	Acritarch	Bears long hair-like processes<ref name=acritarch/>
Crassimembrana	C. crispans, C. multitunica	Acritarch	Bears a thick vesicle wall<ref name="spiky">Template:Cite journal</ref>
Cyanonema	C. attenuatum	Cyanobacteria	Similar to forms from the Bitter Springs formation<ref name=stego/>
Cymatiosphaeroides	C. forabilatus, C. yinii<ref name=acritarch/>	Acritarch	Similar to Membranosphaera, bears cylindrical processes with pointed tips<ref name=micro/>
Dicrospinasphaera	D. zhangii	Acritarch	Bears thin, branching processes<ref name=acritarch/>
Distosphaera	D. jinguadunensis, D. speciosa<ref name=mineralise/>	Acritarch	Bears two layers of cylindrical processes<ref name=spiky/>
Doushantuonema	D. peatii	Cyanobacteria	Earliest reported cyanobacteria from the formation<ref>Template:Cite journal</ref>
Duospinosphaera	D. shennongjiaensis, D. biformis	Acritarch	Bears two layers of processes; an inner cylindrical one likened to hanging icicles and a larger conical one on the outer wall<ref name=micro/>
Echinosphaeridium	E. maximum	Acritarch	Formerly placed in Ericiasphaera due to a misinterpretation of the spines as solid<ref name=mineralise/>
Eotylotopalla	E. apophysa, E. dactylos, E. delicata<ref name=mineralise/>	Acritarch	Formerly placed within Timanisphaera<ref name=micro/>
Ericiasphaera	E. fibrila, E. magna, E. rigida?, E. densispina,<ref name=stego/> E. sparsa<ref name=mineralise/>	Acritarch	Bears dense cylindrical processes,<ref name=micro/> badly preserved acritarchs likely belonging to this genus were misinterpreted as ciliates<ref>Template:Cite journal</ref>
Goniosphaeridium	G. acuminatum, G. conoideum, G. cratum	Acritarch	Similar to Baltisphaeridium<ref name=mineralise/>
Granitunica	G. mcfaddenae	Acritarch	Differs from other sphaeromorph acritarchs in its granular wall<ref name=stego/>
Hocosphaeridium	H. dilatatum, H. scaberfacium	Acritarch	Bears numerous hooked processes<ref name=micro/>
Knollisphaeridium	K. maximum, K. coniformum, K. denticulatum, K. longilatum, K. obtusum, K. parvum<ref name=stego/>	Acritarch	Bears conical processes with a long filament-like tip<ref name=micro/>
Leiosphaeridia	L. tenuissima, L. crassa, L. minutissima<ref name=micro/>	Acritarch	Incredibly abundant<ref name=stego/>
Megasphaera	M. inornata	Protista	Thought represent an animal egg, then revealed to likely be an encysting protist<ref>Template:Cite journal</ref>
Meghystricosphaeridium	M. chadianensis, M?. densum, M. gracilentum, M. perfectum, M. magnificum, M. wenganensis<ref name=acritarch/>	Acritarch	Somewhat unclear which species belong to this genus<ref name=mineralise/>
Mengeosphaera	M. angusta?, M. chadianensis, M. constricta, M. gracilis, M. mamma, M. minima, M. stegosauriformis, M. bellula, M. cuspidata, M. grandispina, M. latibasis, M. spicata, M. spinula, M. triangula, M. uniformis, M. membranifera<ref>Template:Cite journal</ref>	Acritarch	The species M. stegosauriformis is named after the dinosaur Stegosaurus, due to the acritarch's processes resembling the dinosaur's plates in shape<ref name="stego">Template:Cite journal</ref>
Obruchevella	O. minor	Cyanobacteria	Relatively rare<ref name=micro/>
Oscillatoriopsis	O. amadeus, O. longa, O. obtusa, O. majuscula<ref name=micro/>	Cyanobacteria	Common cyanobacterial genus<ref name=stego/>
Osculosphaera	O. arcelliformis, O. hyalina, O. membranifera	Acritarch	Resembles arcellinids<ref name=stego/>
Papillomembrana	P. compta	Acritarch	Formerly placed within Dasycladales<ref name=mineralise/>
Pustulisphaera	P. membranacea	Acritarch	Bears three wall layers, with the middle one bearing pimple-like processes<ref name=mineralise/>
Salome	S. hubeiensis	Cyanobacteria	A fossil identified as a "microburrow" was placed in this genus before being reidentified as an oblique section of a tubular fossil<ref name=stego/>
Sarcinophycus	S. radiatus, S. papilloformis	Eukaryota?	Only known from Doushantuo, consists of bundles of sarcinoid cell packets<ref name=micro/>
Schizofusa	S. zangwenlongii	Acritarch	Similar to Leiosphaeridia<ref name=stego/>
Sinosphaera	S. asteriformis, S. rupina<ref name=mineralise/>	Acritarch	Bears small conical spines and a few larger ones<ref name=stego/>
Symphysosphaera	S. basimembrana	Acritarch	Similar to Eosphaera, but larger<ref name=stego/>
Tanarium	T. acus, T. conoideum, T. elegans, T. longitubulare, T. minimum, T. obesum, T. pilosiusculum, T. pycnacanthum, T. varium	Acritarch	Spine shapes vary from small and triangular to long and needle-like<ref name=stego/>
Tianzhushania	T. spinosa	Acritarch	Bears a many-layered wall with spines penetrating through it<ref name=mineralise/>
Urasphaera	U. fungiformis, U. nupta	Acritarch	Bears mushroom-shaped spines, hence the specific name fungiformis<ref name=stego/>
Variomargosphaeridium	V. floridum	Acritarch	Bears processes which branch at their tips<ref name=stego/>
Vulcanosphaera	V. phacelosa	Acritarch	Bears bundled hair-like processes<ref name=acritarch/>
Weissiella	W. grandistella	Acritarch	Doushantuo fossils resemble Russian specimens, but are smaller<ref name=stego/>
Xenosphaera	X. liantuoensis	Acritarch	Bears extremely thin processes, which have a tendency to not preserve<ref name=stego/>
Yushengia	Y. ramispina	Acritarch	Resembles Weissiella, but has longer spines<ref name=stego/>

Miscellaneous taxa

Miscellaneous taxa
Genus	Species	Higher taxon	Notes	Images
Cucullus	C. fraudulentus	incertae sedis	Originally interpreted as a sponge, then reinterpreted as a microbialite<ref>Template:Cite journal</ref>
Paragraptobranca	P. curvus	incertae sedis	Shares features with both graptolites and macroalgae<ref name=algae/>
Calyptrina	C. striata	Annelida?	Almost certainly a metazoan<ref name=reassess/>	Calyptrina reconstruction
Eoandromeda	E. octobrachiata	Ctenophora?	Originally interpreted as the adult stage of various embryos,<ref>Template:Cite journal</ref> then as a pelagic discoid ctenophore,<ref>Template:Cite journal</ref> then an umbrella-shaped demersal form<ref>Template:Cite journal</ref>	Artist restoration of the "discoid ctenophore" hypothesis
Eocyathispongia	E. qiania	Porifera	Earliest likely sponge fossil<ref>Template:Cite journal</ref>	Reconstruction of Eocyathispongia
Linbotulitaenia	L. globosa	Metazoa	Likely a trace fossil of a wriggling mucus-covered animal, possibly from Wenghuiia<ref name=algae/>
Protoconites	P. minor	Cnidaria?	Likely a cnidarian-grade organism<ref>Template:Cite journal</ref> similar to Cambrorhytium<ref name=reassess/>
Sinospongia	S. chenjunyuani, S. typica	Porifera?	May also be a vermiform alga like the Huainan biota<ref name=reassess/>
Trilobozoa indet.	Unapplicable	Metazoa	Known from an undescribed triradial fossil<ref>Template:Cite journal</ref>
Vernanimalcula	V. guizhouensis	Bilateria?	Originally interpreted as a bilaterian,<ref name=spring/> then found to be more likely an indeterminate acritarch,<ref name=Bengtson2004/> then again found to be a likely bilaterian<ref>Template:Cite journal</ref><ref name=ChenDefendVernanimalcula/>
Wenghuiia	W. jiangkouensis	Annelida?	Putatively the earliest known annelid (and also the earliest known bilaterian), even though it already seems very derived<ref>Template:Cite journal</ref>

Palaeogeography

The formation was laid down on a carbonate shelf, whose rim enclosed a lagoon between tidal flats on the shore, and the deeper ocean. This lagoon was periodically anoxic or euxinic (containing hydrogen sulfide); variations in the chemistry in the lagoon can be detected in isotopic and elemental abundance cycles in the rock and possibly contributed to the fossil preservation.<ref name="Jiang2011">Template:Cite journal</ref>

Geochemistry

The most recent Doushantuo rocks show a sharp decrease in the ¹³C/¹²C carbon isotope ratio. Since this change appears to be worldwide but its timing does not match that of any other known major event such as a mass extinction, it may represent "possible feedback relationships between evolutionary innovation and seawater chemistry" in which metazoans (multi-celled organisms) removed carbon from the water, which increased the concentration of oxygen, and the increased oxygen level made possible the evolution of new metazoans.<ref name="CondonZhuBowring2005UPbAgesDoushantuo">Template:Cite journal</ref>

See also

• Phosphatic fossilization

References

• Template:Cite journal
• Knoll, A. H., 2003. Life on a Young Planet. Princeton Univ. Press.
• Template:Cite journal

External links

• Brief overview of Doushantuo formation.