Yanjiahe Formation

The Yanjiahe Formation is an Ediacaran to Cambrian fossiliferous geologic formation found in South China.Yanjiahe Formation at Fossilworks.org

Dating The Yanjiahe Formation has been dated through various methods. The top of the formation is dated at and using radiometric dating on ash beds within the area. Likewise, the base of the formation has been dated to between to through carbon isotopic correlations.

Beds The Yanjiahe Formation consists of five beds. Every bed within the formation contains fossil material.

The beds are as follows, in ascending stratigraphic order (lowest to highest): Bed 1 is characterized by basal dolomitic conglomerates, with banded black cherts. Bed 2 is mostly consists of siliceous phosphatic dolostone, with flat pebble conglomerates. Bed 3 is characterized by various shales, with the presence of siliceous-phosphatic nodules. Bed 4 is composed of carbonaceous limestones. Bed 5 is characterized by cherts and siliceous phosphatic dolostone, with flat pebble conglomerates.

Paleobiota The Yanjiahe Formation contains a wide range of unique organisms from the base of the Cambrian, from the probable earliest stem group echinoderm Yanjiahella, to the ecdysozoan Beretella, alongside a large wealth of early molluscs, such as Watsonella and Scenella. The formation is also home to several large but incomplete ecdysozoan-like cuticles, exceeding the other fully complete ecdysozoans like Beretella and Saccorhytus in size. Despite their incompleteness, they still offer an insight into the already varied biodiversity of ecdysozoans during the early Cambrian.

Cnidaria

GenusSpeciesNotesImagesOctapyrgitesO. elongatusOlivooid Medusozoan, larger than any known Olivooid.QuadrapyrgitesO. quadratacrisOlivooid Medusozoan.OlivooidesOlivooides sp. O. multisulcatus O. mirabilisOlivooid Medusozoan.PseudooidesPseudooides sp.Medusozoan.SeptuconulariaS. yanjiaheensis S. crassiformisHexangulaconulariid Medusozoan.DecimoconulariaD. isofacialisHexangulaconulariid Medusozoan.CarinachitesC. spinatusCnidarian sclerite, related to the conulariids.CambrorhytiumC. majorElongated cone-like cnidarian.

Chancelloriida

GenusSpeciesNotesImagesChancelloriaChancelloria sp.Sponge-like eumetazoan.

Deuterostome

GenusSpeciesNotesImagesProtohertzinaP. unguliformis P. anabarica P. robustaPossibly a Protoconodont, Paraconodont, or a Chaetognath.TarimspiraT. planaPossible Paraconodont.YunnanodusYunnanodus sp. Y. yanjiahensisPossible Paraconodont.YanjiahellaY. biscarpaAmbulacrarian; possibly earliest stem group echinoderm.YuknessiaYuknessia sp.Unbranched pterobranch.HertzinaH. guizhouensis H. tenuisFurnishinid Paraconodont.

Ecdysozoa

GenusSpeciesNotesImagesBeretellaB. spinosaPossibly adult or larval ecdysozoan.SaccorhytusSaccorhytus sp.Possibly adult or larval ecdysozoan.

Lophotrochozoa

GenusSpeciesNotesImagesConothecaC. subcurvata C. obesa C. nana C. transulcataHyolith lophotrochozoan.HyolithellusH. tenuis? H. decorusAnnelid lophotrochozoan, previously thought to be a Hyolith.LapworthellaLapworthella sp.Tommotid lophotrochozoan.SpinulithecaS. billingsiHyolith lophotrochozoan.MicrocornusM. parvulus?Hyolith lophotrochozoan.CupithecaC. miraHyolith lophotrochozoan.TurcuthecaT. crasseocochlia T. lubricaHyolith lophotrochozoan.LophothecaL. costellataHyolith lophotrochozoan.CircothecaC. longiconica C. longiconicaCircothecid Hyolith.AldanellaA. attleborensis A. yanjiaheensisMollusc with a coiled shell.EohalobiaE. diadongensis Eohalobia sp.Halkieriid mollusc.OcruranusOcruranus sp. O. trulliformis O. finialHalkieriid mollusc.ScenellaS. jijiapoensisScenellid mollusc.SiphogonuchitesS. triangularisSiphogonuchitid mollusc.XianfengellaX. ovata X. primaMollusc.TuberoconusT. paucipapillaeMollusc.WatsonellaW. crosbyiMollusc.AnabarellaA. planaHelcionelloid mollusc.IgorellaI. emeiensis I. maidipingensis Igorella sp.Helcionelloid mollusc.OelandiellaO. korobkoviHelcionelloid mollusc.CeratoconusC. bucersHelcionelloid mollusc.

Porifera

GenusSpeciesNotesImagesBlastulospongiaBlastulospongia sp.Globular demosponge, previously postured to be a radiolarian.

incertae sedis

GenusSpeciesNotesImagesAnabaritesA. trisulcatus A. tianzhushanensis A. gracilis A. ternariusAnabaritid small shelly fossil.TiksithecaT. koroboviAnabaritid small shelly fossil.CambrotubulusC. decurvatusAnabaritid small shelly fossil.ProtoconitesP. minorCurved conical organism, possible relations to Cnidaria.PurellaP. antiqua P. lepiditesSmall shelly fossil.EmeiconusE. antiquaSmall shelly fossil.RugatothecaRugatotheca sp.Small shelly fossil.ColeolellaC. rectaSmall shelly fossil.VendotaenidVendotaenia sp.Ribbon-like organism.TorellellaT. lentiformisTubicolous fossil.

Flora

GenusSpeciesNotesImagesArchaeophycusA. yunnanensisEither a cyanobacteria or the early developmental stage of an alga.(J)KonglingiphytonKonglingiphyton sp.Macroalgae.MegathrixM. longusFilamentous cyanobacterium.MyxococcoidesMyxococcoides spp.Cyanobacteria.ArchaeooidesA. granulatesMicroalgae.

Microorganisms

GenusSpeciesNotesImagesAsteridiumA. tornatumAcritarch.ComasphaeridiumC. annulareAcritarch.HeliosphaeridiumH. ampliatumAcritarch.MicrhystridiumM. regulareAcritarch.YurtusiaY. uniformisAcritarch.DictyotidiumDictyotidium sp.?Acritarch.

Undescribed

GenusSpeciesNotesImagesHexactinellid spicules???A collection of monaxons, diaxons and triaxons.Unnamed probable cnidarian???Curved tubular organism, possible affinities to cnidarians.Form A???Four specimens with a vermiform morphology that is annulated in appearance, maximum known length is . Surface ornamentation noted to resemble that seen in the pancrustacean Yicaris from the Yu’anshan Formation, as well as the ecdysozoan Saccorhytus from this formation.Form B???A singular specimen of a trunk segment covered in spines of varying sizes, maximum length of the specimen is . Is comparable to various ecdysozoan groups, such as lobopods, and more so to the extant kinorhynchs. It is noted that if the latter interpretation is valid, the specimen would likely be placed as a crown-group kinorhynch, although more evidence is needed.Form C???The most abundant, with seventeen specimens known, and found in two modes of preservation. Specimens are covered in fractured spines of varying shapes, and the maximum known length of this form being . Is noted to be comparable to various small shelly fossils such as Protohertzina and Mongolodus, and several ecdysozoans such as Eokinorhynchus, Scalidodendron, and Saccorhytus.Form D???Two specimens with a vermiform morphology, and is only known to attain a length of , making it the smallest of the known forms. These specimens have been compared to the likes of Eopriapulites and Palaeoscolex.Form E???Two specimens, which are evenly covered in small papillate knobs, and attain a maximum known length of . They have been compared to a wide range of papillate knob-bearing acritarchs, embryos, algae-like forms, and tentative sponges, such as Bacatisphaera, Archaeooides, Shaanisphaera, and Aetholicopalla respectively.Form F???Five specimens with a dense covering of short coniform to hook-like spines, and are the largest of the forms, attaining a maximum length of . The five specimens are noted to bear a striking resemblance to Saccorhytus, although they are also notably much larger, suggesting that saccorhytids may have attained much larger sizes than currently known.

Yanjiahe Formation

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