Orsten

The Orsten fauna are fossilized organisms preserved in the Orsten lagerstätte of Cambrian (Late Miaolingian^[1] to Furongian) rocks, notably at Kinnekulle and on the island of Öland, all in Sweden.

Orsten
Stratigraphic range: Miaolingian–Furongian PreꞒ Ꞓ O S D C P T J K Pg N
Hesslandona angustata, a phosphatocopine, showing exceptional preservation in 3D
Type	Geological formation
Unit of	Alum Shale Formation
Lithology
Primary	Shale and limestone
Location
Region	Kinnekulle and island of Öland
Country	Sweden
Type section
Named for	Orsten[a]
Named by	Klaus J. Müller, 1975

The initial site, discovered in 1975 by Klaus Müller and his assistants, exceptionally preserves soft-bodied organisms, and their larvae, who are preserved uncompacted in three dimensions. The fossils are phosphatized and silicified, thus the delicate chitinous cuticle and soft parts are not affected by acids, which act upon the limestone nodules within which the fossils have survived. Acids dissolve the limestone, revealing the microfossils in a recovery process called "acid etching". To recover the fossils, more than one and a half tons of Orsten limestone have been dissolved in acid, originally in a specifically designed laboratory in Bonn, more recently moved to Ulm. The insoluble residue is scanned by electron microscope.^[2] The phosphorus used to replace the fossils with calcium phosphate is presumed to be derived from fecal pellets.^[3]

The Orsten fauna has improved the understanding of metazoan phylogeny and evolution, particularly among the arthropods, thanks in part to unique preservation of larval stages. The Orsten sites reveals the oldest well-documented benthic meiofauna in the fossil record. For the first time, fossils of tardigrades ("water bears") and apparently free-living pentastomids have been found.

The Cambrian strata consist of alum shales with limestone nodules (the Alum Shale Formation), which are interpreted as the products of an oxygen-depleted ("dysoxic")^[b] marine bottom water habitat of a possibly offshore seashelf at depths of perhaps 50–100 m.^[2] The bottom was rich in organic detritus, forming a soft muddy zone with floc in its surface layer.

Other Orsten-type preservation fauna have been found in Nevada, eastern Canada, England, Poland, Siberia, China and the Northern Territory of Australia.^[4]

Paleobiota

Based on data from C.O.R.E. website^[2] and subsequent studies.

Animals
Genus	Notes	Images
Agnostus	An agnostid
Cambropycnogon	A larval sea spider
Cambropachycope	A monocular arthropod of uncertain affinities, possibly placed in stem-Mandibulata
Goticaris	A monocular arthropod of uncertain affinities, possibly placed in stem-Mandibulata
Rehbachiella	A pancrustacean
Martinssonia	A pancrustacean
Dala	A pancrustacean
Musacaris	A pancrustacean
Bredocaris	A pancrustacean
Paulinecaris[5]	A pancrustacean
Skara	A pancrustacean
Sandtorpia	A pancrustacean
Henningsmoenicaris	A pancrustacean
Walossekia	A pancrustacean
Aengapentastomum	A pentastomid parasitic crustacean
Boeckelericambria
Heymonsicambria
Haffnericambria
Oelandocaris	A stem-group crustacean or stem-group mandibulate or megacheiran[6]
Hesslandona	A bivalved arthropod belonging to Phosphatocopina
Trapezilites
Waldoria
Veldotron
Falites
Vestrogothia
Orstenotubulus	A lobopodian
Arthropoda indet.	Several nauplius-like larvae that cannot be associated with any of the other arthropods. The various larvae have been termed A1, A2, B and C.[7][8] Formerly included among them was “larva D”, now Cambropycnogon.

Orsten-type fauna found elsewhere

Animals
Genus	Notes	Images
Skara	Two additional species known from Poland and China
Heymonsicambria	One additional species known from Ordovician of Canada
Vestrogothia	Two additional species known from China
Markuelia	A possible member of Cycloneuralia, known from Australia
Shergoldana
Dietericambria	A pentastomid known from Greenland
Orstenoloricus	A loriciferan larva[9] from Australia
Austromarrella	A marrellomorph from Australia
Cambrocaris	A crustacean, known only from Poland
Unnamed tardigrade	Only known from Siberia
Wujicaris	A pancrustacean known from China
Yicaris
Dabashanella	A member of Phosphatocopina from China
Klausmuelleria	A member of Phosphatocopina from England

Notes

1. Orsten means "stinking stone": the alum shale matrix is rich in organics.
2. The distribution of pyrites in the limestone, together with the organic content indicate levels of oxygen that prevented normal decomposition.