1. Meaning of 'Orsten' in the original sense

The term 'Orsten' has been applied to horizontally laminated limestones nodules. These occur embedded in/surrounded by Alum Shales of the upper part of the Cambrian in Sweden (now uppermost Middle Cambrian, formerly Agnostus pisiformis zone or zone 1 of the Swedish system of the Upper Cambrian), to the Furongian, and here the former zones 5/6 Peltura scarabaeoides of the old UC sequence)(the old zones 3 and 4 did not yield any 'Orsten' fossils, so that Klaus Müller did not investigate there in more depth).

The nodules are actually an accumulation of countless disarticulated calcified head and tail shields of the minute arthropod Agnostus pisiformis (Wahlenberg, 1818). The surrounding Alum Shale is a finely layered compaction series of up to 100 m of bituminous shale with a notable heavy metal content.

For aspects of alum shales see, for example:
Buchardt, B. 1989. Irradiation of organic matter by uranium decay in the Alum Shale, Sweden. Geochimica et Cosmochimica Acta 53(6),1307-1322.).

The term 'orsten' derives from a local dialect word for pig, 'orne' and the Swedish word for stone, 'sten'. It is assumed that the name derives from the use of ground 'orsten' as veterinary medicine for domestic pigs. It is often translated to 'stinkstone' due to the characteristic smell ("rotten eggs") when struck or split. The nodules have also been burnt to produce fertilizer. Most Alum Shale and 'Orsten' quarries are now abandoned. Nowadays, nodules are frequently uncovered at construction areas, e.g. for roads.

According to our experience, only very few 'orsten' nodules actually yield phosphatized arthropod remains. In fact, it were mainly only two nodules from the Gum quarry at Kinnekulle, Västergötland, have yielded the bulk of our material. Most of the nodules, representing a time frame of at least 1 million years, have yielded few to single specimens, if at all. Accordingly, it is rather unlikely that the fossils represent an allochthonous thanatocoenosis or have been killed in a event comparable to stagnant, anoxic conditions at certain times during a year, as occurring today in the Baltic Sea sometimes or in the Mediterranean Sea.

Residues derived from the etching process contain various non-arthropod fragments, "small shelly" fossils, conodonts, shells of (primary?) phosphatic brachiopods (mainly Obolus; see picture of procedure in the chapter methods) and originally non-phosphatic material, such as sponge spicules.

For information on Orsten see also:
Berg-Madsen, V. 1989. The origin and usage of the terms orsten, stinkstone, and anthraconite. Archives of Natural History 16(2), 191-208.
For ideas on taphonomy see:
Maeda, H.,  Tanaka, G., Shimobayashi, N., Ohno, T. & Matsuoka, H. 2011. Cambrian orsten lagerstätte from the alum shale formation: fecal pellets as a probable source of phosphorus preservation. Palaios 26(4), 225-231.
For new ideas on the stratigraphy see:
Terfelt, F., Eriksson, M.E., Ahlberg, P. & Babcock, L.E.: Furongian Series (Cambrian) biostratigraphy of Scandinavia – a revision. Norwegian Journal of Geology, Vol. 88, pp. 73–87.

Note: The new finds outside Sweden have indicated that larger differences between the various types of rock that yield 'Orsten' preservation exist than known before. We will add more on these in due course, with special reference to the new finds in China. Regrettably we have not yet received a text from them about their locations and the occurrences of Orsten in China. Also the Australian and Siberian localities point to slightly different conditions and forms of Orsten formation.

Map of southern Sweden showing alum shale occurrences and localities (1–5) sampled by K.J. Müller. Distance Gum – Öland approx. 330 km.



Time table of major sites that yielded fossils in 3D preservation; note the remarkable amount in the Early Palaeozoic.

2. What are 'Orsten'-type fossils?

'Orsten' fossils in the strict sense are spectacular minute secondarily phosphatised (apatitic) fossils. Until now the majority of taxa described has been affiliated with the Crustacea, representing different evolutionary levels. Also other arthropods, representatives of other euarthropod groups and of stem taxa have been described, and, more recently, also rerpesentatives of the Nemathelminthes, a group of worms considered as the sister taxon to all other gastroneuralian animals. No representatives of other animal groups could be detected so far, notably also not the tiniest fragment of trilobites, whcih are, otehrwise, common in the rock. Remarkably, we did not find any fossil fragment larger than 2 mm.

'Orsten' fossils have the great advantage in being three-dimensionally preserved and with all surface structures in place. Accordingly, they are much easier to interpret than any other fossil material. In fact, 'Orsten' fossils are preserved virtually as if they were just critical-point dried extant organisms. Details range down to less than 1 µm and include pores, sensilla and minute secondary bristles on filter setae and denticles. 'Orsten' fossils also give an insight of meiofaunal benthic life (see picture below) at small scale, including preservation larval stages, and hence a life zone inhabited by the earliest metazoan elements of the food chain.

Therefore, it is not surprising that our material also includes many ontogenetic stages. Even more so, the smaller the better! And in some cases, we were able to establish sets of successive stages, the longest being that of Rehbachiella kinnekullensis with 30 stages, and from larger fragments we even know that this series is still not complete.

Possibly due to impregnation by phosphate (fluor apatite like in our teeth), most of the specimens are hollow carcasses, as the one on lower right. Remarkably, it seems that most, if not all, pentastomids from uppermost Cambrian to Lower Ordovician strata and not co-occurring with any other 'Orsten' taxa, are solid. The reasons for this are still unclear. It is also remarkable that they co-occur with conodonts.

As already briefly mentioned above, 'Orsten' rocks contain also various other fossils, such as conodonts (see the work by Klaus J. Müller and Ingelore Hinz, now Greifswald, in particular) or the so-called small shellies (see papers by the Shwedish colleague Stefan Bengtson, Stockholm), horny brachiopods (investigated by Lars Holmer, Uppsala), and there are also shelly fragments of macrofaunal elements in surrounding rocks, such as agnostids, brachiopods and trilobites (specially investigated by Euan Clarkson, Edinburgh, and Per Ahlberg, Lund), but we do not count these as 'Orsten' fossils because of the lack of cuticular preservation. The exception is Agnostus pisiformis, of which we have numerous immature stages with cuticular preservation (see Müller and Walossek 1987).

'Orsten'-type fossils other than the ones mentioned above are likewise 3D-preserved phosphatized microfossils, which may range from embryonic stages (e.g., early cleavage stages, as occurring in various late Precambrian to Lower Cambrian rocks, but also much further developed egg stages, such as that of the putative nemathelminth Markuelia) to arthropods in much younger sediments. Examples are the Triassic ostracodes from Spitsbergen (described by Wolfgang Weitschat from Hamburg) or Lower Cretaceous ostracodes (see Bates 1972) and parasitic copepods from the Santana formation, Brazil (described by Boxshall and Cressey). 3D silification is another unusual type of preservation of arthropods, known from the Rhynie-Chert (e.g. Scourfield 1926, 1940, Lyall Andersen and colleagues, but also investigated now by us) or from the Tertiary (Neogene), which has preserved crustaceans, spiders and insects incl. immature stages.

If you have red-green glasses around, please enjoy the 3d of a specimen of Skara minuta (click on it to enlarge the image):

We will discuss this further in due course because we use this mehtopd quite frequently, in lectures, but also in our papers.

In the meantime this has been taken over by Joachim and also our doctorate student Verena Kutschera, who also use the flatbed scanner (as I in the "old days") to produce stereo images of various crustaceans and fossils.

3. †Klaus J. Müller, Bonn, the discoverer of the 'Orsten'

Klaus Müller, 1923 – March 12, 2010, the discoverer of this exceptional fauna, was professor for micropalaeontology at the University of Bonn. There he had worked in the Institution of Palaeontology from the early 1960ties onward and led the micropalaeontological section. Extensive exploration for 'Orsten' arthropod fossils started after first by-chance findings in 1975 (his assistant Helga Rehbach found the first isolated legs), with establishing a small workgroup of people picking and sorting the material he had collected on several field trips in Sweden and producing a few first papers presenting the potential of the Orsten.

In 1980, after taking Dieter Waloszek in his workgroup, another phase in Klaus's reseach on the Orsten started with intensive description of the Orsten arthropods, a project funded by the DFG, the German Funding Agency. After several smaller and larger publications produced by both in collaboration, Klaus retired in 1988. Yet he remained active thereafter and supported the ongoing studies. In 1991 Klaus, Andreas and Dieter went to Moscow to explore the possibilities of a collaboration with Russian colleagues. On this occasion, he received some Middle Cambrian material from Siberia that yielded a tiny animal looking lite a real modern tardigrade, with the only exception of having one leg less. In 1992 Klaus and Dieter went to Sweden and had a nice time on the Isle of Oeland and in Östergötland (see the picture to the right). In 2001 Klaus personally funded an expedition of Dieter and Andreas Braun to Siberia.

Soon later, Klaus decided to go into a home for seniors together with his ill wife Ewa. He also became rather ill and after just having slightly recovered, Ewa died in 2003. Although severely suffering from this loss, Klaus recovered slowly and continued to be interested in his gemmen collection and also our continuing studies of the Orsten in Ulm.

Besides the discovery of the 'Orsten', Klaus was well-known as a pioneer of the study of conodonts and he was always interested in exceptional preservations. Already early in his career, Klaus had become a voting member of the Nobel Commission, but received little recognition by the scientific community for his excepptional work. In 1989 Klaus and Dieter received the Keith Prize of the Royal Society of Edinburgh for exceptional papers in their journal TRSE. In fall 2009 the Palaeontological Society of Germany honoured Klaus by making him an Honory Member. The society also held a special congress symposium within their regular annual meeting, and some of us gave talks on the 'Orsten', incl. a lecture on the history of research in Bonn and Ulm.

With Klaus' death in spring 2010 we have lost a really good friend, a continuous and enthusiastic supporter of our 'Orsten' research, and a great colleague.