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File:Agnostus pisiformis fossil trilobites (Alum Shale Formation, upper Middle Cambrian; Andrarum, Scania, Sweden) 4 (15250792196).jpg

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Agnostus pisiformis (Wahlenberg, 1818) fossil trilobites from the Cambrian of Sweden (FMNH P 24, Field Museum of Natural History, Chicago, Illinois, USA) (centimeter scale).

Well-preserved trilobites occur in Sweden’s Alum Shale Formation (Middle to Upper Cambrian). The limestone beds in this unit are often trilobite packstones. Shown here is a black, fossiliferous packstone from the classic locality of Andrarum, Scania, southern Sweden. These rocks are slightly petroliferous, and release a distinctive oily smell when broken. Early Swedish workers called these rocks “stinkstones”. The stinkstone shown here is packed with numerous disarticulated heads & tails of the common agnostoid trilobite Agnostus pisiformis.

Agnostoids differ from "ordinary" trilobites (= polymeroids) by having the following characeristics: two-segmented thorax; blind (no eyes); isopygous (the heads & tails are equal-sized). Agnostoids are usually quite small.

Many modern arthropod phylogenetic studies conclude that agnostoids should be excluded from the trilobites.

Classification: Animalia, Arthropoda, Trilobita, Agnostida, Agnostidae

Stratigraphy: Alum Shale Formation, near-uppermost Middle Cambrian
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Source Agnostus pisiformis fossil trilobites (Alum Shale Formation, upper Middle Cambrian; Andrarum, Scania, Sweden) 4
Author James St. John

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This image was originally posted to Flickr by jsj1771 at https://www.flickr.com/photos/47445767@N05/15250792196. It was reviewed on 6 May 2015 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0.

6 May 2015

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current18:55, 6 May 2015Thumbnail for version as of 18:55, 6 May 20152,042 × 1,354 (1.82 MB)Natuur12 (talk | contribs)Transferred from Flickr via Flickr2Commons

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