File:Trilobite packstone (Alum Shale Formation, Upper Cambrian; Kinnekulle Outlier, Västergötland, Sweden) 14.jpg

English: Fossiliferous limestone from the Cambrian of Sweden.

Trilobites are extinct marine arthropods. They first appear in Lower Cambrian rocks and the entire group went extinct at the end of the Permian. Trilobites had a calcitic exoskeleton and nonmineralizing parts underneath (legs, gills, gut, etc.). The calcite skeleton is most commonly preserved in the fossil record, although soft-part preservation is known in some trilobites (Ex: Burgess Shale and Hunsruck Slate). Trilobites had a head (cephalon), a body of many segments (thorax), and a tail (pygidium). Molts and carcasses usually fell apart quickly - most trilobite fossils are isolated parts of the head (cranidium and free cheeks), individual thoracic segments, or isolated pygidia. The name "trilobite" was introduced in 1771 by Johann Ernst Immanuel Walch and refers to the tripartite division of the trilobite body - it has a central axial lobe that runs longitudinally from the head to the tail, plus two side lobes (pleural lobes).

Well-preserved trilobites occur in Sweden’s Alum Shale Formation (Middle to Upper Cambrian). The limestone beds in this unit are often trilobite packstones. Seen here is an example with abundant sclerites of Olenus truncatus (Brünnich, 1781) and Olenus sp.

Classification: Animalia, Arthropoda, Trilobita, Polymerida, Olenidae

Stratigraphy: limestone interbed in the Alum Shale Formation, Olenus truncatus subzone, Olenus zone, lower Upper Cambrian

Locality: unrecorded/undisclosed outcrop in the Kinnekulle Outlier, southern shore of Lake Vänern, Västergötland, southern Sweden