English: Olenellus sp. - fossil trilobite cephalon in mudrock from the Cambrian of Nevada, USA.

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).

Seen here is an olenellid trilobite cephalon from the Chief Range in Nevada. The specimen comes from a Cambrian soft-bodied fossil deposit called the Ruin Wash Lagerstätte. Within five minutes of my arrival at this site, I found an anomalocaridid feeding appendage.

Classification: Animalia, Arthropoda, Trilobita, Polymerida, Redlichiida, Olenellina, Olenellidae

Stratigraphy: Ruin Wash Lagerstätte, lower C-Shale Member, Pioche Formation, just below the olenelloid trilobite extinction event, ~uppermost Bonnia-Olenellus zone, uppermost Dyeran Stage, uppermost Lower Cambrian

Locality: ICS locality 1044, pit from along-strike fossil quarries, adjacent to Ruin Wash, western side of the Chief Range, south of Bennett Pass & north of Klondike Pass, 121 mm N & 205 mm E of the SW corner of the Bennett Pass, Nevada 7.5' topographic quadrangle map, northeast-central Lincoln County, southeastern Nevada, USA (vicinity of 37˚ 46.647' North latitude, 114˚ 34.247' West longitude)