English: Trilobite pygidium in shale from the Ordovician of South Korea.

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 a trilobite tail from the Ordovician-aged Jigunsan Formation in South Korea. Species of trilobites reported from this unit include: Dolerobasilicus yokusensis, Basiliella kawasakii, Basiliella typicalis, and Ptychopyge dongjeomensis.

Classification: Animalia, Arthropoda, Trilobita, Polymerida

Stratigraphy: float from the lower Jigunsan Formation, upper Taebaek Group, Joseon Supergroup (Choson Supergroup; Chosen Supergroup), Llandeilo Stage, lower Middle Ordovician (sensu traditio)

Locality: loose piece from the eastern side of Route 910 (= stop 6 of the Seokgaejae section for the 9th International Conference of the Cambrian Stage Subdivision Working Group; see Choi et al., 2004, Paleontological Society of Korea Special Publication 8, p. 31), ~16 air-kilometers east-southeast of the town of Taebaek, southeastern Gangwon Province, eastern South Korea (37° 05.234' North latitude, 129° 08.548' East longitude)