Phacops rana crassituberculata Stumm, 1953 - enrolled fossil trilobite from the Devonian of Ohio, USA. (Dave Mielke collection; temporary public display, Ohio Geological Survey, Columbus, Ohio, USA)

This fossil is also known as Eldredgeops rana crassituberculata.

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 famous trilobite whose remains are relatively common in the Middle Devonian-aged Silica Formation of northeastern Ohio. This is Phacops rana crassituberculata (also known as Eldredgeops, an unnecessary genus name based on taxonomic oversplitting). Phacops trilobite fossils occur with other typical Middle Paleozoic shallow marine invertebrates: brachiopods, bryozoans, crinoids, and corals.

Classification: Animalia, Arthropoda, Trilobita, Polymerida, Phacopidae

Stratigraphy: Silica Formation (also known as the Silica Shale), Givetian Stage, upper Middle Devonian

Locality: quarry northwest of the town of Paulding, northern Paulding County, northwestern Ohio, USA (41° 10' 52.55" North latitude, 84° 37' 19.32" West longitude)

See info. at: <a href="https://en.wikipedia.org/wiki/Trilobite" rel="noreferrer nofollow">en.wikipedia.org/wiki/Trilobite</a> and