File:Sthenarocalymene celebra (fossil trilobite) (Cedarville Dolomite, Middle Silurian; Ludlow Quarry, Miami County, Ohio, USA) 1.jpg

English: Sthenarocalymene celebra (Raymond, 1916) - fossil trilobite from the Silurian of Ohio, 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).

This fossil calymenid trilobite specimen is a nice example of dissolution. The original calcareous exoskeleton has dissolved away, and the fossil is now preserved as an internal mold in dolostone. Most trilobites found in dolostones are preserved as molds. This trilobite is Sthenarocalymene celebra - over the years, trilobitologists haven’t agreed on the proper generic assignment for celebra. The species has been variously assigned to Calymene, Gravicalymene, Flexicalymene, and Sthenarocalymene.

Classification: Animalia, Arthropoda, Trilobita, Polymerida, Calymenidae

Stratigraphy: Cedarville Dolomite, upper Lockport Group, upper Niagaran Series (= upper Wenlockian), upper Middle Silurian

Locality: Ludlow Quarry, southwest of the town of Ludlow Falls, just south of Ludlow Creek & just east of Brush Creek, northern Union Township, southwestern Miami County, southwestern Ohio, USA (NE1/4 section 7, T6N, R5E, West Milton 7.5' USGS topographic quadrangle) (39° 59.250' North lattiude, 84° 21.148' West longitude)