File:Flexicalymene meeki (fossil trilobites) (Waynesville Formation, Upper Ordovician; Southgate Hill Outcrop, Franklin County, Indiana, USA) 4.jpg

English: Flexicalymene meeki (Foerste, 1910) - enrolled fossil trilobites from the Ordovician of Indiana, USA.

These fossils are from the famous Cincinnatian Series of the tristate area of Ohio-Kentucky-Indiana. Rocks in the Cincinnatian were deposited in relatively shallow marine facies during the Late Ordovician. The Cincinnatian succession is mostly interbedded limestones and shales. Most of the limestones are event beds (= tempestites), deposited during ancient storms.

The specimens are complete enrolled trilobites, which are extinct marine arthropods. Trilobites first appear in Lower Cambrian rocks and the entire group went extinct at the end of the Permian. They 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 (Examples: 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).

The trilobites are enrolled - many could roll up like modern terrestrial isopods (see: www.flickr.com/photos/vicbao/3417810096/in/photostream/li...). This was usually in response to being buried in sediments - often by storm events.

Classification: Animalia, Arthropoda, Trilobita, Polymerida, Calymenidae

Stratigraphy: float from the Waynesville Formation, lower Richmondian Stage, upper Cincinnatian Series, upper Upper Ordovician

Locality: Southgate Hill Outcrop - roadcut along Route 1, just north of South Gate & just south of the Whitewater River & just southwest of Cedar Grove, southeastern Franklin County, southeastern Indiana, USA (39° 20.272' North latitude, 84° 57.160' West longitude)