Middle Ordovician – Upper Ordovician
Flexicalymene is an extinct genus of nektobenthic carnivores.
Characteristics of the Genus
- The most common trilobite in the Upper Ordovician rocks of southwestern Ohio.
- Can be found throughout the Cincinnatian series.
- Commonly found enrolled in what is thought to be a defensive posture or a response to other stimuli.
- Thought to be due to rapid burial by oxygen deficient sediments, in which the trilobites would have stayed enrolled and died waiting for more favorable conditions.
- Can be found as complete specimens, but it is more common to find only pieces or parts of a trilobite.
- Glabella is plentiful and easy to find, distinguished by its clover-leaf shape.
- Rippled segments or thorax are easy to pick out, often showing up in matrix or among other fossils.
- Free cheeks, pygidium, and the distinctive “three-hump” cross section of thorax that is a product of molting are all signature of Flexicalymene fossils.
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- Second lateral glabellar lobe lacks buttress extending into axial furrow.
Fossils of Ohio (1996):
- Flexicalymene Shirley has an exoskeleton up to 6 cm in length; it is granulose and penetrated by fine canals. The cephalon is rounded-subtriangular in outline; pleural areas are approximately as wide as the axis. The glabella is convex, tapering forward, and has three pairs of deep lateral glabellar furrows separating rounded and convex lateral glabellar lobes; a distinct pair of glabellar pits is present at the anterior corners of the axial furrow. Eyes are small, holochroal, and moderately elevated. Facial sutures are gonatoparian; librigenae are narrow; genal angles are bluntly rounded or have a short spine. The thorax has 13 segments; pleural areas are wider than the axis; each pleura is slightly curved and has a rounded termination. The pygidium is small and lenticular in outline. The axis generally has six axial rings and a terminal piece. Pleural fields generally have 4 pairs of pleural furrows.
Caster, Dalve & Pope (1961):
- The exclusively marine trilobites, related to the crabs, spiders, and insects, (Phylum, Arthropoda) abounded in the Paleozoic seas. They appear among the earliest well-preserved fossils found in the Lower Cambrian (Waucobian), and continue into the Permian, although diminished in numbers after Devonian times. The Cincinnatian rocks are filled with trilobite fragments, and good specimens of the common genus, Flexicalymene, are abundant. Two other genera, Isotelus and Cryptolithus, somewhat rarer than Flexicalymene, and fragments of extremely rare genera may be found here.
Treatise on Invertebrate Paleontology (1959):
- Glabella with 3 pairs of lateral lobes; axial furrows contracted slightly opposite 1p and 2p lateral furrows; preglabellar furrow broad (sag., exsag.); eye lobes opposite, ahead or behind 2p glabellar lobes. Hypostoma without raised area in center of anterior lobe of middle body. Thorax with 12 or 13 segments. Pygidium with deep, pleural furrows and shallow, interpleural groove extending close to margins of pleural regions.
- Thorax with 13, rarely 12 segments; glabella outline subparabolic to bell-shaped; preglabellar field stretched forwards or recurved, without subsidiary ridging; axial furrows slightly contracted at each glabellar furrow.
- Genotype-Calymene caractaci Salter, 1865.