File:Astartella concentrica (fossil bivalve) (Lower Mercer Shale, Middle Pennsylvanian; Rock Cut, Muskingum County, Ohio, USA) 2 (37068151630).jpg

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Astartella concentrica (Conrad, 1842) - fossil bivalve in shale in the Pennsylvanian of Ohio, USA.

Orientation: anterior at right; posterior at left; dorsal at top; ventral at bottom

The Pottsville Group is a Pennsylvanian-aged cyclothemic succession in eastern Ohio that contains nonmarine shales, marine shales, siltstones, sandstones, coals, marine limestones, and chert ("flint"). The lower Pottsville dates to the late Early Pennsylvanian. The upper part dates to the early Middle Pennsylvanian. The Lower-Middle Pennsylvanian boundary is apparently somewhere near the Boggs Member (?).

The rock shown above is gray shale from the Lower Mercer Shale, a marine unit that caps the Lower Mercer Limestone in the Pottsville Group. The grooved, subovoid structure at center is a right valve of the fossil bivalve Astartella concentrica, preserved as a mold.

Bivalves are bilaterally symmetrical molluscs having two calcareous, asymmetrical shells (valves) - they include the clams, oysters, and scallops. In most bivalves, the two shells are mirror images of each other (the major exception is the oysters). They occur in marine, estuarine, and freshwater environments. Bivalves are also known as pelecypods and lamellibranchiates.

Bivalves are sessile, benthic organisms - they occur on or below substrates. Most of them are filter-feeders, using siphons to bring in water, filter the water for tiny particles of food, then expel the used water. The majority of bivalves are infaunal - they burrow into unlithified sediments. In hard substrate environments, some forms make borings, in which the bivalve lives. Some groups are hard substrate encrusters, using a mineral cement to attach to rocks, shells, or wood.

The fossil record of bivalves is Cambrian to Recent. They are especially common in the post-Paleozoic fossil record.

Classification: Animalia, Mollusca, Bivalvia, Heterodonta, Veneroida, Astartidae

Stratigraphy: Lower Mercer Shale (just above the Lower Mercer Limestone), Pottsville Group, lower Atokan Stage, lower Middle Pennsylvanian

Locality: Rock Cut railroad cut - outcrop along the southern side of Ohio Central Railroad tracks (west of milepost 134), ~southwest of Copeland Island & south-southeast of the town of Dresden, northern Muskingum County, eastern Ohio, USA (~vicinity of 40° 04’ 24.41” North latitude, ~81° 59’ 11.25” West longitude)
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Source Astartella concentrica (fossil bivalve) (Lower Mercer Shale, Middle Pennsylvanian; Rock Cut, Muskingum County, Ohio, USA) 2
Author James St. John

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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/37068151630 (archive). It was reviewed on 8 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

8 October 2019

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current12:06, 8 October 2019Thumbnail for version as of 12:06, 8 October 20191,335 × 937 (1.11 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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