File:Megalomoidea canadensis fossil bivalve (Lockport Dolomite, Middle Silurian; quarry at Clay Center, Ottawa County, northwestern Ohio, USA) 1 (14968486774).jpg

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Megalomoidea canadensis (Hall, 1852) fossil bivalve (internal mold) (lateral view of left valve) from the Silurian of Ohio, USA (8.5 cm across at its widest).

This is a famous fossil clam from the Silurian of Ohio. These fossils were frequently found by quarrymen working Silurian dolostones - they called them "beefhearts" because they are remarkably similar in size and appearance to the hearts of cows.

"Beefhearts" are really internal molds of large fossil bivalves - the original aragonite shells have dissolved away. All that's left is impressions of the inside surfaces of the shells. The internal mold itself is composed of the same material as the host rocks - dolostone. Dolostone is a finely-crystalline textured, chemical sedimentary rock composed of the mineral dolomite (CaMg(CO3)2 - calcium magnesium carbonate).

The grayish-brown, glittering crystals just below the center are dolomite. The whitish crystals near the top are celestite (SrSO4 - strontium sulfate).

Orientation: anterior is to the left; posterior is to the right; dorsal (hinge line) at top; ventral at bottom; left valve is facing the viewer

Classification: Animalia, Mollusca, Bivalvia, Heterodonta, Hippuritoida, Megalodontidae (this fossil clam was formerly known as Megalomus canadensis)

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

Locality: quarry at or near the town of Clay Center, southern Allen Township, northwestern Ottawa County, northwestern Ohio, USA
Date
Source Megalomoidea canadensis fossil bivalve (Lockport Dolomite, Middle Silurian; quarry at Clay Center, Ottawa County, northwestern Ohio, USA) 1
Author James St. John

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This image was originally posted to Flickr by jsj1771 at https://www.flickr.com/photos/47445767@N05/14968486774. It was reviewed on 6 May 2015 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0.

6 May 2015

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