Megalomoidea canadensis fossil bivalve (Lockport Dolomite, Middle Silurian; quarry at Clay Center, Ottawa County, northwestern Ohio, USA) 2 : 無料・フリー素材/写真
Megalomoidea canadensis fossil bivalve (Lockport Dolomite, Middle Silurian; quarry at Clay Center, Ottawa County, northwestern Ohio, USA) 2 / James St. John
| ライセンス | クリエイティブ・コモンズ 表示 2.1 |
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| 説明 | Megalomoidea canadensis (Hall, 1852) - fossil bivalve (internal mold) from the Silurian of Ohio, USA. (lateral view of right side; 8.5 cm across at its widest)Orientation: anterior is to the right; posterior is to the left; dorsal (hinge line) at top; ventral at bottom; right valve is facing the viewerBivalves 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.Shown above 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 at & above center are dolomite.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 SilurianLocality: quarry at or near the town of Clay Center, southern Allen Township, northwestern Ottawa County, northwestern Ohio, USA |
| 撮影日 | 2014-10-20 22:08:10 |
| 撮影者 | James St. John |
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