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Summary
| Description |
Many fossils of shelly organisms (e.g., bivalves, gastropods, brachiopods, cephalopods) have had the original hard parts dissolved away. In such cases, the fossil itself is an impression of the outside of the shell (external mold) or an impression of the inside of the shell (internal mold).
Hormotoma (Mollusca, Gastropoda, Archaeogastropoda, Murchisonioidea, Murchisoniidae) (4.9 cm tall) - this fossil snail from eastern Iowa is preserved as an internal mold (= the coiled portion; fine-grained sediment has filled up the originally-hollow shell) and as an external mold (= the cavity in which the coil sits). Note the gap between the external & internal molds - that's where the original CaCO3 shell was.
Stratigraphy: Galena Formation, upper Middle Ordovician to lower Upper Ordovician |
| Date | |
| Source | Internal mold, Hormotoma, Mollusca, Gastropoda, Murchisonioidea, Iowa, USA |
| Author | James St. John |
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This image was originally posted to Flickr by jsj1771 at https://www.flickr.com/photos/47445767@N05/8465377858. It was reviewed on 13 October 2013 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
|---|---|---|---|---|---|
| current | 10:35, 13 October 2013 | | 630 × 994 (169 KB) | Jacopo Werther | {{Information |Description=Many fossils of shelly organisms (e.g., bivalves, gastropods, brachiopods, cephalopods) have had the original hard parts dissolved away. In such cases, the fossil itself is an impression of the outside of the shell (external... |
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