Gryphaea dilobotes (fossil oyster) (Kellaways Formation, Middle Jurassic; England) 5 : 無料・フリー素材/写真
Gryphaea dilobotes (fossil oyster) (Kellaways Formation, Middle Jurassic; England) 5 / 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 | Gryphaea dilobotes Duff, 1978 - fossil oyster shell from the Jurassic of England. (lateral view of right valve)Orientation:Top - dorsalBottom - ventralTo the right - anteriorTo the left - posterior side & posterior flangeMost modern and fossil clams have asymmetrically-shaped but equal-sized shells that are mirror images of each other. Oyster shells depart radically from this general rule. The Gryphaea oysters evolved a greatly enlarged, coiled, highly convex left valve & a greatly reduced, concave right valve. The overall shape of gryphaeid oyster shells was a consequence of their living on soft, fine-grained substrates. All oysters are filter feeders, and practically all are hard substrate encrusters at some point in their ontogeny. The highly coiled Gryphaea oysters are free-living forms as large adults. Their shell shape appears to be the result of repeated downward toppling into the mud along the ventral margin of the left valve by the weight of the shell.Classification: Animalia, Mollusca, Bivalvia, Pteriomorphia, Pterioida, Ostreina, Ostreoidea, Gryphaeidae Stratigraphy: Kellaways Formation, Callovian Stage, upper Middle Jurassic Locality: unrecorded/undisclosed site in England |
| 撮影日 | 2020-10-27 15:34:58 |
| 撮影者 | James St. John |
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