SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY SINCLAIR STAMMERS / SCIENCE PHOTO LIBRARY
Fossilised Gryphaea arcuata, or 'Devil's Toenail', from Jurassic Lower Lias at Hock Cliff, Gloucestershire, UK. This an extinct marine oyster with an exceptionally thick shell that lived in deep marine sediments. The Jurassic period extended from around 200 to 145 million years ago.
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