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Sunday, 26 January 2014

Year 10 Geologists Learn About Ammonites

Year 10 Geologists display some of the fossils in the Stover collection
In a new departure for Stover, 6 Year 10 pupils have taken up the study of Geology this academic year. They are following the WJEC syllabus, and have recently been learning about various fossil groups, including ammonites.

Annie points out an ammonite
Ammonites are an extinct group of marine cephalopod molluscs, which lived in Jurassic and Cretaceous times. Cephalopods (ammonites, nautiloids, octopuses, squids etc.) are the most highly evolved of the molluscs, and in many ways are the most highly evolved of the invertebrates in general (complex eye, large brain etc.). The mouth is surrounded by tentacles, which usually have suckers. Some modern forms have lost their shells (octopus), some have a straight internal shell (cuttlefish, squid) and some still have a coiled external shell (nautilus).

Most ammonites were probably active carnivores and accomplished swimmers. They were able to control their buoyancy by filling the inner chambers of their coiled shells with water or gas through their siphuncle (see diagram). The outside of the shell was often ribbed or keeled in a distinctive way (which is how most fossil species are told apart). Other fossil forms with external shells include: Nautiloids (Cambrian to Recent) and Goniatites (Devonian to Permian).


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