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Ammonites are relatives of the modern chambered nautilus shell.  They flourished some 350 million years ago in warm, shallow seas.  About 65 million years ago great droughts led to their extinction and they were buried by layers of sediment. The fossilization process took many years as the original shells were replaced by the minerals in the sediment.  Most ammonites were coiled discs with complex patterns of ridges and suture lines.  This suture pattern is important to species identification and shows where the inner chamber walls meet the outer shell. 






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