File:Cleoniceras madagascariense fossil ammonite (Lower Cretaceous; Mahajanga, northwestern Madagascar) (15053947408).jpg

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Cleoniceras madagascariense (5.4 cm across) with preserved shell iridescence. This is a commercial specimen attributed to the Albian Stage (uppermost Lower Cretaceous) of Mahajanga, northwestern Madagascar.

Ammonites are common & conspicuous fossils in Mesozoic marine sedimentary rocks. Ammonites are an extinct group of cephalopods - they’re basically squids in coiled shells. The living chambered nautilus also has a squid-in-a-coiled-shell body plan, but ammonites are a different group.

Ammonites get their name from the coiled shell shape being reminiscent of a ram’s horn. The ancient Egyptian god Amun (“Ammon” in Greek) was often depicted with a ram’s head & horns. Pliny’s Natural History, book 37, written in the 70s A.D., refers to these fossils as “Hammonis cornu” (the horn of Ammon), and mentions that people living in northeastern Africa perceived them as sacred. Pliny also indicates that ammonites were often pyritized.

Classification: Animalia, Mollusca, Cephalopoda, Ammonoidea, Ammonitina
Date
Source Cleoniceras madagascariense fossil ammonite (Lower Cretaceous; Mahajanga, northwestern Madagascar)
Author James St. John

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This image was originally posted to Flickr by jsj1771 at https://www.flickr.com/photos/47445767@N05/15053947408. It was reviewed on 6 May 2015 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-2.0.

6 May 2015

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current19:08, 6 May 2015Thumbnail for version as of 19:08, 6 May 20151,071 × 1,000 (140 KB)Natuur12 (talk | contribs)Transferred from Flickr via Flickr2Commons

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