File:Ammonite (Pierre Shale, Upper Cretaceous; Great Plains, USA) 1.jpg

English: (outdoor public display, Ashfall Fossil Beds State Historical Park, Nebraska, USA)

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Ammonites are common and 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.

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From exhibit signage:

Ammonite (A sea creature that lived in Nebraska during the age of dinosaurs)

250 feet below where you are standing is a thick layer of black shale deposited in a shallow sea more than 70 million years ago. Called the Pierre Shale, this deposit covers most of the northern Great Plains and is an important source of petroleum (oil) in southwestern Nebraska and northeastern Colorado. The most common large animal fossils in the Pierre Shale are ammonites - extinct relatives of the chambered nautilus that lives in tropical seas today. These squid-like animals were probably active predators that caught smaller animals with their tentacles.

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Classification: Animalia, Mollusca, Cephalopoda, Ammonoidea, Ammonitida

Stratigraphy: Pierre Shale, Upper Cretaceous

Locality: unrecorded site in the American Great Plains

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Info. at:

en.wikipedia.org/wiki/Ammonitida