Pronounced – Am-mon-nite
Meaning of name – The shell resembles the coiled ram’s horn (a ram was the symbol for the Egyptian god Ammon)
Group – Cephalopods, Mollusc
Age – Lower Jurassic, around 195 million years old
Ammonites are a well known fossil and easily recognised by their coiled shell. They first appeared around 400 million years ago and became a very successful group of animals. They died out around the same time as the dinosaurs about 65 million years ago. Ammonites were free swimming creatures related to squid and octopuses. Like these modern relatives they would have been predators, catching prey with their long tentacles. Their shell was divided up into chambers filled with liquid and gas, which kept them buoyant in the water. They can be preserved in a number of different ways.
Click on the images below to find out more.
Also check out our Facebook page for recent finds and news from the Centre.
Calcite split This calcite ammonite (Promicroceras sp.) has been found by splitting one of the layers of hard limestone rocks with a geological hammer. You should always wear goggles when hitting rocks and ask at the Heritage Centre for advice on how to find them.
Fool’s Gold Ammonite The shells of some ammonites have been replaced by ‘fool’s gold’, also known as iron pyrite. These are some of the most beautiful ammonites from the beaches around Charmouth.
Asteroceras assemblage These ammonites have been painstakingly prepared from the hard limestone rock that protected them. They have been preserved in 3D so you can see the actual shapes of these Jurassic shells which have been preserved in calcite.
Pyrite Ammonite This ammonite has been preserved in iron pyrite (fool’s gold). They are found washed out of the cliffs among the loose pebbles on the beach.
© Photo Copyright David Sole
Beef Rock Ammonite These ammonites are preserved in a type of limestone called ‘Beef rock’.
Iridescent Ammonite Sometimes part of the original iridescent shell is preserved in calcite ammonites. This small band of the shell has stayed the same chemically for 195 million years and is similar to the mother-of-peal that you see on modern polished shells.
Mature Ammonite - This stunning Arnioceras ammonite has a strange process at the end of the opening of its shell. This is called a lappet and can tell us that this is an adult specimen. Many species of ammonites show differences at this part of the shell and experts think the differences mean they are male or female.
This ammonite was found by David Sole and prepared by Andy Cowap. It is now on display at Lyme Regis Museum.
Phone: 01297 560772