From the Seaboard Centre, Balintore

Click on the photo to enlarge this ammonite fossil from The Seaboard Centre in the Highlands of Scotland.

Making sense of ammonite fossils

What are ammonite fossils?

Ammonites are extinct sea creatures with a spiral shell that lived millions of years ago. Today, they are commonly found as fossils, helping scientists to learn about ancient oceans and past environments.

Though they are related to modern-day squid and octopus, ammonites became extinct around 66 million years ago.

Like most body fossils, only the hard parts of ammonites have been preserved. Millions of fossilised ammonite shells are found across the world but we almost never find any evidence of the soft body that they would have had. We can, however, compare ammonites with living creatures. The present is the key to the past.

When scientists examine the shells of ammonites, they can see how they grew.

The importance of ammonites 

In the 1830s, a young man called Lewis Hunton, from Loftus in North Yorkshire, worked out that ammonites were really useful for telling one layer of rock from another.

Lewis noticed that when he looked at the cliffs and quarries in his local area, the rocks often looked very similar, but the fossils changed from layer to layer. This was particularly clear when looking at ammonites because their features changed rapidly (in relative terms) as they evolved in response to the changing environment. If you look carefully at a range of different ammonite fossils, you’ll spot lots of variations between them.   

By carefully observing (looking) and describing (drawing and writing), Lewis made a picture showing which layer contained which type of ammonite. This was the beginning of the science of biostratigraphy (‘life layer writing’), where species of fossil enable palaeontologists to know which layer of rock they are studying.

Ammonites are still used today to divide Jurassic and Cretaceous time into different intervals. Lewis’s work also showed that to do this properly you had to collect fossils directly from the layers, not from fallen rocks on a quarry floor or a beach.

Ammonite from Whitby Museum

Click on the photo to enlarge this ammonite fossil from Whitby Museum.

Ammonite from Whitby Museum

Click on the photo to enlarge this ammonite fossil from Whitby Museum.

Myths and legends about ammonites 

Before scientists came up with our modern ideas of what ammonites were, many different places across the world had their own stories

Around the Mediterranean, the curly fossilised shells get their name from the Egyptian god Amun, or Ammon, who had spiralling ram’s horns on his head. Across the world, though, ammonites are associated with all sorts of other stories. In northern India and Nepal, they are shaligrams, sacred relics of the god Vishnu. To the Blackfoot people of North America, they were insikim, or buffalo-stones.

In Whitby, North Yorkshire, they were called ‘snakestones’, said to be serpents turned to stone by St Hilda.

Ammonites from Scarborough's Rotunda Museum © David Chalmers Photography

Click on the photo to enlarge these ammonite fossils from Scarborough’s Rotunda Museum (photo by David Chalmers).

Why do we find so many ammonites?

Ammonites were abundant and widespread in ancient oceans for millions of years. Their hard shells fossilised well in marine sediments, preserving them in rock layers.

Today ammonites are often found in coastal cliffs where layers of sedimentary rock are exposed. These formed millions of years ago when ancient seas covered the areas we now see as land.

You can also sometimes spot fossils in and on historic buildings. During the 18th and 19th centuries builders often used locally sourced stone, both for practicality and cost-efficiency, and so in some areas of the country this is particularly the case.

Brora, in Sutherland in the Highlands of Scotland, sits in an area with Jurassic-age sedimentary rocks, particularly sandstone, that are rich in fossilised ammonites and other marine life which show up in the building materials.

Ammonite from wall at Brora Heritage

Click on the photo to enlarge this ammonite fossil from Brora Heritage.

At a glance – click to see a range of ammonites from museums across Britain.

Watch the video – coming soon.

Explore ammonites with your group.

 

Talking Points

Have you ever found an ammonite fossil? Where did you find it if so? How big was it?

Before people knew what ammonite fossils are, they made up stories that they were snakes turned to stone? Do you think they look like snakes? What else do you think they look like? 

People have been badly injured whilst collecting fossils on beaches. What dangers do you think can be encountered whilst fossil hunting? What precautions should people take?

 

Vocabulary

Quarry – a place where rocks and minerals are dug out of the ground

Palaeontology – the scientific study of fossils

Biostratigraphy – the science of dividing up layers of rock according to the fossils they contain

 

Hands on History

Click on the pins on the maps to find out more about the museums with these ammonite in their collections

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