Ammonites invite us to look closely. Follow a rib around a fossil shell and a vanished ocean begins to feel a little nearer. Some shells curl into neat spirals. Others wander into hooks, open coils and shapes that seem almost impossible.
This guide brings together Fossil Huntress stories about ammonite shells, unusual forms and the rocks that preserve them. Begin with an introduction, explore a curious shape, then travel into the fossil record of British Columbia.
START WITH THE SHELL
Ammonites were marine cephalopods: relatives of squid, octopuses and cuttlefish. Their shells contained chambers that helped with buoyancy. The animal occupied the outer living chamber, while the shell preserves clues to its growth and way of life.
Start with Ammonites: Chambered Beauty.
WHEN THE SPIRAL TAKES A DIFFERENT TURN
Not every ammonite made a compact, flat coil. Heteromorph ammonites offer a wonderful introduction to the variety of shell forms.
Explore Heteromorph Ammonites, then meet Nipponites: The Ammonite That Tied Itself in Knots.
In a 2020 study, researchers modelled fourteen growth stages of Nipponites mirabilis. Their results suggested that it could remain neutrally buoyant and that its shell allowed rotation around a vertical axis. They proposed a slow, rotating lifestyle while searching for planktonic prey—a fascinating interpretation based on modelling.
Read the original research by Peterman, Mikami and Inoue.
AMMONITES OF VANCOUVER ISLAND
Fossils connect shell shapes to particular rocks and places. For a field story from British Columbia, read Memekay Jurassic Ammonites of Vancouver Island.
Before planning a fossil excursion, check current access, permissions and collecting rules. Conditions described in older field stories may have changed.
MEET A LIVING SHELLED CEPHALOPOD
For another perspective, visit Nautilus: Nautilidae.
A living nautilus can help us ask questions about chambered shells and life beneath the waves. Nautiluses belong to a different lineage, however; they are not surviving ammonites.
TRY LOOKING LIKE A PALAEONTOLOGIST
Choose a fossil photograph from one of these stories. Sketch its outline. Mark the features you can actually see, then write down three questions the photograph cannot answer.
Can you see both sides? Is there a scale? Do you know which rocks it came from?
Observation comes first. A good question is often the beginning of a very satisfying fossil story.
AMMONITE QUESTIONS ANSWERED
WHAT IS AN AMMONITE?
An ammonite was a marine cephalopod with a chambered shell. These extinct animals were relatives of living squid, octopuses and cuttlefish.
ARE AMMONITES STILL ALIVE?
No. Ammonites are extinct. Most disappeared during the mass extinction about 66 million years ago.
IS A NAUTILUS A LIVING AMMONITE?
No. Nautiluses and ammonites belong to different cephalopod lineages. Both have chambered shells, but living nautiluses are not surviving ammonites.
HOW DO AMMONITES HELP SCIENTISTS DATE ROCKS?
Ammonites are ancient timekeepers. Many species evolved rapidly, spread across wide areas and existed for relatively short intervals of geological time. Identifying them helps palaeontologists compare rock layers in different places and work out their relative ages.
This is called biostratigraphy. An ammonite does not provide an exact numerical age on its own; scientists combine fossil evidence with other geological information.
Explore the full story in Ammonite Time Keepers: Index Fossils.
HOW CAN I RECOGNISE AN AMMONITE FOSSIL?
Start with the shell. Many ammonites have a flat spiral, often decorated with ribs, ridges or spines. Some preserve visible chambers or intricate suture lines. But a spiral alone is not enough to identify an ammonite: other shells and natural shapes can look similar.
Look at both sides, the shell edge and any preserved details. The rocks it came from provide important clues, too.
Explore the photographs and shell features in Ammonites: Chambered Beauty.
WHY AREN’T ALL AMMONITES SPIRAL-SHAPED?
Many ammonites grew in a compact, flat spiral, but others developed open coils, hooks, towering spirals and wonderfully tangled shapes. These unusual forms are known as heteromorph ammonites.
Their shells grew in characteristic patterns. Scientists study those shapes to investigate how the animals balanced, moved and lived in ancient seas, although many details remain uncertain.
Explore Heteromorph Ammonites, then meet Nipponites: The Ammonite That Tied Itself in Knots.
WHAT ARE THE INTRICATE PATTERNS ON AMMONITE FOSSILS?
Some ammonite fossils reveal delicate lines resembling leaves, lace or branching rivers. These are sutures: the lines where the internal chamber walls, called septa, met the outer shell wall.
Sutures differ from the raised ribs decorating the shell’s exterior. Their shapes help palaeontologists distinguish groups of ammonites and interpret their fossils.
Take a closer look in Sutures, Ridges and Lobes.
FURTHER READING
Natural History Museum, London: What is an ammonite?
Peterman, D. J., Mikami, T. and Inoue, S. (2020). The balancing act of Nipponites mirabilis. PLOS ONE, 15(8), e0235180.
