Quiz, myth or fact, and the shell sizer
Test yourself. Every answer comes with its source.
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The ammonite quiz
1 What were ammonites?
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Sea animals with shells, related to squid. Ammonites were sea animals with shells: extinct cephalopods, the group that includes today’s squid, octopuses and nautiluses. NHM
2 About when did most ammonites die out?
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66 million years ago. They died out about 66 million years ago, and their fossils turn up all around the world, sometimes in huge numbers. NHM
3 Which part of its shell did the animal live in?
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Only the last chamber. The animal lived only in the last chamber, the body chamber. The earlier chambers held gas or fluid, which it could adjust to rise, sink and move, much like a submarine. BGS
4 What are the walls between the chambers called?
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Septa. Ammonites hatched with tiny shells and added new chambers as they grew, moving the whole body forward and sealing off the old space with a wall called a septum. NHM
5 What is the largest known ammonite species?
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Parapuzosia seppenradensis. The largest known species is Parapuzosia seppenradensis, from the Late Cretaceous. The Natural History Museum says the largest specimen is 1.8 metres across and incomplete; whole, it could have been 2.5 to 3.5 metres. NHM
6 Which town has three snakestones on its coat of arms?
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Whitby. Whitby’s coat of arms includes three snakestones. BGS
7 Which ammonite is named after St Hilda?
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Hildoceras bifrons. The ammonite Hildoceras bifrons, one of the commonest at Whitby, is named after her. NHM, snakestones
8 What does the ending -ceras mean?
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Horn. Many ammonite names end in -ceras, from the Greek keras, meaning horn. BGS
9 When was Mary Anning born?
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1799. Mary Anning was born in Lyme Regis in 1799. NHM, Mary Anning
10 What did Joseph and Mary Anning find in 1811 and 1812?
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An ichthyosaur. In autumn 1811, when Mary was 12, Joseph found a strange fossil skull. In November 1812 Mary dug out the outline of its five-metre skeleton, the Natural History Museum says. NHM, Mary Anning
11 Why are ammonites so useful to geologists?
12 On Monmouth Beach, what should you do with water-worn ammonites in the rock?
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Leave them where they are. But visible water-worn ammonites, especially on Monmouth Beach, must be left, and the ammonite pavement must not be damaged. Undercliffs Code
Myth or fact?
Eight statements. Some are true, some are myths.
1 Ammonites were reptiles.
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Myth. But ammonites weren’t reptiles at all. They were sea-dwelling molluscs. NHM
2 Ammonites coiled to the left or right, like snails.
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Myth. Unlike snails, ammonites coil in one plane, so they are neither left- nor right-handed. NHM, snakestones
3 The animal lived only in the last chamber of its shell.
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Fact. The animal lived only in the last chamber, the body chamber. The earlier chambers held gas or fluid, which it could adjust to rise, sink and move, much like a submarine. BGS
4 Some ammonites were as big as a person.
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Fact. Some species were tiny; others were as big as a person. NHM, fossil sites
5 Nobody has found a fossil of ammonite arms yet.
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Fact. No fossil of ammonite arms has been found yet, so much of what we know about the soft body is inferred from living cephalopods. NHM
6 Victorians carved snake heads on ammonites.
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Fact. To back up the legend, and to sell them more easily, Victorians carved snake heads on ammonites. NHM, snakestones
7 Mary Anning was a member of the Geological Society.
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Myth. Because of her gender, she was never a member of the Geological Society. Geological Society
8 Every single ammonite died out at the same moment as the dinosaurs.
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Myth. Not quite all went at once: a few species lived on into the Palaeogene in the Western Interior Seaway before dying out. NHM
The shell sizer
How do you measure up against the biggest and smallest ammonites? Type your height and find out.
The largest known species is Parapuzosia seppenradensis, from the Late Cretaceous. The Natural History Museum says the largest specimen is 1.8 metres across and incomplete; whole, it could have been 2.5 to 3.5 metres. NHM The Late Jurassic Nannocardioceras was tiny: complete adults are rarely more than 20 mm across. BGS
Type your height and press “Measure me”.
Our own arithmetic from the Natural History Museum’s figures (1.8 m, or 2.5 to 3.5 m if complete) and the British Geological Survey’s 20 mm for Nannocardioceras. The life page shows how the sources differ.