Every fact

192 facts, every one sourced

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1 Ammonites were sea animals with shells: extinct cephalopods, the group that includes today’s squid, octopuses and nautiluses. NHM
2 They died out about 66 million years ago, and their fossils turn up all around the world, sometimes in huge numbers. NHM
3 Ammonites belonged to the phylum Mollusca and the class Cephalopoda. BGS
4 Cephalopods fall into three groups: coleoids (squid, octopuses and cuttlefish), nautiloids, and ammonites. NHM
5 Their shells make them look like nautiluses, but the Natural History Museum says they are thought to be more closely related to the coleoids. NHM
6 The museum’s fossil curator thinks ammonites more likely had eight arms than the many tentacles of a nautilus. NHM
7 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
8 The British Geological Survey calls ammonites extinct relatives of sea creatures such as the modern nautilus. BGS
9 Britannica describes ammonoids as forms related to the modern pearly nautilus. Britannica
10 The Natural History Museum’s folklore article calls the chambered nautilus the ammonites’ nearest living relative, a ‘living fossil’. NHM, snakestones
11 A 2021 study of a rare fossil with soft parts found evidence that squid, octopuses and cuttlefish might be closer relatives of ammonites than had been thought. Imperial College
12 Ammonites had a coiled shell on the outside of the body. In living octopus, squid and cuttlefish, the shell is small and inside the body, or missing. BGS
13 Every ammonite had a shell divided into chambers, which it used to float. NHM
14 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
15 Nobody knows how often a new chamber was built. A monthly rhythm has been suggested, but there is no evidence for it. NHM
16 The septa strengthened the shell and stopped the water pressure outside from crushing it. BGS
17 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
18 The chambers were linked by a tube. NHM, fossil sites
19 Where each septum met the shell wall it left a wiggly line called a suture. The septa had frilled edges. BGS
20 Each complete turn of the coil is called a whorl. BGS
21 Apart from the innermost whorl, the shell had three layers of aragonite, a form of calcium carbonate. The thick middle layer was nacre, or mother-of-pearl. BGS
22 Ribs, spines and knobs on the shell may have made it stronger, and may have helped protect and hide the animal. They also helped with buoyancy and may have been for display. BGS
23 Most ammonite shells grew into a flat spiral, called a planispiral. NHM
24 Shells could be loosely or tightly coiled, flat or twisted like a corkscrew, and some started as a tight spiral and then straightened out. NHM
25 Nipponites mirabilis, found in Japan, is exceptionally rare and looks a bit like a knot. NHM
26 Ammonites coiled in unusual ways are called heteromorphs, from Greek words meaning ‘different’ and ‘form’. BGS
27 Unlike snails, ammonites coil in one plane, so they are neither left- nor right-handed. NHM, snakestones
28 Books traditionally draw ammonites with the body chamber at the top. In life they swam the other way up. BGS
29 A 3D study of a fossil with preserved muscles suggests ammonites swam by jet propulsion, pushing water out through a tube called a hyponome. Imperial College
30 Paired muscles probably pulled the animal deep into its body chamber for protection. Ammonites had no ink sac to hide behind, unlike squid and octopuses. Imperial College
31 That fossil, five centimetres across, was found in Jurassic rock in Gloucestershire in 1998. It was the first time an ammonite’s soft parts had been seen in three dimensions. Imperial College
32 The same study found muscles that nautiluses do not have, so ammonites and the nautilus may be less alike than was thought. Imperial College
33 Males and females looked different. Males (microconchs) could have long prongs called lappets near the shell opening; females were macroconchs. NHM
34 An estimated more than 10,000 ammonite species have been discovered, and possibly more than 20,000. NHM
35 Counting is tricky because males and females of one species were once often named as two separate species. NHM
36 Many ammonite names end in -ceras, from the Greek keras, meaning horn. BGS
37 Each ammonite has a two-part Latin name, the genus followed by the species, plus the name of the person who first described it and the date. BGS
38 The Natural History Museum says the wider group Ammonoidea first appeared about 450 million years ago. NHM
39 The ‘true ammonites’, the Ammonitida, are known from the Jurassic Period, from about 200 million years ago. NHM
40 Britannica says ammonoid fossils are found in rocks from the Devonian Period, which began 419 million years ago, to the end of the Cretaceous, 66 million years ago. Britannica
41 The British Geological Survey says ammonites lived in the Jurassic and Cretaceous, a span of about 140 million years. BGS
42 The Jurassic began about 201 million years ago and the Cretaceous ended about 66 million years ago. BGS
43 Three groups followed one another, each with a more complicated suture. The goniatites, with simple sutures, flourished in the Palaeozoic Era, 541 to 252 million years ago. Britannica
44 The ceratites, with more folded sutures, came next and were most common in the Triassic, 252 to 201 million years ago. Britannica
45 Most of them died out at the end of the Triassic, but a few survived and gave rise to many forms with the intricate ‘ammonite’ suture. Britannica
46 Ammonites lived all over the world, and only in the sea. NHM
47 So if you find an ammonite in a rock, the place you are standing was once under the sea. NHM, fossil sites
48 The Natural History Museum says they tended to live in shallower seas, perhaps down to about 400 metres. NHM
49 The British Geological Survey says they could probably not cope with depths of more than 100 metres. BGS
50 Ammonites ranged from a few millimetres across to many times bigger. Big ones were more common from the Late Jurassic onwards. NHM
51 Some species were tiny; others were as big as a person. NHM, fossil sites
52 The Late Jurassic Nannocardioceras was tiny: complete adults are rarely more than 20 mm across. BGS
53 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
54 The British Geological Survey gives the same specimen as 1.95 m across, found in Germany in 1895, and about 2.55 m if complete. BGS
55 Britannica measures the shell of Pachydiscus seppenradensis (an older name) at 205 centimetres and calls it probably the largest shelled mollusc ever. Britannica
56 Depending on their size, ammonites probably ate much what cephalopods eat today, such as crustaceans, bivalves and fish. Smaller species probably ate plankton, and some may have scavenged. NHM
57 The British Geological Survey suggests small plankton or plants on the sea floor, slow-moving animals of the seabed, and drifting or dead sea creatures. BGS
58 Britannica says nearly all ammonoids are thought to have been predators, with evidence that they ate zooplankton, crustaceans and other ammonoids. Britannica
59 Ammonites were food for others too: there is evidence that mosasaurs and ichthyosaurs ate them, and fish probably did. NHM
60 Their enemies included marine reptiles, crustaceans, fish and even other ammonites. BGS
61 Most ammonites died out with the non-avian dinosaurs at the end of the Cretaceous, when an asteroid hit Earth. NHM
62 A long impact winter stopped photosynthesis on land and in the sea, cutting off food. That was devastating for ammonites. NHM
63 Britannica notes a theory that a sudden fall in plankton at the end of the Cretaceous finished off the last ammonoids. Britannica
64 Not quite all went at once: a few species lived on into the Palaeogene in the Western Interior Seaway before dying out. NHM
65 Nautiluses survived, probably partly because they live in deeper water, which was less affected, and because their larger hatchlings were less limited by the size of food. NHM
66 After extinctions, many shelled animals shrink because they lack the resources to grow, so ammonite sizes can help scientists study past climate change. NHM
67 Studies of the chemistry of the shells, called sclerochronology, are starting to show how long ammonites might have lived. NHM
68 Fossils are the remains of plants and animals buried in sediments such as sand and mud under ancient seas, lakes and rivers. BGS, fossils
69 Rapid burial by sediment that had settled out of water is needed for a fossil to form. BGS, fossils
70 Soft parts rot soon after death, but hard parts such as shells, bones and teeth can be replaced by minerals that harden into rock. BGS, fossils
71 The word fossil comes from the Latin fossilis, meaning ‘unearthed’. BGS, fossils
72 Fossils include any preserved trace of life that is usually more than 10,000 years old. BGS, fossils
73 The commonest way is petrification by permineralisation: mineral-rich water soaks through a buried shell or bone and minerals such as calcium carbonate or silica fill and finally replace it. BGS, fossils
74 If the shell dissolves away it can leave a hollow in its shape, a mould. Sediment can later fill the hollow to make a matching cast. BGS, fossils
75 Usually the coiled shell is the only part of an ammonite that is preserved. BGS
76 Fossils are usually found in sedimentary rock, formed when sand, silt, mud or the shells of sea creatures settle in layers that are pressed together. NHM, fossils
77 Some ammonites look as if they were dipped in gold. The colour comes from iron pyrite, often called fool’s gold. NHM, snakestones
78 Pyrite reacts with air and moisture, and that can make a fossil fall apart. NHM, fossils
79 Some Cretaceous ammonites keep much of their original shell, which gives them a pearly shine. NHM, snakestones
80 Index fossils are used to work out the age of sedimentary rocks: finding the same one in different places shows the rocks formed at about the same time. NHM, fossils
81 Because ammonites were common and evolved fast, much of Europe’s Mesozoic rock has been divided into ‘ammonite zones’. NHM
82 They make excellent guide fossils: each species lasted a fairly short time, they turn up in many kinds of marine rock, they are common and quite easy to identify, and they lived worldwide. BGS
83 Ammonites can pin down slices of geological time less than 200,000 years long, which is very precise for Earth history. BGS
84 Britannica also calls ammonoids important index fossils, for their wide spread, rapid evolution and easily recognised features. Britannica
85 Using ammonites to date rocks was pioneered in the 1850s by two Germans, Friedrich Quenstedt and his former pupil Albert Oppel. BGS
86 Their work used the ammonites of southern Germany’s Swabian and Franconian Alb, part of the range that runs on from the Jura Mountains, which gave the Jurassic its name. BGS
87 The crinkly, complex suture is what tells ammonoids apart from nautiloids. Britannica
88 Ammonites evolved so quickly that sampling up through layers of rock shows the changes from one layer to the next. NHM
89 The Dorset and East Devon Coast, the Jurassic Coast, is a UNESCO World Heritage Site of eight sections along 155 km of coast. UNESCO
90 Its cliffs show an almost unbroken run of Triassic, Jurassic and Cretaceous rocks covering about 185 million years of Earth’s history. UNESCO
91 It was inscribed as a World Heritage Site in 2001. UNESCO
92 The coast has been studied by scientists for more than 300 years. UNESCO
93 Fast erosion keeps the rock faces fresh and keeps the coast producing new fossils. UNESCO
94 Lyme Regis is known for a near-complete Jurassic ammonite zonation, and for the marine reptile fossils first collected by Mary Anning. IUGS
95 The West Dorset coast has one of the finest exposures of Lower and Middle Jurassic rocks anywhere in the world. West Dorset Code
96 High erosion, especially in winter, keeps the beaches supplied with fossils. West Dorset Code
97 Natural England has made this coast a Site of Special Scientific Interest for its geology, fossils and landslides. West Dorset Code
98 Monmouth Beach, to the west of the Cobb at Lyme Regis, is popular with fossil hunters. Ammonites, belemnites, fossil plants and even ichthyosaur vertebrae have been found there. Visit Dorset
99 Its cliffs are said to date from 189 to 199 million years ago, from the Early Jurassic, when warm seas covered most of the UK. Visit Dorset
100 At low tide, a limestone layer at the far end of the beach, the ammonite graveyard or pavement, shows hundreds of large ammonites in the bedrock and boulders. Visit Dorset
101 Monmouth Beach is the way into the Axmouth to Lyme Regis Undercliffs National Nature Reserve, about 6 miles of landslipped undercliffs between Devon and Dorset. Undercliffs Code
102 The shore and cliffs at Lyme Regis and at Whitby in Yorkshire are famous places for collecting ammonites. BGS
103 The Natural History Museum names Lyme Regis in Dorset and Runswick Bay in Yorkshire as good places to find ammonites, in rocks about 201 to 66 million years old. NHM, fossil sites
104 On the Isle of Wight, Watershoot Bay near St Catherine’s Lighthouse has Late Cretaceous rocks about 95 to 99 million years old, good for ammonites, bivalves and brachiopods. NHM, beach guide
105 As a general rule, landowners own the fossils on or under their land. The National Trust is the main landowner on the West Dorset coast. West Dorset Code
106 The West Dorset Code’s best advice for beginners and school groups is to stick to the beaches. West Dorset Code
107 Always check the tide times before you go. The Code advises collecting on a falling tide. West Dorset Code
108 Always tell someone where you are going and when you expect to be back. West Dorset Code
109 Cliff falls happen suddenly and without warning, so keep away from the base of cliffs. West Dorset Code
110 Keep off moving rock falls and mudflows. The seaward edges of mudflows can be hidden under shingle. West Dorset Code
111 There should be no digging into the cliffs without permission. West Dorset Code
112 Ammonites are among the commonest fossils on the Dorset coast, so ordinary finds don’t need recording, though unusual species or very large shells are worth recording. West Dorset Code
113 The West Dorset Code covers National Trust and Charmouth Parish Council land between Lyme Regis and Hive Beach at Burton Bradstock. West Dorset Code
114 In the Undercliffs reserve you may collect loose material found on the beaches and foreshore. Undercliffs Code
115 But visible water-worn ammonites, especially on Monmouth Beach, must be left, and the ammonite pavement must not be damaged. Undercliffs Code
116 Power tools must not be used there without consent from Natural England. Undercliffs Code
117 If you use a hammer or other tools, wear goggles. West Dorset Code
118 The Natural History Museum’s advice: make sure you have permission for where you go and what you take, and look up the rules for each place. At some sites you may look but not collect. NHM, beach guide
119 Never dig fossils out of cliffs: it makes them even less stable, and you would need the landowner’s permission. NHM, beach guide
120 If an exciting fossil is stuck in a cliff, take a photo, note where it is and tell a museum. NHM, beach guide
121 In some places the tide rises much faster than you might expect and can cut you off, so always have a way back. NHM, beach guide
122 The museum’s guide says the best tools are your eyes: in most places many fossils can be found loose on the beach and simply picked up. NHM, beach guide
123 Its suggested kit is sturdy walking boots with good ankle support, a rucksack for your finds and a first aid kit. NHM, beach guide
124 And leave some fossils for other people to find: you don’t have to collect everything. NHM, beach guide
125 Mary Anning was born in Lyme Regis in 1799. NHM, Mary Anning
126 Her birthday was 21 May 1799. BBC News
127 The family were very poor dissenters, Protestants outside the Church of England. NHM, Mary Anning
128 The Natural History Museum says only Mary and her older brother Joseph, out of nine children, survived to adulthood. NHM, Mary Anning
129 The Geological Society says her parents had at least nine children, and only two grew up. Geological Society
130 BBC News says she was one of 10 children, and eight of her nine brothers and sisters died before adulthood. BBC News
131 Her father Richard was a cabinetmaker and amateur fossil collector who taught her to find and clean fossils, and sold them from his shop. NHM, Mary Anning
132 By the age of five or six, Mary was helping him collect fossils. NHM, Mary Anning
133 She had little formal education but could read, and taught herself geology and anatomy. NHM, Mary Anning
134 She even dissected modern fish and cuttlefish to understand the fossils she found better. BBC News
135 Richard died in 1810, and Mary helped pay off the family’s debts by selling her finds. NHM, Mary Anning
136 Mary later told a visitor that her father died when she was ten. Wandering the shore, she picked up a fossil and showed it to a lady collector, who gave her half a crown. Geological Society
137 BBC News says she was 11 when he died. BBC News
138 Lyme Regis was especially rich in ammonites, then called ‘Ammon’s horn’, and in belemnites, the ‘devil’s fingers’. NHM, Mary Anning
139 In the Napoleonic Wars, people holidayed at home, and tourists flocked to seaside towns like Lyme Regis. NHM, Mary Anning
140 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
141 BBC News says that in 1811, aged just 12, Mary discovered a 5.2 m (17 ft) skeleton, now known to be an ichthyosaur. BBC News
142 By 1820 it had been recognised as an extinct marine reptile and named Ichthyosaurus, ‘fish lizard’. It was the first ichthyosaur to be studied scientifically. NHM, Mary Anning
143 Today the specimen is called Temnodontosaurus platyodon, and it is in the Natural History Museum’s collections. NHM, Anning’s fossils
144 In December 1823 Mary found the first complete skeleton of a Plesiosaurus, ‘near to reptile’. NHM, Mary Anning
145 The great French naturalist Georges Cuvier at first thought it might be a fake. The Geological Society of London held a special meeting about it, but Mary was not invited. NHM, Mary Anning
146 Once convinced, Cuvier sent someone to buy a specimen for Paris. Mary bought one from another collector and sold it to him for three times the price. NHM, Anning’s fossils
147 In December 1828 she found a jumble of bones with wings and a long tail: the first pterosaur found outside Germany, now known as Dimorphodon. NHM, Mary Anning
148 She also pioneered the study of coprolites, which is fossilised poo. NHM, Mary Anning
149 In 1830 her childhood friend Henry De la Beche painted Duria Antiquior, ‘A More Ancient Dorset’, and sold prints to raise money for her. NHM, Mary Anning
150 It was the very first picture of prehistoric life based on fossil evidence, the start of what is now called palaeoart. NHM, Mary Anning
151 Male scientists who bought her fossils often didn’t credit her in their papers. NHM, Mary Anning
152 The Geological Society did not admit women as Fellows until 1908. NHM, Mary Anning
153 Because of her gender, she was never a member of the Geological Society. Geological Society
154 As far as we know, her only published writing is a short extract from a letter, printed in 1839. NHM, Anning’s fossils
155 Mary Anning died in 1847, aged only 47, still short of money. NHM, Mary Anning
156 Henry De la Beche, by then president of the Geological Society, read a tribute to her at a meeting, breaking the society’s members-only tradition. BBC News
157 Three years later, members of the Geological Society paid for a stained-glass window in her memory in the church where she is buried. BBC News
158 She is buried at St Michael the Archangel Church in Lyme Regis. BBC News
159 Lyme Regis Museum stands, by chance, on the site of her birthplace and family home. BBC News
160 In 2022 a statue of Mary and her dog was unveiled in Lyme Regis, after a campaign started by 11-year-old Evie Swire. NHM, Mary Anning
161 She has also been honoured with special Royal Mail stamps and a 50p coin. NHM, Mary Anning
162 Several species are named after her, but only one, the fish Acrodus anningiae, during her lifetime. NHM, Anning’s fossils
163 In 2015 a study proposed that one of her ichthyosaurs was a new species, now called Ichthyosaurus anningae. NHM, Anning’s fossils
164 The 2020 film Ammonite, with Kate Winslet as Mary, is not a biopic: its director says so. BBC News
165 A portrait shows her with her dog Tray, looking east towards Lyme Regis and Golden Cap. IUGS
166 In England, ammonite fossils were called snakestones, because they look like coiled snakes turned to stone. NHM, snakestones
167 But ammonites weren’t reptiles at all. They were sea-dwelling molluscs. NHM
168 Snakestone stories came mainly from two places where ammonites are common: Whitby in Yorkshire and Keynsham in Somerset. NHM, snakestones
169 In his book Britannia of 1586, William Camden wrote that if you broke them open you found ‘stony serpents, wreathed up in circles, but eternally without heads’. NHM, snakestones
170 To back up the legend, and to sell them more easily, Victorians carved snake heads on ammonites. NHM, snakestones
171 The British Geological Survey says local collectors and dealers often carved heads on them. BGS
172 In Whitby the legend goes back to Saint Hilda (614–680), the Saxon abbess who was to found an abbey there. She is said to have turned the town’s snakes to stone and thrown them off the cliffs. NHM, snakestones
173 The ammonite Hildoceras bifrons, one of the commonest at Whitby, is named after her. NHM, snakestones
174 Sir Walter Scott told the story in his poem Marmion: ‘Of thousand snakes, each one / Was changed into a coil of stone’. NHM, snakestones
175 Whitby’s coat of arms includes three snakestones. BGS
176 Some versions bring in St Cuthbert, a seventh-century monk said to have cast a beheading curse on the snakes, which explains why snakestones have no heads. NHM, snakestones
177 In Keynsham the story is that St Keyna turned the serpents of the woods to stone by prayer. NHM, snakestones
178 Other stories said snakestones had once been fairies, turned into snakes and then into stone. NHM, snakestones
179 The Natural History Museum says early Greeks linked ammonites with the horned god Jupiter Ammon and called them Cornu Ammonis, ‘horns of Ammon’, the origin of the name ammonite. NHM, snakestones
180 The British Geological Survey says ammonites take their name from the Egyptian god Amun, whom the Greeks called Zeus Ammon and showed with curling ram’s horns. BGS
181 Ammonites have fascinated people since at least the Middle Stone Age, and have been found on every continent. NHM, snakestones
182 Ancient Romans believed that sleeping with a golden, pyrite ammonite from Ethiopia under the pillow could help you dream the future. NHM, snakestones
183 In Hindu culture, black stones holding ammonites are called saligrams, and are treasured because they look like the disc, or chakra, held by the god Vishnu. NHM, snakestones
184 True saligrams come only from the valley of the Gandaki River in Nepal and northern India. Sanskrit texts mention them over 2,200 years ago. NHM, snakestones
185 In Chinese folklore ammonites were Jiaoshih, horn stones, because they look like coiled rams’ horns. NHM, snakestones
186 The 11th-century Chinese scientist Su Sung described a ‘stone-serpent’ shaped like a coiled snake with no head or tail-tip, adding that nobody knew what animal had been turned to stone. NHM, snakestones
187 The Blackfoot people of North America called ammonites insikim, buffalo stones, because they look like sleeping bison, and used them in ceremonies to bring bison herds in. NHM, snakestones
188 It was believed buffalo stones could have babies, perhaps because ammonites tend to break apart along their septa. NHM, snakestones
189 In New Guinea, the Tifalmin people of the Upper Sepik River used ammonites as charms for hunting and farming. NHM, snakestones
190 Farmers in Germany’s Harz Mountains called them dragonstones, and put one in the milk pail to bring back a cow’s milk. NHM, snakestones
191 In parts of Scotland they were crampstones, used on cows with cramp. NHM, snakestones
192 Ammonites have been collected more than 5,000 metres above sea level in the Himalayas. NHM, snakestones