Mudlarking: Fantastic Beasts of the Thames

By Jason Sandy

fossils found in london england

Collection of Thames fossils, Sam Caethoven.

Can you imagine seeing a hippo swimming in the River Thames or a rhino drinking from its cool waters? Millennia ago, London was home to a wide variety of animals typically associated with Africa, not Europe. During the Paleolithic Age, ancient beasts such as straight-tusked elephants, hippos, rhinos, cave lions, wolves, hyenas, brown bears, giant deer, and large oxen (known as aurochs) freely roamed the fertile Thames Valley and grazed in the grassy floodplain along the river. At that time, the banks of the Thames extended to present day Trafalgar Square, and these exotic animals thrived in the warm, tropical climate. During major excavation work under this popular tourist site in the 19th century, a 125,000-year-old hippopotamus tooth and remains from a prehistoric elephant were discovered.

wooly rhino and mammoth fossils from thames

Woolly rhinoceros skull, Nick Stevens. Illustration of woolly rhino by Mauricio Antón, Public Library of Science. Woolly mammoth teeth, Alan Murphy. Illustration of woolly mammoths by Mauricio Antón, Public Library of Science.

Along the River Thames, mudlarks have also found traces of these ancient beasts. Several years ago, Stefano Ambrogi discovered part of a skull from a woolly rhinoceros in the river. Bones from woolly rhinos have also been found in the Thames Estuary and along the river under Battersea Power Station. Although they died out about 8,000 years ago, woolly rhinos were once a common sight in the London area. With its thick fur and dense layer of fat to keep warm in the extreme cold, these prehistoric rhinos survived the last Ice Age.

At low tide along the Thames foreshore, Alan Murphy discovered two fossilized teeth from woolly mammoths who have been extinct for around 10,000 years. Woolly mammoths lived during the Pleistocene epoch and were approximately the same size as modern African elephants, weighing about 6 tons. With their thick coat of fur, they were well adapted to London’s cold climate back then. Their long, curved tusks and large trunk were used to move objects, forage, bathe, and fight. Their four molar teeth were replaced six times during their lifetime, and this is potentially the reason why several mammoth teeth have been found in the Thames. In 1864, a complete 200,000-year-old steppe mammoth skull with tusks was found in Ilford, London. It’s hard to imagine these giant beasts walking through the London area hundreds of thousands of years ago when it was covered by a massive polar ice sheet.

shark teeth found in london

Fossilized Megalodon shark tooth, Nick Stevens. Fossilized sharks’ teeth, Sam Caethoven.

Long before these large herbivores and carnivores roamed the Thames Valley, other prehistoric creatures inhabited the London area millions of years ago. As Nick Stevens was searching the surface of an abandoned barge bed on the Thames foreshore, he spotted a large, fossilized shark’s tooth belonging to a prehistoric Megalodon. It is the largest species of shark ever recorded and has been extinct for millions of years. Dating from the Early Miocene to Pliocene epochs, the Megalodon thrived and feasted on the abundant aquatic life native to the warm seas around the sub-tropical British Isles. It would have fed on whales, dolphins, squid, and even turtles. Growing up to 18 meters (59 ft) in length and weighing approximately 65 tons, this prehistoric shark had approximately 10 tons of biting power. Although they lived approximately 3.6–23 million years ago, some people believe that Megalodon still roam the earth’s deepest oceans, which is the premise for the 2018 Hollywood film, The Meg.

Fossil collector and mudlark, Sam Caethoven, has collected numerous smaller, fossilized sharks’ teeth in the Thames Estuary. Dating to the Eocene period, they were eroded out of the London Clay and are approximately 49–56 million years old. The most common sharks’ teeth which Sam finds are from Striatolamia, a sand tiger shark. Dating to the Early Paleocene to Late Miocene periods, this extinct species of shark is around 10.3–61.7 million years old. Sam has also discovered larger teeth from Otodus sharks, which lived from the Paleocene to Pliocene epoch. Growing up to 12.2 meters (40 ft) long, they were one of the top predators of their time. Otodus sharks preceded Megalodon sharks.

Every year mudlarks discover numerous fossils in the River Thames (top) providing evidence of the diverse wildlife native to England millions of years ago. Sam explains why so many fossils are found in the river: “The Thames cuts through Eocene and Paleocene clays underlain by Cretaceous chalk and overlain by Pleistocene gravels, all of which yield fossils. The ancestral Thames has changed course over the millennia and was historically wider and further north until the effects of major glaciation caused the river to be diverted, laying down terraces of sediments and gravels during the Pleistocene that is extremely rich in fossils. In the Thames Estuary, there are also Red Crag and Corallian Crag deposits, yielding fossils from the Pliocene (1.8–3.6 million years ago) and earlier fossils including Megalodon and earlier sharks as well as rays, crabs, lobsters, corals, and bryozoa.”

“The Eocene age London clay yields fossil remains from sharks, rays, bony fish, crabs, lobsters, fish, sea snakes, and invertebrates such as nautilus. These are more commonly found in the estuary but can also be found further upriver. Some of the fossils in the Thames are local and others are imported. Chalk is also found naturally at the estuary, but there is also a lot of imported chalk which was brought in to form the soft tops of barge beds for use in London’s thriving river trade. Chalk contains fossils and flint fossil casts, the most common of which are sponges of many varieties. The most easily recognizable fossils from the chalk are echinoids (sea urchins). Bivalves, gastropods, and brachiopods can also be found, as can belemnites and ammonites.”

heart urchins from river thames

Micraster fossil, Jason Sandy. Micraster fossil, Sam Caethoven.

Some of my favorite fossils from the Thames are micraster fossils. They are heart-shaped, fossilized sea urchins which come in a variety of colors. Living between 35–100 million years ago, micrasters are an extinct genus of echinoids dating to the late Cretaceous to the early Eocene periods. They are simply beautiful creatures, which I love to collect from the gravel beds along the river.

echinoid urchin fossils from river thames in london

Collection of Thames echinoids, Sam Caethoven.

Over the years, Sam has found many echinoids in the Thames. For centuries, it was believed that these echinoids possessed magical powers and were harbingers of good luck. In Britain, echinoids have been called “Sugar Loaves,” “Shepherd’s Crowns,” “Thunderstones,” “Snake’s eggs,” and “Poundstones.” Some people refer to them as “Fairy Loaves” because they look like small round loaves of bread. These echinoids were sometimes used as charms believed to help the baking of bread, a precious commodity centuries ago. They were also kept in dairies because they were thought to prevent milk from curdling. Fairy Loaves also supposedly protected families against witchcraft. Therefore, they were placed on the windowsills of their homes as a good luck charm and talisman to protect against evil. Although I’m not superstitious, I do keep some of these fossils on my windowsill because they are lovely little objects to look at and enjoy.

thames river ammonite crab squid fossils

Ammonite fossil, Jason Sandy. Basinotopus crab fossil, Sam Caethoven. Belemnite fossil, Sam Caethoven.

I also enjoy finding beautiful, spiral-shaped ammonites in the Thames. They are approximately 65–240 million years old and lived at the same time as the dinosaurs before they went extinct at the end of the Cretaceous Period. Ammonites were cephalopods with a ribbed, spiral shell similar to a nautilus and would have had eight arms, which they used to propel themselves backwards through the water. After millions of years in the Thames, the incredible, spiral shapes of ammonites are still perfectly preserved. Nature’s beauty frozen in time.

One of the most interesting fossils that Sam has found is a Basinotopus crab, which eroded out of the London Clay in the Thames Estuary. Dating to the Eocene period, it is approximately 49–56 million years old. If you look closely, the fossilized crab’s shell looks like a Chinese dragon’s face with a wide mouth, round cheeks, nose with nostrils, and squinting eyes. It’s bizarre, but stunningly beautiful.

Sam has also collected numerous belemnite fossils from the Thames. They originate from an extinct squid-like cephalopod that lived around 100 million years ago. Dating to the Late Triassic to Late Cretaceous periods, belemnites had a cone-shaped skeleton, a pair of fins, and ten hooked arms which were used to swim and capture prey. Made of calcite, the pointed guard is typically all that survives as a fossil. There is much folklore which surrounds these bullet-shaped fossils. They were used to supposedly cure rheumatism and even crushed and ground into a powder to cure sore eyes, which actually had the opposite effect and irritated the eyes.

polar bear frost fair londonPolar bear in front of the Tower, London Photo Walks. Frost Fair in 1814, Julia Fullerton-Batten.

In the Middle Ages, unusual animals were also spotted in the Thames. In 1457, two whales, a narwhal, and a walrus fascinated Londoners as they swam upstream from the English Channel. Even a polar bear was seen swimming in the Thames in the 13th century. What was this hypercarnivorous bear doing in the river? In 1252, King Henry III was given a magnificent white polar bear by the King of Norway as a royal gift. It was kept in the menagerie at the Tower of London castle along the Thames which housed other exotic animals including lions, leopards, tigers, elephants, baboons, eagles, pumas, and even a jackal.

The polar bear was a huge, hungry beast, and it soon became too costly to feed. So, the caretakers let the bear swim in the castle moat and Thames to catch fish to eat. A collar and a “stout cord” were attached to the bear to keep it from escaping. Each day, excited Londoners would gather along the riverbank to watch the bear plunge into the Thames and emerge with a sturgeon or salmon between his jaws. What a fascinating sight that would have been!

During the early 17th and early 19th centuries, Britain experienced a series of extremely cold winters known as the Little Ice Age. Because of the restricted flow of the river caused by the narrow arches of the old medieval London Bridge, the Thames would freeze upstream from the bridge. According to historic records, the river froze over 24 times from 1400 to 1832, when the medieval London Bridge was demolished and rebuilt with wider arches. During the Great Frost of 1683–1684, the Thames was completely frozen for over two months with ice over 11 inches (28 cm) thick. Londoners took advantage of these rare opportunities to be on the ice, and vendors set up booths and tents on the frozen river to sell their goods. During these “Frost Fairs,” all sorts of entertainment were on offer, including ice skating, horse and coach racing, gambling, dancing, playing football, and even nine-pin bowling. In the last Frost Fair, which lasted four days in 1814, a colossal elephant was led across the thick ice on the Thames near Blackfriars Bridge (above). Londoners must have been shocked to see a heavy elephant walking on the ice-covered river. Professional photographer, Julia Fullerton-Batten, recreated this historic spectacle in a short film called “1814 Frost Fair,” which is available to watch on Vimeo.

For hundreds of years, the River Thames was an open sewer and garbage dump. During “The Great Stink” in 1858, the overwhelming smell of the raw sewage and industrial effluent in the river became untenable. The Victorian sewer system alleviated some of the problems, but the discharge of raw sewage into the Thames during heavy rainfall continued.

seahorse seal thames river london england

Seahorse found in the Thames, Nicola White.“Freddie the Seal” by Hammersmith Bridge, Broni Lloyd-Edwards.

Although the river was declared “biologically dead” in 1957 by the Natural History Museum in London, wildlife has fortunately returned in abundance in recent years as the water cleanliness has improved. The Thames is now considered to be the cleanest metropolitan river in the world. Over 125 species of fish, 400 types of invertebrates, and even seahorses now live and thrive in the river. Many types of ducks and seagulls, cormorants, swans, Egyptian geese, Canadian geese, grey herons, and other birds live along the river in London. According to researchers from the Zoological Society of London, over 2,800 grey seals and almost 800 harbor seals live in the Thames and are sometimes seen as far upstream as Richmond and Twickenham in West London. Occasionally, whales are also spotted in the river. The diverse wildlife is evidence that the river is returning to its natural state. Will hippos be seen once again in the Thames in the future?

Mudlarking on the Thames Foreshore requires a permit. Learn about rules for mudlarking in London ›

View some of Jason’s favorite Thames River mudlarking finds


Learn more about mudlarking


Learn more about the experiences of mudlarks, who search the shores of rivers, bays, and seas for historical finds and other objects. Articles ›

This article appeared in the Beachcombing Magazine September/October 2022 issue.

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