A large fossil shark, Kansas, USA, from the Late Creataceous Niobrara Chalk (87-82 million years ago). 25½ x 78⅓ x 1½ in (65 x 199 x 4 cm). Estimate £20,000-30,000. Offered in Sculpted by Nature

How to collect fossil fish (and other creatures of the deep)

From stingrays to sea lilies, ammonites to ichthyosaurs, the fossils of underwater life forms are more common than their terrestrial counterparts. James Hyslop, Head of Science & Natural History, explains what to look for and how to find them

What is a fossil and how did they form underwater?

Fossils are the remains or imprints of organisms from earlier geological periods that have been preserved in sedimentary rock. While most are skeletal, underwater examples can include teeth, skin, sponges, urchins and plant life.

Underwater fossils are typically formed when sea organisms fall to the ocean floor and are covered in mud deposits. Over time, these build up to form limestone.

‘Millions of years ago, when a land animal died, there was a high chance its carcass would be scavenged,’ says James Hyslop, Christie’s Head of Science and Natural History. ‘If something died in the ocean, however, it could sink to the bottom undisturbed, which is why underwater fossils are more common than their terrestrial counterparts.

‘Alternatively, it could have been buried in sediment after a mega tsunami, or by part of the continental shelf collapsing and sending everything to the depths. That would leave a spectacular layer of underwater fossils to provide a snapshot of how life was back then.

The example above, which shows one fish swallowing another, is an incredibly rare discovery, says Hyslop. ‘What are the chances of the predator’s dinner becoming lodged in its throat, choking it, then the pair sinking to the bottom of the sea together 50 million years ago?’

Which species exist in fossilised form?

Fish began to evolve about 530 million years ago. Roughly 110 million years later, they started to develop bones.

The fossil record includes the prehistoric relatives of sharks, turtles, crabs, stingrays, shrimp and starfish, as well as dozens of fish species that ranged in size from minuscule to several metres long.

The fossil skull of a Borealosuchus. Horse Creek Formation, Florida, USA, from the Pleistocene (c. 2.58 million-12,000 years ago). 11½ in (29.5 cm) high on stand. Offered on 25 May 2021, Online
The fossil skull of a Borealosuchus. Horse Creek Formation, Florida, USA, from the Pleistocene (c. 2.58 million-12,000 years ago). 11½ in (29.5 cm) high on stand. Offered on 25 May 2021, Online

Among the larger specimens are fossils of Borealosuchus, which date back to the Jurassic Period, 180 million years ago. ‘They lived alongside dinosaurs, but managed to dodge the bullet when everything went extinct 65 million years ago,’ says Hyslop. ‘Although they no longer exist, they would have looked, walked and eaten very much like the crocodiles and alligators we have today.’

What are the commonest and rarest forms of underwater fossils?

‘Ammonites — ocean-dwelling molluscs — are fairly common, especially in smaller sizes, because their hard shells preserved easily,’ says Hyslop. ‘Jellyfish on the other hand are much rarer because their body parts often cooked away during the geological process of rock formation.’

Underwater plant material is also uncommon, says Hyslop, but that doesn’t mean it didn’t exist in abundance. ‘Historically, it’s just not what excavators were looking for. More of it is coming on the market now, which reflects the fact that people are beginning to appreciate its importance and beauty alongside fossilised fish.’

Where and how are underwater fossils excavated?

Not just at the seaside, says Hyslop. ‘Palaeontologists know exactly where to look for them. They also know the exact tiny bumps in the rock to look for that indicate a fossil, which you or I would miss.’

The Green River Formation in Wyoming and the Solnhofen and Holzmaden sites in Germany are all renowned for their marine deposits. Other important sites can be found in England, Madagascar, the Bahamas, Mexico, Brazil, Australia and Florida.

Some fossils break away easily, because their structure creates a preferential split in the rock. Others require hours and hours of delicate excavation with dental drills and airbrushes. If the rock is particularly crumbly, the fossil can be removed, stabilised, then reset in a slab of harder rock from the layer above or below the fossil. Different species are sometimes even set alongside one another to create an imagined menagerie.

What makes a specimen special?

‘Firstly, no one wants to live with a dead fish, so it’s key that the fossil should look alive and dynamic,’ says Hyslop.

‘Secondly, it’s about condition. Two identical fish might have died within years of each other, but on one the bones and scales might have broken away more quickly, or the fish might have been petrified in a higher-temperature mud and degraded more,’ he continues.

‘There could even be different minerals deposited in the rock that turn one fossil darker than the other, making it easier to see.’

While preservation is key, it’s important to remember that no fossil ever really comes out of the ground completely intact and human intervention is always required to remove it. ‘Restoration is common, so don’t worry about small areas of retouching,’ advises Hyslop. ‘The key is that the work is honest and upfront.’

Similarly, provenance can add value, but if the fossil doesn’t have any, don’t be put off. ‘The market is both primary and secondary,’ explains Hyslop. ‘Lots of great examples have been in private collections for years, but brilliant new material constantly comes out of quarries as well. It’s up to the collector to decide what matters to them.’

Which underwater fossils are the most collectable?

Hyslop knows people who collect only from the Cretaceous Period and aim to capture the last moment the world of the dinosaurs existed, or others that buy only ammonites. Some people collect decoratively to adorn their homes. ‘I have seen people build huge ammonites into the walls of their bathrooms,’ he says.

‘You could even collect marine coprolites — fossilised faeces — if you wanted,’ he adds. ‘I’ve seen it all, so don’t be fearful of specialising in what you love.’

Three specimens of coprolite (probably from a turtle). 9 in (23 cm) the highest (3). Sold for £2,000 on 5 September 2013 at Christie’s in London
Three specimens of coprolite (probably from a turtle). 9 in (23 cm) the highest (3). Sold for £2,000 on 5 September 2013 at Christie’s in London

How has the market changed?

The fossil market has become more global, younger and less scholarly, says Hyslop. ‘I’m now frequently selling to people in their twenties who have made their fortunes in cryptocurrencies. It’s nice to know these are objects that inspire people of all ages. There is nothing like a giant fossil shark tooth to bring out your inner child.’

The market for marine fossils in particular has been historically undervalued, but it is now catching up, suggests the specialist. ‘In 2016 we sold a brilliantly sculptural “mortality” plaque [below] containing dozens of fossilised fish for £32,500 — almost 10 times its estimate.’

Where can I learn more about underwater fossils?

‘I recommend looking up your local regulations on fossil hunting,’ says Hyslop. ‘Then find a beach or mountainside quarry where you’re allowed to pick up things, and try to join a local fossil hunt. This will not only help you to build up knowledge, but also to understand just how hard it is to find things.’

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Hyslop adds that a decade ago, along with 10 of his friends, he visited Lyme Regis — a world-famous site for underwater fossils in Dorset, England — where they all spent the day searching. ‘By the end of it we had only found a handful between us, and nothing larger than a small paperback book,’ he recalls.