Fossil hunting on the Norfolk coast: how to see sea urchins at the seaside

A sea urchin fossil found in north Norfolk. (Image: ©Norfolk Museums Service, photograph by Dr David Waterhouse.)

I look after around 1½ million specimens, from the tiniest gnats to the largest mammoth skeleton (and everything in between).

The collection is internationally important with many unique and significant specimens. However, for this Object of the Month article, I wanted to choose something that at first, sounds a little more ordinary – in fact, they are among the most commonly found fossils in Norfolk. But common doesn’t have to be boring, for fossilised sea urchins (as we’ll find out) can be truly fascinating. With the wonderful Dippy on Tour exhibition at Norwich Cathedral postponed until next year, sea urchins are far easier to find and store in the meantime and are almost as old!

We start our journey some 90 million years ago, in what will become Norfolk. Dinosaurs are roaming on land to the west, but we are covered in a shallow tropical sea. The perilous waters above teem with large marine reptiles such as mosasaurs (often mistaken for dinosaurs, but actually more closely related to the monitor lizards still in existence). The fishes of the ocean are accompanied by strange squid-like creatures called belemnites (related to modern cuttlefish), and the snow-white chalky sea bed is covered in sponges while millions of spikey sea urchins amble slowly over the seafloor.

Sea urchins (also known as echinoids) are related to starfish and sea lilies (crinoids). They all share a ‘five-fold symmetry’, which you can see most clearly in the five arms of starfish. This group of animals is commonly found as fossils within Norfolk chalk. The echinoids are the most widely encountered, with one species, with a tong-twister of a name, outnumbering all the others – Echinocorys scutata.

A near perfectly preserves sea urchin, showing the intricate detail of every pore and tubercle. Picture ©Norfolk Museums Service, photograph by Dr David Waterhouse. (Image: ©Norfolk Museums Service, photograph by Dr David Waterhouse.)

Their delicate shells are often found complete, but it is much rarer to find their spines still attached. You will almost always discover ‘bald’ sea urchins, as their spines fall off very soon after death. Sea urchins have a skeleton composed of plates embedded in their skin, made of the mineral calcite. Just like starfish, they have tube feet, and they move using these, as well as using their spines. The tube feet extend out of small pores which you can still see in many fossil echinoids.

Sea urchins can be preserved in a number of different ways: their shells may be intact, but flint or chalk has filled the inside; the plates may have disappeared, leaving an impression of the inside cast in flint; or an impression of the shell may be left in a piece of flint – this is an external mould. Echinocorys scutata (remember that name, as you can wow your friends and family with your knowledge whilst on your next beach walk!) come in a wide variety of shapes and sizes. This is extremely useful, as the different varieties are from different ages, and therefore layers within the chalk, helping geologists identify how old each layer is. The sea urchins and belemnites found in the chalk of the English Channel even helped engineering geologists steer a path for the Channel Tunnel, as they knew certain layers of chalk were softer and easier to drill than others and were therefore guided by the fossils they found.

Fossil collecting is an enjoyable and rewarding experience, but only if it is carried out in a responsible manner will we be able to maintain our fossil heritage for future generations. Much like Dorset and east Devon’s ‘Jurassic Coast’, Norfolk’s ‘Deep History Coast’ contains many hidden treasures – from the earliest evidence of humans in northern Europe, to the largest mammoth discovered in the UK, and sea urchins galore!

If you want to find a fossil sea urchin here are a few simple rules to follow for responsible fossil collecting (in addition to Government guidelines on how to keep safe during the Covid-19 pandemic of course):

· Stick to the footpaths provided – do not add to coastal erosion by trying to climb up or down the cliffs.

· Never dig into the cliffs – it can add to erosion, is dangerous, often illegal and spoils things for others (there are plenty of fossils on the beach anyway.)

· Take only one, or just a few representative specimens.

· Always make a note of where you find fossils – photographs are very helpful.

· Write a label for your fossil, including exactly where and when it was collected, plus any other observations.

· Remember that fossil sites are for everyone to enjoy, and indiscriminate collecting will damage this resource for future visitors.

Dr David Waterhouse is senior curator of Natural History and Geology at Norfolk Museums Service.