Fossil bones from the North Sea: An easy to way to collect fossil remains from the Ice Age?

Dick Mol (The Netherlands)

Introduction

In 1874, the first known mammoth remains were brought ashore, trawled off the coast of the province of Zeeland, The Netherlands. Fishermen, fishing for flatfish, caught these fossils as bycatch in their nets. (A bycatch is a fish or other marine species that is unintentionally caught while catching certain target species and target sizes of fish, crabs and so on) A museum associate in Middelburg described these bones in an extensive research report. This resulted in a sound basis for ongoing study of the lost life found on the bottom of the North Sea between the Netherlands and the British Isles, about two million to 10,000 years ago.

For years the fishermen brought their bycatches ashore. Usually, these were large bones and teeth, both of mammoths and whales. In fact, the North Sea bottom used to be a vast plain during the Ice Age with mammoths walking around in large herds and this area must have been a paradise for large mammals. Apart from the mammoth remains, other species like wild horses, giant deer, deer, lions, bears, wolves, rhinos and others have also been found.

Thousands and thousands of these remains ended up in Naturalis, the National Natural History Museum in Leiden. Today, this museum holds one of the largest collections of mammoth remains in the world.

The remains, the fishermen brought ashore, are a mixture of the fossil remains of both marine and terrestrial mammals, all of which differ in age. Moreover, the exact locations are usually difficult to pinpoint. As a result of not documenting the locality, it is uncertain whether the fossils were discovered in the Southern Bight of the North Sea or the Brown Ridge area.

The Brown Ridge or Brown Bank is approximately 50 nautical miles off the coastline of Ijmuiden in The Netherlands, and is widely known in the world of palaeontology. Here, the North Sea is about twenty meters in depth, which is considered shallow. Furthermore, most remains are brought up from the Brown Ridge area. When fishermen lower their dragnets for a trawl, success is virtually guaranteed. Mammoth molars, tusks and large bones are abundant.

Cooperation between palaeontologists and fishermen

More than 35 years ago, more attention began to be given to these fossil remains as a result of a growing interest in The Netherlands in the fossil mammals of the Pleistocene. This was the beginning of a close cooperation between palaeontologists and the crew of large vessels, which leave the docks on Sundays to return on Fridays to the harbours with fish and fossil remains.

Now, not only the fossil bones, but also the localities are provided, which is essential. Fossil bones are identified by their morphology and can be assigned to different species. If we take mammoths as an example, there is a clear distinction between the Southern Mammoth, Mammuthus merdionalis, from the Early Pleistocene, the Steppe Mammoth, M. trogontherii, from the Middle Pleistocene and the Woolly Mammoth, M. primigenius, from the Late Pleistocene. Their morphological characteristics differ, along with the state of mineralisation.

The fossil remains of the Southern Mammoth, for instance, usually brought up from deep pits or gullies in the Brown Ridge area, are always dark in colour and heavily mineralised. This is in contrast to the remains of the Woolly Mammoth. These bones are hardly mineralised at all. When tapped with a hard object, the Early Pleistocene remains of the Southern Mammoth produce a high- pitched sound. This is also true for other mammals of the same geological age. This is an additional method of classifying fossil remains.

Eurogully

Many fishermen willingly cooperate in the process of collecting. Some demand payment, others do not. Tons of fossil bones were brought ashore, often accompanied with the relevant locality information, which the fishermen obtain from their onboard computers. As an example, in the period between 1997 and 2003, one collector investigated over 67 tons of bones of which more than 8,000 mammoth molars were not even recorded. Through close cooperation, a good insight was quickly gained into which extinct mammals came from a certain period in the Pleistocene and where they were found.

Several environmental reconstructions have been made for the site that is called the ‘Eurogully’ (the ship lane to the harbour of Rotterdam) off the coast of the province Zuid-Holland. This ship lane is a site of Late Pleistocene and Early Holocene faunal remains. There, the sand off the bottom of the North Sea is dredged for industrial purposes. Anything heavy, like large bones of mammoths and rhinos, remain on the bottom. When a trawl net scrapes the bottom, it is likely that these remains surface as bycatches.

Fishermen have often reported that this area is extremely rich in mammoth bones, almost as if it were a mammoth cemetery. This knowledge lead to the organisation of a palaeontological expedition to the Eurogully. Due to the high oil-prices, this was an expensive enterprise. Moreover, the crew needed to be paid. Nevertheless, the expedition took place, paying big dividends. A large quantity of bones was brought up from a relatively small area. The expedition was very successful and the collection of bones could only be transported with trucks to the laboratory for research.

The results

The results of this first North Sea expedition came in fast. Not one, but two faunas were collected. The first is the so-called Mammoth Fauna, typical of the Late Pleistocene. This fauna includes Woolly Mammoth, steppe bison, musk oxen, deer, giant deer, horse, woolly rhino, brown bear, hyena, cave-lion and wolf. In addition to these terrestrial mammals, a number of marine mammals were found as well – two species of seals, walrus, beluga, killer whale and grey whale. These remains are aged approximately between 35,000 and 50,000 years before present.

The second fauna consisted of the following animals: moose, red deer, wild boar, dog and man. This fauna belongs to the Boreal, which was approximately between 7,000 to 9,000 years ago. The collected peat samples confirm these geological ages – the first sample showed that the mammoth fauna roamed on a treeless grass steppe. Results from the second peat samples indicated we are dealing with a forested area at the beginning of the Holocene, caused by the rising temperatures at the end of the Pleistocene and beginning of the Holocene.

The occurrence of marine and terrestrial mammals in the same fauna is easily explained. During the Late Pleistocene, the Eurogully area used to be a large delta of the rivers Meuse and Rhine, which was then located close to the coastline. This delta, with its shallow waters, was rich in marine mammals, together with seals and walruses. Large mammals came in from the dry grass plains to the rivers to drink and bathe. When an animal died, the carcass was carried off during high tides and deposited on the bottom of the ancient Meuse and Rhine.

The Hole: a special site

One of the most important discoveries, as a result of the close cooperation with fishermen, is the location “The Hole,” (in the Dutch language, “Het Gat”) located to the east of the Brown Ridge. “The Hole” is a deep gully, up to 46m below sea level, where few ships try their luck. In fishermen’s jargon, this location is known as “difficult”, which means it is a problematic site for fishing with dragnets.

The bottom contains erratic boulders, sometimes as big as a car. These erratic boulders were carried here during the Elsterian (Elster Glaciation), transported by the slowly moving ice sheets and remained there, on the sea bottom, after the glaciers melted.

It can be expensive if trawl nets get stuck between these boulders. One ship, however, the vessel GO 41, does take the risk, which often pays off in terms of a great catch of fish. The crew of the GO 41 collect the fossil remains and keeps the finds from each site separate. Heavily mineralised pieces stand out in their bycatches, which are usually from an “old” fauna. These pieces are brownish-black in colour, heavily mineralised and always accompanied by reddish iron minerals.

These fossil bones are linked to several animals, such as the Southern Mammoth, probably also the first Steppe Mammoth, a large hippopotamus, an extinct moose, an early rhino (known as the Etruscan Rhino), several species of giant deer, a small bear, an extinct rodent, a very large horse and the sabre-toothed cat.

As research indicates, this fauna is approximately a million years old. Untermassfeld – a classic site in Germany of the same age – also yields these species and there, the large number of hippopotamus, is noticeable. The coast of East Anglia has a similar fauna in its cliffs as well. A scientific expedition was sent to “The Hole” to investigate the locality. For five days, 24 hours a day, trawls were made to catch bones, with fish as bycatches to cover the expenses. The loot was 161 heavily mineralised fossil remains, all catalogued and already published.

New discoveries

For quite some time, there has been great interest in the bones of the sea bottom. Before, these remains were considered scientifically worthless because they lacked the locality and, especially, the context. Even though this is understandable, we need to realise that a fossil is identified by its morphological characteristics. As the result of the newly found interest, many astonishing discoveries have surfaced from the bottom of the North Sea between the British Isles and The Netherlands.

Based on the results of just a single lower jaw with dental elements of a sabre-toothed cat – Homotherium – we can confirm that this species became extinct much later than generally believed in Europe and Asia (over 300,000 years ago). The specific jaw in the collection of the Natural History Museum in Rotterdam was radiocarbon (14C) dated and the results showed that the sabre-toothed cat was still around 28,000 years ago.

Also, the remains of the straight- tusked elephant, which is typical of the last interglacial (the Ipswichian), was around much longer formerly believed. This insight is based on the fossil remains brought up from North Sea bottom. The 14C results indicated that the straight- tusked elephant roamed the southern part of the North Sea late into the last glacial.

An easy way of collecting?

It is not that simple to collect fossil remains from the bottom of the North Sea. A number of demands need to be met. Good cooperation between the shippers and the crew is a must. Moreover, they also need to have an interest in the life of large, often extinct, mammals. Therefore some palaeontological training is essential. The fishermen need to know that they must store all their catches, not only the large remains, but also the fragments they find in their nets. These fragments can contain essential information.

Apart from this, the GPS coordinates are also very important. This information and the identification of the locality can be verified with geological maps of the Geological Survey in the United Kingdom and The Netherlands. Also, you need to free up a lot of time – most vessels return at night, usually on Thursdays and Fridays. This means late hours practicing “palaeontology at night” – something which is pretty rare in the world of palaeontology.

Image reconstructions by Engelbert van Essen. © Photography by Rene Bleuanus, SQZI ConceptStudio, Arkel The Netherlands. ©.

About the author

Sir Dick Mol is a Dutch palaeontologist, who is a specialist in the field of mammoths. He is a research associate of several museums. His primary focus is on mammals of the Quaternary period, including mammoths and extinct rhinoceros species. He has written extensively for Deposits magazine.