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Fossils recount a bustling ocean 100 million years ago

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The most complete ichtyosaur fossil that has been found. Photo: Natural History Museum

Fossils recount a bustling ocean 100 million years ago

Surprisingly many fossils were found while researchers were considering CO2 storage on Svalbard. New discoveries tell us more about life there in the Jurassic period.

Researchers from the Natural History Museum, UiO, have in recent years dug out fossils from a large number of plesiosaurs, ichtyosaurs and other marine reptiles in Svalbard. The findings have resulted in media reports worldwide, books and television productions – as well as a wide range of scientific articles. Thus we have gained a lot of new knowledge about the marine reptiles that ruled in the sea in the jurassic and cretaceous periods.

In what kind of environment did they live? Under which conditions? Little has been known. Maayke Koevoets has written her doctoral dissertation on this subject, at the Natural History Museum, University of Oslo.

You can also read this article in Norwegian

Since she was 6 or 7 years old and found a toy dinosaur in the schoolyard at home in the Netherlands, Koevoets has been crazy about dinosaurs. At first she wanted to tame them. Then came Jurassic Park at the cinema. Her interest only grew stronger, and she decided to pursue an education that could bring her in close contact with life on Earth hundreds of millions of years ago. Since then, she has worked purposefully to become a palaeontologist.

Maayke Koevoets
"We found that there was more marine life than was previously known", says Maayke Koevoets. Foto: Dag Inge Danielsen/UiO Bruk bildet.

In the autumn of 2013 she came to Oslo and the Natural History Museum to begin her doctorate. The assignment was to uncover new information regarding the environment, living conditions and ecology during the time of the plesiosaurs and ichthyosaurs. 

The disappearing mussel

Koevoets says: "It suited me perfectly to map the marine life in the cretaceous, because that was much of the same I was working on at my master's degree – just that it was about the giant bivalve – a kind of mussel –  Inoceramus, which mysteriously disappeared before the great mass extinction about 66 million years ago.

"How do you find out about the biodiversity hundreds of millions of years ago?"

"I started by analyzing core samples from drilling in the Agardhfjell formation. These samples were extracted in a large area a few years ago, while exploring the possibilities of storing CO2 in the rock deposits of Svalbard," explains Koevoets.

By applying new geochemical methods, she has studied the composition of the sediment samples and made new discoveries concerning oxygen levels and fossils of fish and marine organisms.

It turned out that the samples contained far more fossils than the researchers had assumed. Large amounts of organic matter were revealed – primarily in the top sediment layer, which is known as the Slottsmøya layer. From here, Koevoets has investigated a large number of ammonites, bivalves, snails, belemnites (an extinct octopus) and other organisms.

Many challenges

The Marine Reptiles on Svalbard

The Agardhfjellet formation is the name of a belt of bedrock deposits from the Jurassic era that crosses Svalbard.

The core samples Koevoets has studied consist of sediments that are 500 - 900 meters below the surface of Spitsbergen. In Jurassic and Cretaceous, this seabed was in a shallow sea area that turned into dry land about 50 million years ago.

Koevoets has used various geochemical analysis techniques, including carbonation and the new method Xray Fluorescent.

Plesiosaurs and ichthyosaurs were marine reptiles that lived in the ocean where Svalbard is today.

The first traces of marine reptiles on Svalbard were found in the 19th century.

In 1931, American scientists stumbled across the back of a plesiosaurus on Janusfjellet, a few miles north of Longyearbyen. Then nothing happened until

Professors and palaeontologists Jørn Hurum and Hans Arne Nakrem from the Natural History Museum started an extensive excavations in Svalbard. Since then, the research group has uncovered more than 40 reptiles. Four doctoral theses have been written so far.

Sources: Natural History Museum and Apollon

She encountered many challenges along the way. For example, it was found that the bedrock was sprained and fragmented, so it was often difficult to interpret the geology in the core samples. Fractions found in completely different places could look similar, but did they belong to the same section or not? It was very hard to figure it out. Do the fossils represent one or several species? For ammonites and bivalves, it was almost impossible to determine.

Koevoets also had little literature to consult. Most of the previous research was done in the 1980s and early 90s, and little information has been published about what was found in the sediments.

More fish than previously thought

"One of the main findings was that we could do a lot more analyses of core samples than we had anticipated. Furthermore, we found that there was more marine life than was previously known. It has been believed that the environment in the sea was poor in oxygen, but that proved not to be the case. At least, it was rich in oxygen for long periods," Koevoets says.

"We were amazed to see that there was much more fish in the ocean than we had been aware of. This applies to both the total number of individuals found and the variety of species. In the past, only a few fish fossils had been found near the marine reptiles."

Maayke Koevoets experienced the eureka moment in her PhD work when she found that the same fish fossil she had found, had been described and drawn in 1898. At that time, a Swedish expedition led by Alfred Gabriel Nathorst had been on Svalbard and found a fish fossil that was described by Arthur Smith Woodward.

"It was a great moment to see such an old illustration of exactly the same fish fossil, and that it actually had a name. It may mean that it was quite common. The fish was named after Nathorst, by the way."

"How can your findings be useful?"

"We have gained more knowledge of life in the ocean at the time when the big marine reptiles were around. This makes it possible to provide better information to the public and create more accurate exhibitions at the Natural History Museum. In terms of societal benefit at large, we have gained more knowledge about the geology of the area. This may, for example, be useful if CO2 is to be stored in Svalbard."

The big ones ate the little ones

Maayke Koevoets
Maayke Koevoets' interest in dinosaurs has no limits. Photo: Maayke Koevoets

"Why was there such a rich marine life at the time?"

"One factor can be a rich and increasing nutritional basis for the small organisms, such as mussels and ammonites. These may again have attracted the big reptiles. Also, the oxygen content increased towards the end of Jurassic, that is, about 150 million years ago. And it seems that there were calm conditions on the seabed, without strong sea currents, which allowed mussels, ammonites, belemnites and all the others to live in peace and harmony – until the hungry, big reptiles appeared," says Maayke Koevoets, who is now back with her boyfriend in the Netherlands and is looking for a postdoctoral position.

And if you've ever wondered how a paleontologist spends her free time, Koevoets can reveal that her hobby is knitting dinosaurs. Ammonites, plesiosaurs and various other creatures in different colors and sizes have come to life between her diligent hands. They have been sold at the annual Christmas market in the Botanical Garden – with enthusiastic buyers lining up, making sure they were some of the first items to be sold out.

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