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Trending Science: How climate change probably killed the ichthyosaurs

A multinational team of scientists have claimed that the famed dolphin-like underwater cousins of the dinosaurs, the ichthyosaurs, became extinct due to a dramatic shift in the Earth’s climate.
Trending Science: How climate change probably killed the ichthyosaurs
For generations, children (and many adults) have been fascinated by the mystery of what caused the mass extinction of the dinosaurs and other prehistoric animals. Whilst palaeontologists have solid theories for some of the most major extinctions in Earth’s history, the most famous being an asteroid hitting the planet around 65 million years ago, there are a few famous species whose extinction still baffles scientists. The marine ichthyosaur is one of them.

From the Triassic to the late Cretaceous period, whilst dinosaurs ruled the land, the Earth’s oceans were home to many different species of ichthyosaur. They ate mostly fish and squid and evolved streamlined dolphin-like bodies that were built for speed. They reached their peak in the Jurassic period and then vanished in the Cretaceous, several million years before the last dinosaur disappeared.

Unconvincing theories on ichthyosaur extinction

Scientists have put forward a number of theories, mostly focussed on the animals’ food supply, to explain the ichthyosaurs’ fate but none of them have been able to convince the majority of the scientific community. One argument was that they had been out-competed for food by other marine predators, whilst another claims that they starved to death due to a mass extinction of their principal prey.

Now a team of scientists from Belgium, France, Russia and the UK have put forward the argument that climate change during the Cretaceous period likely caused upheaval in marine ecosystems and spelled doom for the ichthyosaurs. Their findings are published in the journal ‘Nature Communications’.

The researchers combed through museum collections and literature describing ichthyosaur fossil findings, and developed a fully up-to-date and detailed family tree of the many ichthyosaur species that existed over the millions of years that the animals were on Earth. They then conducted an analysis to investigate the links between all the different species and the way they evolved over time.

One of their first conclusions was that the competition hypothesis didn’t quite fit with the available knowledge on the animals. They were unable to pinpoint an animal that existed at the same time that might have had the ability to outcompete the ichthyosaurs for food.

They also discarded the theory that the extinction of their principal food source, a squid-like creature called the belemnite, was the ultimate cause of the ichthyosaurs’ demise, due to how diverse the ichthyosaurs were as a group.

Climate change and its impact on the Cretaceous marine ecosystem

By casting their net wider and by conducting more tests to find out what kind of environmental changes might best provide clues to the mystery, the researchers discovered that extreme climate variations in the late Cretaceous were the strongest predictors. There is strong geological and fossil evidence that there was great environmental upheaval around the time that the ichthyosaurs first started to decline, marked by fluctuating sea temperatures and chemical changes in the ocean.

‘Our results support a growing body of evidence revealing that rising sea levels and sea temperatures profoundly reorganised marine ecosystems about 100 million years ago,’ said lead researcher Dr Valentin Fischer of the University of Liège, Belgium, and the University of Oxford, UK. ‘The ichthyosaurs were unable to adapt [because] they were evolving very slowly during the last 50 million years of their reign. When the environment changed rapidly, they couldn’t keep up with this change.’

By the time the ichthyosaurs were finally all extinct, the marine landscape had substantially changed and was marked by higher temperatures, a lack of polar ice caps and low oxygen levels. These changing conditions correlate with the eventual extinction of other well-known marine reptiles, such as the mosasaurs.

‘Although the rising temperatures and sea levels evidenced in rock records throughout the world may not have directly affected ichthyosaurs, related factors such as changes in food availability, migratory routes, competitors and birthing places are all potential drivers, probably occurring in conjunction to drive ichthyosaurs to extinction,’ added Dr Fischer.

So, whilst many other marine reptiles managed to continue on for longer, life unfortunately did not find a way for the doomed ichthyosaur. However, these results highlight that their disappearance may not have been so spectacular at all, but were merely part of a much bigger set of changes occurring on Earth at the time, primarily driven by climate change and its impact on oceans’ ecosystems.

Source: Based on media reports

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Countries (4)

  • Belgium, France, Russia, United Kingdom
Record Number: 124882 / Last updated on: 2016-03-10
Category: Trending Science
Provider: EC