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Extinctions after the cause

16 March 2007

Species extinctions may occur millions of years after the apparent environmental cause, new research suggests.

We know that major changes in the environment can lead to extinctions. However, the relationship between extinction and environmental change in the sea is complex and remains poorly understood.

Looking back ten million years

To solve this difficult problem, a team of scientists looked at the fossil and living shallow marine animal communities that lived on either side of the Isthmus of Panama during the past ten million years. This land bridge is only three or four million years old. 

Fossil corals such as this Porites porites help us understand how climate change affects coral reefs

Fossil corals such as this Porites porites from Dominican Republic help us understand how climate change affects coral reefs.

During that time, the rising isthmus divided a single ocean into two very different ones and gradually changed the environmental conditions in the Caribbean to what we see today. This resulted in a major extinction of marine animals.

Corals and seashells reveal extinctions

Natural History Museum palaeontologists Ken Johnson and Jon Todd studied more than 250,000 specimens of reef corals and mollusc seashells to determine the precise effects of the rise of the Isthmus of Panama on tropical marine ecosystems.

They showed that up to 50 per cent of the species went extinct between one and two million years ago, around two million years after the Isthmus of Panama formed.

Slow reductions

Scientists are unsure why this delay occurs. 'Probably, the environmental changes were not strongly felt at all places within the Caribbean at the same time' says Ken.

'There may be a slow reduction in distribution and abundance of species until a threshold point is reached, when extinctions happen more suddenly.'

According to Jon, 'it is difficult to explore the geographical dimension to marine extinctions without studying massive collections of fossils.'

'Understanding these mosaics of past extinctions is important because they may teach us what to expect for future extinctions resulting from ongoing global environmental change.'

We are already seeing mass reductions in species all over the world as a result of human actions. Any research to help us understand these processes could become crucial to the survival of many species on our planet.

This research was carried out by a team from the Natural History Museum, the Smithsonian Tropical Research Institute and Scripps Institution of Oceanography and is published in the Proceedings of the National Academy of Sciences.

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