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Tiny sea angels survived Earth’s last rapid warming event, but may not survive the next

A new study co-authored by the museum’s Dr Jon Todd has found that tiny sea angels and sea butterflies have already faced major periods of dramatic global change; and they also faced down Earth's most recent mass extinction event 66 million years ago. 

A new paper was published in the journal Proceedings of the National Academy of Sciences in which researchers discovered that these marine slugs and snails originated during the Cretaceous period (130 million years ago).  Researchers hope they will also be resilient in the face of man-made climate change and the threats it will bring.

Dr Jon Todd explains, 'We were astonished to find that these tiny animals were likely swimming in the global ocean 130 million years ago. Though we haven't found fossils this old it gives palaeontologists something novel to hunt for. This unexpectedly long history shows that the group has survived previous catastrophic episodes of climatic change.' 

Sea butterflies and sea angels can tell us a lot about the effects of climate change on the world's oceans, because they are very sensitive to carbon dioxide levels. A third of the carbon dioxide produced by humans is taken up by the oceans and locked down in the skeletons of marine organisms. Globally, up to 40% of that calcium carbonate is deposited in the shells of pteropods like sea butterflies. When they die, their shells sink to the ocean floor and are buried in deep seafloor sediments and this mass burial plays a key role in mitigating climate change.

The shells of pteropods like sea butterflies are made of aragonite, a soluble form of calcium carbonate, which starts to dissolve in acidic seawater. As the water in our oceans becomes more acidic as a result of climate change, these creatures will be seriously threatened if carbon dioxide levels continue to rise. 

Few of the fossils of these marine creatures have survived in older rocks, and most are only known from the Eocene period onwards (from 56 million years ago), which is just after a very rapid period of global warming. This led to extinctions and a change in the composition of oceanic plankton. Given this, researchers previously assumed the pteropods only evolved after this warming event. Knowing whether they were swimming in the oceans before this period may reveal how pteropods were affected over their long history by other major oceanic events caused by climate change and may even help us predict their future.  

This new study sampled 21 pteropod species from the Atlantic Ocean and collected information about their genetic relationships and their history. Studying the shells of close fossil relatives, sea hares, helped researchers date the origin of the pteropods. They found that sea butterflies and sea angels are much older than previously thought and must have survived previous episodes of widespread ocean acidification, such as at the end of the Cretaceous (66 million years ago) and at the Paleocene-Eocene Thermal Maximum (56 million years ago).

It's not all good news: although the study suggests that sea butterflies and angels have been more resilient to past ocean acidification than currently thought, it is unlikely that pteropods have experienced global change of the current magnitude and speed during their entire evolutionary history, which still puts them at risk. 

The ocean regulates our climate and supports life on our planet. The open ocean is the largest habitat on Earth, microscopic algae produce half of the world's oxygen, and the ocean has already absorbed more than 90% of excess heat and 30% of excess carbon dioxide from the atmosphere since global industrialization. However, this is not without consequences. 

For the first time in millions of years, the role of the ocean and atmosphere has been reversed: today it is the atmosphere that controls ocean chemistry leading to an increasingly acidified ocean. It is still an open question whether marine organisms like the sea butterfly and sea angel have the evolutionary resilience to adapt to these changes in time. 

The new paper, The origin and diversification of pteropods precede past perturbations in the Earth’s carbon cycle, is published in the journal Proceedings of the National Academy of Sciences and available here.

Notes to Editors

Media contact: Tel: +44 (0)779 969 0151 Email: press@nhm.ac.uk 

Additional images are available here

Researchers from all over the world collaborated on this project, including experts from Naturalis Biodiversity Center in The Netherlands, the University of Hawai'i, the Bermuda Institute of Marine Sciences and the Okinawa Institute of Science and Technology in Japan.

This study is part of the Atlantic Meridional Transect programme.

About the Natural History Museum:

The Natural History Museum is both a world-leading science research centre and the most-visited natural history museum in Europe. With a vision of a future in which both people and the planet thrive, it is uniquely positioned to be a powerful champion for balancing humanity’s needs with those of the natural world.

It is custodian of one of the world’s most important scientific collections comprising over 80 million specimens. The scale of this collection enables researchers from all over the world to document how species have and continue to respond to environmental changes - which is vital in helping predict what might happen in the future and informing future policies and plans to help the planet.

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