Marine life in a greenhouse world: cephalopod biodiversity and biogeography during the early Late Cretaceous

What is it about?

Rising greenhouse gas concentrations in the atmosphere lead to global warming and sea level rise. How might marine animals response to such changes? On one hand, animals may be able to move more easily from one ocean to another and to higher latitudes as oceans warm up. This movement would lead to larger geographic ranges and prevent the geographic isolation that leads to speciation. Hence, overall biodiversity may drop. On the other hand, rising sea levels may flood continents to produce isolated shallow seas. Animals living in these seas may become geographically isolated, producing more species and increasing biodiversity. To test these two models, I focused on a time of ancient greenhouse warming and extinction, the Cenomanian–Turonian interval of the Late Cretaceous (about 90 million years ago). I compiled occurrences of fossil cephalopods, relatives of modern squid, octopus, and nautiluses, and studied their biodiversity and geographic distributions over time. Globally, biodiversity dropped during peak greenhouse conditions, but it actually rose in some specific regions. Some regions hosted more and more geographically widespread groups while others did not. It is likely that global warming had different effects on biodiversity in different parts of the world.

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Why is it important?

My research demonstrates the importance of combining global and regional scale analyses when studying biodiversity crises during times of global warming. Studying this ancient episode of global warming and extinction helps us better predict what will happen to life in the oceans in the near future due to modern anthropogenic global warming.

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