Researchers Used Nearly Half a Million Fossils to Solve a 200-Year-Old Scientific Mystery: Why
So far, limited fossil dataprevented scientists from carefully examining how the gradient of diversity came about. Biologists from the Universities of Oxford, Leeds and Bristol used planktonic foraminifera and analyzed 434,113 records in the global fossil database. They cover the last 40 mon years. They then examined the relationship between the number of species over time and space and potential drivers of the latitudinal diversity gradient, such as ocean temperature and salinity.
Modern latitudinal diversity gradientfirst manifested itself about 34 million years ago, when the climate on Earth began to change from warmer to cooler. It was superficial until 15–10 million years ago. This coincides with an increase in global cooling.
Image of planktonic foraminifera (bottom right) surrounded by thin strands of cytoplasm under a light microscope.
This live specimen was recently recovered from the waters of the southwest Indian Ocean aboard the cruise ship GLOW.
Image Credit & Copyright: Tracey Aze, University of Leeds
So, the peak of the abundance of planktonic foraminiferaoccurred at higher latitudes 40–20 million years ago. However, it shifted between 10° and 20° latitude approximately 18 Ma ago, consistent with the pattern of diversity observed today. There was a strong relationship between species richness and sea surface temperature—life was easier to develop in warmer climates.
According to scientists, the results of the studyindicate that the current distribution of species richness of planktonic foraminifera can be explained by an increase in the latitudinal temperature gradient from the equator to the poles over the past 15 Ma.
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On the cover:Scanning electron microscope image of the shell of planktonic foraminifera species Globigerinella adamsi. The sample was collected from seafloor sediments in the southwest Indian Ocean on board the cruise ship GLOW.
Image Credit & Copyright: Tracey Aze, University of Leeds