Whale diversity linked to climate and algae

The diversity of whale species living at any given time period correlates with the evolution and diversification of diatoms–tiny, abundant algae that live in the ocean, according to a recent study.

A paper by researchers at George Mason University and the University of Otago in New Zealand shows a strong link between the diversity of organisms at the bottom of the food chain and the diversity of mammals at the top, George Mason University said in a news statement.

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NGS illustration of humpack whales by Richard Ellis

In the paper “Climate, Critters, and Cetaceans: Cenozoic Drivers of the Evolution of Modern Whales,” which was published in the latest issue of the journal Science, Mark D. Uhen, a geologist at Mason, and co-author Felix G. Mark of Otago show that the more kinds of diatoms living in a time period, the more kinds of whales there are.

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NGS illustration of pygmy right whales by Else Bostelmann

“Looking at thousands of published accounts of whale fossil records, the researchers assembled the records in a database to analyze and pinpoint the various fossils,” Mason said. “The fossil records show a direct link between the productivity of the ocean and the variety of whale fossils.”

The researchers also found a correlation between global changes in climate and fossil variety.

“Modern cetaceans, a poster child of evolution, play an important role in the ocean ecosystem as apex predators and nutrient distributors, as well as evolutionary “stepping stones” for the deep sea biota,” the authors say in the abstract of their paper.

“Previous studies suggested that the rise of diatoms as dominant marine primary producers and global temperature change were key factors in the evolution of modern whales,” they added. “Based on a comprehensive diversity data set, we show that much of observed cetacean paleodiversity can indeed be explained by diatom diversity in conjunction with variations in climate.”

“Diatoms and whales rose and fell in diversity together during the last 30 million years.”

“This study shows that if we look at the bottom of the food chain, it might tell you something about the top,” Uhen said. “Diatoms are key primary producers in the modern ocean, and thus help to form the base of the marine food chain. The fossil record clearly shows that diatoms and whales rose and fell in diversity together during the last 30 million years.”

This is the first time that such a correlation has been shown, Uhen said. “Though scientists in the past have tried to answer the question of how the modern diversity of whale and dolphins arise, this question has been difficult to answer. The fossil record might not truly reflect evolutionary history,” he said.

“Is it possible that the diversity of fossils we find through geological time might really just reflect the amount of preserved sedimentary rock paleontologists can search–the more rock there is, the more fossils we find? This comprehensive study has shown that the diversity of these fossils is in fact not driven by the sedimentary rock record.”

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NGS illustration of killer whales by Else Bostelmann

The researchers hope these findings will encourage other specialists to look at other animals with a similar narrow ecology to see if this link translates, the university said.

Uhen is a term assistant professor in Mason’s Department of Atmospheric, Oceanic and Earth Sciences and is an expert in marine mammal fossils. In the future, he hopes to conduct research on how the body size of whales changes over time, and how whales became the largest living organisms in the world.

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NGS illustration of blue whales by Larry Foster

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