A study by PhD Geology student Felix Marx has shown that the evolution of modern whales was driven by a combination of food abundance and climate change, findings which could help scientists predict the impacts of future global changes on these creatures.
“While we know much about how ancient cetaceans evolved from four-legged ‘landlubbers’ into sea-going creatures, many questions have remained about what drove the evolution of whales after their ancestors became aquatic,” Marx says.
Now, an analysis of the fossil record has shown that the diversity of ancient cetaceans was related to the evolution and diversification of diatoms, tiny plants at the bottom of the marine food web.
“This clearly shows that diatoms and whales rose and fell in diversity together during most of the last 30 million years,” Marx says.
“When diatoms are dominant in oceans, it creates a shortened food web, enabling more efficient foraging by whales. This allows them to grow larger, more abundant and more diverse.”
Oxygen isotope records – which show a chemical “fingerprint” of oceanic temperature and global ice volume over large time scales – revealed that fossil whale diversity was also linked to changes in ancient climate.
“Both food abundance and climate change were in turn probably related to continental drift and changes in the Earth’s geography, particularly the isolation of Antarctica from other continents about 30–40 million years ago.”
This led to a new current spreading high levels of nutrients into the upper layers of the world’s oceans, providing perfect conditions for diatoms to flourish.
“The evolution and diversity of whales may ultimately be the result of geological forces working at the heart of our planet,” he says.
“Due to their position at the top of the marine food web, whales are strongly affected by global environmental change. Discovering the past impacts of these changes will give us new tools to predict how future global changes might affect these animals.”
(The report, published in Science, was co-authored by Dr Mark Uhen, George Mason University, US.)
- University of Otago Postgraduate Scholarship