A new study from the University of Otago provides the “most comprehensive picture of the evolutionary history of baleen whales” to date. Otago Geology PhD graduate Dr. Felix Marx and Professor Ewan Fordyce created a baleen whale family tree stretching back nearly 40 million years.
This family tree – the first to be directly calibrated using dated fossils – shows which whales are related and how long ago each branch first arose. The tree will allow researchers to estimate how many species of baleen whales have existed and how quickly they evolved, and to examine similarities and differences between different lineages.
“We find that the earliest baleen whales underwent an adaptive radiation, or sudden ‘evolutionary burst’, similar to that of ‘Darwin’s finches’ on the Galapagos Islands,” Professor Fordyce explained in a news release. This period of rapid change coincided with a period of global cooling.
The tree reveals that early on whales branched into many different lineages with different body shapes and feeding strategies. Modern baleen whales are known for their unique feeding strategy – they open their enormous mouths, take a big gulp, close them, and then filter out all the water, leaving just the food.
“Rather surprisingly, many of these early whales were quite unlike their modern descendants: Although some had baleen, others had well-developed teeth and actively hunted for much bigger prey than is taken by modern species,” said Professor Fordyce.
Twenty to 30 million years ago, the ‘toothed’ baleen whales died out while the filter-feeders remained. There were still many different kinds of filter-feeders until about three million years ago when the number of lineages suddenly decreased.
“This decline was driven mainly by the disappearance of small species of baleen whale, which left behind only the giants—ranging from 6 to as much as 30 meters—that plough the ocean today,” Dr. Marx said.
The small species were likely wiped out due to the onset of the ice ages, which altered shallow habitats, creating a need for long distance migrations. These migrations are still “one of the hallmarks of all baleen whales alive today,” Professor Fordyce noted.
To learn more:
Read the Otago news release: Otago research details 40 million-year-old family tree of baleen whales.
Read the full study: Baleen boom and bust: a synthesis of mysticete phylogeny, diversity and disparity.
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