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Scientists Create Best Family Tree Ever of Baleen Whales

Apr 16, 2015 12:50 PM EDT
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Scientists have recently created the best, most comprehensive family tree of baleen whales, helping to shed light on this 40-million-year-old species, a new study says.

Baleen whales are not only the largest animals ever to live on Earth, but also among the most unusual. Rather than feeding on plants or preying on one animal at a time like most other mammals, they are known for their long plates of baleen for which they are named. These comb-like plates allow the whales to gulp and filter an enormous volume of water and food.

While family trees of these massive marine animals have been constructed before, a team of researchers at the University of Otago wanted to better picture the evolutionary history of baleen whales. So they created the largest, most detailed one to date, using various dated fossils to do so.

This research is important because it shows which whales are related and exactly how long ago every branch of the tree - whether extinct or still alive - first arose. It also allows scientists to estimate how many species of baleen whale have existed and how fast they have evolved over the past 40 million years.

For example, some of the earliest baleen whales underwent a sudden "evolutionary burst," similar to that of "Darwin's finches" on the Galapagos Islands after a period of global cooling.

In addition, the new family tree is helping to shed light on the similarities and differences between different lineages in terms of overall body shape. It turns out that during their early history, whales branched out into many different lineages, each with a unique body shape and feeding strategy.

"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," co-lead study author Professor Ewan Fordyce said in a statement.

And yet, after a few million years of co-existence, the toothed relatives disappeared, leaving behind only their filter-feeding cousins. This occurred between 30 and 23 million years ago, around the time that the Southern Ocean opened and gave rise to a stronger circum-Antarctic current - providing more nutrients that made filter feeding more advantageous.

Then, about three million years ago the number of small baleen whale species crashed - possibly due to the onset of the ice ages, which changed to the distribution of available food - leaving behind the giant whales that we know today.

The results are described in more detail in the journal Royal Society Open Science.

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