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The appearance of whales on Earth

An artist's reconstruction of the 70-million-year old giant suspension-feeding bony fish Bonnerichthys as it cruises through the seaway covering what is today Kansas.
Image courtesy of Robert Nicholls, www.paleocreations.com

Whales are the largest creatures on Earth today, but new research in Science is showing how the evolution of these humongous marine mammals was linked to the evolution of some of the planet's smallest marine organisms tens of millions of years ago. It also describes how large, bony fish filled their place in the sea for more than 100 million years before the appearance of whales.

Dr. Matt Friedman with fossil skull.
Image courtesy of Oxford University

In the first study, Matt Friedman and colleagues highlight the discovery of several new examples of giant, filter-feeding fish that roamed the seas before modern baleen whales (and a variety of sharks and rays) eventually took their place in the food chain. Previously, researchers had believed that these ancient bony fish only existed for a short period of time, but these new fossils—which have been sitting in museums, either unexamined or misidentified—show that this group actually lived for more than 100 million years during the Mesozoic Era.

Using these old findings and analyzing new fossils, this group of researchers found that the massive filter feeders, which swallowed water with open mouths and filtered out food while water escaped through gill slits, lived from 170 to 65 million years ago. Over that time, they started the unique (and highly effective) filter-feeding strategies that can still be seen in the largest marine vertebrates living today.

Then, in a separate report, Felix Marx and Mark Uhen show that, as whales filled the vacant space left by those extinct, giant filter-feeders, the whales' evolution became controlled by the evolution of diatoms—a common type of phytoplankton and a staple of these filter-feeding whale's diet. These researchers also confirm that the climate during that time period had an effect on the whales' evolution.


This research appears in the 19 February 2010 issue of Science.