Fossil Whale Shows Transition Stage to Tail-Powered Swimming

[Judi Lynn]

December 11, 2019
MADELINE REYES

(CN) – Researchers from the University of Michigan have described a new fossilized whale that represents not only a new species, but also identifies an important step in the evolution of whale mechanics.

In 2007, paleontologists discovered a fossilized creature in the Egyptian desert they called Aegicetus gehennae, dating back to roughly 35 million years ago. The creature was aquatic and able to swim by undulating its mid-body and tail similar to how crocodiles move through water today, according to Philip Gingerich, professor emeritus in the U-M Department of Earth and Environmental Sciences and curator emeritus at the U-M Museum of Paleontology.

Details of the discovery were published in the journal PLOS ONE on Wednesday.

Whale evolution, according to fossil records, transformed land-dwelling ancestors walking on all fours to the ocean-dwelling cetaceans we know today. During the transition came an early, semi-aquatic whale known as the protocetid, present during mid-Eocene epoch 56 million years ago to 33.9 million years ago. Remains of this ancestor have been uncovered in parts of Africa, Asia and the Americas.

The fully aquatic modern whales use their tails to maneuver through the water, but protocetids were only semi-aquatic and had limbs that helped them swim. In their paper, Gingerich and his colleagues describe Aegicetus gehennae, the first late-Eocene protocetid.

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