The Evolution of Modern Whales

By John Crandall

Library 1210

Winter 2009

Mammal

What was the first thing that you thought of? Was it a cat? An otter?

Most people wouldn’t think of a whale, but they are indeed mammals.

And at one time (millions of years ago) the ancestors of today’s whales looked a lot like the more familiar and furry varieties of mammal.

So…What happened?

What happened was that the furry land dwelling ancestors of the whales had to undergo some serious changes

These evolutionary changes were vital to their adaptation to an aquatic lifestyle

Starting at the beginning of the whale’s evolutionary journey, I’ll highlight the most important adaptations that allowed these creatures to terminate their land based existence.

This is Pakicetus

The fossils of this critter mark the beginning of the whale’s story

What makes it a whale ancestor is it’s teeth: they have a lot in common with later whale species

It is covered in fur, and has tiny hooves on the end of it’s feet. This means that it belongs to a group called the Artiodactyls,

which include animals like pigs, hippos, and giraffes.

The Artiodactyl Family Tree

Pakicetus fits in right about here

Meet Ambulocetus

This animal displays the result of a few million years of improvement on Pakicetus, and the next step towards whalehood

Ambulocetus’ legs are much shorter for swimming, but it can still walk on land

The special shape of the ear bones mean that it could hear underwater

It’s Rodhocetus

The evolution of Ambulocetus results in Rodhocetus It’s hind legs have continued to shrink Nostrils have started to move away from the end of the snout,

towards the blowhole position The pelvis is weakly attached to the spine, improving the

animal’s ability to swim (but it probably couldn’t move well on land)

Dorudon

Dorudon looks a lot more like a whale, and is an improvement of Rodhocetus

It’s pelvis is completely unattached from the spine

The hind legs are hilariously tiny

Dorudon

Special isotopes trapped in the teeth mean that it was able to live without fresh water, and metabolize salt water

Nostrils are closer to becoming blowholes Bones of the forelimbs suggest a flipper- like shape and function

The Modern Whale Dorudon marked the last big step in whale evolution, and

finally we arrive at the modern whale. Today’s whales fall into two groups

1. those with teeth, called porpoises

2. those with baleen, which are filters made out of the fingernail material (keratin)

They also have a tail fluke, but it was not mentioned because it can’t fossilize.

What did you learn?

Here’s a nice recap of the major adaptations of modern whales:

1. Hind leg and pelvis reduction

2. Underwater hearing

3. Blowhole at the top of the head

4. Saltwater metabolism

5. Flippers

ReferencesInfo: Chadwick, D. (2001). Evolution of whales. National Geographic, 200(5),

64. Retrieved February 18, 2009, from Academic Search Premier database. Monastersky, R. (1999). The whale's tale. Science News, 156(19), 296.

Retrieved February 16, 2009, from Academic Search Premier database.

Sutera, R. (2001). The origin of whales and the power of independent evidence. Retrieved February 8, 2009 from http://www.talkorigins.org/features/whales

Pictures: “Dorudon3,” and “Dorudon5” by quantumdtell, from Flickr, used in accordance

with Creative Commons License http://commons.wikimedia.org/wiki/File:Pakicetus_BW.jpg http://scienceblogs.com/voltagegate/2007/12/finding_little_cubists_the_per.php http://locolobo.org/CetaceanEvolution.html http://commons.wikimedia.org/wiki/File:Dorudon_BW.jpg http://evolution.berkeley.edu/evosite/evo101/IID2Understanding2.shtml http://en.wikivisual.com/index.php/Endangered http://taxonomy.zoology.gala.ac.uk/~rdmp1c/teaching/L1/Evolution/l1/

geology.html