whale evolution
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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
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