Take a good, long look at this fossilized skeleton:Courtesy of Northeast Ohio University.

Now, take a look at this (more current) skeleton:Courtesy of The New Bedford Whaling Museum.

What do they have in common? They’re both whales. Separated by 50,000,000 years, these two animals are evolutionary cousins. For the next few weeks, I’d like to explore the core fundamentals of evolution by covering how whales transformed from small, hoofed, dog-like animals into the sea going behemoths we know today.

The explanation of how such transformations can occur boils down to one core tenant of evolution: Adaptive Radiation.

To answer what adaptive radiation is in less words than this sentence: nature abhors a vacuum. If a biological niche (lifestyle) is suddenly gone, you can bet money that new creatures will fill it up. There are tons of examples of this. The perennial favorite has always been Darwin’s Finches (these finches, whose lifestyles go from sipping nectar to pecking out holes in wood famously led Darwin to conclude that adaptive radiation does exist.) However, there are also the cases of Australia’s myriad of marsupials and Hawaii’s Honey Creepers.

In short, a small group of animals put into a new environment will probably diversify and evolve to fill the various niches of said environment.

So, how does our dog-like Pakicetus relate to adaptive radiation? According to various fossil dating techniques, Pakicetus came onto the scene about 10 million years after the giant, sea going reptiles (think Nessie) had vanished from the earth. Since the Cretaceous extinction, only a few sharks and crocodilians made the ocean their home.

This is the perfection environment for adaptive radiation because there is an open niche, no dangerous competitors (Nessie), and plenty of food (fish stocks rebound in the face of few predators). Pakicetus and it’s later descendants took to the water essentially because the opportunity presented itself.

How do people know that Pakicetus is a whale? It may seem a bit far-fetched to suppose a coyote like creature to be a distant ancestor of the humpbacks, especially since Pakicetus has, you know, legs. The key is to look at the skull.

Skull of Pakicetus:Courtesy of University of California, Berkeley

Skull of modern day Orca:
Courtesy of skullsunlimited.com

In addition to the similar dental plan, you may also notice that there are no holes for ears at the side of either skull. It is thought that Pakicetus had internal ears, much like today’s whale.