Given that this is an evolution/paleontology blog, I get disproportionately excited any time some group of people finds a few bones in a hole that they've been digging for years.

It's one of those days.

After three years of digging in the freezing cold, polar bear-infested island of Spitsbergen, scientists have unearthed an absolutely gigantic Pliosaur. This monster was as big as a humpback whale, and a whole lot meaner.

Large Pliosaur skeleton with person for scale. Courtesy of Sarah Katzenell

Today, I think it would be interesting to use this discovery to show a core principle of evolution- Body structures are related to the animal‘s environment and behavior.

Take a look at this creature’s flippers- there are four of them. All other fully aquatic animals have eventually lost their hind limbs, in what is thought to be a response to better hydrodynamics. Flippers tend to create drag when traveling through open water, which means more energy is spent swimming and less spent on eating and reproducing.

So, why would four massive flippers exist on an animal? To know this, we need to look at the Pliosaur’s environment.A world map of the Jurassic Period. Notice the continents are partially fused together. Courtesy of Dr. Ron Blakey

As you can see on the map, there is one giant ocean, a few shallow seas, and thousands of miles of coastland. The coasts and shallow waters make excellent habitats for reefs- and creatures that like to hide in reefs. Now, animals hide for two reasons; to avoid becoming prey, or to wait until your next dinner comes close enough to be convenient. As the Spitsbergen monster was quite possibly the largest animal in the ocean at that point, it can be assumed that its behavior was the latter.

Tests done with robots show some interesting benefits that come with swimming with four flippers. This style allows the animal more maneuverability, and short bursts of speed, something associated with an ambush method of hunting.

Fossils are nothing short of amazing. When looking at the case of the four-flippered pliosaur, one can not only learn about how this creature may have behaved, but also get a better glimpse of what kind of environment this animal lived in.