The world's first mammals heaved themselves out of the water to inhabit and walk the Earth, but unlike other mammals, the globe's first whales, the forerunners of today's baleen and toothed whales (of which there are over 80 species) returned back to the water becoming ocean dwellers once more — the only creatures to perform an evolutionary U-turn.
This evolutionary U-turn freed the predecessors of today's whales from any gravitational constraints, allowing their descendants to become the giants of the ocean. The blue whale which inhabits the planet's waters today is the largest animal to ever live.
But, how did these majestic behemoths evolve to become the whales we know and love today and why did they return to the water after walking upon the land?
All whales and dolphins are descendants of terrestrial mammals
The earliest whales lived around 55 million years ago along the eastern shores of the (now non-existent) Tethys Ocean during a time in which global temperatures spiked.
The Tethys Ocean was salty and warm, teeming with marine life and free of aquatic dinosaurs (these went extinct about 10 million years prior). As the earth heated up, the first known whales waded into the ocean leaving land behind, chasing new types of food sources further and deeper into the water.
This return to the ocean was a smart move, these early whales attained access to an environment which was unreachable to most other mammals. An underwater utopia plentiful with food, offering shelter and safe haven with much fewer competitors and predators to contend with.
The watery depths of prehistoric Earth at this time provided not only an ideal habitat to survive in, but also the ideal conditions for another evolutionary explosion to take place
In the following eons a starburst of evolutionary experiments took place, all paving the way for the emergence of the whales we now today. It is important to note that these first whales were not necessarily direct ancestors of our modern whales, but rather, it is more likely they're side branches of the same family tree.
Most of the early whale species which were created during this adaption experimentation phase are now extinct.
As time passed, these earliest whales evolved, adapting to their new watery home. The first whales developed longer snouts and sharper teeth ideal for snaring fish. Then, 50 million years ago, they reached the stage of the Pakicetus: 4-legged swimmers which could still roam land.
A few of the earliest extinct whales:
Pakicetus was the earliest of the Archaeocetes (primitive cetaceans).
Ambulocetus was an amphibious animal with forelimbs equipped with small hooves and fingers, along with hind feet adapted for swimming — a creature which likely lived in estuaries, or bays thriving between freshwater and open ocean.
Basilosaurus was fully marine adapted and would have resembled a colossal eel. It's likely this whale had a tailfin along with small, almost non-existent weak hind legs which could not carry it on land.
The evolution of whales is incredibly remarkable and even caused the great Charles Darwin to pause, this was the only creature whose evolutionary steps he could not speculate about with confidence.
He attempted to explain whales in his 1859 'On the Origin of Species', using the hypothetical example of North American black bears which could catch insects by swimming through the water with their mouths wide open, proposing the theory whales could have evolved from bears given the right selective pressures. This idea received much ridicule from the public and so Darwin omitted it from later editions of the book.
It wasn't until a century after Darwin that giant leaps were made in explaining the evolution of whales thanks to new ancient whale fossils which were uncovered far and wide across the world.
The whale fossil record now affords Darwin the last laugh, later studies and especially work done by palaeontologist Philip Gingerich have in more recent times confirmed Darwin's bear explanation wasn't far off. Rather than whales refuting his theory, modern scientists now know these marine mammals are actually one of the best examples of Darwinian evolution!
Darwin had the right idea, but was discussing the wrong animal, instead of bears, he should have looked at hippopotamuses — the closest living relative to whales!
Now you've discovered the origins of these incredibly intelligent marine mammals, why not visit them in their aquatic habitat aboard the MV Eye Spy.
Book a whale spotting trip with Brisbane Whale Watching and cruise out into Moreton Bay Marine Park to see these behemoths of the ocean for yourself.