Thursday, August 7, 2008
HOW WHALES EVOLVED
A whale is not as small as us.
Most whales are bigger than a bus!
Whales are not like fish in the sea.
Whales breathe air like you & me.
Whales can't walk upon the ground.
Whales must swim to get around.
A whale is a mammal just like me.
But its home is in the deep blue sea.
How could a whale have evolved from a mammal that lived and walked in the forest to an animal that lives and swims with its flippers in the sea? When most animals were developing limbs and climbing out of the oceans, the whales were developing fins and walking into the oceans. Whales evolved from warm-blooded, air breathing mammalian ancestors that lived on land, had large brains, and gave birth to their young alive, to an efficient swimming and eating machine that lives in the great oceans of the world.
In nature, nothing is more constant than change. Animals adapt by producing anatomical, physiological, and behavioral traits that promote survival and reproduction. Adaptations evolve in response to interactions with other organisms and with the physical environment. Animals that adapt better, survive better, and leave more offspring with a copy of their genes than others in the population.
HOW DID IT HAPPEN?
About 57 million years ago, certain animals lived near the sea and would hunt just off the shoreline for fish. Because the sea was not very deep they could do this easily. As the hunt required further excursion into the deeper waters, the proto-whales who were best at swimming reproduced in greater numbers than those who weren’t. Gradually, their front legs became smaller and were useful as flippers, while the hind feet became larger and helped better propel the animal through the water. Later, the back legs changed into the horizontal extension of the tail, known in the modern whale as the fluke. They further evolved adaptations for diving and hearing under water. The transition from land to sea presented difficulties for which adaptations developed over many generations. Smooth skin and loss of protruding ear parts and hind limbs streamlined whales for swimming. The nostrils moved to the top of the head to facilitate breathing and an insulating layer of blubber replaced hair for warmth. The body, supported by water, was able to reach its enormous size.
ANCIENT FOSSIL PROOF
Whale fossils show the intermediate stages in the evolution of early whales to be of four distinct types. These fossils are evidence that whales evolved from a terrestrial animal.
A 52 million year old fossil found by Dr. Phil Gingrich, consisted of a very primitive whale skull with teeth and ear structures akin to those of terrestrial mammals, yet it had other features, which defined it as a whale. While it fed on fish, it could not dive deeply and probably spent much time on land.
A 50 million year old fossil shows a whale that was adapted to life in water as well as land. This transitional whale had large hind legs like a land dweller, and may have used them for walking as well as swimming. Its spine was long and flexible, with a tail not yet modified for propulsion. The most extraordinary feature of this animal was his enormous hind feet, which must have provided the major propulsive force in swimming.
A 45 million year old fossil shows an animal that had leg bones large enough to support the body on land. It is believed these whales spent most of their time in water, feeding on fish, but reproducing on land.
A 40 million year old fossil, Basilosaurus, burst onto the scientific scene with a bang. It was an advanced form of whale with a long flexible spine, forelegs modified into flippers for steering and stabilization, and a modified tail for propulsion. The hind legs were very tiny, and unable to support the animal’s weight. It was not able to walk on land.
Dr. Castello Banfi found 5 million year old, practically complete, 33-foot long fossil in 2007 in Itlay. We’re all anxious waiting for the exciting findings of his investigations.
REMNANTS FOUND IN TODAY’S WHALE
Inside the fin of a modern whale, you can still find the bones of an arm and hand. Today’s whale is equipped with a pelvis bone, which has long ago lost its function. And unlike fish, modern whales have lungs and nostrils called blowholes, and must surface occasionally to breathe.
When climates change due to geologic processes, animals have to adapt or face extinction. Whales certainly changed in a most unusual way. By reversing the water to land adaptation, and becoming an efficient mammal for ocean life, it is remaining one of the most fascinating evolutions of all time.