Thursday, October 28, 2021

Dolphin Evolution: Where Did They Come From?

Stepping Stones

Everybody loves dolphins! It’s always a treat when they come to the surface and look around.

It seems as if they are always smiling, but have they had that smile forever? Their gracefulness and athleticism amaze us as well. Were they always this talented? To find these answers we need travel back in time, way back!

Dolphins are mammals and have characteristics which are distinct to all mammals. There only a few that live in the water so it might be logical to conclude that dolphins evolved from land animals. Of course, no one was around to produce written words a long time ago, but science can give us some clues to the evolution of these intelligent creatures. Genetic and molecular studies as well as DNA can provide some insight regarding where dolphins came from.

Dolphins are “cetaceans” and belong to the same group such as whales and porpoises. As we discover more fossils on our planet, pieces of a puzzle begin to fall into place. Terrestrial ancestors and current cetaceans have several similarities. Ancient whale skeletons were discovered with well-preserved ankle bones. The pectoral fins of today’s dolphins have a similar structure to that of current human hands and arms. They have a humerus with a ball and socket joint, a radial bone and ulna, and the same hand structure as humans including five finger bones. Those terrestrial beings of long ago had similar skeletal features as our current dolphins!

The dolphin blowhole evolved from the nose, as a land animal, to the top of the snout as a semi-aquatic mammal, to the current location on top of the head, all part of the evolutionary process to make breathing easier.

When animals moved into unoccupied areas of the planet closer to water, they evolved at a rapid rate to successfully adapt to new surroundings. Fifty million years ago a semi-aquatic species called “Ambulocetus” developed, adding credibility to the theory that cetaceans first roamed on land. This “link” in the chain began to resemble marine mammals more than the land animals. Legs became shorter and took on a paddle shape. Nostrils of the Ambulocetus migrated to the top of the snout, possibly to breathe more effectively….it only had to place its nose above the water rather than the entire head, thus expending less energy. Since the legs were shorter and paddle shaped at this time in history, but not completely useless some theories suggest that this new generation was semi-aquatic and not yet completely amphibious.

Moving forward in time 15 million years the fully aquatic species known as “Basilosaurus” was established. The pectoral fins (flippers) became elongated to easily navigate in water. The cartilage in the finger bones fused to prevent the joints from curling. The nasal cavity enlarged, and the hind limbs gave way to a tail, or “fluke.”

Over the next 20 million years this process of evolution continued to change these mammals until the family “Delphinidae” came to be, about 11 million years ago. This was the beginning of what we now refer to as dolphins, and more specifically, ocean dolphins.

From that first aquatic venture 50 million years ago, we now know of about 40 species of Delphinidae and another five types of river dolphins. In the Marco Island waters we commonly see the bottlenose dolphins, but not too far offshore reports of spotted dolphins and rough-toothed dolphins have been seen as well.

Did our current population always have that well-known smile? Probably not. Were they always so talented? Hmmmm……it might be difficult to differentiate “talent” from “evolutionary change.” In any case, their long and successful journey over time has placed them in our surroundings for us to enjoy and to give us wonder.

Bob is a Naturalist on board the dolphin survey vessel Dolphin Explorer. A successful author, columnist and speaker, he enjoys the opportunity to share his findings with the local community. Bob loves his wife very much!


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