Dolphins have ancestral connections to terrestrial mammals and it is believed that the ancestors of dolphins that we know today entered the water about 50 million years ago! Having been terrestrial animals originally, several changes had to take place as outlined below for survival in aquatic environment. Dolphins’ earliest ancestors were land-based hoofed creatures that became aquatic, losing their hind legs and gaining flippers over time.
The size and shape of the skull has enlarged an indication that the fat pad in the lower jaw emerged which extends to the middle ear and this helps the dolphins to be able to hear as well as to use the process of echolocation. The early dolphins were smaller and believed to have consumed small fish as well as various organisms in the water.
The nasal openings moved from the end of the snout to the top of the skull area. This is what is referred to as nasal drift. Those nostrils later evolved into blowholes so that they can get to the surface of the water, take in air, and then be submerged again with ease.
Dolphins have evolved surprisingly big brains over the last couple million years, according to the largest fossil study ever done on the animals. By 40 million years ago, ancient dolphins were fully aquatic and propelled exclusively by flukes. Flattening of the final few vertebrae indicate a foundation to which the connective tissue of the flukes had evolved. These paddle-like structures provided the animals with a powerful way to propel themselves.
Earlier dolphins fed on small fish and other small aquatic vertebrates and invertebrates. Over time the dolphins feed on larger aquatic animals such as seals. Other changes that had taken place were the loss of hair, the development of insulating blubber, the ability to hear underwater, the eyes and kidneys adjusting to salt water, and the development of nasal plugs to keep water out of their airways while diving.