A favorite line of mine that I’ve used to educate & confuse many, many people over the years is, “All dolphins are whales, but not all whales are dolphins!”
The scientific order Cetacea is comprised of whales, dolphins, and porpoises. These aquatic creatures are the most specialized of all mammals, with adaptations that allow them to spend their entire lives in water. Living cetaceans are divided into two distinct suborders, Mysticeti and Odontoceti. The Mysticeti suborder contains those whales which have baleen plates instead of teeth. A baleen whale feeds by straining water through the baleen, trapping the fish, shrimp, crustaceans or krill inside its mouth. This suborder is comprised of the largest whale species, including the blue whale, the humpback whale, and the grey whale.
Those cetaceans classified in the suborder Odontoceti are toothed whales, dolphins, and porpoises. They are generally smaller, faster, and more agile than their baleen counterparts. Scientists have identified approximately 80 species of toothed whales, ranging in size from the 60-foot sperm whale to the five-foot harbor porpoise. The various species are incredibly diverse and display a multitude of body shapes, behavior patterns, and lifestyles. Some spend barely any time on the surface, rising occasionally to take a breath; others can leap 20 feet out of the water almost effortlessly. Some species live in the shallows close to shore, some reside in deep oceans, and still others are found only in freshwater rivers. Odontoceti may have anywhere from eight to 250 teeth, and their eyesight ranges from poor to excellent.
The actual Dolphin family, Delphinidae, is the largest family within the Odontoceti suborder. Scientists have discovered fossil records of ancient dolphins, which date back 11 million years. There are over 30 different species in this family, the largest of which is the Killer Whale. Dolphins are characterized by sharp, cone-shaped teeth; most (but not all) possess a dorsal fin and a melon joined to a distinct beak. Though dolphins are occasionally referred to as porpoises, so as not to confuse them with the Dolphin fish, Mahi Mahi, actual porpoises are typically smaller, have more rounded, spade-shaped teeth & rounded dorsal fins.
Dolphins have ancestral connections to terrestrial mammals which is a fact that many people don’t know about. Plenty of the research that has been conducted indicates that the ancestors of dolphins that we know and love today entered the water about 50 million years ago!
There are many telling signs that the dolphin has terrestrial origins. The fact that they need to come to the surface of the water to get air is the most dominant factor. Researchers have carefully examined the bones of dolphin flippers. What they find is that they strongly resemble the limbs of many animals that live on land. Dolphins have spines that move vertically, and this is a characteristic mainly found in animals that are able to run on land. When you look at the movements of fish, their spines move horizontally.
It is believed that dolphin ancestors were carnivorous, wolf-like animals that theoretically went from being land predators to shore-line predators to fully aquatic ocean predators.
What is interesting though is that unlike many other mammals, they didn’t change to being herbivores once they became fully aquatic. For example, manatees, dugongs and the now extinct Stellar’s Sea Cow feed exclusively on vegetation. Instead, dolphins continued to be carnivorous in the water as they would have been on land.
The dolphins’ mastery of their underwater realm is another aspect of this animal that is truly awe-inspiring. Dolphins may live in the ocean, but they’re mammals that are fully adapted to live in water. There are a number of adaptations that dolphins developed during evolution living in water instead of on land. For instance, dolphins and other cetaceans have no hair whatsoever, with the exception of a few follicles on their lower jaws and snouts.
Probably one of the most important difference between land mammals and dolphins is the way they communicate/vocalize. While most mammals have a larynx or a similar structure that allows them to vocalize using throat vibrations and exhaled air, dolphins and other cetaceans are no different; however, they’re specially adapted to make extremely high-pitched sounds used for echolocation as well as more human-pitched sounds used for ordinary communication with others in their pod.
In addition, dolphins have extremely sharp hearing, and much better vision than one might expect of an animal that uses echolocation as its primary means of sensing the world. Dolphins can see limited colors, and even have limited binocular vision like a primate. They do not possess much of a sense of smell, however.
Unlike other mammals, a dolphin’s hind quarters are much, much more developed than its front musculature; the flippers are only to steer, while the tail provides most of the force of motion. Dolphins have also developed horizontal flukes on their tail to make propulsion more efficient, and they’ve developed a dorsal fin just like fish. External parts that get in the way of a dolphin’s streamlined shape, like the genitalia or the ears, have been entirely lost, turning into internal organs instead.
Dolphins, like other mammals, breathe air instead of water, and thus use lungs instead of gills. A dolphin that cannot surface also cannot breathe, and thus will drown; this is why dolphins caught in fishing nets are given such a poor chance of survival. Unlike most fish, dolphins are very much creatures of the surface of the ocean.
Like whales and other cetaceans, dolphins breath through a blowhole on the tops of their heads, breathing in air when they break the surface of the water. Unlike humans, dolphins do not breathe reflexively; instead, they have to remember to breathe. An unconscious dolphin is likely to be a dead dolphin. Though when actively swimming they must breathe fairly often, dolphins can hold their breath for fifteen minutes or more.
All these aquatic adaptations have turned the Dolphin into an amazing piece of predatory excellence. Dolphins spend plenty of time finding food daily. They can consume up to 30 pounds of fish per day as adults. They have the ability to use a variety of different feeding techniques that have proven to help them in a variety of settings. In addition to dining on fish, squid is popular.
What may surprise you is that dolphins don’t use their teeth to eat their food. They have 100 teeth but that allows them to grasp food. They swallow their meals so they must consume food that isn’t too large. They have two stomachs like a cow – the one for storing food is first and then food moves to the second one for digestion to take place.
Experts believe that the process of migrating is often connected with finding enough food. Dolphins will move long distances in order to find enough food at various times. If they have enough food though where they reside and the temperature of the water is also acceptable they aren’t going to migrate.
When humans took the sea for survival, they marveled as the dolphins physical adaptations as well as feeding abilities. This early contact eventually lead to the current image of dolphins in human culture.
Image Credit: Peter Asprey