The Evolution of Dolphins

Dolphins are a fun and playful species. They have evolved to be well suited for their aquatic environments. Over many years these animals have gone from land dwellers to deep-sea divers. These amazing creatures are considered one of the top predators in the marine ecology system.  Imagine you are at Six Flags Discovery Kingdom swimming with the dolphins. The trainers explain that all these dolphins have been bread in captivity, and to not try this in the wild, because these dolphins have been properly tamed to work along side humans. This essay will explain some features of how dolphins evolved physiologically to become better suited to their environment. How the Dolphin has adapted to its current environment

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The most common misconception is that dolphins are fish, but they aren’t, they are actually mammal’s called cetaceans. Dolphins are warm-blooded and breath air into their lungs. They also give birth to live young and nurse them. “Inside their pectoral fins, dolphins have a skeletal structure similar to a human arm and hand. They have a humerus, complete with a ball and socket joint. They have a radius and ulna, as well as a complete hand structure, including five phalanges, or finger bones.

This is one of the many internal physiological structures leading scientists to believe that dolphins and whales evolved from a terrestrial ancestor”. (Dolphin research center) Dolphins are possible descendants from Mesonychidsize, which is about the size of a small dog to a large bear. These creatures started to frequent shallow waters looking for food and safety from land predators. Another theory is that dolphins are descendants from the Basilosaurus, the largest known advanced Achaeocete, (family of archaic whale). Their skeleton has been found as far south as Antarctica showing its successful adaptation to aquatic life. The Basilosaurus forelimbs were like paddles or flippers; the hind limbs were mainly used for pushing off the ocean floor, if used at all. And it’s also a well-known fact that when evolution works, it doesn’t just work on the outside; it works on the internal organs as well. Thus making a dolphin well suited for it’s aquatic environment. Retia Mirabila

The Retia Mirabila acts as the dolphin’s buffer protecting it from a surge in blood flow during influxes of heart rate. When dolphins dive deep in the ocean they slow their heart rate to 12 BPM and utilize the retia mirabila that acts like a sponge, so rather than blood rushing to its brain, which could lead to a stroke in most humans, it filters through the retia mirabila. Dolphins normal heart rate is 120 BMP, but evolution stepped in and created the retia mirabila which is a dense mass of blood vessels found under the ribcage that acts as a sponge allowing the dolphin to dive to deep depths without passing out. Goose Beak

Dolphins breathe air directly into their lungs through the blowhole, not their mouth like most mammals. What allows them to be evolved to live in aquatic life is the Goose Beak. The trachea and esophagus are completely separate with the aide of a goose beak. The goose beak is a modified larynx; it bridges the gap between the nasal passage and the trachea. Its purpose is to keep everything out of the lungs except air. It’s located inside the sporacular channel found in the skull underneath the blowhole. Digestive System

Dolphins have a three-chamber stomach just like a cow or deer, showing further proof of its evolution of a terrestrial ancestor. Dolphins don’t chew food; the mastication of food is completed in their first stomach. Then digestion happens in the second stomach and in the third stomach takes care of the rest of digestion before empting out into the intestinal region. Renal System

When cetaceans made the change from terrestrial living to aquatic living, they needed a way to accommodate to their higher salinity environment. They did this by changing their kidneys from just a two singular renules to multiple renules. These extra renules function is to filter out all the extra salt that the dolphins deal with in their (new) environment in aquatic life. The current living environment of the Dolphin

Dolphins have evolved to be an important part of a marine ecosystem and are considered a top predator. In captivity “Tank water must be treated or filtered or both to avoid health problems for the animals, although they may still suffer from bacterial and fungal infections that can be deadly”. (Animal welfare institute) In the wild dolphins run in pods of hundreds and can travel up to 100 miles per day. In most cases for captive dolphins they are usually left alone or with one other species they don’t normally socialize with, and can’t travel in a linear line for long. In the wild they are naturally playful and very active, but when in captivity they often become aggressive because all day long they perform for large crowds. When dolphins are trained and kept in captivity, they are food deprived to teach them tricks. So when you see a dolphin waving at you from the water, it’s because it is hungry. A lot of dolphins can die from human infection and bacteria because they have not evolved to be kept in captivity with these diseases; they have evolved to be in the wild aquatic life. Conclusion

In conclusion I have discussed how dolphins have evolved physiologically to become well suited to their now current aquatic life. I have discussed possible species that the dolphins have descended from as well as organs that have adapted to the dolphin’s current living conditions. In the end it is better for the dolphins to be kept in the wild and not in captivity. If you love dolphins, don’t buy that ticket!


Simon, E. J., Reece, J. B., & Dickey, J. L. (2010). Essential biology with physiology. (3rd ed.). San Francisco, CA: Pearson/Benjamin Cummings.

The Dolphin research center (2013). Grassy Keys, Fl Six
Flags Discovery Kingdom (2013) Vallejo, CA Animal Welfare Institute (2014) Washington, D.C.

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