The Dolphin & the Mesonyx

The Dolphin & the Mesonyx

Evolution Occurs in Many Ways

Many people believe that life evolved from the oceans. This theory, while having a great deal of merit, tends to be looked at in a narrow focus. Laypersons often think of species emerging from the oceans, as these creatures slowly evolve become land dwelling creatures over time. For example,

In the fossil record, there are a number of different tetrapodomorphs, or transitional species between fish and four-legged vertebrates called tetrapods. Most date back to the Devonian period, often called the “age of fish,” roughly 393 to 359 million years ago. These creatures probably lived in a number of environments, from the bottom of the ocean, to the shallow waters of rivers and streams, to mudflats… (Bennington-Castro, 2014)

These transitional creatures have begun to provide evidence that there were many creatures that were both adapted to land and sea. Most likely these creatures were responding to pressure in the environment such as food shortages which would force these creatures to seek feeding grounds in shallower waters. As these pressures from the environment continued over time species would grow legs from fins or lungs from gills. While this accepted view of transitional species is common what is less discussed is the idea that many creatures have undergone an opposite form of evolution.

The tremendous time in which evolution occurs dictates that it is possible for species to experience evolution in a variety of ways. It is certainly possible that many species evolved from land dwelling creatures into ocean dwelling creatures. For example, the evolution of the dolphin is believed to have occurred in this manner. When one examines the internal organs of the dolphin, there is an obvious similarity between these organs and the organs of many mammals. The dolphin has lungs and must rise to the surface of the ocean in order to breathe. Many creatures such as fish, possess a gill bladder which filters oxygen from sea water. Dolphins also have a three sectioned stomach that is more like a stomach of a cow (Dolphin Evolution, 2013). In contrast to the dolphin, fish possess a single section stomach. This type of stomach evolved in this way most likely due to the less dense foods such as plankton and plant life. The more revealing clue that the dolphin evolved from a land creature is the fact that it possesses a pelvis that seems to have no purpose. Fish do not possess a pelvis and the only practical reason for a dolphin having a pelvis would be because it once had legs.

The Dolphin & Mesonyx

By Sceptic view — CC BY-SA 4.0

One might think that the idea of dolphins being land dwelling creatures might seem like farfetched. In fact this is one of the major controversies in evolutionary theory sometimes referred to as the “missing link”. This controversy stems from the fact that there is a lack of fossil record to show the transition from one stage of evolution to the next. However, science has been able to find genetic evidence support this idea.

Researchers at the Tokyo Institute of Technology were able to develop a method of genetic tracking. This tracking method is works on the basis that come DNA elements present in genomes will not disappear as animals evolve over time. These DNA elements allow researchers to track DNA sequences through history and through species. One of the animals which has been tracked with DNA are dolphins. Researchers have traced dolphins through time and found that they are more closely related to “cows, antelopes, giraffes, and that pigs may be their closest relatives” (Dolphin Evolution, 2013). This relationship explains why “the dolphin’s 3-chambered stomach functions in the same way as the 4-chambered stomach of a cow” (Dolphin Evolution, 2013). It is believed that about 95 million years ago the dolphin was a land creature known as the Mesonyx. which has been linked by DNA elements appearing in the fossil record (Dolphin Evolution, 2013).

The Mesonyx

By Apokryltaros — CC BY-SA 4.0

As well the teeth of the Mesonyx match the teeth of whales and other sea mammals. It is likely that the Mesonyx, under the pressure of environmental changes, such as geological changes, forced to feed in waters slowly adapting to hunting in the water (Bennington-Castro, 2014). This would explain the loss of legs in lieu of fins and loss of fur for smooth skin (better for water motion) (Bennington-Castro, 2014). These findings provide evidence that species are capable of evolving in many different ways and from one environment to another, e.g. land to sea or sea to land.


“Dolphin Evolution.” Dolphin Evolution. N.p., n.d. Web. 22 Dec. 2013.

Bennington-Castro J. (2014) New Discovery Could Explain How Sea Creatures Evolved to Walk on Land


Triola Vincent. Wed, Feb 03, 2021. The Dolphin & the Mesonyx Retrieved from

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