GeoMag

T H E L AY E R E D E V O L U T I O N O F A S E A L

SEB MANSFIELD

THE LAYERED EVOLUTION OF A SEAL

Ocean Life Darsh Tulsian

species. Penguins were now in the southern hemisphere and echo locating dolphins had just entered the waters. The new species of dolphin created competition for food, meaning the seal had to become more adapted to fishing - which it did! The seal became more agile as its spine became more flexible. The seals and new sea creatures offered food for larger predators such as the raptorial sperm whales, which ate vertebrate prey such as seals. This may have also explained their new, more flexible spine. These new sea creatures also showed how the ocean has evolved and therefore is layered. Four hundred million years ago, the ‘Balian’ whales started to reach their full size. This could have led to the extinction of the ‘Megalodon’ and subsequently the era of ‘Super Predators’ and started the era of the smaller apex predators such as ‘Great Whites’ and ‘Orcas’. This was because the super predators were whale hunting specialists and when the whales got bigger the ‘Super-Predators’were therefore unable kill the whales. The ‘Super-Predators’ were not seal-hunting specialists, meaning the super predators had a lack of food, which – along with other factors – led to their extinction. These new apex predators focused on hunting seals. This meant that seals may have led to selective pressures, ultimately changing the apex predators of the ocean. This meant they drove the evolution of some apex predators, ultimately changing the oceanic environment. To conclude, there is absolute certainty, based on DNA and other scientific evidence, that seals are definitely related to their early land ancestors, as they have changed from the ‘Puijila Darwini’ to ‘Enaliartcos’ to ‘Eotaria Crypta’ to the seals which we know today. This clearly shows layers of evolution within the seal. The evidence indicates that the seal’s evolutionary process has been one out of necessity. Many scientists wonder which future evolutionary changes there will be for the seal, due to what is going on environmentally. However, the evolution of seals doesn’t just suggest changes in very early times. There is a lot of evidence to suggest they had to evolve in the early 1970’s as well, due to their environment being destroyed and a lack of food available. This shows how the layers of the seals are only going to continue diversify as they adapt to the changing world in which we live.

There is evidence to suggest that seals have been on the Earth for around 23 million years (the early Miocene). There was a mammalian creature which lived in Canada. It looked like an otter and behaved like an otter; however, it was actually related to the seal. This creature was called a ‘Puijila Darwini’. The fact that it acted and lived like an otter shows that these seals were once predominantly land animals. During the same period, there was another freshwater otter like the seal that lived in the Northern Hemisphere around Germany and France, called ‘Patamotherum’. At this time, there was also a more seal like sea mammal that would have swam on the West coast of America, called ‘Enaliarctos’. These two types of seal overlapped for a large amount of time. This showed layers within the earliest seals. Within the ‘Pinnipedian’ group there are 3 sub-sections. The ‘Phocidae’ ( earless seals and most Arctic seals), the ‘Otariidae’ ( Seal Lions) and the ‘Odobenidae’, ( the walrus ). All three types use different methods of propulsion. This suggests that these seals came from two land heritages. This evidence clearly shows how the seal’s history is layered. The ‘Enaliarctos’ is the only type of seal that lived on to the present day. It has a short tail and legs, which you could say were fins. However, the legs of this species were still much longer than a common seal. This was because the ‘Enaliarctos’ swam with it’s back legs. This means that over time their appendages have changed into flippers, making them better adapted for life in water. The ‘Enaliarctos’ would have spent more time on the shore than seals nowadays as they are better adapted to killing their prey out of the water, as their teeth were more similar to those of the bear, and therefore were better at slicing than piercing – meaning they had to return to shore. If this change did not occur, scientists believe that the seal would have been extinct millions of years ago. However, a seal called ‘Eotaria Crypta’, that lived 16 million years ago, showed the beginnings of the modern seal, as its jaw moved away from the previously bear-like jaw. This newly evolved seal jaw meant that they were more adapted to aquatic life, as they could now eat their prey in the water. This clear anatomical change shows how seals have had multiple evolutionary layers. In the late Oligoceine and Miocene ages, the environment was changing, leading to the seal we know today. There was an increase in ‘Balian’ whale

Evolution is defined as the process by which different kinds of living organism are believed to have developed from their earlier forms during the history of the Earth. There is evolution in every animal on this planet and it can be seen more clearly in some animals compared to others. Seals are carnivorous sea mammals, scientifically known as ‘Pinnipeds’. There is scientific evidence that seals have evolved from land animals in the past, to the seals that we know today. In this process of evolution, there are layers of change within the ocean and within the seal itself.

Seal Seb Mansfield

26 | Geographical Magazine • Merchant Taylors’ School

2021/22 Edition | 27