Sharks were first found on earth over 450 million years ago. Majority of the early sharks were reasonably small. A lot of evidence suggests that they looked more like small fish when they first originated. Many among them were found to have great resemblance with eel.
An important point to remember about sharks is that they do not have a structured brain. But, they evolved to have an excellent ability to smell and are known as one of the most intelligent species under the oceans. Sharks have many other characteristic features that have evolved with time.
Sharks used to have smooth teeth. In early times, sharks used to depend upon plants for their food. Something would have been occurred later, which affected the growth of plants and made sharks to consume living creatures in water. Sharks have a skeleton both inside and outside, which provides remarkable protection and movement to its body. They breathe with the help of a slit present in their gill. The diverse species were capable to familiarize themselves to fresh and salt water environments and also able to survive in a diversity of unlike temperatures.
There are 3 universal categories of sharks that eventually evolved. These categories have been formed according to the structure and function of their body. The categories are:
- Sharks that swim at the upper part of the ocean at a slow pace
- Sharks that move towards the centre of the ocean and have an influential force while swimming
- Sharks that reside at the base of the ocean, finding their food on the bottom of the ocean by moving slowly
The territory of sharks is not only in various levels of the ocean, but is also extended to different geographical regions.
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