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Whales are some of the biggest creatures on this planet, the blue whale being the largest animal to ever exist. Another interesting feature of whales: they breathe air. This is because whales are mammals. Whales, along with dolphins, belong to a group of fully aquatic mammals called Cetacea. They live their entire lives in the water, straight from birth to death. Another interesting fact is that all cetaceans evolved from a common ancestor.
Whales and dolphins started evolving around 50 million years ago. Their evolution starts with a family of animals called Pakicetidae. The Pakicetus was a characteristic animal of this family. It was a furry mammal that looked like a mix between a dog and a crocodile.
There aren’t many similarities between the Pakicetus and whales today. One of the features that helped link these ancient animals to their modern relatives is their ears. Their ears showed adaptations to help them hear underwater. Other than this, the Pakicetus is believed to have been semiaquatic, having lived on land and in freshwater environments.
A gradual move towards living a more aquatic lifestyle is seen in the Ambulocetus. This animal had shorter legs, and its feet and hands were bigger and flatter, like paddles. These whale ancestors still used to live some of their lives on land. Evidence for this habit is seen in how they had well-developed hind limbs and toes, leading them to be called “walking whales.”
Scientists also did an oxygen isotope analysis of the Ambulocetus fossils. This means they checked for special oxygen atoms in their fossils. They found that they had isotopes of oxygen from freshwater as well as isotopes from ocean water. This discovery shows the first steps that whales took towards becoming completely marine creatures.
The ancestors after this, such as the Kutchicetus, showed more amounts of oceanic oxygen isotopes in their fossils. This change in isotopes indicated that whales were slowly making their way to becoming fully marine animals. In the evolutionary progression, y ou can also see the loss of hind limbs as their tails grew stronger to help with their movement in the water.
Around 35 million years ago, there were certain changes in ancestors that led to the separation of baleen whales from dolphins and other toothed whales . So, it is from here on that you see changes that make these whales unique. They lost their teeth and evolved baleen to help them with filter feeding. Their nostrils slowly evolved to reach the top of their head to become blowholes .
Baleen whales today consist of 14 different species spread across the globe from the North Pole to the South Pole. They have evolved in many interesting ways, with many interesting adaptations that help them live their lives as colossal giants of the sea.
Semiaquatic: With respect to animals, it refers to those animals that live part of their life in water and part of their life on land. A frog is a good example of a semiaquatic animal.
Isotope: Atoms of same element with different mass and physical properties.
Baleen: A brush-like feature found in the mouths of baleen whales that helps them with filter feeding. Unlike teeth, it is made of keratin, the same substance as your nails and hair
Filter feeding: Feeding by filtering out plankton or nutrients found in the water.
Blowhole: The nostril of a whale or dolphin on the top of its head.
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Berta, A., Sumich, J. L., & Kovacs, K. M. (2015). Cetacean Evolution and Systematics. In Marine Mammals: Evolutionary Biology (second, pp. 51–88). essay, Elsevier.
Perrin, W. F., M., T. J. G., & Würsig, B. G. (2009). Neoceti. In Encyclopedia of Marine Mammals (Second, pp. 758–763). essay, Academic.