Unlike fish, marine mammals such as whales and dolphins evolved from other animals to become marine creatures.
Let’s examine together from which animals the marine mammals evolved and attained their present appearance and how they differ from fish.
They evolved from four-legged animals!
Tail fins are used to propel water. Fish muscles move the spine from side to side. A vertical fin is therefore required to propel the body forward in a slippery motion.
However, cetaceans still have vestigial pelvic bones, despite the disappearance of their hind limbs during the evolutionary process. Unlike fish, whales and dolphins evolved from four-legged land creatures with limbs under their bodies and survived until today.
First ancestors of whales and dolphins: Pakicetus
We have many fossils from the 50-million-year evolutionary process before marine mammals took their present form. When we go to the oldest of these fossils, the creature we encounter is Pakicetus.
Pakicetus is estimated to be the first mammalian ancestor of whales and dolphins. Pakicetus, known to live within the borders of present-day Pakistan, is a fish-eating carnivorous animal.
Tails of marine mammals also have functions.
Of course, since cetaceans continued to use their tails during their evolution, these tails did not atrophy. For example, whales strike the surface of the water as a form of communication or stun their underwater prey in this way.
- Sources: Prof. Adriana Heguy, UK Whales, American Museum of Nature History
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