From a small land mammal to the largest animal on the planet: whale evolution.
- Asya Chub
- Apr 17
- 4 min read
Whales, the majestic creatures roaming the oceans of the Earth. What if I tell you it was not always like that? Unlike sharks, who’ve been here before trees (another fun evolutionary fact), whales have gone through a recent (in palaeontology terms) unexpected evolutionary history.
Whales evolved from the same branch that cows, pigs and camels came from, called Artiodactyla, four-legged, even-toed hoofed (ungulate) land mammals that are adapted for running. Some of the descendants of the ancient artiodactyla returned to the oceans and became the whales we know today. But, how exactly do we know this? A quite extensive fossil record and some vestigial anatomical structures found in modern whales allow scientists to say that cetaceans (the whale order) evolved this way. One of the structures that is present in whales, as a remnant of the hinder legs, are pelvic bones, which are now useless to the animal. Another structure that is present in all whales and their ancestors from the same lineage, is a specific thick ear bone that supports the middle ear.
It is important to note that evolution is not linear, and all the species appearing in this article are not direct ancestors of any modern whale, but just species that were in the whale lineage millions of years ago. The first animal considered a cetacean is the Pakicetus, a wolf-like mammal found in Pakistan. It had both the ear bone and a similarly structured pelvis. It was still a land-dwelling animal, but it had likely hunted and spent a lot of time in water.
The next, so-called “transitional” species, is Ambulocetus, still a four-legged animal that looked more aquatic, with its streamlined body and long snout. It is hypothesized that they had a lifestyle similar to crocodiles: hunted in water by ambushing their prey. Their ears were more similar, with thick ear bone, adapted for being underwater. One of Ambulocetus’ fossils was found with a fetus inside, which was positioned head first (unlike modern whales), indicating that although they all spent their time in water, they might have given birth on land.
The next two interesting species that lived in the same period, 40 MYA are Dorudon ("spear-tooth") and Basilosaurus (“king lizard”). The first one was very much akin to a whale, with little knobs instead of hind limbs. Their long and strong tail and mammalian backbone helped them glide through water in an up-and-down motion.
Basilosaurus lived in the same areas as Dorudon, but was a lot larger (up to 18 meters, compared to 5 meters). Its name is quite misleading, as it was definitely not a lizard, but was identified as such in the 19th century because of the resemblance to Jurassic marine reptiles, which look similar due to convergent evolution.
At this point, whales started to become enormous. Take Livyatan, for example – the whale that could be a possible predator of the Megalodon. The reason for this growth is thought to be nutrients flowing into the ocean when the Earth’s ice caps were melting due to that time’s global warming.
This unusual evolutionary path led to the whales we know today, the largest animals on the planet, reaching 150 thousand kilograms in mass, beautiful and terrifying at the same time.
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