This lousy "big-tailed wolf" of Buggy is actually a whale?

This year's species calendar includes many large animals, such as the Guinea worm and the Komodo dragon, which are the largest animals in their group. When it comes to large animals, many children's first impression is dinosaurs. The giant sauropod dinosaurs are undoubtedly an extremely brilliant chapter in the history of earth's evolution. However, the crown of the largest animal still falls on the head of mammals: the blue whale can reach nearly 30 meters in length and weigh 190 tons, but what were its ancestors like? Were they also so tall and strong?

An embryo of the spotted dolphin Stenella attenuata has hind limbs in the embryonic stage (left, with the h-shaped bump), but these disappear later in development (right), suggesting that whales are descended from ancestors with four limbs | Norman A Johnson et al. / Evolution: Education and Outreach (2012)

The weird "big tail wolf"

This has to start with the catastrophe that wiped out the dinosaurs 66 million years ago. With the extinction of the dinosaurs, mammals ushered in their own prosperous period, and our relatives began to occupy various ecological niches vacated after the extinction of the dinosaurs, and also evolved into various weird guys.

As we all know, today all animals with hooves are vegetarians. However, in the Indian subcontinent at that time, there was a group of animals with strange hooves, such as the Indohyus. This deer-like creature probably lived near water and would jump into the water to swim away if it encountered danger. Its eyes were located on the upper part of its head. This physiological structure allowed the Indohyus to lower its head to look for food on the ground while observing the surroundings. At the same time, it was also convenient to keep its head above the water to observe when it dived to escape. The ancestor of whales may be a close relative of the Indohyus.

Left: Indian hog heron, right: raccoon. Although it doesn't look "whale-like" at all, the ectotympanic bone of the Indian hog heron's ear formed a unique shape of the auditory bulla, which is only seen in ancient and modern whales. | Akrasia25 / Wikimedia Commons

About 50 million years ago, the first whales in the world, the protagonist of our story today, Pakicetus, appeared. Although it is a whale, I believe that most people's first reaction when they see it is: "Isn't this just a big dog with a long face?" Indeed, the whales at this time did not look like fish at all, and had four legs and a long tail.

Model of a whale skeleton from Pakistan | Kevin Guertin / Wikimedia Commons

The Pakicetus fossils discovered by American paleontologist Philip D. Gingerich in Pakistan in 1997 look like a weird-looking "big-tailed wolf" to laymen like me. However, paleontologists have sharp eyes. The skull fossils of Pakicetus reveal its origin. It actually has the same prominent ear bones as living whales!

Model of a whale skull from Pakistan | James St. John / Wikimedia Commons

Subsequently, some more Pakicetus fossils were discovered. After research, paleontologists found that Pakicetus's body had begun to transform into one that was suitable for aquatic life. Its original hooves had turned into webbed feet, which were more suitable for swimming in water. Its ears also began to shrink in size to reduce the resistance of water when swimming. Its mouth became longer to facilitate preying on fish in the water.

The family tree of whales will give you a big surprise

When Pakicetus lived, the Earth was relatively warm and humid. Its home was full of streams and ponds, and the food in the water was relatively abundant, which made Pakicetus "like a fish in water" and became more and more like a fish. Its successors also began to conquer the ocean generation after generation.

Ambulocetus looked like a crocodile and probably lived a life similar to that of a crocodile, ambushing animals that came to drink water in the water; Rodhocetus' tail and limbs became more like paddles, allowing it to move more flexibly in the water, and probably lived a life similar to that of a seal; the appearance of Basilosaurus showed that whales began to covet the throne at the top of the marine ecological niche; Livyatan seemed like a tyrant descending on the ocean, making all marine creatures tremble under its rule...

Archaeocetei from different geological periods | Conty / Wikimedia Commons

People used to think that the ancestors of whales were closely related to carnivores, and even speculated that the ancestors of whales were animals closer to bears. Darwin wrote in "The Origin of Species" that bears were observed in North America swimming with their mouths wide open, catching insects in the water, much like whales (filter-feeding plankton).

The main marine mammals living today are whales, sea lions, walruses, seals, manatees and dugongs. Although they have all evolved streamlined bodies and flippers for swimming, and look very cute, their taxonomic relationships are very different: seals, sea lions and walruses belong to the suborder Pinnipeds of the order Carnivora, and are more closely related to cats and dogs, while the ancestors of manatees and dugongs are related to elephants. The whale family is more likely to surprise you. Whales are members of the order Even-toed Toads and are quite closely related to hippos. Whales were once listed as a separate order of Cetaceans, but are now "downgraded" to the order Infracape, and are included in the "command" of the order Even-toed Toads.

Reconstruction of ancient whales, including Basilosauridae, Ambulocetidae, Protocetidae, Pakicetidae, and Remingtonocetidae | Ana Claudia Rocha e Charbel Niño / Wikimedia Commons

Calendar Girl's Tips

Even-toed ungulates were once called Cetartiodactyla, but this name was later cancelled because it emphasized the uniqueness of whales. Only when "whales" and "other even-toed ungulates" were in full bloom and each had its own merits, could the name that put "whales" and "other even-toed ungulates" together be established. Although whales look nothing like cows and sheep, they are actually not that special and are one of the many branches of the Even-toed ungulate family.

The "little deer" that once searched for food in the depths of dense forests and among fallen leaves has become the largest animal in the world after tens of millions of years. This is so unexpected. The fun of exploring the history of life evolution lies in the fact that there are always unexpected truths.

Drifting by | Pixabay

A little episode during the creation of this article:

My mother is a typical Beijing old lady who can make the most of homophonic puns and can suddenly drive fast without any warning. When my mother saw the restoration picture of Pakicetus in the information I looked up, she asked me curiously: "What kind of mess are you studying? What is this thing?"

Me: "It's called Pakicetus, a type of whale."

My mother: "You can tell from the first glance that this is not a good whale. It smacks its lips and acts like a big shot."

Me: "...Mom, please stop talking and let me be quiet, okay? The manuscript is due tomorrow..."