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How paleontologists put together the strange story of the evolution of whales

Rare humpback whale spotting off the coast of Sri Lanka, February 19, 2011 Photo: Navodya Ekanayake / Wikimedia Commons, CC BY-SA 4.0 (horizontally inverted by The science of wire).

It was a cool November morning in 1973, and paleontologist Vijay Prakash Mishra searched for fossils on the flat hills of Kach, Gujarat.

“There have been reports of large skulls, but in fact no one in India has identified them,” said Ashok Sahni, 78, a sensei of Indian paleontology and Mishra’s teacher who carried out this detective mission.

Mishra spends days wandering the silver, salt-covered desert crust, trying to find ancient remains. Finally he came across some unusually large fossils.

“I kept looking and looking,”

; Mishra said. “Then I found teeth and bones in some sea rocks. But they were not reptiles. These were distinctly mammals, but far more primitive than similar fossils found elsewhere. “

The discovery is the first of its kind in India. These are the remains of ancestors of the largest animal on our planet – those belonging to the order of aquatic mammals, called cetaceans, including whales, dolphins and guinea pigs.

Skeletons collapse

“The story of the ‘real’ whale begins with about 47-48 million annual rocks in Pakistan and India,” said Sunil Bajpai, a paleontologist at IIT Roorkee who followed in Sahni and Mishra’s footsteps. “It documents the transition of a whale-like mammal from land to water.”

For three decades of discovery, this fascinating story of mammalian evolution has been intertwined through discoveries that reveal unexpected facts.

For example, when Baipay began his research in the 1980s, geneticists had just tracked whales to ungulates. Dolphins and whales have been shown to be more closely related to hippos and cows than to sharks and sardines. In fact, the fossils in northern Pakistan and Kashmir and Kach in India confirmed these ideas.

During several trips during this decade, Baipay and his collaborator Hans Tevisen, a Dutch-American paleontologist, crashed into bright red and yellow rocks in Kutch, belonging to a geological era called the Eocene, a time of calm global time.

That was about 50 million years ago. The Indian subcontinent was approaching Asia, squeezing the Tethys Sea at its northern ends. The habitat, with its leafy river banks, was a cozy place for deer-like cat boots. This was Indochia, the Indian pig.

Illustration of Indochina. Image: Anupama Chandrasekaran

While Thewissen and Bajpai searched for fossils in Kutch in the 1980s, Indian territorial geologist A. Ranga Rao excavated fossil trucks from Kalakot in Kashmir, including Indohyus. In 2005, a fossil of Indohyus fell into Thewissen’s lap through Rao’s widow.

Back in the United States, the fossil warrior of Thewissen accidentally cut a bone similar to a walnut shell while shredding the Indohyus relic. It was trouble, a cup-shaped ear bone that definitely identified whales.

“Only whales hear this way using this structure,” Thewissen said during a phone call.

The hoof, a land-eating herbivore that looked nothing like the lightened whales of the new age, remained the front page in the whale fossil case. Indochia is perhaps one of the earliest ancestors of four-legged whales, which dived into water to avoid predators or seek food.

Next in the evolutionary tail of cetaceans was the sharp-toothed Pakiket. The fossil of this primitive wolf-faced whale was discovered in 1981, this time in northern Pakistan by an American paleontologist named Philip Djindjic.

Illustration of Packet. Image: Anupama Chandrasekaran

This signals another incredible transformation. In this version of primitive whales, the eye cavities have migrated from the sides of the head to the top of the skull. Like a crocodile, this trait may have allowed it to spot prey on the edge of a river while remaining submerged – a valuable evolutionary trait, as this ancestor of whales prefers water.

“For any animal or organism to change its habit or the way it gets its food source or where it lives, there must be environmental stress,” Sahni said. “This ancient ocean, Neotetis, which separated India from Asia, was becoming shallow and narrow. Create environmental opportunities. “

Next in line was the clumsy, otter-like Ambulocet. Thewissen discovered this fossil in 1991 in Pakistan. Ambulocetus, literally a “walking whale,” was an amphibian. It had a strong muscular tail and possibly walrus-like legs and was cozy in salty river environments.

Illustration of Ambulocet. Image: Anupama Chandrasekaran

For 10 million years, archaic whales have evolved from terrestrial Indochium-like deer to amphibious ambulocetus.

Now the evolutionary compass was heading for the first truly marine whale: Remingtonocetus. Sahni discovered this fossil in the 1980s. This ancestor with a crocodile head probably sprayed around muddy lagoons and had small eyes, which means that he used his sense of smell to catch fish.

Sahni had designated the aquatic short-legged Remingtontocetus after Remington Kellogg, a famous American paleontologist. Ironically, in the 1930s, Kellogg rejected the existence of whales in the Indian Ocean during the Eocene. The earliest fossil whales were then known from the Fayum Basin in Egypt, a place now called Wadi Al-Hitan, or “Valley of the Whales.”

Illustration of Remingtonocetus. Image: Anupama Chandrasekaran

Four decades later, cetacean remains erupted from the banks of the Indus River in Pakistan, the rocky outcrops of the Himalayas and the barren Kuch Desert in India. The area is marked as a cradle and cemetery for the early whales of the Earth.

“The earliest really looked more like wolves than whales,” Thewissen said, sculpting an image of ancestral whales. “Shortly afterwards, there were those that looked like crocodiles. Then there were whales that looked more like seals or sea lions and otters. “

Sunil Bajpai with a skull of Remingtonocetus Photo: Anupama Chandrasekaran

Under the sea

In the next stage of evolution, water whales lower their limbs – whether hooves or braided legs – for fins and oars. More spindle-shaped predators, their bodies make it easier to swim better, now follow their prey into deeper seas, which explains why these fossil finds are not limited to India.

“Protocetids are part of the history of the early whales, but they are quite cosmopolitan,” Bajpay said.

Fossils of marine flat-tailed protocetids have been found on many continents – Africa, Europe, North America and South America. They probably wore a fluke. The tail of cetaceans – flat instead of vertical[/footnotes] and were about 10 feet long. Their nostrils had migrated from the tip of their snout halfway up.

Illustration of the protocetide. Image: Anupama Chandrasekaran

“Only when they become pursuing predators can they cross larger bodies of water,” Tevisen said. “So by the time you get to the basilosaurus, they’re basically all over the world.”

Basilosaurus is Latin for “royal lizard”. The discoverer of these 19th-century fossils initially mistakenly identified them as a giant sea snake. The wrong name remained.

This primitive whale had a narrow body, almost as tall as a school bus. He wore front paddles like modern gaskets with small hind limbs. The nostrils or hole were already at the top of the head.

Like modern whales, the basilosaurus had facial bones that supported echolocation, which meant that they could use a sonic echo in water to orient themselves or find prey. There were thick tissues in his ears to withstand the pressure, which allowed him to dive deeper and longer.

These are signs that we recognize in some of the largest animals found today – whales and whales.

The blue whale (Balaenoptera musculus) belongs to the order of whales bales. Photo: NOAA

More than 50 million years ago, a cat-sized terrestrial animal originated around a river bank adjacent to the Thetis Sea. It evolved into a zigzag across the seas and reached alien shores and eventually became an aquatic mammal and the largest creature on Earth.

“The beauty of the story is that you had a terrestrial animal that was able to fully adapt to life in the water,” Sahni said. “There was no big predator in the ocean at that time. The sea monsters were done with the dinosaurs. There were large sharks, but no large mammal to be the best predator. So it was an opportunity for a medium-sized animal to try to use this ecological niche. “

Anupama Chandrasekaran is an independent podcast and publishes audio documentaries focusing on deep history through desistonesandbones.org.

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