What Did Ancient Whales See?

This article was originally published by Hakai magazine.

It is almost impossible to know how extinct animals behaved; there is no Jurassic Park where we can watch them hunt or mate or avoid predators. But a developing technique is giving researchers a physiological cipher to decipher the behavior of extinct species by reconstructing and analyzing the proteins of extinct animals. This molecular necromancy can help them understand traits that are not in the fossil record.

In the latest example of this technique in action, scientists led by Sarah Dungan, who completed the work as a graduate student at the University of Toronto (U of T) in Ontario, have tracked the visual pigments from some of the earliest ancestors of Ceticians had to revive it. . Dungan and her colleagues are given new insight into how proto-meteorites would have survived just after a pivotal evolutionary moment: the time about 55 to 35 million years ago when the animals that became whales abandoned and in their dolphins their terrestrial lifestyles. return to the sea.

Dungan’s interest in the evolution of whales began when she was 8 years old. As a child, she loved spending time in the water and learning about marine biology. Her father told her as she passed by that the ancestors of modern whales once lived on land. The notion that an animal could change from living entirely out of water to not being able to live outside of it stuck with her. Learning about the evolutionary transition that modern whales took—from ocean to land and back again—”completely blew me away,” she says. “The paper is the end of a story that started when I was really young.”

In 2003, researchers at U of T pioneered a technique to recreate ancient animal visual proteins. They applied the technique across the animal kingdom, learning more about how extinct species saw the world. But studying extinct cetaceans is extremely interesting because the transition from land to ocean changed the animals’ visual realms.

In the study, the researchers compared rhodopsin, the visual pigment responsible for light vision, in the animals that marked the land-to-ocean transition. They focused on the common ancestor of Cetacea and Whippomorpha (the group of animals that includes whales and hippos), which represents a time period of about 55 to 35 million years ago.

Scientists have not yet recovered genetic material from the fossils for these two extinct species. Because of that, they can’t even tell exactly what species they are. But Dungan’s technique can infer ancient protein sequences even without this information. The approach follows the evolutionary breadcrumbs left in the proteins of modern animals to infer what the ancient forms would have looked like, even without the DNA of the species themselves. By comparing the putative proteins of Whippomorpha and Cetacea during the land-to-ocean transition, scientists can pinpoint the subtle differences in their vision. These visual differences could reflect differences in the behavior of the animals.

“There’s only so much you can learn from fossil evidence,” says Dungan. “But the eye is a window between the organism and its environment.”

Using the rhodopsin structures known from modern whales, Dungan and her team constructed an evolutionary tree that they used alongside similarity models to help predict the versions of the ancient animals. They made these visual pigments in the laboratory in mammalian cells and tested the light they are most sensitive to. The scientists found that compared to ancient Whippomorpha, extinct Cetacea were probably more sensitive to blue wavelengths of light. Blue light penetrates deeper into the water than red, so modern deep-sea denizens, including fish and cetaceans, have blue-sensitive vision. The result indicates that the Cetacea had disappeared from their comfort in the deep sea.

​​​​The scientists also found that the ancient Cetacean version of rhodopsin appears to have quickly adapted to the dark. Today, the eyes of many modern whales adapt to dim light, helping them move between the bright surface where they breathe and the dark depths where they eat. This result is “what really sealed the deal,” says Dungan.

Based on their findings, the scientists think that early Cetacea were probably approaching the bright zone of the ocean, between 200 and 1,000 meters. Eye sight was critical during diving. Ancient Cetacea could not echo sound like dolphins, so they relied more on vision.

The finding is surprising, says Lorian Schweikert, a neuroecologist at the University of North Carolina at Wilmington who was not involved in the study. She thought that the first Cetacea would have stayed near the surface. “She started from the bottom, we’re here now,” she jokes, referring to Drake’s hit song.

Schweikert says studying eye physiology is a reliable way to understand an animal’s ecology because visual proteins don’t change much over time. The rare changes are almost always correlated with environmental changes.

The most important conclusion of Dungan and her colleagues’ work, says Schweikert, is that it further clarifies the sequence in which the extreme diving behaviors of cetaceans evolved. The rhodopsin research builds on earlier work that paints a similar picture. In a previous study, researchers reconstructed ancient myoglobin and showed that cetaceans’ early transitional ancestors supercharged their muscles’ oxygen supply while holding their breath—further evidence that they were capable divers. Another study, this time on ancient penguins, showed that when the birds had their own transition to sea life, mechanisms emerged in their hemoglobin to manage oxygen more efficiently.

Dungan and her colleagues are now launching their molecular Ouija board to resurrect rhodopsin from the earliest mammals, bats and lizards. This will help them understand how nights, loads and flight developed.

The approach is “just really fun,” says Schweikert. “You want to look at the past to understand how these animals have changed. I love that we can watch a video to solve some of these problems.”

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