By: April Carson
More than 35 million years ago, the first mammals to return to the ocean had keen eyes for deep water. According to new research, cetacean visual systems – which include whales, dolphins, and porpoises – all evolved from a common ancestor with powerful underwater vision.
Hippos and whales both evolved from four-legged land animals about 50 million years ago. While both are aquatic, only one of these branches may dive deep into the water.
"What we found is that, in fact, all of the cetaceans have eyes that are optimised for underwater vision," said study author Nicholas Pyenson, a curator of fossil marine mammals at the Smithsonian Institution's National Museum of Natural History.
When and why that ability developed is still a mystery, although the latest studies imply that it happened shortly after arriving on land.
The researchers studied a protein found in the mammalian eye known as rhodopsin, which is particularly sensitive to dim, blue light like that prevalent in the deep ocean. Researchers were able to determine the ancestral gene sequence that enabled deep underwater dives by analyzing the genes behind this protein for living whales and related species.
"This is the first time we have been able to reconstruct the ancestral gene for rhodopsin in a vertebrate," said Mengel-From, who co-authored the study with Ishiyama. "It provides us with new insight into how cetaceans adapted to their aquatic environment."
This signature pattern was able to "reanimate" a long-forgotten pigment protein when applied in lab-grown cells.
This protein is more susceptible to low light conditions in comparison to land animals. It also responds quickly to changes in light intensity.
Scientists believe the first aquatic cetacean may have foraged for food at depths of 200 meters or more (about 650 feet) where light begins to fade in the ocean, suggesting that such a sensitive protein might have existed in the first aquatic cetacean.
"Together, these ancestral changes in rhodopsin function suggest that some of the first totally aquatic whales may have dived into the mesopelagic zone," according to the study's authors. "Moreover, our reconstructions indicate that this behavior appeared before the division of toothed and baleen whales."
Instead, it appears that all cetaceans had a common ancestor who could see in the deep, even those that now reside in shallow areas.
"The results of this study suggest that early cetaceans were well-adapted to life in the mesopelagic zone and provides new insights into the ecology and evolutionary history of these fascinating animals," said study co-author Michael McGowen, a research fellow at George Mason University.
Finally, says evolutionary biologist Belinda Chang, "later species developed all of the distinct foraging specializations that we observe in modern whales and dolphins today."
Some researchers have concluded that the first aquatic cetacean had a dolphin-like body with vestigial hind limbs for swimming and tail flukes, according to previous studies of fossilized whale remains.
The current study, on the other hand, is one of the first to look at how these creatures' eyes may have functioned in their hunting for underwater prey. Even more remarkable, no actual fossil was used.
The fossil record is the gold standard for understanding evolutionary biology. Extracting DNA from fossils, on the other hand, is uncommon owing to their poor condition. According to evolutionary biologist Sarah Dungan from the University of Toronto, "The fossil record is the gold standard for understanding evolutionary biology. However, despite what Jurassic Park would have you believe, extracting DNA from fossil specimens is rare because the condition is generally bad."
"You turn to mathematics modeling and a large sample of genes from living creatures if you're interested in how genes and DNA change over time."
But DNA can degrade over time, making it difficult to glean information from ancient samples. Dungan and her colleagues used a novel technique to analyze the eyes of an extinct whale called Maiacetus inuus.
The study was published in the journal BMC Evolutionary Biology.
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About the Blogger:
April Carson is the daughter of Billy Carson. She received her bachelor's degree in Social Sciences from Jacksonville University, where she was also on the Women's Basketball team. She now has a successful clothing company that specializes in organic baby clothes and other items. Take a look at their most popular fall fashions on bossbabymav.com
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