The first mammals to return to the sea had eyes for the deepest part of the ocean.
According to new research, the visual systems of modern whales, dolphins, and porpoises all derive from a common ancestors.
About 50 million years ago, whales and Hippos are thought to have evolved from land mammals. Only one branch can dive into the ocean.
It's a mystery when and why that skill evolved, but the new findings suggest it happened soon after taking to the sea.
The rhodopsin is found in the eye of the mammal and is sensitive to dim blue light.
Researchers were able to predict the ancestral gene sequence that first allowed for deep underwater dives by analyzing the genes behind this proteins.
This signature sequence can be expressed in lab-grown cells.
It appears to be more sensitive to low light levels than to high light levels.
Researchers think the first aquatic cetacean may have foraged for food at depths of 200 meters or more, where light begins to fade in the ocean.
The authors of the study concluded that some of the first fully aquatic cetaceans could dive into the mesopelagic zone.
Our reconstructions show that this behavior began before the whales separated.
It seems that all cetaceans share an ancestors that could see in the deep.
"Later species evolved all the diverse foraged specializations we see in modern whales and dolphins today."
The first aquatic cetacean may have had a dolphin-like body with a combination of tail flukes and vestigial hind limbs, according to previous studies.
One of the first studies to investigate how this creature's eyes might have worked is the current study.
The authors didn't have a fossil.
Understanding evolutionary biology can be traced back to the fossil record. Sarah Dungan is an evolutionary Biologist from the University of Toronto.
To understand how genes and DNA are evolving, you need a strong sample of genes from living organisms to complement what we know from the fossil record.
The study was published in a peer reviewed journal.
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