The human eye consists of cells in the shape of rods and cones, and now, a team of researchers have discovered the same shaped cells in the fossil of an eye of a 300 million-year-old fish. It is presumed that fishes could possibly possess color vision.
A 10 centimeters long fossil of a fish was found by the scientists at Hamilton Quarry, located near Hamilton in Kansas. Hamilton Quarry was a shallow lagoon in ancient times and fossils discovered from the area are usually well preserved as they got buried very swiftly in the sediments of the lagoon, the researchers believe. The fossil that is uncovered is possibly of an extinct fish species named Acanthodes Bridgei as suggested by Gengo Tanaka at the Kumamoto University, Japan, who is also the lead author of the research. The cells in the fish eyes were well preserved probably due to a bacterial activity that deposited a thin film of phosphate over the eyes before it was buried. Some parts of the visual system are not commonly preserved in the fossil record as the soft tissue found in the brain and eyes decay very rapidly after death- infact, in just 64 days after the death, the tissues in the eyes begin to decay.
“Rods and cones are not usually preserved, because these soft tissues are more fragile,” says Tanaka. However, the fossil of the latest fish was so well-preserved that rod and cone cells are still visible in the eyeballs under an electron microscope.
Basically, rod and cone shaped cells line the retina of the human eye- rod cells are long and thin, while cone cells are obviously triangular. While rod cells are much more sensitive to light as opposed to the cone cells, it is the presence of cone cells that allows us to have colored vision.
Both these cells depend on certain pigments when it comes to absorbing light, and the researcheres have discovered the presence of one of these in the fossil of the fish.
The eyes of the modern day Rhinogobius fish species, which is very similar in size to the Acanthodes bridgei too, were compared to the eye of the fish fossil in the study. The rod and cone cells ratio in both the fish species were similar, which indicates that the Acanthodes bridgei was active in the day and depended on its vision to survive was found by the researchers.
Modern eyes developed millions of years ago and the latest discovery provides a definitive proof is long believed by the scientists. Journal Nature Communication published the said study.