According to Dr. Gengo Tanaka, the fossil below was found about 50 years ago.
“I have a friend [who owns a] fossil shop,” he wrote in an email. “I bought this specimen from him.”
Dr. Tanaka explained that his friend attributed the fossil find to his father, who discovered it in a quarry five decades ago.
It’s a small fish known as Acanthodes bridge, and it is thought to have lived in shallow waters 300 million years ago in what is now Kansas.
[image of fossilized Acanthodes bridge, courtesy of the Natural History Museum, London]
It might be a little fish, but it is providing enormous and exciting information about the evolution of color vision.
In their recent paper, Dr. Gengo Tanaka of Kumamoto University, Professor Andrew Parker of the Natural History Museum, London and 13 other scientists describe evidence of color vision 100 million years earlier than previously known. They are the first to record fossil rods and cones—the cells responsible for enabling sight.
“The soft tissue of eyes are usually the first to decompose when an animal dies, and before they are fossilized. In our fish, however,” wrote Professor Parker, “the soft tissue was preserved before burial (by sediment) and turning to rock. The original organic material has been altered (but in some cases not too much), although remains relatively soft.”
Using SEM (scanning electron microscope) and TEM (transmission electron microscopy), the scientists studied the fossil eyes in more depth. They compared rods and cones of 509 retinal cells, obtained from the fossil itself and from existing freshwater fish. Cones within the eye are the key to color vision, although they assert that the discovery of opsins in the fossil record would provide “conclusive evidence” for such vision.
“Cone cells are those responsible for colour vision in extant animals,” Professor Parker further explained. “They contain the opsins that react to different wavelengths of light.”
When asked if he expected to find color vision in this fossil, Dr. Tanaka wrote, “I have discovered fossilized rod and cones in several Cenozoic fishes. So, I expected that we could discover fossilized rod and cone cells in other specimens.”
Similarly, Professor Parker wrote, “I would expect to find colour vision in the geological record at some point, but I did not expect when.”
[details of Acanthodes bridge, courtesy of the Natural History Museum, London; a: Complete dorsoventrally compressed specimen, b: details of the head region, c: details of right eye]
“We were a team interested in the emergence and history of vision, when Gengo [Tanaka] found the fossil fish,” he continued, describing how it came to pass that these 15 scientists collaborated on the paper.
But why would color vision be significant for a species such as Acanthodes bridge?
“That such ancient fish had colour vision tells us that the type of ecologies and behaviours that exist today, where light plays a major role, were also in place 300 million years ago. For the fish, they could distinguish predators and prey with greater accuracy and in some cases crack the camouflage of these animals.”
“This is the first time that colour vision has been identified in any extinct animal, regardless of geological age,” he wrote. “It suggests that our modern behavioural system, or way of living, where colour plays a major role, has been in place over at least 300 million years.”
“This can explain,” he continued, “why things have changed little over that period: predators and prey have changed form in some ways, but the balance of the different types of animals and plants living together has remained similar. Triceratops has been replaced with rhinos, ichthyosaurs replaced by dolphins, but their roles in the ecosystem are similar. That they saw in the same way helps us to understand this.”
An enormous thank you to Chloe Kemberry, Dr. Gengo Tanaka and Dr. Andrew Parker! What a great pleasure connecting with you about such an exciting discovery!
- Tanaka, G. et al, Mineralized rods and cones suggest colour vision in a 300 Myr-old fossil fish. Nat. Commun. 5:5920 doe: 10.1038/ncomms6920 (2014).