First Land Creatures Had Wider Range of Color Vision than Humans

The first prehistoric creatures to leave the oceans for a life on land could see in a wide range of colors, scientists have found. In fact the creatures saw their new world in more vivid colors than humans would have. A new study suggests that these ancient ancestors could see wavelengths of light that human eyes can’t register.

How did they come to this conclusion? Scientists found recently that the retinas of Australian lungfish (Neoceratodus forsteri) contain visual pigment genes that are more similar to those of tetrapods—four-legged land animals with backbones—than those of other fish. They also found that the fish appear to see in ultraviolet.

Australian lungfish are thought to be the closest surviving relatives of the first land animals. Sometimes referred to as "living fossils" , the fish have remained virtually unchanged since first appearing in the fossil record 135 million years ago. They still live in Australian rivers as they did millions of years ago.

Helena Bailes of the University of Queensland in Australia and her colleagues analyzed the Australian lungfish DNA that codes for opsin, a visual pigment found in cone cells required for seeing in color.

"The visual system of N. forsteri may represent an evolutionary design most closely reflecting that present just prior to the emergence of land vertebrates in the Devonian Period," Bailes said.

The team also spotted four types of cone cells in the lungfish eyes, suggesting the fish can see in colors we humans can't. "From looking at the DNA sequence, they certainly have the potential to see in the [ultraviolet] range and further into the red range than humans," Bailes said.

Cones are light receptors in the eye that are sensitive to color, while "rods" are better at seeing in dim light. Humans have three types of cone cells in their eyes: red, green, and blue. "That's why TVs are made of red, green and blue pixels," Bailes explained.

Color vision is good for increasing contrast between objects and could have been useful for the creatures to find prey or elude predators, Bailes theorized.

A past study by her team found that the eyes of lampreys, a jawless living fossil whose origins stretch further back than even the lungfish, also had cone visual pigments, suggesting these jawless, fully aquatic fish also could see in color.

"It's thought that color vision evolved in these lamprey fish, through the lungfish to land vertebrates," Bailes said.

Most mammals do not see color the way that humans and other primates do, but in a genetic engineering experiment earlier this year, scientists were able to transfer genes to mice that allowed them to see in color. http://www.dailygalaxy.com/my_weblog/2007/03/colorblindness_.html

Posted by Rebecca Sato

*If you’re curious about what animals see in what colors