Until now, ancestors of modern sharks from 374 million years ago were the oldest known creatures to have both rods to see in dim light and cones, for bright light.
Recently, the genome of the elephant shark, Callorhinchus milii, a chimaerid holocephalan, has been sequenced and therefore becomes the first cartilaginous fish to be analyzed in this way. The chimaeras have been largely neglected and very little is known about the visual systems of these fishes.
By searching the elephant shark genome, Hunt's team have identified gene fragments encoding a rod visual pigment and three cone visual pigments. It also has two copies of the long-wavelength cone pigment gene, a duplication which may have given them trichromatic vision like primates.