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While color vision is dependent on many factors, discussion of the evolution of color vision is typically simplified to two factors: the breadth of the visible spectrum (which wavelengths of light can be detected), and; the dimensionality of the color gamut (e.g. dichromacy vs. tetrachromacy).
This list of ichthyosauromorph type specimens is a list of fossils serving as the official standard-bearers for inclusion in the species and genera of the reptile clade Ichthyosauromorpha (Hupehsuchia included).
Researchers studying the opsin genes responsible for color-vision pigments have long known that four photopigment opsins exist in birds, reptiles and teleost fish. [3] This indicates that the common ancestor of amphibians and amniotes (≈350 million years ago) had tetrachromatic vision — the ability to see four dimensions of color.
Color vision is categorized foremost according to the dimensionality of the color gamut, which is defined by the number of primaries required to represent the color vision. This is generally equal to the number of photopsins expressed: a correlation that holds for vertebrates but not invertebrates .
The ichthyosaur’s jawbone, or surangular, was a long, curved bone at the top of the lower jaw just behind the teeth, and it measured more than 6.5 feet (2 meters) long.
The retina uses "cones," a specific type of photoreceptor, to differentiate color, according to the American Academy of Ophthalmology. Human eyes have three types of cones: red-sensing, green ...
Dichromacy in humans is a form of color blindness (color vision deficiency). Normal human color vision is trichromatic, so dichromacy is achieved by losing functionality of one of the three cone cells. The classification of human dichromacy depends on which cone is missing:
For example, staring at a saturated primary-color field and then looking at a white object results in an opposing shift in hue, causing an afterimage of the complementary color. Exploration of the color space outside the range of "real colors" by this means is major corroborating evidence for the opponent-process theory of color vision.