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In humans, the pupil is circular, but its shape varies between species; some cats, reptiles, and foxes have vertical slit pupils, goats and sheep have horizontally oriented pupils, and some catfish have annular types. [3] In optical terms, the anatomical pupil is the eye's aperture and the iris is the aperture stop.
The black skimmer has an additional adaptation and is the only species of bird known to have slit-shaped pupils. [4] the forehead, ends of the secondaries, tail feathers and under parts are white, the rest of the plumage is black and the basal half of the bill is crimson. [5]
Many scientists have found the evolution of the eye attractive to study because the eye distinctively exemplifies an analogous organ found in many animal forms. Simple light detection is found in bacteria, single-celled organisms, plants and animals. Complex, image-forming eyes have evolved independently several times. [1]
The tapetum lucidum, in animals that have it, can produce eyeshine, for example as seen in cat eyes at night. Red-eye effect, a reflection of red blood vessels, appears in the eyes of humans and other animals that have no tapetum lucidum, hence no eyeshine, and rarely in animals that have a tapetum lucidum. The red-eye effect is a photographic ...
The forelimbs have five toes, while the hind legs have only four. [16] The skull is light and slender, elongated. Sagittal crest not developed at all or weakly defined. [17] Vulpes species have vertically slit pupils, which generally appear elliptical in strong light like those of cats, which provide them with significant advantages. [18]
They use the disadvantage of most prey animals' poor nocturnal vision to their advantage. The light receptors in crocodilians' eyes include cones and numerous rods, so it is assumed all crocodilians can see colours. [47] Crocodiles have vertical-slit shaped pupils, similar to those of domestic cats.
Several species of Felidae (cats) and snakes have vertically elongated (slit) pupils, advantageous for nocturnal ambush predators as it helps them to estimate the distance to prey in dim light; diurnal and pursuit predators in contrast have round pupils. [30]
In other animals that possess UV vision such as birds, ultraviolet sensitivity can be advantageous for courtship and reproductive success. This is because some birds have feathers with certain favourable colourations that can not be distinguished by human vision outside of the UV spectrum. [8]