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However, front-facing eyes are a highly evolved trait in vertebrates, and there are only three extant groups of vertebrates with truly forward-facing eyes: primates, carnivorous mammals, and birds of prey.
Anatomy of the avian eye. The main structures of the bird eye are similar to those of other vertebrates.The outer layer of the eye consists of the transparent cornea at the front, and two layers of sclera — a tough white collagen fibre layer which surrounds the rest of the eye and supports and protects the eye as a whole.
The frontal eye fields (FEF) are a region located in the frontal cortex, more specifically in Brodmann area 8 or BA8, [1] of the primate brain. In humans, it can be more accurately said to lie in a region around the intersection of the middle frontal gyrus with the precentral gyrus , consisting of a frontal and parietal portion. [ 2 ]
The rate of eye evolution is difficult to estimate because the fossil record, particularly of the lower Cambrian, is poor. How fast a circular patch of photoreceptor cells can evolve into a fully functional vertebrate eye has been estimated based on rates of mutation, relative advantage to the organism, and natural selection.
Primates have forward-facing eyes on the front of the skull; binocular vision allows accurate distance perception, useful for the brachiating ancestors of all great apes. [69] A bony ridge above the eye sockets reinforces weaker bones in the face, which are put under strain during chewing.
The youngest and best known species, M. balearicus, is noted for a number of unusual morphological adaptions, including forward facing eyes suggestive of binocular vision, as well as a long lifespan, which developed in an unusual ecosystem where only a few other mammal species were present, terrestrial predators were absent, and Myotragus ...
The eyes of vertebrates usually contain ciliary cells with c-opsins, and (bilaterian) invertebrates have rhabdomeric cells in the eye with r-opsins. However, some ganglion cells of vertebrates express r-opsins, suggesting that their ancestors used this pigment in vision, and that remnants survive in the eyes. [ 53 ]
Through convergent evolution as night hunters, they resemble owls, with large front-facing eyes. [citation needed] Up to three white eggs are laid in the fork of a branch, and are incubated by the female at night and the male in the day. [citation needed]