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Animals that are monochromats
Placentalia (placental mammals)
 * Xenarthra (sloths, armadillos, anteaters)
 * Cingulata (armadillos)
 * Dasypus (long-nosed armadillo)
 * Nine-banded armadillo (Dasypus nomcinctus) rod monochromat
 * Pilosa (anteaters, sloths)
 * two-toed sloths
 * Hoffmann's two-toed sloth (Choloepus hoffmanni) rod monochromat
 * Boreoeutheria
 * Euarchontoglires
 * Euarchonta
 * Primates
 * Haplorhini (tarsiers, monkeys, apes)
 * Simians (Simiaformes) (monkeys, apes)
 * Owl monkey (Aotus) L-cone monochromat
 * New World Monkeys (Platyrrhini)
 * Strepsirrhini (lemurs, lorises, etc.)
 * Lorisoidea (lorises, bushbabies)
 * Bushbabies
 * Glires (rodents and lagomorphs)
 * Rodents
 * African mole rats
 * Naked mole-rat (Heterocephalus glaber) rod monochromat
 * Laurasiatheria
 * Eulipotyphla
 * moles and shrew moles
 * Star-nosed mole (Condylura cristata) rod monochromat
 * Scrotifera
 * Chiroptera (bats)
 * Fereuungulata
 * Ferae
 * Pangolins (Philodota)
 * Carnivora (dog-like and cat-like)
 * Caniformia (dog-like)
 * Procyonidae
 * Procyon (genus) (raccoons)
 * raccoon, crab-eating raccoon and kinkajou
 * Pinnipeds (seal-family)
 * Feliformia (cat-like)
 * Ungulates (Euungulata)
 * Odd-toed ungulates
 * Even-toed ungulates
 * Cetacea (dolphins and whales)
 * Afrotheria
 * Afrosoricida (Golden moles and tenrecs]]
 * Golden moles
 * Cape golden mole (Chrysochloris asiatica) rod monochromat

Existing Article
It used to be confidently claimed that most mammals other than primates were monochromats. In the last half-century, however, evidence of at least dichromatic color vision in a number of mammalian orders has accumulated. While typical mammals are dichromats, with S and L cones, two of the orders of sea mammals, the pinnipeds (which includes the seal, sea lion, and walrus) and cetaceans (which includes dolphins and whales) clearly are cone monochromats, since the short-wavelength sensitive cone system is genetically disabled in these animals. The same is true of the owl monkeys, genus Aotus.

Researchers Leo Peichl, Guenther Behrmann, and Ronald H. H. Kroeger report that of the many animal species studied, there are three carnivores that are cone monochromats: raccoon, crab-eating raccoon and kinkajou and a few rodents are cone monochromats because they are lacking the S-cone. These researchers also report that the animal's living environment also plays a significant role in the animals' eyesight. They use the example of water depth and the smaller amount of sunlight that is visible as one continues to go down. They explain it as follows, "Depending on the type of water, the wavelengths penetrating deepest may be short (clear, blue ocean water) or long (turbid, brownish coastal or estuarine water.)" Therefore, the variety of visible availability in some animals resulted in them losing their S-cone opsins.

Vertebrate visual opsins
Vertebrates are normally tetrachromats, with four-color vision (and four opsins), having inherited this condition from the first vertebrate. Jawed vertebrates (all vertebrates except lampreys and hagfish) also have rhodopsin for vision in low-light situations. All five opsins combined are generally known as the vertebrate opsins. One of these five opsins (Rh2, blue-green) was lost in the first mammal (or one of its ancestors) making the earliest mammals trichromats. The ancestor of monotremes (egg-laying mammals platypus and echidna) lost another opsin (SWS1, ultraviolet), making them dichromats, while the ancestor of live-bearing mammals (Theria = placental mammals + marsupials) lost the blue opsin SWS2, also making them dichromats. As a result, mammals are normally dichromats, with rod opsin (Rh1) and two cone opsins, LWS (green, yellow or red) and either SWS1 (ultraviolet, violet) in placental mammals, or SWS2 (blue) in egg-laying mammals.

In Haplorhini (tarsiers, monkeys, and apes, including humans) a gene duplication resulted in a high incidence of trichromacy, with LWS duplicated to M- and L-cone opsins.

Placental mammals are divided into three major clades, Xenarthra, Afrotheria, and Boreoeutheria. All xenarthrans are rod monochromats. They comprise sloths, anteaters and armadillos, and constitute the smallest of the three clades of placental mammals.

13 species of cetaceans (dolphins and whales) are rod monochromats. All other cetacians are S-cone monochromats.