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On Earth, while birds and reptiles can be quite brightly colored, it's rare for mammals to have any bright colors, and the rare times they do, it's either just slightly different (like with orangutans) or from outside sources (like symbiotic algae). There are several interlocking reasons for this - most mammals don't have good enough color vision for it to have real evolutionary value, there isn't enough bright color in most environments mammals live in, and melanin doesn't have brightly colored variations.

I'd like an Earth-like planet, with overall near-identical flora and fauna, but where there's one mostly isolated ecosystem that has brightly colored mammals. How could I make an evolutionary pathway that leads to that happening?

(I would preferably like for the environment with the brightly-colored mammals to be a temperate rainforest for unrelated worldbuilding reasons, but I'm fine with a different environment.)

Thanks in advance.

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    $\begingroup$ Orange isn't brightly coloured? $\endgroup$ – nzaman Nov 25 '19 at 13:11
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    $\begingroup$ @nzaman I think they just meant that orange is just a lighter shade of brown. So it's not a radically different color, like a bright blue primate would be. $\endgroup$ – overlord Nov 25 '19 at 13:38
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    $\begingroup$ Polar bears are white. You cannot get more bright than white, and they are far from the only white-colored mammals; I very much like the look of the snow leopard. Other mammals with pretty colors include red foxes, many horses, orange house cats, red pandas, tigers, leopards, jaguars, zebras and so on. There are many mammals with vividly contrasting stripes, for example. $\endgroup$ – AlexP Nov 25 '19 at 16:14
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    $\begingroup$ ...but the white animals you (@AlexP) list are typically white because that's what works as camouflage. And even so, all the examples you listed are some combination of black, white, red and yellow. There is precious little green, blue or purple. (Although, there are mandrills...) There aren't many mammals that don't tend to blend in, and most of them are primates, or at least arboreal. (Domestic animals don't count, since their selection pressures are what humans think is pretty.) $\endgroup$ – Matthew Nov 25 '19 at 17:49
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    $\begingroup$ I am a mammal and I am really bright. Almost snowman like. How are humans not the answer to this question? $\endgroup$ – Trevor Nov 25 '19 at 18:01

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Mating selectivity

Color vision of mammals is good enough to appreciate things like a peacock's tail. And that's the possible mechanism. Female selectivity of male display. Mister Hopeful has colorful hair, maybe colorful skin markings. And he struts and displays them to attract the attention of Miss Prospective. The guy with the most colorful markings gets the girls. The girls with the most discernment get the most colorful guys, who in turn father the most colorful children.

There is even some direct survival information. A bird (or gentleman) who can wander through the jungle with that huge colorful display, and not get eaten, that's a guy that has something special going on. He's either very alert and agile, or he's fast, or he's lucky. Whatever, he's got potential daddy genes.

It becomes a positive-feedback. This is how such things as peacock and bird-of-paradise tails arose. The females select for colorful display. The males display selects for female discernment and sharpness of eye. And the overall process selects for whatever-it-is that lets the boys carry that display around in a predator filled environment.

Edit: Paragraph added for emphasis. At the same time it pushes for colorful displays by males, it pushes for more critical viewing by females. And so pushes the vision of the species to become more sensitive to color and detail, and the brain power to be able to compare and contrast fine detail and composition.

Other options might be that the color only shows up during the attract-a-mate season. And then it fades. Maybe he grows a really brightly colored beard and chest hair for six or eight weeks in the spring, then it all falls out. Or maybe he starts to grow blue-and-purple patches on easily-displayed portions of his anatomy. Then later, after he gets his girl, they turn grey or brown. It would only take minor adjustments to pigments to make the colors much more camouflage-like, much more like the shadows under the trees.

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    $\begingroup$ Colour vision of primates is good enough to see the interesting colouration of peacock tails, but mammals as a whole do not possess that faculty. Though I'm not certain, mammals as a whole don't seem to exhibit handicapping sexual ornamentation in the way that birds do. It could be done without the need for bright colours (though whites and oranges would suffice, surely) and yet we don't see much of it. Colouration and the handicapping you're thinking of therefore seem like they're orthogonal. $\endgroup$ – Starfish Prime Nov 25 '19 at 14:57
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    $\begingroup$ @StarfishPrime: "handicapping sexual ornamentation": deer and their antlers... $\endgroup$ – AlexP Nov 25 '19 at 16:16
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    $\begingroup$ @AlexP: Antlers aren't all that much of a handicap, especially when male sexual selection is by combat rather than display. $\endgroup$ – jamesqf Nov 25 '19 at 17:53
  • $\begingroup$ @jamesqf Display is still the primary function. There is an optimal size (and structure) of antlers for combat, but that's not what is actually selected for. There probably was a time where combat efficiency was important, but not in modern deer. $\endgroup$ – Luaan Nov 26 '19 at 7:46
  • $\begingroup$ @Luaan In modern deer, arguably evolution is screwed anyway. Living circumstances have changed quite something in the past 100 years compared to the 1900 before it. $\endgroup$ – Mast Nov 26 '19 at 12:18
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How could I make an evolutionary pathway that leads to that happening?

Sounds like you already answered your own question, right here:

most mammals don't have good enough color vision for it to have real evolutionary value.

Mammals probably lost two of their four cone cell types waaaay back in the time of the dinosaurs, for as-yet unknown reasons, but seemed to cope OK. Primates subsequently evolved trichromacy and regained their colour vision. Some marsupials also appear to have trichromacy, presumably independently.

Keeping better colour vision from earlier in mammalian history, or re-evolving it (possibly multiple times) subsequently but at an earlier stage than primates, might allow for more complex colour signalling and camouflage patterning to arise. Most mammalian predators lack colour vision as good as ours, though how much of an edge it would given them in hunting is unclear to me. It certainly doesn't harm avian, reptilian or amphibian predators, that's for sure.

Other things might include different kinds of diet. The bright red plumage of some cardinal birds and the pink of flamingoes is not caused by pigments that the birds express, but rather from things that they eat and some of the excess colours are laid down in feathers. Having the colours laid down in hair or fur, especially as a form of aposematism (warning colouration often used by poisonous or venomous animals) is entire justifiable, and doesn't necessarily need any drastic evolutionary changes.

Additionally, some colours may be incidental... the pigment psittacofulvin gives parrots their bright yellow and red colours, but it turns out that feathers containing that pigment are more resistance to damage from bacteria like Bacillus licheniformis. Many humans change colour in the sun, as expressing greater levels of melanin in skin cells helps protect against damage from UV light, but perhaps other influences (such as problematic bacteria or fungi) in various species could be resisted by chemicals which just happen to be interesting colours.

To finish though, I'll just leave a picture of a mandrill for you. Orange ain't the only colour! I'll spare you the pictures of baboons in heat though.

Mandrill

(image by Amit Patel, from flickr)

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  • $\begingroup$ Actually, the loss of color vision fidelity isn't too surprising when you remember that back in the dinosaur days, mammals were mostly nocturnal and/or underground dwellers. Color vision in the dark sucks, so there would be little selection pressure to maintain good color vision. When the mammals became dominant, the ones for whom good color vision became imporant "quickly" regained it (e.g. fruit eaters benefit from telling a red fruit apart from a green fruit). $\endgroup$ – Luaan Nov 26 '19 at 7:51
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I guess the thing with non-colorful mammals is they typically don't have ways to escape easily like birds or insects from predators, so they have to rely more on sneaking and hiding, and this would be a natural reason to not be very distinguished with colored fur. Therefore ecosystems where mammals don't have to fear being eaten nor need to sneak to their prey could produce some more colorful species.

P.S. Maybe look at skunk-like or zebra-like, they are quite distinct with their colors and patterns.

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  • $\begingroup$ Skunks aren't particularly stealthy in either their appearance or their behaviour, because they can use chemical weapons in self defence. Mammals do use aposematism, it just doesn't look as funky as it does in other groups of animals with more pigments to hand. $\endgroup$ – Starfish Prime Nov 25 '19 at 14:43
  • $\begingroup$ Mammals can have quite pick in pigments, just look at all colors of different breeds of cats. $\endgroup$ – Guy with jewels' names Nov 25 '19 at 15:07
  • $\begingroup$ They're not different pigments though, just patterns and changes in density of the pigment. They have the same melanin-based colouration you do. $\endgroup$ – Starfish Prime Nov 25 '19 at 15:10
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Well we humans are pretty much mammals and even thought it's not through (biological) evolution we started to dye our hair in different colors. Perhaps you are able to find an evolutionary reasoning in that? Like standing out to find a mate?

Also an option would be a plant based one, certain sloths for example have a greenish appearance through moss growing in their fur. Adding a colorful (possibly parasitic) moss that attaches it to the fur of animals as a way of spreading could give them a colorful appearance.

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    $\begingroup$ I like this for its out-of-box thinking. Make cosmetics ubiquitous in the mammal species! $\endgroup$ – SRM Nov 25 '19 at 20:20
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I can see a few factors that would encourage that trait :

  • a lack of predators: without the need to run and hide from predators, animals can afford to have flashier colors that makes them easier to spot
  • Alternatively, perhaps the colors, while appearing flashy to us, blend in quite well with the equally colorful flora present.
  • Continuing the adaptation to flora, animals can change colors throughout the year. You almost certainly know of the chameleon, but mammals like the arctic fox or hare do change colors to snow white fur in winter for example and birds can do the same. Your creatures wouldn't then necessarily be brightly colored all year round, they'd adapt to the environment.
  • mating preferences: think peacock. Perhaps brighter colors are better at attracting potential mates, ensuring the genes spread.
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Birds and Reptiles usually develop colorful displays for mating purposes. The general concept is that the colors denote exceptional health of the individual (usually the male). In some cases, like the Peacock, the display actually suits no functional evolution purpose other than showing off to the female that, in addition to being suited to live in it's environment, it can do so to egregious success. One thing to note is that in this evolution paradigm, it's usually the gender that is typically supposed to court the discerning other gender that is the more colorful member of the species (Compare the always male "Peacock" to the drabber always female "peahen" which is usually shades of brown. The gender neutral term for the species is "Peafowl", FYI). So your aliens would likely see vibrant color displays a sexy and attractive.

Other elements are more enviornmental. Tigers, Cheetahs, Leapards, are considered quite colorful for wholly different reasons, namely, camouflage. Humans actually have very developed eyesight that mixes both trichromatic vision (our eyes are simulated by three colors, but all colors we are capable of seeing are combinations of various levels of those colors. It's like how computers use the RGB values to display color... only humans have a wider range of color discernation than computers are capable of producing.). There are some animals with four color vision (turtles) and some with better range (raptors (birds of prey, not dinosaurs... well... Jurrassic Park Dinosaurs...) can see up to two miles away, but have terrible short range vision.) and other animals have low levels of light of nocturnal vision.

I say this, because much of hominid development was focused on becoming apex predators, and members of the Homo genus are uniquely the only predators that are ranged hunters on planet earth, which requires a rather unorthodox set of evolutionary developments to accomplish. Bipedalism was thought to be a means of attaining better height for vantages, our arms are developed for throwing (Our nearest evolutionary cousins throw at 1/5th our ability)... and of course our vision was developed to better assess the lay of the land and see things we should be, which is why we don't think of the tiger and zebra as all that hidden... because it counts on tricking animals with less developed sight... Even intelligence is thought to be a result of developing towards this hunting niche, take a look at the physics of throwing a thing, and remember the best hominids relied on understanding that skill.

Other colors in the wild are based on consuming biological componants that the body cannot break down or dispose of easily. Flamingos, for example, eat shrimp almost exclusively and the material that makes shrimp pink isn't digested or excreted, so they grow pink overtime. There are conditions where humans can have this happen too. The biological compound known as Beta Carotine is responsible for a lot of fruits and vegitables we eat that have a red color. The protein isn't synthisized in animals, but does play some roles, even in humans. For example, it's used to make menolin, which blocks UV rays from damaging skin cells in humans... and if consumed in excess, humans can have an almost "orange" appearance, both in skin color and hair color, since it's usually digested for use in skin pigmentation, and not excreted in bulkier waste products (It typically will leave the body through dead skin).

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  • $\begingroup$ re trichromatic vision: Its a little-known fact that a very tiny proportion of people have a genetic anomly that gives them tetrachromatic vision; ie four colour receptors. These people often have no idea that they are seeing the world differently to everyone else. $\endgroup$ – Spudley Nov 26 '19 at 9:07
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Start with an discretionary omnivorous apex predator with good color vision and an instinctive appreciation for vibrant colors and contrast. If this predator was sentient, we would call its effect on the environment, "selective breeding", but since it is not sentient, this predator's preferences are comparable to the preferences of pollinating insects for bright colored and aromatic flowers; just a natural force.

Now all you need is deep time. Insects didn't inspire flowers to become beautiful overnight. It took millions of years. Similar, this apex predator would inspire its environment by eating the bland prey animals, leaving the prettier ones around to multiply. Over the ages, bland colors would become an survival disadvantage and like most such disadvantages, it would succumb to the tides of evolution.

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  • $\begingroup$ Brightly coloured things would find themselves more vulnerable to every other kind of predator, though. $\endgroup$ – Starfish Prime Nov 25 '19 at 14:41
  • $\begingroup$ ...Unless the apex predator ate those other predators. So now we need another environmental pressure to avoid the emergence of colorful predators which the apex wouldn't eat. That might take some more thought. $\endgroup$ – Henry Taylor Nov 25 '19 at 14:49
  • $\begingroup$ It might take a lot of effort to stop it destroying an entire ecosystem, especially given the sheer range of habitats and sizes of mammalian predators. I'm not aware of this sort of super-predator having arisen in the past in a large environment, but that's not to say it hasn't, or couldn't. $\endgroup$ – Starfish Prime Nov 25 '19 at 14:59
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Other answers have described the various evolutionary reasons why coloration evolves such as sexual selection and aposematism. However, mammals already have these evolutionary pressures driving the evolution of dramatic appearances and many mammals do have highly conspicuous appearances. Why then do mammals not use bright colors to make their appearances even more remarkable? The answer to this is not that they lack the evolutionary motives or rationales but rather that they lack the ability.

Practically all coloration in mammals comes from various forms of the pigment melanin which is limited to producing blacks, browns, greys, and whites. However much of the beautiful coloration in the animal world isn’t pigment-based at all. Structural color is responsible for nearly all of the bright blues and greens we see in the animal kingdom. Structural color is produced by microscopic structures, in the size range of light wavelengths themselves, which refract and reflect specific colors of light. A male peacock’s beautiful tail is, in fact, brown in pigment, but the feathers are coated in these nanostructures which give it it’s iridescent appearance. Structural coloration is responsible for much of the coloration seen in birds, reptiles, amphibians, insects, and fish.

So the simple answer to why mammals don’t have vibrant colors is because mammals never evolved the ability to produce structural coloration using their hair. The only instance of structural coloration existing in animal hair is the slight iridescence of the Golden Mole which is completely blind.

However at least one mammal does have structural coloration, just not in its hair. The best example of brilliant coloration in mammals, the mandrill, actually uses structural coloration in the collagen fibers of its skin to produce the red and blue colors of its face. This example tells us that colorful ornamentation is useful to mammals but that mammals can’t produce it on their hair. Perhaps this is because mammalian hair is incompatible with structural coloration in some way.

So, to produce mammals with bright coloration you could make them hairless, like humans, and produce colors on their skin like the mandrill, or have them utilize a distinctive form of hair that is capable of being structurally colored.

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  • $\begingroup$ But the lack of structural colors in hair is a circular argument: it would be no more difficult for hair to evolve microstructure than for feathers. $\endgroup$ – jamesqf Nov 25 '19 at 17:56
  • $\begingroup$ @jamesqf Hair and feathers are very different structures so I don't think differences in structural coloration are impossible, but I agree with you that a reason for this is not immediately apparent. Nevertheless, the point remains that all of the evolutionary pressures that drove the independent evolution of color in birds, insects, and fish are present in mammals. The most reasonable explanation for its absence in mammals must be the difficulty for mammals to attain coloration. The mandrill's face tells us this is not an issue with mammals in general, but rather with hair in particular. $\endgroup$ – Mike Nichols Nov 25 '19 at 18:46
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    $\begingroup$ I disagree. I think (but I'm certainly no expert :-)) that there are two inter-related reasons why mammals don't really get into vivid coloration. Most mammals (except primates) are dichromats, which makes colors useless for sexual selection. Most birds are tetrachromats, so they see more colors than we do. (And the nocturnal birds that don't have good color vision, like owls, are generally drably colored: nwf.org/Magazines/National-Wildlife/2012/AugSept/Animals/… ) Second is that mammalian ancestors were nocturnal burrowers. $\endgroup$ – jamesqf Nov 26 '19 at 5:11
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    $\begingroup$ (continued) Birds had ~150 million years of life in the sunlight to evolve color vision & coloration, and their dinosaurian ancestors much longer. (Indeed, tetrachromatism is common in reptiles & fish.) Mammals lost two cone types, and so most were stuck with the dichromatic vision they inherited, primates having re-evolved a third color receptor relatively recently: en.wikipedia.org/wiki/Evolution_of_color_vision_in_primates $\endgroup$ – jamesqf Nov 26 '19 at 5:21
  • $\begingroup$ @jamesqf That third color receptor is present in all Old World Monkeys and Apes suggesting it arose ~30 million years ago. Additionally, we know from comparing the Mandrill and the Drill that the structural coloration of the Mandrill's face arose within the last 3 million years. The various forms of structural coloration have evolved independently at least dozens of times throughout evolutionary history. The fact that we do not see structural coloration in mammalian hair is most likely a consequence of a particular difficulty rather than a lack of evolutionary incentives. $\endgroup$ – Mike Nichols Nov 26 '19 at 16:41
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"Bright" is often not a good survival characteristic for land animals. Ideally you want lack of predators. Of course, some mammals are predators so you may need to prevent their evolution/arrival in that environment.

Fisherian Runaway is a good way to explain the evolutionary process; in fact it is why peacocks evolved such ornate displays. The theory rests on an attribute that initially indicated a genetic advantage, but ends up in a vicious cycle of purely "aesthetic" selection.

So why would being colourful (initially) indicate fitness?

Toxic minerals

There are trace amounts of toxic minerals in the environment which can be used to form pigments (lead, arsenic, cadmium) and displaying these pigments indicates a greater tolerance to them.

Genetic association

Albino animals generally have poor health and short lifespans. Solution? Don't mate with them.

This doesn't quite explain why animals would prefer to mate with more colourful individuals. You either have albinism or you don't, right? So there needs to be a range of pigmentations.

For some reason (retroviruses) all the mammals in this environment received a gene that conferred some advantage*, with a side effect being visible pigmentation. Initially the gene would not be expressed strongly. But the more this gene was expressed, the greater the advantage—and pigmentation. Naturally, pigmentation would become a desirable attribute. Eventually, animals would evolve other pigments to stand out more, leading to Fisherian Runaway.

* an "invisible" advantage like more competitive sperm; something that would not be obvious from fighting one's way to alpha male

Insect repellent

In a rainforest environment you've got... insects. Insects such as mosquitoes are attracted to infra-red light because it indicates body heat. Darker materials absorb more light and emit more of it as infra-red. Brighter colours do the opposite.

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My understanding of evolution on (this) Earth is that the mammals we see today, evolved from small, nocturnal animals, which had found success in a niche where they could hide from the dominant group: the dinosaurs, whereas birds are dinosaurs; the ones that survived the big meteor strike 65 million years ago. Going further back, what became the mammals separated from what became the dinosaurs, and were for a while dominant, but about 252 million years ago, another extinction event occurred, and the dinosaurs becam dominant (I'm borrowing heavily from Wikipedia here).

The mammals were living a nocturnal life for a long time, and their colour vision was lost, since it wasn't useful, whereas the diurnal dinosaurs (and later birds) kept (or evolved) good colour vision, since that was advantageous. Having bright colours can be an advantage as a way of signaling good health, but only if your species can see the colours - hence birds tend to be brightly coloured and mammals tend to be relatively drab.

So, from this you can see how it could have been different: if the mammal ancestors had become dominant and diurnal, they would (or could, at least) have become brightly coloured.

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  • $\begingroup$ or to put is similar have your mammals be able to actually perceive a decent range of colors. $\endgroup$ – John Nov 26 '19 at 23:57
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Evolution is a random and uncaring monster, nothing is inevitable and everything is possible, so it's entirely possible that vibrant colours could have evolved in mammals.

The most obvious possible cause is Amotz Zahavi's Handicap Principle. It benefits neither prey nor predator species to be brightly coloured, but this handicap would be a costly signal that is difficult or impossible to fake.

Consequently, other individuals, be they the same species or a potential predator, will evolve to recognise the relative strength of the signal, and respond appropriately. Predators won't try and eat the strongest looking prey, because they know it's not bluffing and will be hard to kill.

Here evolutionary pressure is applied twice: first, that members of the same species look for the most beautiful (colourful) mates, and second, that predators will notice the less vibrant members as more accessible food.

This is entirely possible so long as the common ancestor evolved using colour as a handicap.

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If the things that prey on mammals have poor color vision, then color is not a major problem for the mammals to adopt. So make the top-tier predators be colorblind reptiles. Next, you need something to drive the color. Imagine if species had lots of recessive genes that we’re really bad to pair up, and imagine that those traits were correlated with color. In that case, it is an advantage for any blue female to pick a non-blue mate, and red female to pick a non-red mate. That would encourage more color diversity.

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You cannot. There is no way an extraterrestrial creature to be classified as a mammal.

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    $\begingroup$ Could you please expand on that? Please offer alternatives in order to enable OP to build an interesting setting. $\endgroup$ – Gustavo Nov 26 '19 at 10:54
  • $\begingroup$ The definition of a mammal is, "a warm-blooded vertebrate animal of a class that is distinguished by the possession of hair or fur, the secretion of milk by females for the nourishment of the young, and (typically) the birth of live young." Please explain why a non-Earth entity cannot possibly be described as being a warm-blooded vertebrate with hair/fur, mammary glands, and giving live birth. $\endgroup$ – Frostfyre Nov 26 '19 at 13:24
  • $\begingroup$ @Frostfyre because "mammal" is a philogenic clade describing how the species evolved, not what "features" it has. Mammalia is a subclade of tetrapoda, tetrapoda is a subclade of chordata, chordata is a sublade of bilateria, bilateria is a subclade of animalia, animalia is a subclade of choanoflagellata, choanoflagellata is ia subclade of opistokonta (posterior-flagellum) which is subclade of unikonta (one-flagellum), which is subclade of eukariota etc. Only something evolved from Mammalia can be classified as Mammalia. $\endgroup$ – Anixx Nov 26 '19 at 14:13
  • $\begingroup$ The theory of panspermia disagrees that the extant, human-defined category of "mammal" can only ever possibly exist on Earth in that regard. If OP states mammals can occur on other worlds, then mammals can occur on other worlds. $\endgroup$ – Frostfyre Nov 26 '19 at 16:26
  • $\begingroup$ Even if this is technically true, the intent of the question is obviously "creatures that are analogous to Earth mammals" and it's asking for how this feature would evolve rather than a discussion of taxonomy, so it isn't really a useful answer. $\endgroup$ – John Montgomery Nov 26 '19 at 23:44
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It may help to look at how animals are coloured here on earth. Many herbivorous mammals' coats are camouflage as a result of evolution. Think of a gazelle or a zebra, or insects, or even many small birds.

If the Flora is brightly coloured, so would the Fauna that eat it.

Another reason we see bright colours in real life are as a warning to stay away. Think of poison dart frogs, etc. Over time all the bright ones weren't eaten as they're obviously poison.

The last I can think of is specifically with birds, where the males are often very colourful and flamboyant. If all the animals prefer brightly coloured mates, eventually they'll all be brightly coloured.

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You need creatures that can see color.

Mammals as a group are basically colorblind. Only some primates and monotremes can see a decent range of color, everything else is either dichromatic or monochromatic, which in humans we refer to as being colorblind. So your "mammals" need to be able to see color. for earth mammals green, red, yellow, and orange are the same color (see below), so why use them. Your creatures are not mammals, not unless the are descended from earth life humans shipped to the planet. mammals lost color vision due to a weird quirk in our evolutionary history and there is no reason for that to be true for your aliens.

Since your "mammals" won't actually be mammals they will probably see color.

On the left is what primates see, in hte middle and right is what the rest of mammals see, as you can tell bright display coloration is pointless in mammals since your mates can't see the color. this is why primates are the only mammals with a sexual coloration. and the only reason for a large animal to be brightly (stand out against the background) colored is for sexual selection. in fact your alien mammal like things will probably be able to see color we can't just like birds and reptiles today can. enter image description here

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