And don’t forget the Malabar giant squirrel! I would add photos of those giant chonky bois, but all my photos are on Inat, who is catching some z’s.
1 Like
Cute! UV glowing possums? Another reason to visit America!
1 Like
Interestingly, bright colours in mammals seem to be not just not needed, but also a disadvantage. Otherwise there wouldn’t be a good explanation for why most colours completely disappeared.
I think you are right about scent being more important. Especially early mammalian ancestors were probably nocturnal and lived in burrows. Even our hair probably initially evolved to increase surface area for more efficient spreading of scent.
From some quick and messy research about vertebrate pigmentation: the most basal morphology of vertebrates (conserved in fish, and reptiles) can produce 4 types of pigments: bright red (through cells called erythrophores), yellow (xanthophores), rusty/brown/black (melanophores), and iridescent (iridophores). Blue, as @jasonhernandez74 and someone else already said, can be produced by a special arrangement of melanin as a structural colour.
That way, all colours can be “mixed”.
In birds and mammals only the melanophores are conserved. However, birds (parrots, most notably) evolved their own yellow to peachy pigments, so they can also produce a lot of colours too (like bright green).
Perhaps the absence of blue mammals can indeed be explain by hair not allowing for structural colours (as @dlevitis mentioned)
P.S.: am I going crazy or blind? I could swear someone said something along the lines of “blue in animals is always due to structural colours”, but I cannot find it, and I read all posts here 3 times in order to find it
1 Like
I’m not sure that is 100% true. There tend not to be any really hard rules in biology. However, there is a Science news article that discusses this briefly and mentions some actual studies (What’s Behind a Blue Behind) that suggested aligned collagen fibrils to be responsible for the blue color in mandrills and a couple other species. Take it with a grain of salt though, as the links in the article are mostly broken or don’t actually take you directly to relevant information and the study cited in the article is actually primarily about structural blue colors in birds rather than mammals.
3 Likes
The main reason most mammals lack colour is that most mammals cannot see colour very well.
Primarily, mammals are bichromatic (vaguely similar to red-green colourblindness in humans); some are even monochromatic (most aquatic mammals, I think).
Early in evolutionary history, the common ancestor of placental mammals was a crspuscular or nucturnal species, with little to no use for the ancestral tetrachromatic vision of early tetrapods (and fish), so they lost two of the four cones.
With colour vision, mammals also lost the ability to produce pigments and structural colour.
If being colourfull were not an advantage, birds and reptiles would also be all brown; but that is demonstrably not so.
One of the few groups of mammals with couour visions are old world monkeys, which tend to be more colourful than the average mammal.
2 Likes
Which probably includes humans, doesn’t it?
I suggest An Immense World: How Animal Senses Reveal the Hidden Realms Around Us
by Ed Yong.
1 Like
yes, Catarhini/Old World monkeys include apes, and therefore, humans.
1 Like
Evolutionarily speaking, the ability to perceive the color is really secondary to whatever benefit the color may provide. E.g. in the cases of toxic insects or frogs, it doesn’t matter if the insects and frogs can see the colors or not, only that their potential predators can recognize it as a warning. Color for mating purposes would rely on the animal’s ability to perceive the color in members of its own species, however, so color perception does play a role there. The driving factor, though, comes down to what kind of evolutionary advantage the trait provides, and for mammals, it just isn’t the most advantageous to have bright colors.
2 Likes
This is my last response to this topic in this thread, as I am not sure we are staying on the scope of the topic.
the point you are missing is that the ancestors of mammals were already tetrachromatic, and that ability was lost due to quite a long period in history where mammal ancestors were nocturnal, and colour vision was unnecessary and even detrimental, as it took space for more sensitive type of cells, useful in the dark.
With it was lost the advantage of being colourful; and ability to make many of the pigments and structural colour; we only kept the two types of melanin which also serve other functions, not just pigmentation.
For diurnal animals; colour vision is huge advantage, and when groups of mammals* turned diurnal again, they kept bichromatic vision for a simple reson it is difficult to re-evolve tri-or tetrachromatism;
not because trichromatic vision did not offer advantage
(which it does - we see predators better as we distinguish hues better that hoofed mammals, and this is probably why tigers get away with being relatively brightly coloured; and it is a significant advantage at distiguishing hues of ripe fruit and/or poisonous plants).
Old world monkey have colour vision, and are more frequently brightly coloured for sexual messaging (bright anogential regions and face), communication (face) and social status (young animal are often lighter and brighter in colour).
This all suggests that being colourful is generally advantageous for different sorts of communication; and when they can see color, mammals evolve color, (and would be probably even more colourful had we not also lost pigments and structural coloration of ancestral tetrapods, along with the ability to see it).
In the absence of adequate colour detection, mammals of course evolved other methods of attracting a mate and communicating, and do not need colour vision for that.
But that is not because colour vision would not offer an advatage, but because it is difficult to evolve once it is lost.
Aposemantism (messaging toxicity) in vertebrates is mostly secondary, even in many amphibians it seems sexual selection plays a strong role in shaping it (in insects sexual selection in colour is mostly absent and most aposemantic insects are yellow/black and sometimes reddish with stripes (more rarely, dots) across multiple unrelated groups, in posion dart frogs, there are many patterns and colours inside the same species, which suggests something in addition to aposemantism); and it may be that it is just that poisonous vertebrates can evolve brighter colours for sexual selection than non-poisonous ones.- there are plenty of poisonous vertebrates without aposemantism.
*many are still nocturnal, for those there is little to no advantage; but there are many diurnal mammals also