milewski's Journal

(writing in progress)

Here are some new facts and realisations, based on Estes (1991), on the topic of facial expressions in baboons and Old World monkeys.

SMILING
 
It is easy to assume that only humans have the facial expression we call smiling.

However, cercopithecoid monkeys and anthropoid apes also smile, in a way. The expression is called not a smile but a ‘play face’.

The important aspect is that the configuration of the mouth is similar to that of the aggressive fang-baring expression, but the eyes look different. “The teeth are bared as in bared-teeth threat but there is an obvious difference in the eyes, which are often slitted or partially closed, never staring”.
 
Apart from the opening of the jaws, why could this not be called a ‘happy-grin’? I do not see the openness of the mouth as a disqualifying factor, because baboons also perform the fear-grimace, at least part of the time, with an open mouth.
 
Could it be that many of our relatives smile in a way that is both homologous and analogous to our human smile? I suspect that, if anyone has written anything erudite on this, it will be Desmond Morris.
 
DENTAL ADVERTISEMENT

I now realise that baboons have both visual and audial displays of their dangerous canines. They ‘fang-bare’ conspicuously by both yawning and the ‘canine threat display’. However, they also use what Estes (1991) describes as ‘tooth-grinding’.

I suspect that it is not the molars that are being grinded here, but the upper canines against the lower premolars that function as ‘whetting stones’. I.e. when a male baboon grinds its teeth, it is actually sharpening the canines, and the sound is warning the other by reminding it of the sharpness of the canines.
 
If there is any member of the Carnivora that has an audial display of the canines, it has slipped my mind. I suspect not. In this sense, primates out-canine the carnivores:

• their canines are in some species proportionately larger than those of carnivores;
• the canines remain sharp because they are whetted against a special lower premolar; and
• there is an audial as well as visual display of the canines.

Balancing this, though, is the fact that in most primates the female has far smaller canines than the male (I seem to recall this is not true for gibbons and I need to check which other species of monkeys and apes have impressive canines in the female).
 
Estes (1991) does not feature the gelada. However, photos on the web establish for certain that females of the gelada often use an expression which is either an assertive fang-baring, or a fear-grimace. I suspect that it is mainly a fear-grimace, although not usually described as such.

One of my reasons is that the canines, although discernible, are not large enough to be dangerous-looking in females of the gelada (please see photos below). If I am right, the main difference between the gelada and other cercopithecids is the lip-flip, performed in the fang-baring expressions (yawning, fear-grimace, canine threat in male, etc.).
 
PENIS DISPLAY

The accounts in Estes (1991) leave me in no doubt that, in not only baboons but Old World monkeys in general, the penis is used to display confidence, self-assertion, and status, way beyond any purely sexual communication.

For example, not only baboons but most cercopithecid monkeys have a display in which a mature male individual takes a sentinel role, guarding over the group, with his legs slightly spread and his penis partly erected, the conspicuousness of the penis accentuated in some species by bright hues.

It seems that the non-sexual display of the penis is quite different in Old World monkeys and baboons on the one hand, and the spotted hyena (Crocuta crocuta) on the other. In the former, the display of the penis is assertive, whereas in the latter the display of the penis is submissive/self-effacing. I have not found anything in the literature that actually states this basic difference. However, it seems obvious on reflection. If I am right, this puts a new complexion on the evolution of the peniform clitoris of Crocuta.
 
Coming back to the face:

One of the main differences between monkeys and the spotted hyena is that in the former the eyebrows and eyelids are used in various facial expressions, in combination with the mouth. Although the eyes are more expressive in hyenas than in felids, canids, viverrids, etc., the spotted hyena has no eyebrows and no display of eyelids.

The closest thing I have seen, in the spotted hyena, to the primate pattern is the complex wrinkling of the skin on the forehead, particularly right between the ears. This produces a quizzical look. However, I do not assume this to be a functional expression, because it is so subtle, and there is no accentuation of it by colouration, as far as I know.
 
I now see that the gelada and the spotted hyena both show the fear-grimace in extreme ways, by particularly stretched mouths. In the spotted hyena it is mainly the gape that stretches to the maximum in the fear-grimace, while in the gelada it is mainly the upper lip, which actually flips inside-out.

It remains to be seen whether the gelada ‘smiles’ (i.e. a happy expression) with the lip-flip, i.e. whether it possesses a positive version of the fear-grimace, that also shows the maximum exposure of the upper gums. If so, I doubt whether any primatologist has noticed it, for more or less the same reasons as the failure to notice the fear-grimace in the human species.
 
spotted hyena with gelada: not only do both species use extreme exposure of teeth and gums in some facial expressions, but it may also be true that both species have a ‘happy-grin’.
 
Theropithecus gelada female:
 
What is almost certainly a fear-grimace:
http://www.shahrogersphotography.com/gallery/Upload/SM08FR-520.jpg

In the spotted hyena there is a greeting ceremony, in which one individual sniffs the erected phallus of the other at some length. We have noticed that this takes trust, because of the vulnerability of the phallus should manners break down in an animal with such dangerous dentition.
 
We have also noted the similarity in complex social structure between the spotted hyena and baboons – something well-recognised in the literature.
 
Today I discovered a deeper level of analogy here: in baboons there is likewise a kind of genital greeting (among males) which signifies trust and reinforces the social order.
 
I have before me pp. 191-193 in Frans de Waal’s (1996) ‘Good natured: the origins of right and wrong in humans and other animals’.
 
I quote from a section devoted to discussing the difference between coercion and persuasion.
 
“Perhaps the best-known form of negotiation among primates is the way adult male [anubis] baboons greet other males in their troop...one male will typically walk up to another with a rapid, swinging gait. He looks the other straight in the eye with some friendly expression, such as lipsmacking, which makes it absolutely clear that he only wants to initiate a greeting...The encounter...follows a certain protocol that varies with the kind of relationship the two males have. Often, the other welcomes the approach with a similar friendly expression, and one male presents his rear end while the other touches or grasps his hips. They may then proceed to mounting, or, if they really get intimate, one male may fondle the other’s scrotum or pull at his penis. Known as ‘diddling,’ it is a sign of tremendous trust. The contact lasts only a few seconds, after which the two males separate again. Male baboons do not seem comfortable enough in each other’s presence to associate or groom; their predominant modes of interaction are fighting and greeting. The same behavior was studied...in a large colony at the Madrid Zoo...found the encounters to be extremely tense, occasionally erupting into fights. The reason is that they often serve to test and confirm who is on top, hence the jockeying for position to decide which male is going to be the mounter (generally the dominant) and which the mountee. Greetings thus seem a way of assessing intention: a male who used to elicit presentation in another learns from his partner’s refusal that their previous roles are no longer working, and that a serious challenge may be in the air. Since tensions remain under control in the vast majority of greetings, the advantage of this sort of information exchange is that matters can often be worked out without physical confrontation...A few combinations of older males have...reached the point at which dominance hardly matters anymore; they have moved from asymmetrical to symmetrical greetings...two devoted allies [Boz and Alexander]...every day, first thing in the morning, the two males would go through a series of intimate greetings so carefully balanced that one would think they were keeping count. Boz would present to Alexander to let him touch his genitals, while both gazed into the other’s face and lipsmacked. Two minutes later Alexander would present to Boz for the reverse procedure...The formalization of roles and the remarkable involvement of vulnerable body parts made Smuts and Watanabe draw a parallel with biblical oaths in which one man places a hand under another’s loins. Considering that the words ‘testify’, ‘testimony’, and ‘testicle’ share a common Latin root, it does not seem too far-fetched for these primatologists to speculate that ‘the genital touching that sometimes occurs in greetings perhaps serves to enhance the truth value of whatever these males are ‘saying’ to each other within the formally circumscribed context of greeting. Lacking articulate speech, and unable to swear oaths, perhaps male baboons make a gestural equivalent by literally placing their future reproductive success in the trust of another male. Such risky gestures may help to enhance whatever verity is presumed in the greeting because they impose a potential cost on the presenting male.’”
 
In the spotted hyena it is females that are dominant, but the principles seem similar. One individual is ‘under oath’ to another as signified by the presentation of the vulnerable genitals as ‘collateral’ as it were. It is easy to see how this mortgage promotes honesty as opposed to deception, not so?

I note again that there is much more going on here than mere submission; in baboons as in the spotted hyena my interpretation is that there is a demotion/humiliation for the inferior partner. In male baboons, the reproductive future of the individual is placed at stake in the ‘oathing’ or ‘mortgage’.

If there is a similar ‘mortgage’ in females of the spotted hyena, do you see that it would take more than just the normal female genitalia to make this oath credible? This is because the vulva is not crucial and vulnerable in the same way as the testes are. The testes are so precious for producing sperm that they should actually be protected deep in the body in terms of security; the fact that for whatever physiological reason they are on the outside means that for males to ‘swear on oath’ their hierarchical agreement has real credibility – because the implication is ‘if I cheat this hierarchical agreement, you have the right to destroy my testes next time we greet’.

So this obviously leads to the crucial question ‘how can females make an analogous oath as credible, in a female-dominated society?’ The answer is to evolve a genital anatomy in which there is indeed some external organ that is crucial to reproductive success.

Hence, I argue, the fact that the clitoris of the spotted hyena is not only prominent but also the birth-canal.

By converting the clitoris into the birth-canal, the spotted hyena is producing the hyenid equivalent of the exterior wearing of the testes. This is because the clitoris can kill the animal if  it is infected under stress, and such infection can possibly spread to the whole genital tract including uterus and even possibly ovaries.

Furthermore, in mature females that have already passed that test, infection of the clitoris continues to be risky because of how close the clitoris is to the udder. Infection of the udder would certainly detract from reproductive success. If it is true that there is an ‘immunity-proving’ involved in birth through an inevitably ruptured bottleneck, can readers see that having the same organ bitten by another would also risk lethal infection? (this seems simply consistent in terms of this rationale).
 
In considering that the bottlenecked birth-canal of the spotted hyena is the vulnerable equivalent of testes in terms of providing credible collateral for social oaths, it is interesting to consider the reasons for the mimicry by females of the spotted hyena of the scrotum. Although I do not think the peniform clitoris shows sexual mimicry, it is hard to argue against sexual mimicry in the case of the pseudo-scrotum of females of the spotted hyena.

It is almost as if this species is saying with its anatomy: "I’m female but I’ve got balls, and these balls are on the line if I cheat our agreement." Because the animal cannot place its ovaries in its pseudo-scrotum, it does the next best thing: it places, close to the ‘false balls’, a structure that does much the same thing: risk damage that reduces future reproductive success, whether via the birth process or via the lactation process.
 
Based on the above thoughts, I can add something conceptually to the idea of immunity-testing, as follows:
 
It is not just at first birth that the immunity of females of the spotted hyena is being tested by the anatomical peculiarity of the peniform clitoris. Even after the individual has passed this first and most painful test, she continues to be tested because any injury to the clitoris risks infecting the UDDER. It is no accident that the clitoris is so close to the udder that it almost looks like an extra teat. Why is there this proximity? The answer may be: infection of a wounded clitoris means infection of the udder. Since the udder is as crucial to the niche of the spotted hyena as its unique premolars, this is significant.
 
An immunity-based interpretation: it is not just first birth, it is throughout the life of individual females that changes in rank can occur owing to performance of the immune system just after birth, when even just stretching, stressing and slight injury of the mature clitoris could infect the udder. Furthermore, the same anatomical arrangement also provides the credibility needed in social oaths during the greeting ceremony.
 
This approaches a rationale to explain why the clitoris of the spotted hyena is BOTH a particularly vulnerable example of genitalia AND the birth-canal. (To refresh reasers' memory of the conceptual puzzle here, it would have been strange enough for the spotted hyena to have the most penis-like clitoris on Earth, without this also containing the birth-canal; so there is a double-puzzle here, which the literature on this species is not clear enough in stating.)
 
A question of the use of English: I feel that part of the reason why no student of the spotted hyena has previously solved this problem is poor definition of words and poor description of the structures involved. What about ‘mortgage’, a word perhaps not previously suggested in explanation of the peculiar anatomy of the spotted hyena.

This word seems apt because its derivation is from the root for death (mort, as in mortuary or mortality) and gage, which means pledge/commit (same root as in ‘engage’). So, a mortgage is a ‘pledge/commitment on pain of death’ as it were. I am coming to see that this is what the peniform clitoris of the spotted hyena, which is really a bottleneck birth canal plus immunity-test teat, really is: it mortgages the animal for purposes of social status, the social status being crucial for reproductive success.

In the following, the expression seems more confident and assertive based on eyebrow display plus solidarity, but the mouth posture seems indentical to fear-grimace:
 
https://yooniqimages.blob.core.windows.net/yooniqimages-data-storage-resizedimagefilerepository/Detail/10531/8b063afa-029b-48de-9e9b-1308696d4824/YooniqImages_105314822.jpg

(writing in progress)

(writing in progress)
 
A typical genus of mycorrhizal fungus in grasses is Glomus (please see https://en.wikipedia.org/wiki/Glomus_(fungus) ). The kingdom is Fungi, the Class is Glomeromycetes, the Family is Glomeraceae, and the genus is Glomus. This type of fungus is incapable of living free, and is obligately dependent on plant roots.
 
Unlike ectomycorrhizal fungi associated with pines, oaks, eucalypts and other trees, which form mushrooms, Glomus has no mushroom and simply releases its spores underground, from its hyphae.
 
Glomus is called an arbuscular mycorrhizal fungus because of its arbuscules, which are in effect minuscule ‘roots’ within the grass root cells. So at one end the fungus has a network of hyphae permeating the soil more thoroughly and more rapidly than the root hairs of any plant could do, and at the other end the fungus has hyphal branches within the root cells of the grass. The fungus takes up sugar at the arbuscule and uses it to grow and to metabolise, its various functions on behalf of the grass including immunity (mainly from pathogenic fungi), uptake of nutrients, and uptake of water. The fungus has no source of energy other than the photosynthesis of the grass, in contrast to free-living saprophytic fungi and also, I think, ectomycorrhizal fungi (which certainly take much energy from the tree but also possibly get some of their energy by breaking down litter in a way similar to white-rot fungi).
 
It is hard to say which function of the fungus (immunity, nutrition, or hydration) is most expensive from the viewpoint of the grass. Possibly this varies according to the grass taxon and the habitat.
 
You’ll seldom see this written anywhere, but it’s safe to assume that the fungus is aerobic. There is little oxygen underground and as I understand it grasses are fundamentally designed to supply air to the fungus. As you know, grasses have aerenchyma, so that in e.g. aquatic rice the plant acts as a conduit of oxygen from the air down into the waterlogged root-zone. It’s easy to assume that the grass roots need this air but I think a more correct way of viewing this would be that it is the arbuscular mycorrhiza of rice (and I can confirm that Glomus occurs also in rice Oryza) that has the main need for oxygen. I suspect that, per unit biomass, the fungal cells consume oxygen an order of magnitude more rapidly than the root cells themselves.
 
So when a gardener aerates a lawn, by driving holes through the turf, I assume that it is really the fungus (often Glomus) that is really being aerated. And the particular need of lawns to keep their roots aerated has several implications.
 
Furthermore, the benefit to lawns of frequent watering (to a degree apparently far in excess of what the plant itself could possibly need for its transpiration) may be to the fungus. As you know, fungi are easily dehydrated. Many or most of the hyphae of Glomus probably permeate the topsoil, because this is where much of the organic matter and nutrients are. For lawn to thrive, there must be enough air for the fungus to breathe, and enough water for the fungus to drink. The fungus can be expected to exceed the grass in its dependence on both breath and drink, because it catabolises so much more rapidly than the grass and because its hyphae are so narrow and thus so vulnerable to desiccation.
 
Because lawns tend to be maintained by large grazers, which trample the turf, I infer that the lawn-grazer relationship would not work well without a means of aeration. Not only do lawns tend to have earthworms (and, in the tropics, termites such as Hodotermes) which continually aerate the root zone, but the herbivores themselves promote the continual burrowing of invertebrates because their faeces are consumed by e.g. dung beetles. A grazing lawn is thus not so much a two-way partnership as a three-way partnership. It is easy to forget that the mutualism between grass and grazer would possibly not work in the absence of the third partner, the burrowing invertebrates (earthworms are typical in temperate climates and Charles Darwin was on to them in a big way although I’m not sure that he thought the grazing lawn concept through).
 
What nobody seems to have thought of before – although for many decades now there has been a virtual army of researchers worldwide working on mycorrhizae – is the role of selenium for the mutualism between grass and arbuscular mycorrhizal fungi such as Glomus.
 
I think it’s safe to assume that the cells of the grass itself, including its roots cells, have such a small requirement for Se that it is to all intents and purposes both immeasurable and negligible. However, that is not to say that the grass-fungal symbiosis has a similarly negligible requirement for Se.
 
I predict that if one were to work at the minute scale necessary to sample the hyphae themselves of Glomus, and if one were to analyse these for concentration of Se, one would find a concentration of Se an order of magnitude or more greater than that in the cells of the grass plant.
 
It’s interesting that, while even the most oligotrophic and fire-prone of grasses, such as Triodia, have arbuscular mycorrhizae, the entire family Restionaceae lack this fungal assocation, having cluster roots instead. This implies that restios lack the (indirect) requirement for Se that I postulate for all grasses. Of course, I assume that a hummock grass requires less Se than a lawn grass, but it’s interesting that hummock grasses – although sharing sclerophylly with restios – differ qualitatively in the presence/absence of mycorrhizae.

(writing in progress)

(writing in progress)

The Highveld clearly turns brown in winter, with the dormancy, and above-ground drying-out, of the grasses. However, this phenological pattern cannot be ultimately explained by either desiccation or frost.

Throughout the dry season in the Highveld, soils remained wet in bottomlands. The dry season is in winter, but temperatures are not extreme, and then days remain sunny. Ambient temperatures in the Highveld during winter remain above those of the peak growing season in the tundra (Bonan and Shugart, 1989),

This indicates that the winter dormancy of the dominant grasses is a phenological tactic rather than a reflection of absolute physiological constraints imposed by air temperature.

suggesting that interrupted photosynthesis is part of a life-history strategy of grasses as opposed to being an inevitable consequence of the seasonal drought and cold in the Highveld.

In seasonal marshes in the Highveld, the topsoil in vleis remained moist in the middle of winter, when all the grasses are dry and brown. What can be seen repeatedly, in the treeless grasslands of southern Africa, are situations in which winter dormancy in grasses cannot be explained by the seasonal drought of the winter season.

just because no rain falls in winter; the dormancy of grasses at vlei edges proves this because the topsoils remain moist there.
 
So what could cause the dormancy? Another possible cause is the seasonal cold. However, this too makes little sense, because grasses actually grow in the Arctic summer at temperatures lower than those prevailing in the Highveld winter. With appropriate adaptation, grasses should be able to grow all winter long in the Highveld because there is plenty of moisture in the soils in that season, and grasses elsewhere on Earth are known to grow despite the cold.
 
One example taxon: Arctic cottongrasses (Cyperaceae: Eriophorum spp.) are known to be able to maintain growth and positive photosynthesis at temperatures as low as –4 degrees Celsius, i.e. 4 degrees below freezing!
 
Perhaps fire is involved, but perhaps there is a World War 1 trench warfare ‘mentality’ or ‘tactic’ at play here. The grasses/sedges are perhaps resting to save their reserves for the intense battle that plays out in spring and summer when conditions are optimal for growth (and war against competing entities). I am suggesting here that the battle between grasses and trees is not necessarily a continual one; there are peaks and troughs in the battle; and the plants need to have sufficient energy available for the peaks. I am suggesting further that grasses/sedges would lose condition, so to speak, if they grew in winter, relative to grasses/sedges that ‘choose’ not to.
 
When grasses in the Highveld go dormant in winter, what they are doing could either be

• suffering an environmental limitation, or
• exhibiting a strategic choice.

Most naturalists in South Africa, if asked to explain the seasonal behaviour of the vegetation, would assume that environmental limitation is the correct answer.

However, ifnstrategic choice is the right answer, what are the costs and benefits of the choice to enter seasonal dormancy despite the possibility of continuing growth? Why do grasses not just grow throughout the year in the Highveld (obviously, more slowly in winter than in summer, but growing nonetheless in the dry and cold season, which is far warmer than the growing season of Arctic grasses)?
 
This is where it gets conceptually interesting. Just as the dominance of herbaceous plants means that the tree niche is empty here, so the dominance of winter-dormant herbaceous plants means that the ‘Arctic grass’ niche is empty here.
 
Put a different way: the fact that Highveld does not support native trees, despite their being ample soil, water, and nutrients for trees here, means that what prevails is a plant community that chooses to fall short of its maximum potential biomass/woodiness/height. Something else is instead maximised, possibly overall rate of catabolism, or biological energy intensity. And the fact that Highveld does not support winter-growing grasses, despite their being more than enough sunshine, ample water (at least in bottomlands), and adequate temperatures (cold but not prohibitively so for grasses as a life-form), means that what prevails is a plant community that chooses to fall short of its maximum potential period of activity. In the niche hyperspace, evolutionary/adaptive decisions have been taken to ‘switch off’ or ‘decline’ certain opportunities despite the resources being available for exploiting those opportunities. The option of growing into tall, woody plants has been declined, and this growth-form has been ‘switched off’; and the option of growing all year long has been declined, and the phenological behaviour of growth during winter has been ‘switched off’ as well.
 
My point: by this thinking the Highveld is doubly ‘self-restrained’: it has opted to forgo a whole ‘spatial stratum’ of plants, namely trees and tall shrubs (which are elsewhere deemed to be the superior competitors for light), and it has opted to forgo a whole ‘temporal stratum’ of plants, namely winter-growing herbaceous plants (or even trees for that matter).
 
Now, the theoretical juice in this is as follows.
 
If opting for treelessness means that the grassland achieves greater power without trees than with trees, and if this is because the most powerful way of using the available resources is expressed by small plants as opposed to big ones, then could it be that the winter dormancy of the grassland also somehow achieves greater power than a theoretical grassland that grows all year long? If so, how exactly does a winter-dormant grass ‘overpower’ a theoretical competitor in the form of an ‘Arctic grass’? What exactly is the payoff in desisting from growth in winter, such that this payoff is more profitable than the alternative payoff of continuing to photosynthesise and grow? And what is the resource parameter in which this payoff should be measured?
 
One possible line of thought: by choosing winter dormancy, the grasses promote seasonal fire, which pays off by .....?

(writing in progress)

In the subfamily Chloridoideae (https://en.wikipedia.org/wiki/Chloridoideae) of the family Poaceae, there is a tribe called Pappophoreae. The common name of this tribe is pappusgrasses. There is nothing weedy- or vulgar-looking about these grasses, yet they are widespread.

Pappusgrasses are insubstantial-looking. However, when one gets an eye for them, they turn out to be important grasses in semi-arid ecosystems on at least four continents – that is, functionally, if not in terms of sheer biomass.
 
In the strict sense, pappusgrasses consist of just three genera: Schmidtia, Cottea and Enneapogon.

Pappophorum (American and also called pappusgrass, https://www.inaturalist.org/taxa/166120-Pappophorum-vaginatum) is similar, but probably not particularly closely related.
 
Pappusgrasses, at the level of tribe, genus and species, are remarkably widespread.

Cottea (https://www.inaturalist.org/taxa/140214-Cottea-pappophoroides) is monospecific and restricted to the semi-arid USA.

Schmidtia occurs in Africa and Pakistan, and the two species common in South Africa, viz. the annual S. kalahariensis and the perennial S. pappophoroides, both occur also in the Sahel. They are not naturally restricted to southern Africa. So, there are situations north of the equator in which Schmidtia - which South Africans tend to associate with Kalahari sands - occurs with presumably equivalent commonness.

The largest genus of pappusgrasses in the strict sense is Enneapogon. Its species present as local grasses, but the genus and some of its species are actually widespread.

For example, Enneapogon desvauxii (formerly called E. brachystachyus or brachystachys in South Africa) occurs commonly in the Karoo, where it is regarded as exologically typical and an important part of the diet of the springbok (Antidorcas marsupialis, https://www.inaturalist.org/taxa/42283-Antidorcas-marsupialis). However, the same species occurs naturally also in America, as far south as Chile and Argentina.

For some reason, pappusgrasses seem absent from Patagonia, which surprises me because that might seem to be idea habitat for them. Perhaps they are restricted to warm climates?

About 16 spp. of Enneapogon occur in Australia, where they are an important part of the diet of the red kangaroo just as their congeners are important to gazelles in Africa and presumably Asia.

If I recall correctly, Ken Tinley’s explanation of the former treks of the springbok has to do with Enneapogon and the periodic usurping of this resource by irruptive locusts in the Karoo. Discussing Enneapogon over the years with Ken, I always had the sense that this was a genus of grasses which, if not restricted to southern Africa, was closely associated with indigenous grazers here. I now see this differently, i.e. with a wider perspective.
 
Summarising so far, for emphasis:
What passes off as a typical Karoo grass, associated with the springbok, is actually a cosmopolitan grass (putting aside the details of which species is which), abundant and widespread also in Australia.

All pappusgrasses seem similar in growth-form: perennial or annual, too flimsy to be called tussocks, but on the other hand only weakly able to spread vegetatively. I would not call them lawn-forming. The seeding culms are fairly short (< 50cm and usually < 30cm). All seem to dry off in the dry season. These grasses are unsuitable for bulk-and-roughage grazers, but are particularly suitable for gazelles (and hartebeest/tsessebe) and kangaroos, and presumably guanaco in South America and pronghorn/hare in North America.

As far as I know, all pappusgrasses are palatable and easily digestible. However, that they are not substantial enough to form a staple for most grazers.

Some species have a peculiar mode of regeneration, in which the small ‘tussock’ appears to be perennial because greens re-emerge from the dry plant. On closer examination, what has happened is that the plant has died (i.e. it is actually annual) but the seed-heads have a special design in which they remain lodged at ground level within the plant, and then germinate in-situ instead of being dispersed.

Some qualify as cleistogamous (https://www.wikiwand.com/en/Cleistogamy), somewhat like the peanut (Arachis hypogaea, https://en.wikipedia.org/wiki/Peanut). However, the fruit is not actually borne underground, as far as I know.

I am unsure if this self-pollination and 'anti-dispersal' is, at least in part, an adaptation to grazing, i.e. some kind of alternative to lawn-formation. However, it does seem to mean that herbivores can keep the sward short (eating whatever seed-heads emerge above the leaves) without destroying the regenerative capacity of these apparently flimsy plants.
 
In a sense, what this hints at is that pappusgrasses tend to be something analogous with a lawn - but suited to semi-arid conditions, and never achieving the kind of conspicuousness that most ecologists notice. They seem to be a mere tissue (low, sparse, and usually dried-out looking), but may actually be quite productive for grazers overall.
 
It seems obvious that pappusgrasses have little to do with fire. Not only do they tend to be eaten/decomposed before becoming flammable, but they grow with limited biomass, unable to carry fire even in drought.
 
The important inference of all this is as follows:

Australia is the only continent on which both pappusgrasses and hummock grasses are locally dominant (in separate areas). Therefore, it is to Australia that we should look for the environmental distinctions (particularly edaphic differences) between hummock grasslands (which accumulate biomass and are adapted to wildfire) and pappusgrasslands (which support herbivores and do not benefit from fire).

Australia may show that the main difference is based on soil texture (hummock grasses more on sands). However, the vegetation on loams in e.g. the Pilbara is complex, so this needs further investigation.

Enneapogon desvauxii:
http://www.zimbabweflora.co.zw/speciesdata/images/10/104430-1.jpg

Distribution of Enneapogon desvauxii in southern Africa:
http://redlist.sanbi.org/imgs/distribmaps/9/Plants-90095.png

Distribution of Enneapogon desvauxii in North America:
http://bonap.net/MapGallery/County/Enneapogon%20desvauxii.png

Examples of the distribution of Enneapogon spp. in Australia, showing about a dozen of the ?16 spp.:
https://www.google.com.au/search?q=enneapogon+distribution+map&biw=1366&bih=643&source=lnms&tbm=isch&sa=X&ved=0CAYQ_AUoAWoVChMIj6bX2LisyAIVZS2mCh1mBwV1#tbm=isch&q=enneapogon+distribution+&imgrc=BLWgOpEI54LTBM%3A

Global distribution of genus Enneapogon:
http://www.discoverlife.org/nh/maps/Plantae/Monocotyledoneae/Poaceae/Enneapogon/map_of_Enneapogon.jpg

Cottea pappophoroides, southwestern USA:
https://c2.staticflickr.com/8/7313/10063786573_2550b1f716.jpg

@dewald2 @alexdreyer @_3foxes @dhoare @jan-hendrik @zawalker @wielies @wynand_uys @shobie @tonyrebelo @botaneek @danbeckman @vorontsovams @darren_fielder @kallred

Mokala National Park (https://en.wikipedia.org/wiki/Mokala_National_Park) in South Africa is ecologically interesting because it occurs at the junction of three major vegetation types, viz. treeless grassland, savanna, and low shrubland. In other words, this small national park straddles the Highveld (https://en.wikipedia.org/wiki/Highveld), the Kalahari (https://en.wikipedia.org/wiki/Kalahari_Desert), and the Karoo (https://en.wikipedia.org/wiki/Karoo).

A particularly abundant grass in Mokala National Park, particularly on sandy substrates, is Schmidtia pappophoroides (https://www.inaturalist.org/taxa/336805-Schmidtia-pappophoroides).

See https://www.inaturalist.org/observations/103383472 and https://www.inaturalist.org/observations/72990067 and https://www.inaturalist.org/observations/103383477.

This is puzzling, because S. pappophoroides is not particularly typical of any of the three biomes referred to above.

How, then, can this abundance be interpreted in ecological terms?

Schmidtia is a pappusgrass (https://www.inaturalist.org/journal/milewski/67844-introducing-pappusgrasses). As such, it is related to Enneapogon - which occurs in Mokala National Park but also has a cosmopolitan distribution (https://en.wikipedia.org/wiki/Enneapogon).

We can best find clues to the ecology of pappusgrasses in Australia, because Enneapogon

• is fully indigenous to Australia, and diverse here in number of species, and
• has been particularly well-studied on this continent.

Beadle (1981, https://books.google.com.au/books/about/The_Vegetation_of_Australia.html?id=_5rwAAAAMAAJ&redir_esc=y and https://catalogue.nla.gov.au/Record/1562329) gives information on Enneapogon in Australia, on pp. 540-541. This suggests that this genus can best be thought of as successional, and suited to times/places where only limited biomass can be supported.
 
Enneapogon occurs in ‘ephemeral grasslands’ on sandy soils in Australia. The vegetation is always woodlands or shrublands, not treeless grasslands. The grasses are called ephemeral because, even if they are technically perennials, they tend to be killed by drought after only a few years.
 
Here are further facts that I gleaned from Beadle (1981):
 
In dry parts of tropical Australia, woodlands of Eucalyptus terminalis and E. argillacea occur on slopes, with mean rainfall 300-600mm per year. Here, the grasses restricted to annuals, leaving much bare ground. The soils are not particularly sandy. Enneapogon is patchily common in these woodlands, the spp. being E. pallidus, E. avenaceus, and E. polyphyllus. Sporobolus is always co-dominant. Other genera of grasses occurring in these communities are Tragus, Chloris, Dactyloctenium, Aristida, and Brachyachne.
 
Over large areas of the arid zone of Australia (formerly dominated by Acacia or Atriplex/Maireana), the vegetation has been degraded by pastoralism. As a result Enneapogon avenaceus has become common, functioning effectively as an annual. It now commonly covers large areas as monospecific stands, only 20 cm high. Beadle shows this in a photo, Fig. 20.19, which is obviously a form of treeless grassland, although not fully natural. “Even if the tussocks of Enneapogon do not grow during the second year, the dead tussocks remain and, in these, either new plants of E. avenaceus or another annual species become established.”
 
Furthermore, Beadle (1981) informs us that:

• In the mulga lands, Enneapogon (e.g. summer-growing E. avenaceus) are restricted to hills with rock exposures. Sandy patches of mulga have hummock grasses (Triodia, https://en.wikipedia.org/wiki/Triodia_(plant)) instead.
• Enneapogon avenaceus also occurs in eucalypt woodlands in the arid zone, on loams, where it is just one of various grasses (Aristida, Danthonia, Eragrostis, Neurachne, Paspalidium, Stipa).
• Enneapogon avenaceus also penetrates areas characterised by the saltbush Atriplex vesicaria on gilgaied clay soil, although it is not dominant here. Ditto for saline/sodic sands bearing the shrub Maireana pyramidata (which vaguely resembles 'ganna' in southern Africa, https://en.wikipedia.org/wiki/Caroxylon_aphyllum).
• On some claypans, the dominant grass is the tall Eragrostis australasica, with E. avenaceus forming a peripheral zone, in this case mildly sodic rather than saline.
• Right across the arid zone of Australia, one finds narrow belts of clay, bearing the grass Eragrostis xerophila. Sometimes Enneapogon planifolius is one of the associated grasses, along with Chloris, Dicanthium, Eragrostis (other spp.), Panicum, Sporobolus and Triraphis.

What emerges is that Enneapogon

• occurs widely, here and there, in semi-arid Australia,
• tolerates sodicity and even perhaps salinity, and ranges from sand to clay and stony shallow soils,
• is always naturally associated with shrubs or trees, but is capable of achieving a rather unnatural commonness on degraded surfaces where the woody plants have largely died off, and
• does not grow with hummock grasses, being mutually exclusive with them.

The edaphic and climatic distinctions between hummock grasses (which are fire-prone) and Enneapogon are rather subtle within Australia.

Enneapogon obviously prefers somewhat nutrient-richer soil than that typically associated with hummock grasses, with a corresponding difference in soil texture. However, the main point about Enneapogon is that it is essentially a grass of somewhat degraded sites, i.e. it is only competitive where larger plants have been removed.

It would be simplistic to describe Enneapogon as an annual. Instead, it is best thought of as a small, short-lived, insubstantial grass which cannot compete with more substantial plants. It is one of various smallish tussocks forming an ‘understorey’ to woody vegetation (typically Acacia but also halophytic amaranths) in semi-arid Australia.

It is only where the competitors have been removed that Enneapogon can approach dominance, and this is not strictly natural.
 
This may help us to understand the abundance of a related pappusgrass, in South Africa. The implication is that part of the reason for the dominance of Schmidtia pappophoroides in Mokala National Park is disturbance - originally by livestock, and now by dense populations of wild grazers.

Australia is the continent of wildfire. Fire is unlikely in mulga (https://en.wikipedia.org/wiki/Mulga_(habitat)) and saltbush vegetation, except on sandy patches suited to Triodia = hummock grasses. Although many grasses in Australia benefit from fire, nothing in Beadle’s description hints at any role of fire w.r.t. Enneapogon.

Beadle does not state this as such, but I infer that fire-prone vegetation is mutually exclusive with Enneapogon in Australia, as I think it is on other continents. I see this as more important than any distinction in substrate-preference between hummock grasses on the one hand and Enneapogon on the other.

The main aspects that I have learned about Enneapogon are as follows:

• These are small, annual-like grasses, superficially looking as if they might spring up after fire, in a kind of successional stage as the main fire-prone plants recover. However, I doubt this.
• As effectively an 'annual', Enneapogon is not a post-fire successional grass. Instead it characterises categories of disturbance other than fire, i.e. usually overgrazing.
• Some of the features of Enneapogon are somewhat specialised for herbivory (in a positive sense, i.e. supportive to grazers instead of being inimical). This is because it manages to regenerate from seed within the previous small tussock. That is to say, it regenerates in its own infrastructure, and thus achieves some of the continuity and reliability of a lawn grass, without having to produce the same mat-form and rhizomes as a lawn - which would be impractical in such a dry climate and where woody competition is so strong.

Enneapogon, Schmidtia, and other pappusgrasses are not fire-weeds, not lawn-formers, and not unpalatable ‘scab-plants’ that keep herbivores off until cover has been restored. Instead, they are adapted to a regime of herbivory where the following conditions apply:

• no grass can be really vigorous because the dominant plants are woody plants, and
• there is enough grazing to ensure that the biomass of grass is kept sparse.

In conclusion for now:

The inference is that it is the herbivores in Mokala National Park that are responsible for keeping pappusgrasses dominant. Were the herbivores to be removed or drastically reduced, I suspect that S. pappophoroides would become scarce. I am unsure what would replace it in savanna of Vachellia erioloba (https://en.wikipedia.org/wiki/Vachellia_erioloba) on Kalahari sand. Perhaps a coarse species of Stipagrostis?

(writing in progress) 
 
There is a remarkable parallel between North and South America in the introduction of the domestic horse, its subsequent population explosion as a feral species on treeless grassland, and the adoption of the horse by the aboriginal people.
 
The best counterparts in North America, for the indigenous peoples who waged guerilla warfare on the gauchos in Buenos Aires Province, were the Comanche. Other tribes were also involved, but the Comanches epitomised the way the horse transformed the lives of native Americans in the Northern Hemisphere, and delayed their subjugation by European invaders.
 
Please see below for a map showing the area inhabited by the Comanche. This area comprises about half of Texas plus parts of adjoining states to the northwest. I estimate the range of the Comanche to be about 600,000 square km. In this area, at their heyday in the 1700’s or early 1800’s, the Comanche numbered about 45 thousand persons, living partly on the bison (Bison bison), and doing so to an unprecedented degree among native Americans.
 
Buenos Aires Province is only about 300,000 square km, so is a smaller area. But both areas contain hundreds of thousands of square km of treeless grassland, on which the domestic horse bred rapidly between about 1500 (when introduced by the Spanish) and about 1650. It is estimated that the total population of the domestic horse, in feral form, in Comanche territory reached a maximum of about two million, i.e. more than all the migratory ungulates in the whole Serengeti ecosystem today.
 
The Comanche tribe in fact only came into existence because of this advent of the domestic horse. Before 1550, the ancestors of the Comanche were Shoshone, living farther north near the Rocky Mountains in Wyoming. I don’t know which tribe lived in the treeless grassland of northwestern Texas and adjoining states, but I suspect that they were sparse and poor, being unable to hunt the bison systematically although I’m sure they scavenged the bison whenever possible. Whoever they were, these aboriginal Americans probably lived not much more complicated lives than those of the Pampas aboriginals of the time. One difference was that the North American aboriginals of the treeless grassland used the domestic dog as a beast of burden (I’ll find out more but I think they had wheel-less sleds used to drag possessions across the ground, particularly in winter when there was snow). I don’t know if the original inhabitants of the Pampas even kept the domestic dog – and possibly nobody ever will know this.
 
Both original, primitive tribes were to be swept into oblivion by the increase in the horse and the advent of other tribes, originating on mountain ranges to the northwest (North America) or southwest (South America) which could rapidly adapt to the new opportunities presented by the horse.
 
By virtue of the horse, the Comanches came into existence in 1650-1700, and came to utilize the bison in a way never previously possible. The whole culture was revolutionised, leading to the invention of e.g. the tepee (made from buffalo hides).
 
Although other tribes also came to utilise the horse in North America, it was the Comanche who did so first, pioneering the whole enterprise for themselves and gaining such power that it was only in the late 1800’s that they were finally overcome by ‘civilisation’ – actually in the form of contagious diseases rather than direct outgunning by the Europeans. During their period of control of their range the Comanche took many captives from the Mexicans, ‘Americans’ and surrounding indigenous tribes, whom they sold into slavery. They actually systematically enslaved white people, i.e. the pioneers who passed through or tried to settle in Comanche land.
 
Please see below for a map of Comanche lands, which were about as extensive as Texas although only partly in Texas. Also see various other maps putting the size of Texas, and thus the size of Comanche lands, in context geographically in various parts of the world, including West Africa whence you’ve just returned. As you can see, Niger is more extensive than Texas (and former Comanche lands) but the sizes are comparable.
 
The bottom line is that I see the Comanche as the Northern Hemisphere counterparts for the Mapuche of South America. Both groups moved into the areas of interest (Texas in the USA and the Pampas in Argentina) about the same time, and both held sway for remarkably long, terrorising Europeans who dared to enter their lands. Both owed their new-found power to the feral horse, which transformed lands once occupied by poor hunter-gatherers to lands occupied by warlike people who actually matched the firepower of European guns and ammunition by means of their great mobility as equestrians. The main difference is that the main food of the Comanche – namely Bison bison – was a native bovine, whereas the main food of the Mapuche was a feral bost. So the Argentinian situation is the more extreme and remarkable in that the Pampas was not as remote as the lands northwest of Texas, and the whole way of life of the Mapuche was owing to European introductions of livestock – not only the horse but also a feral ecological counterpart for the wild bison of North America. 
 
https://en.wikipedia.org/wiki/Comanche#/media/File:Comancheria.jpg
 
http://www.search.ask.com/search?&q=texas+map&psv=&apn_dbr=cr_29.0.1547.66&apn_dtid=%5EOSJ000%5EYY%5EAU&itbv=12.12.2.83&p2=%5EBBK%5EOSJ000%5EYY%5EAU&apn_ptnrs=BBK&o=APN11412&ctype=pictures&gct=hp&pf=V7&tpid=ORJ-V7C&trgb=CR&pt=tb&apn_uid=3AE4B883-B390-4AB8-8CE7-BF4C3F9333B4&doi=2014-06-12&tpr=2&ts=1446261956193&imgs=1p&filter=on&imgDetail=true

http://www.texasmonthly.com/the-daily-post/how-big-is-texas-compared-to-other-land-masses/

http://www.texasmonthly.com/the-daily-post/how-big-is-texas-compared-to-other-land-masses/

(writing in progress)

In a previous Post, we have seen that baboons, in general have eyes that are inconspicuous owing to their colouration.

This generalisation does not apply to macaques (Macaca spp.), which are the closest counterparts to baboons in Eurasia. The eyes of macaques tend to be somewhat conspicuous, owing to various features of small-scale colouration on the sclera, the eyelids, and the adjacent parts of the face.

The species I examine here is the bonnet macaque (Macaca radiata, https://www.inaturalist.org/taxa/43448-Macaca-radiata) of southern India.

Two facts emerge in this species of monkey.

Firstly, scleral pigmentation is absent at birth despite being characteristic of the species.

Secondly, despite the tightness of the eyelids, the scleral pigmentation is so dark that it confers the most salient feature of the face of all ages and sexes (except the infant): dark-accentuated eyes that appear to stare. 

The following shows clearly that the sclera adjacent to the iris in infants of the bonnet macaque is unpigmented.
http://walkthewilderness.net/wp-content/uploads/2012/05/BM.jpg 
Ditto but with a hint of pigmentation starting on the lateral (as opposed to medial) side of the iris: 
http://i1.treknature.com/photos/7695/dsc_7143.jpg 

Pigmentation appears in the sclera of the bonnet macaque in young juveniles, as shown by the following.
http://thumbs.dreamstime.com/x/baby-bonnet-macaque-portrait-8766933.jpg

In young juveniles of the bonnet macaque, the eyes already assume a staring aspect accentuated by the dark sclera immediately adjacent to the iris, as shown in the following. Please note that the iris in the bonnet macaque is not particularly dark, and not dark enough to confer a stark appearance to the eyes in the absence of its dark scleral definition.
http://cdn2.arkive.org/media/ED/ED2F9E48-3448-4C62-904A-D41721DD6371/Presentation.Large/young-bonnet-macaque-head-profile.jpg

The following of a juvenile of the bonnet macaque shows the pigmented sclera.
http://fc02.deviantart.net/fs70/f/2013/009/f/f/bonnet_macaque_monkey_goa_india_by_rixresources-d5qyem6.jpg 
Ditto:
http://thumb7.shutterstock.com/display_pic_with_logo/304825/304825,1239469005,1/stock-photo-bonnet-macaque-in-bandipur-national-park-india-28318396.jpg

In adults of the bonnet macaque, there is a hint of pale eyelids, further accentuating the dark-rimmed stare. However, this is not as well-developed as in e.g. Macaca fascicularis.
http://cdn2.arkive.org/media/EC/ECB6F34D-BD9D-4B92-B541-8759DB6C3378/Presentation.Large/adult-bonnet-macaque-head-profile.jpg

In adults of the bonnet macaque, the facial skin remains pale enough that the dark sclera gives the eyes a dark-rimmed stare. However, the eyelids encompass the eyeballs too tightly to show as much of the sclera as in humans.
http://3.bp.blogspot.com/-_VmfAm7zeok/Uql03VQ_fUI/AAAAAAAADeM/mspxUe_fJhM/s1600/img-850+Bonnet+Macaque+Monkey.jpg

The following, of an adult female of the bonnet macaque, glancing sideways, shows clearly that the sclera is dark-pigmented, with no incidence of pale scleral exposure as seen in the infants above. Most of the sclera is presumably white (as in all mammals), but none of the white surface seems ever to be exposed in this species in adulthood, partly owing to the breadth of the pigmented ring adjacent to the iris and partly owing to the tightness of the eyelids.
http://walkthewilderness.net/wp-content/uploads/2012/05/BM+2181.jpg

Mature females of the bonnet macaque sometimes have a blush on the flesh-coloured bare skin of the face. However, this is not dark enough to cancel the effect of the dark sclera in accentuating the stare.
http://thumbs.dreamstime.com/z/bonnet-macaque-closeup-portrait-8747516.jpg 

The following shows a warning expression in mature females of the bonnet macaque. Although the face is as dark in this blushed mother as in any member of the species, the eyes still tend to stand out as dark-rimmed items in an accentuated stare, in which any paleness of the upper eyelids plays a negligible role (in contrast to M. fascicularis, in which the pale eyelids greatly accentuate the stare in conjunction with the dark sclera).
http://www.drkrishi.com/wp-content/uploads/Bonnet_Macaque-05.jpg 

The following shows an adult male of the bonnet macaque, proving that the dark sclera occurs likewise in the male, and that the male like the female has an essentially dark-rimmed accentuation of the stare on a pale face.
https://s-media-cache-ak0.pinimg.com/236x/dd/2b/90/dd2b9024d030098310ef22b3bcefac1e.jpg

The following again shows an adult male of the bonnet macaque. Please note the tightness of the eyelids, showing little of the sclera. What little is evident of the sclera is all dark-pigmented. In this view there is no noticeable pale display of the upper eyelids.
http://farm5.staticflickr.com/4153/4847724313_90d5431381.jpg

In the following self-asserting expression, an adult male of the bonnet macaque does seem to be showing pale eyelids, but the main impression remains of dark-rimmed eyes on an overall pale face.
https://theamazingworldofpsychiatry.files.wordpress.com/2011/03/mainbaringteeth.jpg

The following confirms the difference between mother and infant, w.r.t. the pigmentation of the sclera.
http://thumb1.shutterstock.com/display_pic_with_logo/304825/304825,1243282988,4/stock-photo-bonnet-macaque-nursing-in-bandipur-national-park-30886564.jpg
Ditto.
http://www.drkrishi.com/wp-content/uploads/Bonnet_Macaque-06.jpg

The following (which states bonnet macaque but could possibly be closely related toque macaque in Sri Lanka, in view of the dark ear pinnae) confirms the overall aspect of the face in the bonnet macaque: dark-rimmed eyes staring from an essentially pale face. What this photo-series does is to establish beyond doubt that in this species the pigmentation of the sclera is absent at birth, but develops early in life, remaining as the most conspicuous feature of the face, overall.
http://cdn1.arkive.org/media/45/45DD9C6A-5DFE-4887-82F2-FD88657CC478/Presentation.Large/bonnet-macaque-females-with-infants.jpg

A pattern possibly overlooked by all primatologists in the past is as follows.

The eyelids themselves, immediately adjacent to the eyeball, develop dark pigmentation at the same time (early in life), when the dark scleral pigmentation appears. If one looks closely at this photo-series, one can see this clearly in several photos. In the infant, the eyelids are flesh-coloured. However, in juveniles and adults, the lower eyelid in particular, between the eyelash line and the eyeball, shows a dark pigmentation, possibly no broader than 1 mm – but sufficient to accentuate the stare in conjunction with the dark sclera.

This is a noteworthy observation because

• I have never previously read of any mammal with a pale (flesh-coloured) face but dark-pigmentation on the edge of the eyelids, and
• in the normal stare, the eyelids marginally overlap the cornea.

The latter point means that, in the normal stare, the sclera is only visible laterally and medially to the iris, and the dorsal and ventral edges of the iris would lack accentuation were it not for the narrow dark rim provided by the eyelids themselves.

This eyelid darkening is extremely narrow but quite discernible. It is a case of natural ‘make-up’, adding to the already known paleness of the upper eyelid in various spp. of macaques.

@tonyrebelo @dejong @jeremygilmore @ludwig_muller @alexanderr @beartracker

When one thinks of baboons in even the most cursory or superficial way, something that stands out is their long muzzles (https://www.alamy.com/profile-portrait-of-baboon-papio-on-the-green-background-image150562437.html?imageid=BB6F778D-228C-44C4-945F-145C2737138D&p=100776&pn=1&searchId=7dd3a4a6119b57395b529ee64a66712f&searchtype=0 and https://www.alamy.com/chacma-baboon-papio-ursinus-adult-kruger-national-park-south-africa-image65346120.html?imageid=FD6E9040-BD80-4357-B80B-39B76FBE0943&p=642197&pn=1&searchId=7dd3a4a6119b57395b529ee64a66712f&searchtype=0 and https://www.alamy.com/stock-photo-female-yellow-baboon-papio-cynocephalus-and-young-on-a-fallen-tree-93105945.html?imageid=B2B71921-BD0B-4141-B4CF-78E6D269A6C7&p=277722&pn=1&searchId=7dd3a4a6119b57395b529ee64a66712f&searchtype=0).

Baboons (in the loose sense, including Mandrillus, https://en.wikipedia.org/wiki/Mandrillus and https://es.123rf.com/photo_5612584_an-african-male-mandrill-baboon-in-profile.html) are the only 'higher primates' with long muzzles.
 
What is the adaptive value of long muzzles in baboons?
 
One possible answer is the deployment of the extremely-developed canines, for self-defence against predators. This hardly makes sense, because

• females have unremarkable canines (http://www.skullsite.co.uk/Chacma/chacma_f_lat.htm), of little use for fighting, and
• even in males, it does not seem that the canines evolved mainly for anti-predator defence (see https://www.inaturalist.org/journal/milewski/67745-why-have-extreme-canines-evolved-in-old-world-monkeys#).

Another possible answer is for foraging.

Canids have long muzzles to facilitate biting prey, and ungulates have long muzzles to reach into foliage and to compensate for the length of the limbs, which tends to distance the mouth from the herbaceous stratum. Bears have long muzzles for both reasons.

However, there is nothing about the foraging methods of baboons that makes it adaptive to use the muzzle to reach into anything. Instead it is the hands that are used to bring food to the mouth.
 
A third possible answer is for chewing.

It is noteworthy that, unlike most other mammals with long muzzles, baboons lack a diastema (https://en.wikipedia.org/wiki/Diastema and https://www.reddit.com/r/natureismetal/comments/de8u59/the_skull_of_a_baboon_i_like_to_this_this_is_how/), the toothrows instead being continuous from front to back. So, it is possible that baboons eat food so hard or fibrous that a particularly long row of cheek-teeth is needed to chew this food sufficiently.

Baboons do indeed eat grass - a fibrous and abrasive food - to a greater extent than any other primates, and their dentition is also tough and massive enough rapidly to crack hard objects such as acacia seeds.

Perhaps a fairly satisfactory explanation emerges if one combines the chewing by both sexes with the deployment of canines by males.

However, detracting from this is the fact that the gelada (Theropithecus, https://www.flickr.com/photos/helenehoffman/45441924365) – which is the species most specialised for grazing – has a shorter, not longer, muzzle than those of baboons (including Mandrillus). Also, grazing and seed-cracking would hardly explain why the muzzle is sexually dimorphic, being noticeably longer in males than in females in baboons and Mandrillus. The two sexes, after all, have similar diets.
 
To summarise the explanation so far:
Baboons (including Mandrillus and Theropithecus) have long muzzles mainly because they rely on tough, fibrous foods, and this length is further extended in males because of the use of the canines - which is mainly intraspecific, for masculine rivalry, and includes ‘fencing’ with the canines as a mode of fighting.
 
However:
 
I have pointed out, in previous Posts (https://www.inaturalist.org/journal/milewski/67780-how-do-baboons-use-their-eyes-in-social-communication#), that baboons have hidden eyes, particularly compared with humans.

Whereas humans display the eyes in various ways (eyebrow hair, extensive exposure of the sclera, paleness of the sclera in contrast to either iris colour or skin colour, or both), baboons obscure the gaze by means of pigmentation of the sclera and shading of the orbits by superciliary ridges. Instead of displaying the eyeballs themselves, baboons display the pale upper eyelids by blinking (this can be either friendly or antagonistic depending on context).
 
The crucial observation is that, the hiding of the eyes notwithstanding, the direction of gaze is a powerful factor in social interactions in baboons.

See Fagot and Deruelle (2002, https://pubmed.ncbi.nlm.nih.gov/12136705/ and https://www.researchgate.net/publication/11244626_Perception_of_pictorial_gaze_by_baboons_Papio_papio and https://www.semanticscholar.org/paper/Perception-of-pictorial-eye-gaze-by-baboons-(Papio-Fagot-Deruelle/4d76d913856a9c7504a07213d246e335e0eca6d1).

Baboons are extremely sensitive to being gazed at directly, and take this as a sign of aggression. The eyes seem to be adapted to be inconspicuous (apart from the displaying of the closed eyelids). And a feature of baboons is that they remain extremely observant of each other as individuals, without looking at each other directly; they have extremely attentive peripheral vision and manage to observe each other directly by means of furtive and fleeting glances rather than outright staring.

For baboons it is crucial to keep an eye on each other socially while not looking at each other directly as we humans normally do. Baboons want the information but direct gazing is taken as offensive.
 
Hans Kummer (https://de.wikipedia.org/wiki/Hans_Kummer) relates his own experience, which is fascinating in the insight it gives into the psychology of baboons.

Kummer was studying the hamadryas baboon (Papio hamadryas, https://en.wikipedia.org/wiki/Hamadryas_baboon) in remote Ethiopia, by sitting right in among the habituated animals. He was sometimes at risk of being attacked by mature males as the result of some misunderstanding in which he became accidentally implicated in some social faux pas. What he observed was that if one pretended not to notice the angry stare of the mature male individual in question, and its fang-baring, eyelid-flashing yawns, and just looked somewhere else in a relaxed way while busying oneself normally, this would invariably ‘switch off’ the aggression. The masculine anger of the hamadryas baboon would be thus appeased.

The psychology of baboons seems odd to us, because honesty is punished. The fact that Kummer’s ignorance/naivety was completely a pretence was obviously far less provocative to the angry baboon that it would have been for Kummer simply to look back in a questioning and friendly way in a peacemaking attempt - which would have provoked attack. Baboons value feigned innocence more than they value honest and empathetic interaction, and the biology of the eyes reflects this amoral value-system (see https://www.inaturalist.org/journal/milewski/67769-is-it-baboons-rather-than-chimps-that-really-epitomise-machiavellian-intelligence#).
 
This is where the long muzzle may matter.

It occurs to me that the sheer length of the muzzle gives this part of the face considerable value as a pointer to the direction of gaze. All that one individual has to do to see where the other is looking is to glance quickly sideways at how its whole face is oriented, something that is so obvious from its long muzzle that the information can be gleaned even by peripheral vision. So, in a sense we can see that the long muzzle of baboons goes with, i.e. is consistent with, the hiding of the eyeballs by means of dark sclera and shading by the ridge between forehead and orbits.

No baboon wants to look much at the eyes of its kind, because this is usually a fearful experience. However, every baboon wants to know where important individuals are looking, because the mind of baboons is acutely and continually tuned in to keeping track of everyone’s status, via watching and analysing the interactions of every individual in its group.
 
So, is it possible that, in a strange way, the social complexity of baboons goes with their facial shape in profile? The muzzles are, at least in part and at least as a corollary function, pointers to gaze. This is part of the sly indirectness with which baboons juggle/balance the use of gaze as a clue to attention, and the use of gaze as a ‘weapon’.
 
It may be hard for a human to consider this, because our minds work differently.

We do have an element of ‘what are you staring at, asshole’ about us when it comes to strangers. However, by and large – at least among those we know and more or less trust - we value and respect an honest and direct gaze according to our basic value of exchange of technical information, explanation, and emotional candour as part of an empathetic mindset in which honesty is rewarded rather than punished. In us, the ambivalence of the direct gaze is heavily weighted towards valuing this as ‘honest’, ‘good’, and ‘moral’, with the aggressive aspect as a minor part, whereas it is the other way around in baboons.

Hence, I suggest that the extremely projecting muzzle of baboons and flatter-than-flat face of the modern human go together with the differences in the eyes (as well as the specialisation of the dentition, explained above).
 
Supporting the idea presented above is the dual difference between macaques (Macaca, https://en.wikipedia.org/wiki/Macaque) and baboons.

Macaques have showier eyeballs than do baboons (https://www.agefotostock.com/age/en/details-photo/crab-eating-macaque-macaca-fascicularis-adult-close-up-of-head-bong-rong-thailand/FHR-10780-00090-225 and https://primarilyprimates.org/product/bojangles/ and https://www.alamy.com/northern-pig-tailed-macaque-macaca-leolina-portrait-thailand-image184170264.html?imageid=FC800E71-9171-4CFF-B152-62096081E12F&p=704031&pn=1&searchId=2700b3bec091286c405053774f940af6&searchtype=0 and https://www.alamy.com/pigtail-macaque-macaca-nemestrina-portrait-image255394909.html?imageid=7CD77AF8-BA2A-49A9-9F7E-77E3785A9C7D&p=851480&pn=1&searchId=2700b3bec091286c405053774f940af6&searchtype=0 and https://www.alamy.com/pigtail-macaque-macaca-nemestrina-male-thailand-image255233008.html?imageid=41FEBB2C-40FA-4579-B4BC-B10FD1EE212E&p=853403&pn=1&searchId=2700b3bec091286c405053774f940af6&searchtype=0 and https://www.alamy.com/southern-or-sunda-pig-tailed-macaque-macaca-nemestrina-female-portrait-wild-but-used-to-being-fed-by-local-people-gunung-leuser-national-park-sumatra-indonesia-image263193550.html?imageid=76257C35-D2A5-45F0-806B-20CB5E97C633&p=215387&pn=1&searchId=2700b3bec091286c405053774f940af6&searchtype=0), depending on the species.

Furthermore, the eyes are not as shaded by the superciliary ridges as is the case in baboons.

Accordingly, no macaque has a muzzle as long as that of any baboon. Even the superficially baboon-like macaques of Sulawesi have ventrally elongated faces rather than horizontally elongated faces (https://www.dreamstime.com/beautiful-celebes-crested-macaque-macaca-nigra-aka-black-ape-old-world-monkey-tangkoko-nature-reserve-indonesian-image171038437 and https://www.jungledragon.com/specie/1489/celebes_crested_macaque.html and https://www.alamy.com/stock-photo-close-up-side-profile-of-a-captive-sulawesi-crested-macaque-macaca-74752550.html).

So, if one looks at the whole group of baboons and macaques, it does seem that long horizontally-oriented muzzles correlate with ‘hidden eyes’ (except for the pale upper eyelids, which occur in both baboons https://www.alamy.com/stock-photo-yawning-olive-baboon-in-akagera-national-park-rwanda-africa-82189781.html?imageid=E228F186-753D-41B7-ACA8-E7E3260EC65B&p=12354&pn=1&searchId=a8dcfe1380fa4b839f6fc3ec2e5d9cee&searchtype=0 and macaques https://www.alamy.com/a-macaque-monkey-licking-its-fingers-whilst-feeding-his-closed-eyes-show-the-white-eyelids-which-look-as-though-the-monkey-is-wearing-eye-shadow-image369197643.html).

(writing in progress)
 
Several genera of coniferous plants are foliar-spinescent, such as

• Juniperus (https://www.inaturalist.org/observations?place_id=any&taxon_id=47574&view=species),
• Picea (https://www.inaturalist.org/observations?place_id=any&taxon_id=63573&view=species),
• Podocarpus (https://www.inaturalist.org/observations?place_id=any&taxon_id=85284&view=species), and
• Araucaria (https://www.inaturalist.org/observations?taxon_id=53718).

In most of the foliar-spinescent spp., only the ‘juvenile’ (including recrudescent) foliage is spinescent.
 
Juniperus communis (https://www.inaturalist.org/taxa/58725-Juniperus-communis and https://www.conifers.org/cu/Juniperus_communis.php) is a particularly strong example of foliar spinescence in conifers because

• it is extremely widespread, being described as the most widespread sp. of woody plant on Earth,
• it never attains adult/mature foliage even when it reaches its maximum height of up to 16 m, and
• the spinescent leaves can be conspicuous in a way that suggests aposematic colouration (warning colouration) directed at large herbivores.

Please see https://en.wikipedia.org/wiki/Juniperus_communis .
 
In North America and Eurasia alike, J. communis inhabits mainly the boreal ecosystem (https://en.wikipedia.org/wiki/Boreal_ecosystem), which is the biome of coniferous forest on permafrost. It ranges right up to the Arctic Circle (https://en.wikipedia.org/wiki/Arctic_Circle), where trees give way to tundra (https://en.wikipedia.org/wiki/Tundra#) and J. communis itself adopts a nearly prostrate growth-form contrasting with the nearly cypress-like shape adopted in milder climates.

In Europe it extends into the mediterranean climate (reaching as far south as Greece, Sicily, and southern Spain) to a degree not seen in North America. Juniperus communis does occur in California, but only in small areas of the Sierra Nevada (https://en.wikipedia.org/wiki/Sierra_Nevada), a mountain range too high to conform strictly with the mediterranean-type climate.
 
In several photos of J. communis, the leaves appear conspicuously pale, which has puzzled me. The pale surface seems to be on the underside (ventral surface) of the leaf, which is flanked by the rolled-under, green margins of the leaf (https://www.arbolapp.es/en/species/info/juniperus-communis/).

It is not odd for semi-sclerophyllous small-leafed plants in mediterranean-type climates to have leaves with rolled edges, or pale-coloured undersides, features which are usually explained in terms of drought-tolerance and protection of the stomata in the interests of conserving water in transpiration.

However, what is odd is that in several photos the pale surface seems to be uppermost on many of the leaves, indicating that the leaves have been twisted somewhat at the petiole, turning them in a sense ‘upside down’ (https://es.123rf.com/photo_109513477_leaves-of-juniper-juniperus-communis.html and https://www.agefotostock.com/age/en/details-photo/common-juniper-ground-juniper-juniperus-communis-twig-with-leaves-germany/BWI-BS331761).

Since the leaves are prickly (https://en.wikipedia.org/wiki/Juniper#/media/File:Juniper_needles.jpg and https://www.alamy.com/stock-photo-common-juniper-juniperus-communis-with-ripe-and-unripe-berry-shaped-85995011.html?imageid=10BCA4F5-A69F-4DC6-A1F3-6D12670DF40C&p=245512&pn=1&searchId=3cbf2f655c2f750afbd620385a909f13&searchtype=0), it is tempting to think that this sort of display of dark/pale contrast (in which the leaves look like pale needles against a dark background) is a form of warning colouration to browsing herbivores, such as deer, which would forage on the plants.
 
The following (https://en.wikipedia.org/wiki/Juniperus_communis#/media/File:Juniperus_communis_range_map.png) illustrates the distribution of J. communis. The species spans Eurasia and North America above certain latitudes and altitudes.

Nowhere does this species reach the latitudes of kwongan (https://en.wikipedia.org/wiki/Kwongan) in Australia, which (except possibly for Tasmania, https://en.wikipedia.org/wiki/Tasmania) is warmer in winter than any habitat of J. communis.
 
The following shows that J. communis can attain a growth-form similar to that of a typical cypress (https://www.botanikfoto.com/en/details/image-photo-common-juniper-juniperus-communis-558123.php and https://3dbaza.com/juniperus-communis-11832m-109413). However, as I understand it the species retains its ‘juvenile’, spinescent foliage even when its crown attains this mature form, above the height of even the moose (Alces alces, https://en.wikipedia.org/wiki/Moose).

The following shows the nearly prostrate growth-form of J. communis in cold and windy climates, at high latitudes and/or altitudes. I do not know if the leaves are more spinescent in this growth-form than in that shown above.

The following shows J. communis in vegetation otherwise dominated by the erica Calluna vulgaris (https://en.wikipedia.org/wiki/Calluna). This sort of vegetation is a ‘heathland’ comparable with kwongan although growing in a colder climate and being far simpler floristically.
 
The following again shows the coexistence of J. communis with a heathy stratum, the conifer adopting a cypress-like growth-form but apparently retaining ‘pungent’-tipped leaves right to the top of its crown, which in this instance I estimate to be perhaps 5 m high.
 
The following two photos show J. communis in a shrubby growth-form: https://www.alamy.com/stock-photo-alpine-juniper-juniperus-communis-var-alpina-growing-between-rocks-17413802.html?imageid=E624C926-9F6D-42A2-8421-A12BACDF0937&p=56319&pn=1&searchId=3cbf2f655c2f750afbd620385a909f13&searchtype=0 and https://www.alamy.com/stock-photo-common-juniper-juniperus-communis-26690581.html?imageid=5F691C5D-D99D-41C2-B403-7F0E17A20D27&p=9998&pn=1&searchId=3cbf2f655c2f750afbd620385a909f13&searchtype=0.

The following three photos show the conspicuous paleness of the ‘ventral’ surfaces of the spinescent leaves, which are here for some reason turned upwards instead of being invisible in ventral orientation as expected. I suggest that this functions as warning colouration.

(writing in progress)

(writing in progress)
 
I have chosen the photos below, to illustrate the patterns in one species, the olive baboon (Papio anubis, https://www.alamy.com/baboon-watching-people-image212685725.html?imageid=B20E51A4-A813-4CB9-BC93-DCDA260BFDDD&p=712118&pn=2&searchId=f18f8dbc0aebad12c7e209bc20f334f0&searchtype=0 and https://www.alamy.com/a-chilling-baboon-image350846739.html?imageid=AE8F3A6D-1B5E-480F-A74B-83981A861C35&p=1853940&pn=3&searchId=dba7984e064df383c40987807c76a568&searchtype=0). The chacma baboon (P. ursinus), not shown here, is similar.
 
Baboons differ from humans in that they generally hide their eye movements.

Humans reveal our direction of gaze, and we can read these movements by virtue of the shifting proportions of dark and pale in an eyeball exposing the whitish sclera. The system is different in baboons, which do use their eyes to communicate, but in a crude way and mainly by means of the closed eyelids, something missing in the repertoire of humans.

Humans read another’s intentions with great subtlety by means of eye movements. Baboons are morphologically adapted not to do so. Humans share information by means of their eyes; baboons withhold information by means of their eyes.
 
Baboons differ from macaques (Macaca spp.), which do accentuate the gaze by means of scleral tone, albeit in a simper way than in humans and only for restricted messages.

Although baboons and macaques are convergent in that both include the most terrestrial of monkeys on their continents, they are not convergent in the use of their eyes for social communication. Baboons have specialised on eye-hiding while macaques have specialised on eye-display (with more variation within the genus Macaca than within Papio/Theropithecus/Mandrillus.
 
From a human point of view, the eyes of baboons seem inscrutable/obscure/beady/shadowed. In another Post, I show photos of Papio hamadryas (which has flesh-coloured facial skin) and Theropithecus gelada (which has an extraordinary lip-flipping display). Although the various genera and species of baboons differ greatly in various ways, they all seem to have the same approach to the display of the eyes: all hide their eye movements as much as possible, presumably to avoid divulging their intentions.
 
Please follow the captions below, which use selected photos to convey the limited complexity in the appearance of the eyes in adults and juveniles (but not infants) of the olive baboon.
  
The following photo is unusual in showing the irides brightly against the dark facial skin. Usually the eyes are harder to see than this. And even in this view, please note the lack of any visible sclera, the part of the eyeball that is so conspicuously whitish in all humans, including black-skinned human races.
 
http://cache3.asset-cache.net/gc/155378445-olive-baboon-portrait-gettyimages.jpg?v=1&c=IWSAsset&k=2&d=gWJ5WdTxAB0bFWiV4aXd79b0rX7ThH1KkEZoWhetq9tRsbdrR9mfG4ExaquHePV4

The following close-up of the eyes shows that the sclera of the olive baboon is actually dark-pigmented, more or less matching the darkness of the facial skin. This effectively hides eye movements by reducing tonal contrast. The same is true for chimpanzees and gorillas.
 
http://4.bp.blogspot.com/-qxckP2088-c/UR5aD_wfQgI/AAAAAAAAHP0/BgKHWu58EOk/s1600/vision_Olive_Baboon_Papio_anubis_in_Tanzania_4426_cropped_Nevit.jpg

The following again shows that the sclera is dark in the olive baboon, where it would be pale in all humans. Although the direction in which this individual is looking is clear in such close-up, well-illuminated view, in normal views it would be hard for one baboon to see exactly where another is looking.
 
https://c2.staticflickr.com/4/3473/3699887696_eb8e81e50e_b.jpg
 
The following photo shows that, although the irides are somewhat brighter-hued than the facial skin, the tone (in terms of dark vs pale) is similar to the facial skin, and in the absence of exposure of a white sclera the whole eye is rather hidden.
 
http://thumb9.shutterstock.com/display_pic_with_logo/2235800/216456676/stock-photo-olive-baboon-portrait-in-ethiopia-216456676.jpg
 
The following photo shows that, although the upper eyelids are pale (grey) in the olive baboon, this is not obvious when this surface is shaded, which it tends to be owing to the brow-ridges.
 
http://www.macleans.ca/wp-content/uploads/2013/04/Anup-Shah-baboon.png
 
The following photo shows that the upper eyelids are rather pale in the olive baboon, but this is not normally conspicuous (in contrast to e.g. the long-tailed macaque Macaca fascicularis).
 
http://hayleyanderson.com/wp-content/uploads/galleries/post-107/full/Baboon%20Face%20W.jpg

The following photo shows that in intraspecific confrontation the olive baboon does not stare, but instead partly closes the eyes, signalling by means of its pale upper eyelids. Although this is common among monkey spp., baboons have reduced the repertoire of eye displays to this display alone, which is a crude system of signalling.
 
http://cache2.asset-cache.net/gc/183746488-olive-baboons-fighting-ngorongoro-gettyimages.jpg?v=1&c=IWSAsset&k=2&d=E71v4mODx8JEapRLnb%2FZh2WFl7c%2FrsUUbOG3yw7MX6w%3D

The following photo is revealing because it shows that the olive baboon can do something with its brows beyond what humans can do: it can contract the brows far back above the eyes, stretching the pale upper eyelids to the point that they actually cover the brow-ridges, greatly expanding the pale flash. This was even more spectacularly illustrated in my email on the gelada Theropithecus, which really goes in for this ‘pale eyebrow’ display in conjunction with lip-flipping. Spectacular but still a relatively crude signal.
 
http://cdn1.arkive.org/media/48/48D6B615-D8D2-415E-94D1-313E2AD8D418/Presentation.Large/Juvenile-olive-baboons-play-fighting.jpg

The following photo shows that the pale of the upper eyelids is not normally displayed when the animal raises its eyes to survey the sky or the treetops.
 
http://cache4.asset-cache.net/gc/149714078-olive-baboon-juvenile-head-and-shoulders-gettyimages.jpg?v=1&c=IWSAsset&k=2&d=YSLw6ZY9l3VDeSrm9bfKj%2Badk9QXy3Fk7IAY3OEmiH4%3D

The following photo shows that the passive-aggressive fang-baring display by males of the olive baboon involves shutting the eyes to show the pale upper eyelids. This is, in a sense, a ‘false-stare’, but the meaning it conveys is simple and crude.
 
http://www.sciencephoto.com/image/384927/350wm/Z9100134-Yawning_olive_baboon-SPL.jpg
 
The following photo shows that the pale upper eyelids in the olive baboon are found in all age/sex classes beyond infancy.
 https://www.alamy.com/stock-photo-yawning-olive-baboon-in-akagera-national-park-rwanda-africa-82189781.html?imageid=E228F186-753D-41B7-ACA8-E7E3260EC65B&p=12354&pn=1&searchId=a8dcfe1380fa4b839f6fc3ec2e5d9cee&searchtype=0 and https://www.alamy.com/stock-photo-olive-baboon-starting-to-yawn-in-akagera-national-park-rwanda-africa-82189777.html?imageid=0295F0EA-C30A-4BFF-8F6F-FBE0DDF1B3F9&p=12354&pn=1&searchId=a8dcfe1380fa4b839f6fc3ec2e5d9cee&searchtype=0 and https://www.alamy.com/stock-photo-olive-or-anubis-baboon-papio-anubis-female-asleep-ghana-west-africa-80393791.html?imageid=CDD78B55-F006-403A-B055-61FC710A095B&p=77483&pn=3&searchId=dba7984e064df383c40987807c76a568&searchtype=0

The following photo of the olive baboon in Uganda shows unusually extensive pale upper eyelids. This is perhaps a geographical variation? However, once again the shading by the brow-ridges ensures that the pale is not conspicuous unless the eyes are closed.
 
http://www.sareptiles.co.za/gallery/albums/userpics/14135/Papio_cyanocephalus_anubis_-Olive_Baboon(2).jpg

The following photo shows once again that the visible part of the sclera, in a sideways glance, is dark enough in its pigmentation to hide the direction of gaze. This is not true in various spp. of Macaca, in which there is a panel of whitish that accentuates a sideways glance/gaze.
 
http://www.greenscreenanimals.com/large_stills/baboon_still_MG_0405.JPG
 
The following photo, and its enlargement, show how even an extreme sideways glance is hidden in the olive baboon where it would be obvious in humans and certain species of macaques. This is because of the pigmentation of the sclera adjacent to the iris. Chimpanzees and gorillas show the same pattern. At any distance, an observer cannot easily see the direction of movement of the eyes.
 
http://upload.wikimedia.org/wikipedia/commons/f/fc/Papio_anubis_(Serengeti,_2009).jpg
 
The following photo shows that, in some individuals of the olive baboon, there is a macaque-like exposure of a pale surface of the sclera. This is exceptional in the olive baboon although normal in some spp. of macaques.
 
http://thumb1.shutterstock.com/display_pic_with_logo/893566/144975304/stock-photo-a-baby-olive-baboon-and-his-mother-papio-anubis-in-gombe-stream-game-reserve-tanzania-144975304.jpg

The following ‘toddler’ of the olive baboon still has its unpigmented sclera (as at birth), because the scleral pigmentation sets in only when the distinctively infantile black-and-pink colouration of the face is lost.
 
http://i.dailymail.co.uk/i/pix/2012/09/07/article-2199741-14E1FBBA000005DC-944_634x470.jpg

The eyelid/brow is also used in courtship – in chacmas at least - where males and females use rapid blinking in the direction of a potential mate.

(writing in progress)