Keeping on your toes (Frustrating Feet III)

 My last post was placed here on 16 December, and it is already almost March. The reason for that delay is that I had to get The Book ready for the publisher. And I did! The files have now all been sent off, neatly categorised by chapter and number. My wife and I proofread the text of over 60,000 words once more. I also went over all full-page illustrations again, as the page format was broader than I had originally used (there will probably be close to 200 illustrations in total). Luckily, digital paintings allows many ways to alter illustrations, and I only had to paint new parts of paintings a few times.

Right! Back to posting. Feet again this time. Let’s focus on toes.  

Why have toes at all? As discussed in the first post on feet, some animals get away without any toes at all (crabs) and others have just one toe per foot (horses). Feet, rather obviously, contact the ground. For small animals ‘contact’ may primarily mean the ability to actively adhere to the substrate, also discussed in the first foot post. For large walking animals, gravity will ensure that the contact surface is pressed against the ground.

That contact surface can be relatively small and hard, such as a hoof, and such small contact surfaces work best when the substrate is hard, so the foot will not sink into it. In contrast, the contact surface will need to be large if there is a risk of sinking into soft soil. There are two ways to enlarge the surface area.

Click to enlarge: source here

‘Elephant feet’
The first variant is a foot with embedded toes, ensheathed to form a sort of club foot ending in one large flat round surface, such as the soles of elephant or sauropod feet. In elephant and sauropod feet the toes are bundled up to form a kind of cone, broad side down. Such a structure is useful to spread weight through the toes across the shared sole.

T.rex foot; click to enlarge; source here

‘Bird feet’
The other variant consists of long independently mobile toes, such as ostriches and theropods have (I know, birds are dinosaurs). I will approach the question of whether independent toes are useful for two circumstances: dealing with uneven terrain and walking.

Which variant is best under which circumstances is not something I have been able to find in the literature, so, as always, students of speculative biomechanics find themselves on an insecure footing (sorry for that one). As an aside, perhaps courses on biomechanics should use speculative biology as a teaching tool: it forces students to ask questions that normal biology, dealing with observable facts, regards as givens.

Conforming to uneven ground; Click to enlarge; copyright Gert van Dijk

Dealing with uneven terrain
If that elephant foot with a large continuous foot surface is stiff and does not deform easily, placing one side of the foot on an elevation such as a stone will create a large bending moment. That can be solved by providing the ankle joint with some leeway to turn in all directions: the foot will rotate a bit relative to the leg until both sides of the foot will contact the ground. Mind you, that ankle motion must be tightly controlled, or else the ankle joint may move too far and is hurt (that's how you sprain an ankle).

In variant two, with independently movable toes, the ankle joint does not have to do anything as the solution then lies in the toes themselves. If such a foot is placed on uneven terrain, each toe can move until it contacts the ground. In reality, you can have a combination of the two designs

The two variants, one with big round feet and one with splayed independent toes, seem to be linked to lifestyle: sauropods, with big plodding feet, were immense, slow, and herbivorous while theropods were smaller (still large!), fast, and carnivorous. The dinosaur example has the advantage that the two groups have a shared ancestry, so the answer cannot lie in a different starting point. There must be a functional reason, and that is why I summed up size, speed and feeding method. The feeding method is probably not crucial, but lifestyle is, in the sense that an agile animal must have legs and feet to allow agility. Agility hare can be defined as meaning not only speed, but also the ability to turn, accelerate, absorb hard landings, get a grip, etc. I think that independent toes provide more agility than toes that are encased in a common sheath. My reason to think so is that animals with large round feet also had vertical leg bones, while those with independent toes tend to have leg bones that are slanted with respect to the vertical. Such ‘crouching’ postures require much energy just to stand still but allow jumping and hard landings.     

The image above overlays an elephant with T. rex at the same scale. Notice how the legs of T. rex are slanted while the elephant has vertical legs.     

Additional toe propulsion; click to enlarge; copyright Gert van Dijk

Walking
Elephants and brontosaurs on one side, and ostriches and T. rex on the other side. Both types of animals walk well, so one is not necessarily superior to the other. But we can speculate about consequences of foot designs.

There is probably one more factor of interest here, one that has to do with the direction of toes relative to the direction of walking. Toes usually point forward, or a bit to the side as well as forward. Is that a given? On Earth, very few animals have toes that point backwards. Some walking birds, such as roadrunners, have backwards toes, but you can argue that these legs are there only because they fit the Bauplan of animals that have to grasp branches or need to hold on to tree trunks, for which backwards-pointing toes are useful.  

A good reason to have forward-pointing toes is that they contribute to walking, by moving backwards relative to the ankle. The main propulsive force of the leg of an ostrich or a T-rex must come from movement in the hip, knee and ankle joints. But moving the toes backwards will still add force. The situation is similar to throwing a tennis ball: you can grip it in your fist but also with the tips of your fingers. To throw it far, the main acceleration will come from simultaneous extension of the shoulder, elbow and wrist joints, but if you hold the ball with your fingers, straightening your fingers will add a bit of acceleration. Not much, but worthwhile.

The image above aims to show that: the blue triangle shows where the heel/ankle touches the ground, and the red triangle where the tip of the toe touches the ground. By rotating the toe backwards the animal effectively gains that additional distance each step.  

The toes of T-rex probably also added a bit of acceleration by moving back in unison with the other leg joints. In contrast, the toes of elephants and brontosaurs probably hardly moved at all compared to their ankle joints. Does that put these clubfooted animals at a speed disadvantage? Yes, it does, but that toe assembly is part of a large set of traits that together illustrate that the animal is designed for weight carrying at the price of agility.

In summary, independently movable toes offer more agility and add propulsive force, which is why they may be tied to a more active lifestyle.

Barlowe's rayback; click to enlarge; copyright W Barlowe

Consequences for speculative biology
You probably know Barlowe's Expedition book. I always admired his paintings skills, but at the same time I also always felt that he often gave too much weight to 'alienness' , disregarding biological likelihood. In the past, I discussed why I though a planet filled with blind animals would be very unlikely (Here; the short answer is that vision seems to evolve very readily). Something I hadn't mentioned yet is that I always felt it odd that his very large agile bipeds had feet like those of elephants. I had an inkling that such feet did not fit such a lifestyle. I still cannot prove that, but at least I can now provide some reasoning rather than just a feeling.

Rusp toes; clich to enlarge; copyright Gert van Dijk

A second consequence is how toes should be placed on alien feet. As you may know, Furahan hexapods have jointed legs with three large segments and a few smaller segments at he end. There are there to provide that extra acceleration in running animals.  You will also find that rusps have two toes, or rather nails, at the side of their feet. These do not help with acceleration; rusps are fairly slow and do not benefit from a little bit of additional acceleration. As they have many feet, the surface of each does not have to be large. The bottom of the feet amounts to a horizontal strip, with nails digging in at either end. Rusps like a solid grip!        

From erect dinosaurs to pivoting fly feet (Frustrating feet 2)

This post is long, fairly complicated and rambles along a bit, so do not say I did not warn you. We are so used to seeing big mammals that most ‘alien’ legs in drawings and films are just mammal legs. One thing you will find in many books is that a key feature of mammal locomotion is that the legs are 'erect'. 

 

Click to enlarge. From Box 4.3 in: Fastovsky & Weishampel. Dinosurs A concise natural history. Fourth Edition Cambridge University Press 2021

 

The image above shows such a scheme, making the point that dinosaurs legs are as erect as mammal legs, using a human as an example. I have always felt that the legs of the dinosaur in the picture are not really 'erect', while the human's leg both are less erect than they usually are in a standing human. 

Click to enlarge; copyright Gert van Dijk

Let's explore this further. Above, you see the species Disniformis inexpectus and on the left its cousin, D. expectus. The elbows and knees of D. inexpectus stick out sideways, while those of D. expectus do not. Which animal stands in the most energy-efficient way, and which is the most 'erect'?

 <pause to think>

Many readers may feel that D. expectus wins on both accounts. But have a closer look: in both animals the feet are placed precisely underneath the hips, and the leg segments are tilted in opposite directions as you move down. Because the joints are angled, energy has to be spent to keep these joints from bending further under the influence of gravity. How much energy depends on the angle of the joints and how far these joints are situated from the vertical line connecting hips and feet. Guess what: the legs and joints angles are exactly the same. The legs were just rotated, except for the feet, so exactly the same amount of energy is needed to keep the joints stable.

Personally, I would call a leg fully 'erect' only if the segments are all vertical, as they largely are in standing elephants (and standing people!). If all segments are fully erect, the feet must end up directly underneath the hips. In the dinosaurs and both species of Disniformis, the feet are also placed directly underneath the hips, and it seems some authors use the word 'erect' to mean only that aspect. The opposite of 'feet underneath hips' (FUH) must be 'feet away from hips' (FAFH). If the feet are placed well to the side of the animal, you get a sprawling stance, like salamanders and insects use.         

Perhaps you feel that all this changes when the species start to walk, and then we will see that D. inexpectus can only plod along while D. expectus trots elegantly out of sight. Not so! The legs of both species can extend to the same length and the joints move through the same arcs. This means that  elbows and knees can be kept close to the centre of the animal regardless of whether they deviate to the inside, outside, back or front.

 

Click to enlarge; copyright Gert van Dijk

Still, D. expectus will have a gait advantage in that its joints can be designed much simpler than in D. inexpectus. The dinosaur drawing and the reworked D. expectus above show simple hinge joints that allow the legs to move only in a fore-and-aft direction. That save energy; nice, right?

It would be nice if animals were like trains, only moving along predefined linear tracks. But they also need to turn and to step sideways and do other things beside walking in a straight line. An animal must be able to move its feet fore and aft, but also to the side, and must also be able to turn toes in or out. This requires rotation along all three axes. You can be creative and appoint different movements to different joints, but iff you wish to obtain the largest reach for the foot, you should give the hip joint the most freedom. That is probably the reason mammal hips have ball joints (and dinosaur hips too, as far as I know). My guess is that the most proximal joints (hips/shoulders) in alien animals will also have three axes of rotation. Mind you, the three axes do not have to be used to the same degree in daily life (fore-aft movements will see more use than toe in/out movement).

The ankle joint should allow the foot to adapt to uneven ground, so the joint must allow a toe up/down rotation and also a thumb up/down rotation. That is two axes already; we will get back to the third axis. This leaves joints in between, and these need only have one direction of rotation, like mammal knees (that need not be universal though and is probably something for another post).

 

Click to enlarge; copyright Gert van Dijk

We are now getting to something that has vexed me for years. Above is an image from a post from 2010, showing D. salamandris. This is what I wrote at the time: "To get a movement suitable for walking, its foot should move in a straight line from front to aft … But ensuring that the foot always points forwards also requires that there is a way to rotate some of the bones around a longitudinal axis."

It is the need for that third rotational movement in animals with FAFH ('sprawling') legs that vexes me. Humans are very good at this movement, called pronation and supination (if you hold your arm in front of you, turning the palm down is pronation and turning it up is supination). But I couldn’t find good discussions on this type of movement in the prototypical sprawlers: arthropods. If readers know about such studies, please let me know.

I looked at some internet videos of walking insects to see whether their feet remained fixed to the surface while the leg rotated; if so, these insects had pro- and supination. I would expect the tarsus to allow that movement, even though the text I found previously said that the tarsus only allowed flexion and extension. If the foot would rotate along with the leg, it would pivot over the ground, something hardly compatible with a firm grip.

There weren't that many videos that allowed such close scrutiny, but here is one, showing a fly walking across glass. The foot stays in largely the same position and does not rotate along with the leg. To allow it to that while the hip is moving forward, something has to 'bend'. The tarsus indeed seems to bend a bit, but not much. In fact, the tarsus keeps on pointing in the same direction all the time. 

 

Click to enlarge; copyright Gert van Dijk

I thought of a possible explanation, and it involves a different kind of hip movement. Above are two spidrids. The first has a typical vertical axis of rotation through the hip; that's a normal spidrid. The rest of the leg lies in a plane, and the movement is shown by two 'ghost legs' (this is typically how crabs move). The second image has another hip, with the axis horizontal. The animal can still reach fore and aft, but the results looks different.

 

Here is what the differences amount in an animated view: first a typical spidrid movement with a vertical axis. The gray structures indicate the planes in which the legs move.

 

And now a Neospidrid with a horizontal axis (the model caters for intermediate angles too).

An thay means we can get back to flies; in a textbook of arthropod anatomy (Manton 1977) I found indications that insects hips have an added 'rocking' movement that would indeed allow some rotation around a horizontal axis. But there's a rub. With such an axis, you still need pro- and supination to keep the insect's 'palm' against the surface. I still do not know how insects solve the need for this longitudinal foot movements. Crabs are probably easier, as they have no feet in the common sense, so they can just pivot on the tips of their legs. 

I confess that designing alien animals is sometimes easier than studying Earth animals. In particular when it comes to feet!                    

 

 

'The Book' has found a publisher!

Just a short update on the progress of The Book. 

When I discussed this subject matter last, in my August post, I wrote that I was making some progress with getting acceptable colours from Amazon's self-publishing programme. My conclusion at present is that printed lighter colours are quite reasonable, but that dark portions come out dull and lack detail. It turned out that I included more dark portions in my paintings than I was aware of, so many paintings became disappointingly lacklustre. Light colours were much closer to what I had in mind. I also saw some self-published Amazon books that I liked, but I was never really satisfied with how my own paintings looked. I therefore decided that I would try to find a suitable publishing company again. I therefore sent off a proposal, along with synopsis and sample images, as requested. 

Well, I am happy to say that I have signed a contract with a UK publisher! 

I will not say much more now but can add that books from this publisher are readily available internationally, including through firms such as Amazon. I can also add that the actual production of a book takes a lot of time, so the projected publishing date is the third quarter of 2025. 

I know, it’s a long wait, but it's not as long as it has taken me to produce The Book. Should you ever wish to produce a book yourself, my advice is to just write a text and NOT add over 180 illustrations. Anyway, I aim to produce two more posts about feet in this blog in 2024 (one, certainly); that should help a bit!

Feet are frustrating! (Feet I)

A long time ago, I promised I would write about feet or toes, but it took ages to find my footing (sorry). Why? Well, animal feet proved to be very complex. My first associations included shock absorption, weight distribution, pivoting, friction, toes or no toes, walking upside down on the ceiling, walking on water, feet as attack weapons or digging instruments, etc. All that did not immediately suggest one simple theme. Moreover, this blog is about speculative biology, but as Wikipedia has no entry 'Feet across the universe', I found myself in uncharted territory, once more. Other speculative biology projects do not help much either: there is the usual tendency to copy Earth's vertebrate or arthropod legs. I think I will have to write more than one post on foot design' because the subject is too large. I must warn you that the result may be quite speculative.

I thought to start with foot anatomy of various Earth animals, reasoning that a comparison of independently evolved foot designs should help detect universal foot design elements, if there are any. The first rule I thought of (I was making up these rules as I went along) was to limit the discussion to walking on land, so I would not have study specialisations for walking on ceilings or climbing vertical walls. I will disregard microscopic and very small animals and will not discuss walking with tentacles (it's been done; start here and search the blog for tentacles). Wikipedia says that eleven animal phyla invaded the land, but omitting legless animals and overly small groups left only vertebrates and arthropods.

To start with vertebrates, various fish lineages crawl onto land, but as they haven't become completely terrestrial, they did not count. Tetrapod vertebrates are monophyletic as far as I can tell, so they all count as having one basic foot design anyway.

As for arthropods, at least six groups seem to have left the water on their own: arachnids, insects, myriapods, woodlice, some sandhoppers and crabs. However, if some or all of these had a common aquatic ancestor with fully formed legs, shouldn't they count as one design? Then again, these animal groups had a very long time to evolve different feet, so perhaps they should all count? In the end, I selected arachnid, insect and crab legs to add to vertebrate legs, giving me four largely independent foot designs to talk about. I had a look at robot feet too as a possible source of designs.  

Scheme of tetrapod limbs. The point is that the hand or foot ('autopod') consists of a number of parallel radiating elemets: fingers or toes. From Young et al 

Tetrapod feet
The basic tetrapod foot or hand has five radiating toes. Early tetrapods may have had more toes, which  did not necessarily all have to radiate from the same spot. Instead, they may have radiated sequentially, meaning one toe at a time branched off if you moved along the leg in the direction of its end. (see here how that 'Devonian pattern' shaped the feet of Furahan Scalates/Hexapods). During evolution, some toes became completely separated, such as those of predatory dinosaurs and birds, while others are encased in a common hull, such as those of elephants and sauropods. Some animals developed additional pseudotoes (panda's and elephants), while horses reduced the toes to just one. In many walking tetrapods the toes all point forwards and make a front-to-back excursion while walking, but I am not yet certain whether that should be a Foot Law or not, so a future post will ask whether backward-pointing toes or sideways toes impair walking. In any case, tetrapod feet consist of multiple segments: in human hands, for instance, fingers start with metacarpal bones in the middle of your hand leading to the three phalanges in your fingers (two in thumbs).  

Obviously, tetrapods are generally large than the other animals to be discussed, and that means that physical circumstances make their world quite different from that of insects and spiders. That definitely affects foot anatomy, and perhaps that merits another post.  

 

Typical spider leg. From: Nentwig et al. All you need to know about spiders. Springer 2022 

        
Arachnid feet
Spider (and scorpion) feet consist of a long leg segment, the tarsus, but only the end touches the ground. The end carries impressive claws and hair tufts. Why? Well, gravity presses the feet of large animals securely against the ground, but animals of insect and spider size need to deal with other forces too, such as wind: a breeze may blow them over, which is why they have splayed legs and why their legs need to hold whatever it is they walk on (the 'substrate'). That is why there are hairs, suction pads and claws to get that grip. 

 

Spider feet showing haiors and claws. From: Labarque et al

Claws are easy to understand as they simply grip the surface with friction, but pads and hairs are not as intuitively understandable: they rely on electrical Van der Waals forces as well as capillary forces to cling to the surface. This gripping has as a consequence that letting go of the surface is not a given, so they may have to peel their legs loose every step. Most spiders have two claws, but some have three, and the third one is apparently used to get a hold on the silk threads of their webs. There's a challenge other foot designs do not have to cope with.   

 

Insect leg from Wikipedia showing the tarsus

Insect feet
The insect tarsus consists of five or more segments at the end of which there is an attachment device that once again bears claws hairs or suction pads to adhere to a surface. The tarsus is segmented in insects, in contrast to that of spiders. The segments can flex, meaning the whole tarsus can curve down if a flexor muscle pulls on a single tendon that runs through the entire chain of segments. When the tendon is released, elastic forces in the exoskeleton straighten the chain again. It cannot curve upward, and the segments also cannot move sideways. 

 

Robotic insect tarsus, From Tran-Ngoc et al

The image above shows a robot foot, copied from an insect foot design. Pulling the tendon in an insect tarsus operates the claws and bends and stiffens the tarsus. This structure reminded me of human fingers that also consist of a chain of segments (phalanges) that flex in one direction only. The similarity stops there, as we use our fingers to curl around objects, whereas insect tarsi do not do that: only the claw/pad/hair assembly at the end does the touching. It is therefore not clear to me why the insect tarsus consists of many segments.   
 

Crab firmly gripping tree bark. From Wikipedia

Crab feet
Crab feet offer a surprise: there aren’t any. Of course, crab legs touch the ground, but the last limb segment, the dactyl, is slightly inwardly curved and ends in a somewhat blunted point. You can call the tarsus a foot, but if so, it is one the claws, pads, sticky hairs of smaller animals, and also without the fingers / toes of large animals. The dactyl itself resembles a claw, which made me think of a reason for the absence of additional clawy or sticky elements. Crabs, evolved in water, had to withstand the  sideways forces of flowing water. One way to avoid being swept away could have been to equip each leg with nice graspers at the end, such as fingers of claws. That would work, but only if the surface had irregularities small enough to hold with one foot's graspers. If the surface elements were larger, they cannot be held with one leg. But another solution would be to treat the entire crab as an eight-fingered hand, with each finger ending in a claw (the dactyl). This larger hand can grip on fairly large objects, provided, first, that the legs/claws clench inwards; second, that there are always few legs clenching the surface from opposite angles; third, that you have enough legs to do that. If I look at the photo of a crab hanging from a tree, I can see it as one large hand. 

A robot crab with such curved dactyls squeezing inwards did a lot better than when the dactyls did not squeeze inwards.  

In this view, instead of saying that crabs have no feet, you can instead regard the entire animal as one big grasping hand or foot.       

The robot Spot from Boston dynamics; the feet are just blobs. 

Robot feet
I guess everyone over the years has seen clips of Boston Dynamics' walking robots. The photo above shows Spot. I have always been surprised that the legs of these robots have only two segments, whereas tetrapods and arthropods have lots more. I guess the engineers felt that two segments were complex enough to start with. The robots also have no wrists or ankles and the 'feet' are just balls, probably made of a substance that provides friction. I suppose that the engineers were avoiding additional complexity. The design shows that you can get away with having no feet; well, robots can. I suspect that having feet is much better than having no feet, and that the difference lies in walking animals having sophisticated nervous systems that can easily control a large number of segments. 

There are many other examples of robot feet, but their makers used animals to base their designs on, so those do not count as aseparate designs. 

Conclusions
The various feet designs allow some rather tentative conclusions. Small animals, of insect size, apparently need feet that provide an active way to adhere to the surface while large animals may simply rely on gravity to press their feet to the ground. That's probably universal Foot Law Number One. Do you remember that my first rule was that I would look a walking only. not climbing or walking upside down? That may have been naïve, as insects seem to use the same mechanisms to stick their legs to horizontal surfaces below as they use for any other surface; in other words, the slope of the surface doesn't really matter for them. It matters for us, as large lumbering creatures hampered by gravity.

Radiating toes are a feature of tetrapods only, and tetrapods are also the only group with really large animals. The two features do not mean that all large animals must have multiple toes. After all, horses have one toe per leg, and so do crabs, in a way. I wouldn't say that multiple toes are necessary. So no Law here.

That leaves the presence of multiple segments placed one behind the other, as occur in insect tarsi and vertebrate feet. Arachnids and robots can do without, so no clear Law here either.

That's it for now. There will be more posts on Feet!      

The ‘prancing grec’, a secondarily flightless Quadripterate (Tabulae Mortuae VII, Archives XVII)

 I know, I know; a post on this blog was long overdue. But there are mitigating circumstances. About a year ago I started painting completely different subject material in a completely different style. The style in question is the ‘ligne claire’ (‘clear line’), which is the style made popular by the Tintin ‘bandes dessinées’ (comic strips). The subject material in question is the old city centre of Leiden, where I live. Somewhat to my surprise, people liked them so much that I had two small back-to-back expositions. Preparing for an exposition turned out to take time, so I couldn’t also work on The Book or on the blog, or at least not as much as either deserves.

I hasten to add that I did work on the long-postponed blog about animal feet (working title: ‘What are feet for?’). But that isn’t ready yet, so here is a post about one of those old oil paintings that will not make it to The Book. In this case that is not because I no longer like the painting, but because the anatomy of the animals needs such a thorough make-over that it will be easier to start anew.

Click to enlarge; copyright Gert van Dijk

What you see are two animals going through a mating ritual, involving some synchronised stepping (by the way, I never understood why that is called ‘goose-stepping’; geese don’t walk that way, I think). The animals walk bipedally but are of obvious hexapodal stock. The first two pairs of limbs have evolved into wings, which makes the animal ‘quadripterates’. Their silly small wings definitely cannot lift them, so they are secondarily flightless. While their ancestors slowly adapted to a full terrestrial mode of life, there was apparently no new purpose for the wings, so the wings slowly become smaller. You can imagine successive generations, at first impressing one another with their large wings and implied aerial prowess, while later generations kept flapping their ever smaller and ever sillier wings ever faster.

You can tell that these animals are from a very early stage in the Furaha project (meaning the 1980s). Their scientific name is Penancephalon perplexus, suggesting they are not the brightest of beasts. Their single pair of eyes is on stalks, and the animals may well have a single an unpaired vertebral column or analogue rather than a typical ‘scalate’ anatomy. The hind legs are completely mammalian, with an upper leg, lower leg and extended foot all bending in the expected directions. The toes point forwards, which is something I will get back to in the ‘What are feet for?’ post. One question to be answered there is whether toes must always point forward in running terrestrial animals or whether you can also have backwards-pointing toes. We’ll see.

Meanwhile, the animals are going through their choreographed little mating dance. They look back at the viewer as if to say ’Who are you calling ridiculous?’.                 

Prober and bobbuck II

Recently, I asked readers which colour scheme they preferred regarding the reworked Prober and Bobbuck (P&B) painting, giving them three choices. The one I chose in the end was the ‘African dawn scheme’, with strong yellow and orange as the main colours. If you see such colours in photographs from Africa, you can be almost certain that the photograph was taken at dusk or dawn against the light. There is always dust in the air in a dry climate, and if you look against the sun, that dust provides the yellow-orange glow. The P&B image tries to catch that feeling, and this is also why the sun is low and we are looking into the light.

Click to enlarge; copyright Gert van Dijk

Anyway, I kept part of the prober’s colours bluish, if only to provide some contrast to the otherwise overly monochromic painting. I read a few recent papers about camouflage patterns to see whether there were new developments (here is a recent textual review without figures as examples). The major theme of that review was that many mechanisms can be combined. The P&B painting shows several mechanisms: background blending, countershading, disruptive colouration and probably a bit of motion dazzle.

Background blending is just what the words suggest, meaning an animal has colours and patterns that make it inconspicuous against the background. Countershading is simply having the underside of the body colour lighter than the top. As the belly of an animal will be shaded by the body, shade makes the light belly colour seem darker, and if all goes well, the result is that the belly is just as dark as the top of the animal. This helps with background blending and makes the animal lose its three-dimensional appearance. Disruptive colouration  means an animal has patches of colour that make the overall shape of the animal more difficult to discern. This works best when the colours of the various patches also appear in the background. Many of these effects work best when an animal is motionless, but apparently some also work when an animal is in motion. In fact, ‘motion dazzle’ describes the effect that the motion of patterned objects is more difficult to judge than that of bland, unpatterned objects.  (tis is not the same as motion camouflage).  

Click to enlarge; copyright Gert van Dijk

 

Back to Furaha and to the P&B painting. The prober and the bobbuck both show multiple camouflage features. Countershading should be obvious in both. Without thinking much about it, I made the belies of both animal an even light colour, whereas I could simply have continued the patterns on the rest of the animal but in lighter colours. Apparently, this occurs in Earth biology a lot too (from where I had unconsciously picked it up). The bobbuck’s horizontal stripes mimick the low hills and patches of low vegetation in the plains where it lives and may also help provide motion dazzle. The stripes are broken, both to break up the outlines of the legs and to increase the resemblance with natural features. The prober has a combination of stripes and spots that again help to break up its outlines. You may note that the stripes are largely at right angles to the animal’s contours. By the way, when stalking and in its initial attack run, the prober holds its ‘raptorial appendages’ (its graspers) back and down, closer to the centre of gravity. Its bright undersides are then not visible from the front. Probers only bring the graspers forwards to the attack position when the hunt is on, when camouflage is no longer an issue.    

Does it all work? You may have noticed that I changed the header of the blog to reflect the updated P&B. Somewhat to my surprise, the shape of the animals is not immediately obvious on such a small picture. That may be because of their fairly unearthly shapes, motion blurring and camouflage. I like it myself, but perhaps I overdid it.          

Was there anything else? Let’s see… Oh yes, both animals of course show features of the Great Hexapod Revolution (here and here), with their kinked distal and proximal necks. You may also note that the functions of the vertical (upper and lower ) jaws are separate from those of the horizontal (left and right) jaws. You will not find advanced hexapods in whom all four legs come together to catch prey; doing so poses overly complex demands on how teeth should work together, so the lateral jaws evolved into food gathering aids. If you look closely, you can see that the prober’s oesophagus runs alongside the proximal and distal necks, and not underneath the joints. You may have to wait for The Book to see that level of detail though.

Speaking of The Book, there is progress. Amazon’s self-publishing scheme makes it difficult to predict colours and shades on the printed page. The only way to get a useful result seems to be to change the colours beforehand, in expectation of then the printers will do with them. Or to them. As this takes trial and error using proofs, I am now at the fourth round of adapting colours, saturation, and brightness, among other things. On screen the results now look garish and cheap, but the proofs are slowly approaching how I wish them to look.