Echolocation: a sound choice?

In January I wrote a post on whether detecting heat could supplant vision, and concluded that it was, in fact, just a form of sight. I wished to tackle echolocation next, but wondered where to start: with echolocating animals in fictional biology? Other possible questions would be which atmosphere would be best, which frequencies to use, how it can be compared with vision, etc. In the end I decided to start -there's more!- with a post on the nature of echolocation; so here we go...

The basic principle is simple: you send out a sound and if an echo returns, there is something out there. As everyone knows, dolphins and bats are expert echolocators., but it is less well known that some blind people are quite good at it, and that they in fact use their occipital cortex to process echoes, a brain region normally busy with analysing visual signals. That direct link between vision and echolocation is perhaps not that surprising, as both senses help build a spatial representation of the world outside: what is where?

A major difference between vision and echolocation is how distances are judged. In vision, judging distances depends on complex image analysis, but in echolocation the time between emitting a sound and the arrival of the echo directly tells you how far an object is away. The big problem here is that echoes are much fainter than the emitted sound. The reason for that is the 'inverse square law', something that works for light as well as for sound.

Click to enlarge; copyright Gert van Dijk

The image above explains the principle. Sound waves emanate from a source near the man in the middle and spread as widening spheres (A, B and C). As the spheres get bigger, the intensity of the sound diminishes per 'unit area'. A 'unit area' can be a square meter, but can also be the size of your ear. When you are close to the source your ear corresponds to some specific part of the sphere, and when you move away your ear will correspond to a smaller part of the sphere: the sound will be less loud. Now, the area of the sphere increases with the square of the distance. If you double the distance from the source, the area of the sphere increases fourfold, and the part your ear catches will decrease fourfold. To continue; increase the distance threefold and the volume decreases ninefold. Move away ten times the original distance from the source, and the sound volume becomes 100 times smaller!
In the image above, only a tiny fraction of the original sound will hit the 'object', a man, at the left. Not all of that will bounce back, and the part that is reflected forms a new sound: the echo. The echo in tun decreases immensely before arriving at the sender, and that is the essence of echolocation: to hear a whisper you have to shout.

Click to enlarge; copyright Gert van Dijk

As if the 'inverse square law' is not bad enough, there is another nasty characteristic of echolocation. At the left (A) you see a random predator using echolocation. Oh, all right, it's not random, but Dougal Dixon's 'nightstalker' (brilliant at the time!). It sends out sound waves (black circles) of which a tiny part will hit a suitable prey; there's that man again. As said, the echoes travel back while decreasing in strength (red circles).
There will be some distance at which a prey of this size can just be detected. Any further away and the returning echoes will be too faint to detect. Suppose that this is the case here, meaning 10m is the limit at which a nightstalker can detect a man (as mankind is extinct in the nightstalker's universe no-one will be hurt).
Here's the catch: most of the sound emitted by the nightstalker travels on beyond the prey. These sound waves can be picked up easily by other animals further away than 10 meters (I assume you recognise the creature listening there; it's pretty frightening). For animals out there the sound only has to travel in one direction and none of it gets lost in bouncing back from the prey. The unfortunate consequence of all this 'shouting to hear a whisper' is that the nightstalker is announcing its presence loudly to animals that it cannot detect itself!
This suggests that echolocation could be a dangerous luxury. One way to use it safely would be if other predators cannot get to you anyway. Is that why bats, up there in the air, can afford echolocation? Another solution would be to be big and bad, so you can afford to be noisy? If so, echolocation is not a suitable tool to find a yummy carrot if you are an inoffensive rabbit-analogue. The carrot does not care, but the wolf-analogue will.

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Getting back on topic, we now know that echolocation tells you how far away an object is. To make sense of the world you will also need to know where the object spatially: left and right and up and down. With hearing this is more difficult than with vision, but it can be done. The spatial resolution of bats is one or two degrees (see here for that), which is impressive but still 60 to 120 times less good than human vision. For now, let's take it for granted that an echolocating animal can locate echo sources. Next, let's try to visualise what it may be like.

Click to enlarge; copyright Gert van Dijk

Here is a scene with a variety of objects on a featureless plain. The objects have transparency, colours, shadows, etc. At one glance we see them all, as well as the horizon, the clouds, etc., without restrictions regarding distance, all in high resolution. The glory of vision, for all to see.

Click to enlarge; copyright Gert van Dijk

Colour is purely visual, so to mimic echolocation it has to go. All the objects are now just white. They are also all featureless, but that is for simplicity's sake only: vision and echolocation can both carry information about things like wrinkles and bumps, so I left texture out.

Click to enlarge; copyright Gert van Dijk

In sight the main source of light is the sun shining from above, but in echolocation you have to provide your own energy. To mimic that, the only light source left is at the camera. The resulting image looks like that of a flash photograph, for good reasons: the light follows the inverse square law, as does sound. Nearby objects reflect a lot of light (sound!) for two reasons: they are close by, and part of their surfaces face the camera squarely, turning light directly back at the camera. This is an 'intensity image'.

Click to enlarge; copyright Gert van Dijk

However, you can see nearby and far objects at the same time, but that is not true for sound. Sound travels in air at about 333 m/s, so sound takes about 3 ms to travel one meter. An object one meter away will produce an echo in 6 ms: 3 ms going to the object and 3 ms travelling back. The image above shows the same scene, but now the grey levels indicate the distance from the camera. Light areas in the image are close by, dark areas are further away. This is a 'depth image', formed courtesy of the ray tracing algorithms in Vue Infinite.

Copyright Gert van Dijk

Now the scene is set to mimic echolocation. Let's send out an imaginary 'ping'; each interval in time determines how far away an echo-producing object is. For instance, the interval from 6 to 12 ms after the 'ping' corresponds to objects 1 to 2 meters away. While the depth image tells us how far away objects are, the intensity image tells us how much of an echo is produced there. To make things easier for the human eye a visual clue was added: echoes returning early are shown in red, while those returning later are blue. Above is a video showing three successive 'pings'. As the echoes bounce back, areas close by will light up in red, and objects furet away will produce an echo in blue, later on. I blurred the images a bit to mimic the relatively poor spatial resolution of echolocation.
I personally found it difficult to reconstruct a three-dimensional image of the world using such images, but my visual system is not used to getting its cues in such fashion.

Copyright Gert van Dijk

One easy processing trick to improve the image is to remember the location of early echoes. The video above does that, by adding new echoes without erasing the old ones. The image is wiped as a new ping starts. More advanced neuronal analyses could take care of additional clues such as the Doppler effect, to read your own or an object's movement. By the way, the above is in slow-motion. In real life echoes from an object 10 m away would only take 60 msec to get back. Even without any overlap you could afford 16 pings a second for that range. That is not bad: after all, 20-25 frames a second is enough to trick our visual system into thinking that there is continuous movement.

So there we are. Is this simple metaphor a valid indication of what echolocation is like? Probably not, but it does point out a few basic characteristics of echolocation. Echolocation must be a claustrophobic: no clouds, no horizon, just your immediate surroundings. It would seem the meek cannot afford it, as it may be the most abrasive and abusive of senses.
Is it therefore completely inferior to vision? Well, yes and no...

Salsa invertebraxa

Some books cannot be classified into a category with any ease; 'Salsa invertebraxa' is definitely such a book. It deals with fictional animals, which criterion by itself reduces the number of books in the putative category enormously. It is not told in a pseudoscientific manner as if the life forms in it actually exist. Dougal Dixon's books are pseudodocumentary in nature, and so is Barlowe's 'Expedition'. If Snaiad, Nereus or Furaha ever make it into book form, they will also fit in the same pseudofactual category. 'Salsa' does none of that; its focus is to tell a story of life through images. It deals with fictional insects functioning as characters with heart and wit, and does this admittedly surprising job brilliantly, I think. I first learned about it through the magazine ImagineFX, and then soon found it on the Behance site. I was intrigued but puzzled by the wonderful but complex images. I found reviews, but the reviewers seemed at a loss to describe what to make of the book. The author, Mozchops, has a page on DeviantArt as well as his own site. If you are interested you should visit all these sites, as they show a fairly large number of the digital paintings Mozchops produced for the book (there is a still larger number of unpublished paintings in the book though. When I found the site of the publisher, Pecksniff Press, I needed but a day or so to decide that I just had to have the book. It was promptly delivered a few days later, but meanwhile I had already contacted Mozchops (Paul Phippen), who was kind enough to explain one or two things about his work. So what is 'Salsa invertebraxa'? You could describe it as a 'graphic novel' telling the story of two insects, comrades from different species travelling through a forest. They are pranksters, stealing eggs from spiders and centipedes. They adorn themselves with the moulted exoskeleton from a cicada-like insect. Decked out in such fashion, they capture colourful caterpillars, suspend them from threads and ride them through the air as if they themselves are knights in armour sitting on war horses. While true, this description might cause the book to come across as silly or even childish. It is neither. It is in fact an extremely complex work that does not give away its secrets lightly. Working out the story needs attention to detail, and there is more to the story than just the above synopsis. The images themselves need careful analysis, because they are full of details and because the artist makes no concessions nor steps down to clarify what it is about. The reader has to rise to the challenge, one I personally enjoyed. There are bits of sparse text, but the words are there to evoke an atmosphere, certainly not as a legend to explain the images. I found myself studying the book several times, and only then did the story start to become clear in my mind. If you like your fantasy biology straight, with little arrows pointing to biological details, you may not like this book. But you would risk missing the incredibly capable artwork. There are certainly enough odd insect shapes in there to satisfy those who like alien animals. Or perhaps their shapes are the result of an alternate evolution on Earth; who knows? I do not think everything in this biology can work. For one thing, I very much doubt that there is space in an insect's head for the neural machinery needed to produce an intelligent prankster, but this is one of those instances where such criticisms are completely beside the point. Ignore it. On rereading the above text, I still doubt that it gives you a full idea what the book is about; you will probably have to read it yourself. I will show a number of images I chose that Mozchops was kind enough to send me in a high-resolution form.

Click to enlarge; copyright Mozchops 2011

Here is an early scene of the two protagonists flying about; the one on the left has clublike extremities while the other is mosquito-like. Just note the shimmer of the wings of the 'mosquito'; it takes skill and belief in your skills to dare paint motion-blurred wings like that, with so little indication of what you see.

Click to enlarge; copyright Mozchops 2011

This image is out on the web already, I think. The two heroes encounter an army of termites, armed to the teeth. I include it so you will get a feeling for how the text adds to the image.

Click to enlarge; copyright Mozchops 2011

Obviously, I could not resist including this one. Regular readers may remember that I did some calculations regarding 'ballonts' some time ago. I had to conclude, to my considerable irritation and disappointment, that my idea of filling Furahan skies with ballooning plankton was not going to work: small ballonts do not work. Luckily, Mozchops had not read that and had designed animals like that. He provided a twist to the idea that I like very much: you are probably all aware of the peculiar mating flight of some dragonflies: the male clasps the female by the neck using claspers on his abdomen. Together the two then fly around to deposit eggs in suitable places. Well, in Mozchops' view the male has a balloon instead of wings, and so the two can float around serenely. Aren't they wonderful? It makes me wish to ignore my own reasoning that small ballonts cannot work...

Click to enlarge; copyright Mozchops 2011

This is one you may have to look at for a while. One of the protagonists, the one with the clubby legs, is riding a caterpillar, as colourful as the saddle cloth of any mediaeval war horse with pennants trailing behind it.

Click to enlarge; copyright Mozchops 2011

At the end of the book the two are met by a host of insects working together as a troupe, the purpose of which is our guess. I wish to show it to you so you can see the inventiveness of the insect shapes. Note the one flying on the right, with its near-mechanical shape and its protruding tongs. The multi-species insect armada contains some of the most wonderful insect shapes in the book.

Click to enlarge; copyright Mozchops 2011

Click to enlarge; copyright Mozchops 2011

Here, a host of insects, from small to majestic, takes to the skies in an exodus the reasons of which we are not told. Mozchops was kind enough to send me an early sketch of this painting, which is an exclusive for this blog. I would like to draw your attention to one insect at the left, the one with twin booms sticking out backwards. I love its shape, with its twin booms evoking the shape of aircraft such as the P38-Lightning. Note that the entire painting is filled with many such inventions. Other people would probably be content to paint just one such design on one painting; here, we are spoilt for choice. All in all, this may be one of the oddest books I have, but it certainly is also among the ones I like best. It certainly deserves more attention, and I hope that this post helps bring that about.

The order electrus

From time to time I search the internet in a search for interesting machines that could lend themselves to be turned into an animal design, or that represent a technical version of a -much older- biological principle. For past examples, see here or here.

While doing so, I came across a website of a countryman of mine, one Jarno Smeets, who was apparently working on human powered flight. That has been done more than once, using propellers driven by a bicycle gear and chain transmission. But what this inventor proposed was that he was going to take of using his arms to provide the propulsion, by flapping the wings. Now that is simply not going to work: human arms are not strong enough to flap wings large enough to lift a human. I lost interest, until my attention was drawn to the site by other sources: now the site had a video purporting to show that he had actually done it. I did not believe it, which was just as well as otherwise I would have been one of many people fooled by the blog: it was all a hoax! The artist/perpetrator was Floris Kaayk. Here it is.

The video is cunningly made: it has all the nice clumsiness of a rather poorly executed home video. There is even someone shouting excitedly into the camera that the flight should have been recorded with another camera, from in front. What you do see is something flapping into the air from quite some distance, and then there are some shots of him flapping, and shots taken from a flying vehicle.

I was intrigued by the elaborate nature of the hoax and found that he Mr Kaayk had done more work bordering on the fantastic. I would like to show you one video in particular, 'The Order Electrus', as it comes close to the usual topics of this blog. It is a documentary showing 'life forms' consisting of electronics parts, running around like little robots. If ever artificial life comes into being, and I cannot think of any reason why this should be impossible, it will not look like this. But that does not matter too much here. As is often the case, when there is enough of a sense of humour, the need to be critical evaporates. I love the film's tongue in cheek attitude. As nature documentaries go, this is a very nice one. It follows here, but if you wish to see it in more detail, please visit Mr. Kaayk's website.

Moebius, Major Gruber, and Rusps (Rusps II /Archives V)

Click to enlarge; copyright Casterman 1995

Click to enlarge; copyright Casterman 1995

Click to enlarge; copyright Casterman 1995

Jean Giraud (also known as Moebius or Gir) died on March 10 this year. I first encountered his work in the seventies, probably in the magazine 'Métal Hurlant'. I do not think anyone disputes that he was a Grand Master of what the French call the Ninth Art ('Neuvième Art'): 'bandes dessinées', or 'comics'. You might that, regardless of his qualities, his work does not really belong here; while he did draw alien animals and plants, you could see that they were never meant to be realistic. The ones above prove that point, I think, while also underlining the facility with which he drew. To get another view of that, here is a YouTube take of him at work.

'

Click to enlarge; copyright holder unknown to me

The image above appeared on the cover of Métal Hurlant in 1976. Such images came as a welcome shock at the time. The way had perhaps been prepared by underground comics, but there still was else nothing like it; remember that science fiction films were not mainstream at all, and that computer-generated imagery was in fact science fiction. The cover impressed me so much that it stayed in memory to the present day. Major Gruber, the main character, just exudes character (stiff upper lip anyone?), as does his alien assistant. But look at that 'wall' behind him: it is part of the head of an animal slain by the 'great human hunter' Major Gruber. You cannot see the head well, partly because it is such a large animal, and partly because it is obscured by lettering, which does not hurt the design. This seems to be a magnificent example of telling a better story by not telling all of it.

So when does the major meet rusps? Well, he doesn't really, but just wait. Once rusps had evolved their imaginary existence, their place in the ecosystem required attention, so specialised armoured predators started ramming their way through the rusps' carapaces, keeping their heads tucked away below their bodies to avoid being blinded or decapitated by the rusp's whips. But after imagining this first onslaught, the question came up why rusps would stand still while attacked in this way? Could even a troupe of such predators bring a rusp to its many knees? Perhaps, but the losses to the predators would probably be unacceptable. An obvious solution would be to introduce a mega-predator, so large and strong that it could attack an adult rusp and expect to win. For reasons unclear to me I do not find that concept appealing; for now, adult rusps do not suffer from predation. But rusps die anyway, and a dead rusp constitutes a mountain of succulent meat.

Click to enlarge; copyright Gert van Dijk

Above is my first image of an animal working its way into a rusp carcass, at left. The right panel shows a specialised rusp predator, or perhaps a scavenger. It is not fast but very sturdy, and its two 'raptorial appendages' have developed into two different shapes. The left one is the prototypical blunt instrument, while the right is more useful as a scraper, to reach those parts where other scavengers cannot.

Click to enlarge; copyright Gert van Dijk

My sketchbooks show more versions of this particular scene, in between a variety of other topics. Here are three different versions from different periods. Do you see the influence of Moebius' scene in the back of my mind? The scavenger looks back towards the camera in the same way as the major looks into it. As for the dead rusp, I contemplated showing it as a wall of carapax over a tangle of collapsed legs, directly facing the camera; but would anyone understand what they were looking at? In Moebius' case, the wall was recognisable as a head. The three-quarter views represent moments where I thought I should provide more clues, while the straight-on views were more daring in this respect: the viewer would not know what kind of animal was dead here.

Click to enlarge; copyright Gert van Dijk

I later felt that perhaps the perspective of the predator was too complex. To see if I could improve on the sketches, I recently did a quick rough sculpt of such an animal in Sculptris (above).

Click to enlarge; copyright Gert van Dijk

I then imported the model into Vue Infinite (left), and exported the image into Painter 12 to paint over. Some very rough brush strokes indicate the structure and legs of the rusp. It is not too bad, but still definitely needs more work; perhaps the design works better on a square canvas. Once I feel that I can do the idea justice I will finally paint that scene, and I will be glad and than to have been inspired, as have many others, by Jean Giraud / Gir / Moebius.

Click to enlarge; from 'Faune de Mars'; copyright Moebius.
This is from a small book only available through Moebius' official site here.

The black, black grass of home...

Black? I hoped that by substituting 'green' with 'black' in the title of this evergreen ('everblack'?), your mind would create an image in which plants are suddenly no longer green but black. Plants hardly ever feature as more than background material in science fiction. SF artists may try to come up with odd plant shapes, but the general colour of your generic SF plant is green. Personally, I also often used green plants in my Furahan paintings without conscious thought.

Click to enlarge; copyright Gert van Dijk

What you see here are 'blackgrasses' on Furaha. In effect, they are largely brownish, but in this case at least I did not fall for the 'plants are green' trap. There are exceptions to ubiquitous greenery though, and the best-known one is probably Well's Martian 'red weed'. Anyway, perhaps it is time to think a bit harder about the colour of plants, first on Earth, then elsewhere. This post will be a bit technical; sorry for that. For more thoughts on this issue, see here and here.

The 'green, green grass of Earth' may trigger associations chlorophyll and photosynthesis ('chloro' means 'green' and 'phyll' is derived from 'leaf' in classical Greek, so it means 'green leaf stuff'). Photosynthesis concerns the trick of capturing the energy in light and transferring it to chemical energy (ATP), and chlorophyll is at the centre of that trick: it captures a photon, setting loose an electron that sets a cascade of motions going. As Chlorophyll is green, you might think that a green colour is good for photosynthesis. It is not: green light is almost useless for photosynthesis using chlorophyll.

Click to enlarge; from Wikipedia

Remember that what we call white light is a composite of a range of wavelengths in the electromagnetic spectrum, ranging from deep purple through blue, green, yellow and red to deep red. It is no coincidence that we call that portion 'visible light'. When light falls on an object some wavelengths are absorbed, while others are reflected. If an object looks green to us, that means that green light is reflected, meaning it is NOT used by photosynthesis. Above is an image of the absorption spectrum of two chlorophyll variants. A peak at a specific wavelength means that light at that wavelength is absorbed and used by chlorophyll. There are peaks in the red and blue parts of the spectrum, but not in the green portion of the spectrum. Does that matter? The answer depends on whether there is in fact a lot of light in that part of the spectrum, so let's compare the absorption spectrum of chlorophyll with the light output of the sun.

Click to enlarge; from Wikipedia

The atmosphere selectively absorbs some wavelengths, so what is relevant is how much of each wavelength reaches the Earth's surface. That is shown above. Try to find the visible part of the spectrum , from about 350 to 750 nanometer. You will see that there is a lot of light there.

Click to enlarge; from here

Here is a graph combining all the previous information. Note that the title states that chlorphyl is well-adapted to use solar energy. Well, yes, in the sense that it is roughly sensitive to light in the area where there is most energy. However, there is this big conspicuous gap, meaning that lots of light is unused by plants, mostly of the green variety. In fact, Earth plants would get on quite well if the sun did not emit all that energy at green wavelengths. (We would not like that though, as there would be about 40% less light to see with, and our ability to see details would be harmed as that depends to a large extent on green light; but that is another matter).

All this suggests that chlorophyll is not the best of all possible light absorbers on Earth. To make the most of sunlight, you would want a molecule that is responsive to a much broader part of the spectrum. Such a molecule would reflect very little light, so it would be black or at least very dark. You can also argue that, if chlorophyll can get away with using just part of the spectrum, so could another molecule. In fact, chlorophyll is not the only molecule used in photosynthesis.

Click to enlarge; taken from this site

'Bacteriorhodopsin' is a well-known example, occurring in some bacteria. Above is a graph in which its spectrum is overlaid on that of chlorophyll. This pigment has a rather broad absorption spectrum, but with a peak at precisely the spot where you would want it, meaning where the sun puts out much light: in the green / yellow parts of the spectrum. As a result, it looks reddish. There is a theory that these bacteria formed mats overlying the very first plants. The only light they let through was at wavelengths the bacteria did not use, so chlorophyll evolved to pick up just those wavelengths. This is a fascinating idea, but one thing that has me worried is the following: if chlorophyll could evolve such a detailed sensitivity to particular wavelengths, why did it stop evolving once plants outgrew those bacteria? Wouldn't it have made sense to retune it afterwards? If it would be sensitive to green light as well we would have black plants, and if it would be mostly responsive to green light plants would be purple.

I have no idea how easily evolution can tinker with light-sensitive molecules to shift their absorption spectrum. Still, light-sensitive pigments occur in vision as well as in photosynthesis, and there is an astonishing variety of pigments for colour vision in the animal kingdom. It seems that such pigments can evolve readily. But chlorophyll seems just to be sitting there, blind to all that glorious green light. Adding insult to injury, the chemical steps following chlorophyll are also singularly inefficient. Part of the problem seems to be that there is very little CO2 in the atmosphere, and that the molecule that takes in CO2 to strip the carbon from it leaving O2, quite readily works in the wrong direction, so the work is partly undone. After all this, the calculated efficiency of chlorophyll photosynthesis is on the order of 4-7%. Seeing how life on Earth depends on photosynthesis, that is a bit worrying.

In summary, the blindness of chlorophyll to green light suggests that other molecules with a different absorption spectrum could be just as efficient (or inefficient). It also suggests that you cannot tell the colour of plants well from the spectrum of the sun in their solar system. If you apply that reasoning on Earth, you will proclaim that Earth's plants are purple...

click to enlarge; copyright Chris Webb or Scientific American

In order to show something besides graphs, I will show a nice image used on the cover of Scientific American. I found it on the website of the artist (Chris Webb) right here.

In another post I may go into the consequences of all this for alien plants. For now, just consider some parallel evolution going on, resulting in different groups of 'plants' using different pigments. Forests on such planets need not show shades of green only, but could sport a riot of colours. Ah! The green, blue, yellow, purple grass of home...

An aside about rusp insides (Archives IVb)

This post is an additional one: having decided that rusps must have an endoskeleton, I started wondering what its structure might be, and here are some sketchy results.

Click to enlarge; copyright Gert van Dijk

In principle rusps have segmented bodies, just like Earths arthropods and vertebrates. But just like those animals on Earth, that basic structure is no longer visible in all aspects of their biology. In the rusp case the skeleton still shows strong evidence of segmentation. Each of the twelve pairs of legs should carry its own portion of the animal's weight, and the skeleton should reflect that. What you see above is one segment of the middle part of the body; the heads and whips are not shown. The legs are greenish in colour, and the beige ring is the main skeleton of the body. Note the two arched bones, situated directly above the hip joints. They meet in the middle high up near the animal's back. The mass of the animal is slung underneath these arches. There is a secondary arch in the belly of the animal acting as a sort of load-bearing floor. In the back a bone extends forwards and backwards, joining the segmental rings together in the form of a 'dorsal column'. The ensemble looks suspiciously like a vertebral column with ribs, but appearances are deceiving! In vertebrates, ribs are suspended from the vertebral column and do not transfer the weight of the animal to the legs. Instead, these rusp arches function exactly like arches in architecture, and transfer weight to the legs.

Click to enlarge; copyright Gert van Dijk

Here you see are twelve locomotor segments together. The sort of orange coloured bones at the sides provide another link between adjacent segments on the level of the hips. There is a joint in the middle, normally held in position by strong tendons,. Their purpose is explained in the next image. The skeleton of the anterior and posterior heads is not shown, and neither are the whip skeletons. However, you can easily imagine the dorsal column giving rise to the fore and aft whips.

Click to enlarge; copyright Gert van Dijk

Here is the animal bent sideways. The orange hinge bones at the sides are pulled together on ne side and extended on the other. I suppose the animal can flex more than this, but not really that much.

Click to enlarge; copyright Gert van Dijk

And finally another possibility. Here, the main weight-bearing structure is also a curved beam, but this one sits much lower in the body. The beam again supports a central column, that now gives rise to a vertical 'mast' supporting the body. The sides are linked in the same way as previously. I am less certain how to support the whips with this design; perhaps the central column simply rises up through the skulls to form the whip skeleton. Alernatively, it could find its origin in the top of the masts.

I haven't decided which design will be the final say on rusp anatomy, and in a certain sense it is not necessary to settle on a specific design, as not all of it is necessary to paint a rusp. Then again, thinking about what makes an animal work certainly will have its effect on a painting and is likely to add details. Those details do not serve to explain everything about an animal there is to know. Instead, they make viewers think that there is more than you can see. That work best if there really is more than meets the eye...

Archives IV: once and future rusps

The archives of the Institute of Furahan Biology contain the evolutionary lineages of almost all Furahan animals, in the form of sketches that show how the animal and its depiction evolved over time, before their shapes were frozen in the form of a painting. Well, that is how it seemed: as I have started reworking my paintings digitally, evolution has suddenly leapt ahead again. Sometimes I also revisit old designs again; rusps are an example.

Click to enlarge; copyright Gert van Dijk

Rusps feature on the 'walking with rusps' page on the main Furaha site (on the 'land' page). The image above shows the first ever sketches of 'rusps'. (Their name is inspired by how Dutch children may have difficulty with the word for caterpillar, and end up saying 'rusp' instead of 'rups'.) As you can see, rusps have multiple legs and are protected by a strong carapax. My notes alongside the sketch stated whether such presumably slow animals could survive in an environment of agile large animals. But I also noted that sea urchins are bright nor fast, but do quite well. Such considerations made me add stings, evolved from stings alongside the body through poisonous hairy plumes into mean-looking fore and aft tentacles equipped with poisonous barbs. Their bodies are segmented, and there are multiple eyes on the front and back; in fact the lower rusp also has secondary eyes along the body. The reason there is a tentacle at both ends had to do with my wish to protect the animal. I have always been surprised by the inability of earth's animals to protect their rear end well, a weakness exploited with great success by predators such as lions and hyenas. Of course, this 'active rear' design, with eyes, a tentacle and the corresponding neural circuitry, represents a departure from Earth patterns, where no large animal has a 'split brain' to this degree. It reminds me of the claims for a 'secondary brain', such as was once implied for stegosaurs? Such a design goes against the theme of 'cephalisation', and I am not at all certain that it could actually work. Then again, I see no definite reason why it could not.

Click to enlarge; copyright Gert van Dijk

I almost immediately wished to make them bigger, at least elephant sized. Here is another early sketch, showing how a large rusp crosses a stream sunk into the ground. Animals such as elephants have great difficulty in doing so, as they cannot jump at all and dislike steep inclines. I thought that rusps would have the advantage of being able to use their long bodies: they can hold the front part of their body in the air at some energetic cost until they are able to find a foothold on the other side.

Rusps probably evolved from millipede-like ancestors. In contrast to Earths arthropods these ancestors were obviously equipped with respiratory and circulatory systems allowing adaptations for large bodiess. They were also endoskeletal, for similar reasons. The carapax is not a part of the skeleton, but simply an outer protective covering; it is leathery rather than hard.

Click to enlarge; copyright Gert van Dijk

The top image shows one from a low viewpoint, a trick that by itself suggests large size, as viewers often assume a viewing point at eye level. What you can also see is how the legs move in a sort of ripple, with adjacent legs moving a bit out of phase with the ones in front and behind. That is the usual gait of Earth's millipedes and centipedes, by the way (this is also animated on the main Furaha site). The sketch in the middle show transverse sections, illustrating my thoughts on their possible body shapes. I did not want their legs knocking into one another, so I thought that successive pairs could be offset to the left or the right, giving each room to move. To evoke an atmosphere of large size, I played with the idea of making them high and narrow rather than wide and squat. If you take a good look at elephants and many dinosaurs you will see that they are often relatively narrow. I also played with the site of attachment of the legs: underneath the animal or along its sides? The sketch at the bottom shows a resulting rusp of the narrow type. I rather like their tentacles, but realised that they woud pose biomechanical problems: holding them horizontally with muscle power alone would be as comfortable and efficient as humans holding their arms horizontally in the air all day: try to do it for 10 minutes...

Click to enlarge; copyright Gert van Dijk

Rusps only made it to a painting once, a detail of which is shown above. But even on that painting they were in the middle distance. One of the reasons they never received their own painting was that I had problems in finding a suitable design. With their long horizontal bodies they present a somewhat passive shape. One solution would be to show them from the front with a considerable degree of foreshortening, such as in the images above, or I could show only a part of their body, such as in the 'fording a stream' design above. But there were other problems as well, such as the relative positions of the legs, the 'active rear' with its corollary 'split brain', and of coarse the tentacles, that cannot just be held in the air horizontally like that. For a structure held up with muscle power only, such a position is virtually impossible; just try to hold your arms with extended elbows horizontally in the air for 10 minutes, and you will find out why...

Click to enlarge; copyright Gert van Dijk

I keep coming back to rusps, and above is a recent study done with Vue Infinite. Here, too, the successive legs are offset resulting in a double track on each side. It has as a disadvantage that the hip joint is not directly above the foot. As a painting it results in a rather sedate view, but the well-lit afternoon sunshine could make up for that. Rusps ought to look grandiose, and perhaps a design like this brings that out.

The one thing I am not worried about at all is the leg pattern. The two animations are newer 3D versions of rusp locomotion. The essence of centipede or millipede locomotion is that there are successive phase differences between successive legs. Depending on whether a leg is either just ahead or behind in its cycle compared to the leg behind it, the legs tend to clump together either on the ground or in the air. The effect is that the movement appears to ripple either forwards or backwards along the animal. For centipedes and millipedes the choice seems to depend on how far sideways the legs are held. In rusps, the legs are always held vertically, so leg tangles have to be avoided in another way. Possible solutions are of course to make the legs shorter, place them further apart, or, as I wrote above, to have their feet offset. On the other hand, the animation shows that manipulating the phase differences can avoid leg entanglement quite well, so the simplest solution is probably the best one. In short, there seems to be little need to offset the legs.

Click to enlarge; From: Steven Vogel. Comparative biomechanics. Princeton Oxford 2003

Click to enlarge; from:Klein et al; biology of the sauropod dinosaurs. Indiana University Press 2011

As for the tentacles, some further thought suggested a solution. Sauropod necks and tails are very long structures held out horizontally in positions that at first glance seem impossible. This is possible because they are not tentacles but trusses: there are bones resisting compression at the bottom and tendons to withstand pulling forces at the top. With a design like that, rusps whips could function and wreak havoc on any hexapod predator foolish enough to enter the rusps' range of motion, at its front or back. Rusps whips will not curve in three dimensions as gracefully as they do in the sketches above, but will be a bit stiffer. Expect the cross section of future rusp whips to be narrow and high.

The next diversion into the archives will explain the relation between rusps and major Gruber, a creation of the late Moebius, a French grand master of bandes dessinées (comics).