Tuesday, 10 April 2018

Ten years on

The first post of this blog was published on April 22, 2008, or ten years ago. I wrote several earlier progress reports. It is time for a new one, especially because of the festive nature of ten years of blogging. Well, more or less, because the rate of new posts has been low in the past few years. More on that later. 

Let's start with a comparison with 5 years ago, when I also wrote a progress report. Then, there had been 307,000 page views according to the blogger 'stats' page, and now the counter stands at 639,478 views. I am not altogether certain that all these visits represent actual people; perhaps there were bots  as well. What is certain is that I had written 197 posts five years ago, whereas the counter now stands at 233 posts, so it is obvious I wrote more posts in the first five than the second five years.  There were 1638 comments in all, and I must say that I enjoy the interactions. The comments have quite often made me think a bit harder about what the project, and gave rise to new animals on more than one occasion. Thanks to all who read my posts with such enthusiasm!

The 'stats' section also tells me what the most-visited posts were over these ten years. Here they are, with their previous ranking from five years ago between parentheses:

1. (1) Swimming in Sand 1: the Sandworms of Dune; 5 Feb 2011; 8854 views       
2. (5) A future book on future evolution from France; 19 Nov 2011; 6239 views       
3. (4) Avatar's 'Walking with hexapods'; 11 Feb 2010; 4862 views
4. (2) Warren Fahy's "Fragment"; 8 Aug 2010; 4010 views                   
5. (-) Future evolution from France: 'Demain, les animaux...; 30 May 2015; 3327 views
6. (3) A century of thoats; 5 May 2012; 2996 views
7. (-) Create your own planet (using Celestia); 13 Aug 2011; 2717 views   
8. (-) The anatomy of giants in 'Game of Thrones'; 11 Jun 2016; 2661 views           
9. (9) Ballooning animals and Newtonian fitness; 15 Jul 2011; 2338 views   
10. (-) Second part of a review of 'Demain, les animaux...; 13 Jun 2015; 1958 views   

There are four newcomers in the top-10, but it seems that the sandworms of Dune are unbeatable. My French friends Marc Boulay and S├ębastien Steyer will be pleased to learn that their work occurs no less than three times in the top-10: first as an announcement in 2011, and then as a two-part review in 2015. I hope that this signals an immense interest in books on speculative biology, because that would be good more my own project: The Book.

Click to enlarge; copyright Gert van Dijk
Some of you may recall that I had announced that I would spend less time blogging to have more time to work on The Book. The graph above shows the cumulative number of blog posts in red, from 0 in 2008 to 233 now (the present one excluded), as well as the cumulative number of spreads in blue, starting in 2011. A spread is a two-page account of a species, a chapter introduction, or of any topic worthy of devoting two pages to. The number of spreads started in 2011 because I had made the switch to digital painting and started collecting the slowly increasing number of spreads in an InDesign manuscript. I am at present working on the fiftieth spread, so within a short while the manuscript will have exactly 100 pages. Not bad, hey?

But did the reduction of blogging benefit The Book? The two vertical red lines indicate the post in 2014 in which I announced a temporary stop, and the one in 2015 in which I said that I would stop blogging except for the occasional post. Have a look at the rate of increase of the two lines: the total number of posts rose much slower from then on, while the number of spreads rose appreciably faster. The rate of new spreads since then is about nine spreads a year, which is less than the 12 I hoped to be able to manage. But please remember that this is not a job and that each spread takes presumably 20-30 hours to produce. I you ever write a book, do just that: write it; don't paint it! Mind you, The Book does not consist of images only: there are over 32,000 words at present, which is the length of a novella.

I always aimed at something like 125 pages, simply because comparable works have such a number of pages. At present I think the number will be more like 130, but we'll see. The good news is that I expect that the number of spreads per year will increase, so producing the remaining 15 spreads shouldn't take very long. Mind you, 'not very long' should be considered from the perspective that such a project may take a few decades...              
    
Because this is the tenth year of blogging, I also aim to write a few extra posts this year. I think I will finally write the long-awaited post 'What are toes for?' There will also be posts on equations: the Drake equation, the Seager equation and possibly the Nastrazzurro equation...

Friday, 30 March 2018

From freezing the anatomy of tetropters to op art (Tetropters VIII)

Tetropters have been discussed in this blog several times. Eight posts were devoted to them (one, two, three, three bis that doesn't really count, four, five, six, and seven) and they were mentioned more often. In fact, they first featured in the third post ever, published on April 27, 2008. Attentive readers may note that the 10 year anniversary of this blog is coming up, and I intend to write more posts this year to honour the occasion.

Tetropters are flying animals with a radial symmetry, something that was not common at their time of invention, well before they featured in the blog. They fly with a 'clap and fling' mechanism, also used by various flying animals on Earth: the animal brings its wings together over its back and then separates them again, starting at the top. This apparently creates a lower pressure above the animal, which helps the animal to stay in the air. Earth animals, with their two wings, have one 'clap' in each movement cycle of the wings; Wikipedia has a short section on it. Tetropters have four wings and move them in such a way that there are two 'clap' events in every wing cycle. I was delighted to learn, years after their 'evolution' as Furahan animals, that someone had had the same idea but with the purpose of building an actual flying robot using the double flap and wing scheme. I wrote about that in this post.

At present I am working on the second of what will probably be three two-page spreads on tetropters. The first detailed paintings of a specific animal (or plant or mixomorph) always represents a bit of a crisis, as the characteristic features of a group, its Bauplan, have to settled for good: it has to be frozen. Tetropters had  four wings and I knew their movement pattern, but that left many other decisions to be made. How many eyes should they have and where are these eyes placed? They are presumably related to spidrids, so which features should they share? Should they have eight legs or four? If the mouth is placed at the underside of the animal, how does that reach its food? The list goes on. I have frozen the Bauplan of spidrids, cloakfish and Fishes I to VI in the past, so the process is familiar by now. I confess that I have kept one of the most difficult decisions for last, and that is the suspension system and leg anatomy of large hexapods: I wish to avoid a mere doubling of hind legs or of front legs, which is how most illustrators solved the problem of designing animals with six or eight legs (see my posts on Avatar and thoats).

The first decision regarding tetropters was that it dawned on me that I had not considered the etymology of the word well. The word is derived from the Greek roots for four, 'tetra', and wing, which is either 'pterux' or 'pteron'. In biology just the stem 'pter' is used often. So where did the 'o' come from? I guess I just used 'o' to string the two roots together, or perhaps because of an association with 'helicopter' (a combination of 'helikos', meaning winding, rolling, turning, and 'pter'). As an aside, the Lexilogos websites for Latin and Classical Greek are useful for such things). But as 'tetra' already ends in a vowel, no other sound is necesary to connect the two words, so 'tetropters' are now 'tetrapters'. In the posts I will stick to tetropters or other posts will be difficult to find.

Click to enlarge; copyright Gert van Dijk
Readers will be more interested in what the animals look like. Well, here is a drawing from the famous 'Field Guide to Imparian Tetrapters', showing the male and female forms of the 'Red Baron'. These animals are large, for tetropters that is, predatory tetropters that prey on other tetropters, catching them in flight. They have long wings and are very manoeuvrable. You may note that the outer legs have evolved into grasping limbs, leaving just the inner legs as a landing gear and to walk around on.


To help me get a good idea of tetropter wings in flight I dusted off earlier tetropter animation programs, relying on an unwieldy combination of Matlab, python and Vue Infinite. When I first made these programs I dreamed of producing 5 or 6 minutes high quality films; the one above was made with this idea in mind. Later I realised that these required considerable investments in time, time that might be better used working on The Book directly. So I gave up on nice backgrounds with leaves moving in the wind, etc., and just use animations as a scaffolding for the paintings.


This first animation shows a general undetailed tetropter in 'helicopter mode': the wings are relatively long, and when they move through their 90 degree movement from one clap to the next, they do not move down very much. The 'angle of attack', that is the angle of the plane of the wing compared to the direction of movement, is low. One extreme angle of attack would be a flat plane moving at a right angle to the wind, creating maximum drag but no lift. The other extreme has the plane moving exactly parallel to the wind: no drag, but again no lift. The optimum angle of attack should be one that for a given air speed creates the most lift for the least drag. This is also the flight mode for the Red Baron.

I have played with the structure of the wing, which is transparent with some bright red spots. The structure is much like that of insects, with a thin membrane, taut between 'spars' that give it its shape. There are two main spars to help control the curvature of the wings during flight. I tried to envisage completely unearthly spar structures, but all my attempts ended up looking like insects; let me know if you find a workable unearthly design. Note that the speed of movement shown here is not at all the natural one: for earth insects, wing frequency varies between 4 and 250 Hz, with low frequencies for large butterflies (I might write a short post on tetropter wing beat frequency taking air density and gravity into consideration).



This second example shows a 'rowing' mode of flight. Here, the wings beat down over a large angle and the plane of the wings is at a large angle to the direction of movement, somewhat in the way the blade of an oar is at a right angle to the direction of the stroke.  I should probably have made the body a lot smaller in relation to the wings, so the animal can beat its wings like Earth moths or butterflies: slowly, so the colour pattern can be appreciated. Just think of the animations as showing the animal in extreme slow motion.


Still, I could not resist adapting the animation to show a wing movement at 4 Hz, which is really low for Earth insects.  The colours stand out less.


The third and last movement concerns a mixture of the two flight patterns shown above: not too flat nor too steep, but just right. Again, this should be probably a large animal with a smaller body. There is some reasoning behind the bold colours.

I assumed that animal vision in relevant Furahan animals deals separately with colour contrast and with luminance contrast, just as the human visual system does. Generally, if you wish to see detail, use a large contrast between light and dark (i.e., a big luminance difference). You might think that colour differences are more important, but they are not. Designers know such things; here is a nice NASA image that explains the use of both types of contrast from a design point of view.

Click to enlarge; copyright Gert van Dijk
Colours can do strange things: the visual resolution differs between colours, with blue as a particularly poor colour to use for spatial information. Here is a trick to show that: the original is at the top left. I used that to blur two of the three colours red, green and blue, leaving one colour in its original sharp form. You will see that the clarity of the image really suffers f the green channel is blurred, but that the image does not suffer that much if green is unaffected. What this simple experiment shows is that blue and red, mostly blue, have a poor spatial resolution. Interesting things happen if you put two contrasting colours side by side, and tweak their luminance until they appear equally light or dark. This contrast has a poor spatial resolution, making shapes seem to float or flicker. This is just one of the properties of the visual system that op art relied on. Just type in op art in Google and do an image search.

I used such a design for the wings in this tetropter. Each wing has a bold pattern of two colours. Two wings have their colours placed opposite to the other two. The idea was that the wings in a near-clap position would provide a visual shock. Theoretically the to and fro sides of each wings could have contrasting patterns as well, to provide even more dazzle.


Here it is again, manipulated to result in a 4 Hz cycle. Does it work? Such visual effects rely on the properties of the visual system, and those will differ greatly between different animals. One species op art is another species' drabness. I have often wondered whether the colour patterns of some  Earth animals evolved to create a specific visual effect in a specific visual system. For instance, what effect do the stripes of a zebra have on the visual system of a lion, perhaps at night?

I will equip a Furahan farfalloid tetropter with a similar pattern, in the expectation that its colours will ignite at least one visual system, probably those of potential mates, to make it something like 'Wow!'.


Saturday, 17 February 2018

Rusps turn out to follow biological rules about the weaponisation of tails

I recently came across an interesting paper on the evolution of the use of tails as weapons in Earth animals. This turns out to be a fairly rare occurrence, and perhaps that rarity helps explains why animals with tail weapons are so spectacular. After all, we take the common for granted, and it is the departure from the common that attracts attention.

The glyptodont Doedicurus; click to enlarge. https://en.wikipedia.org/wiki/Doedicurus

A nice example on an animal with a tail that is obviously useful as a weapon is the glyptodon genus Doedicurus, a giant armadillo-like mammal, the size of a small car. Doedicurus was encased in strong armour and endowed with a tail with an impressive thickened club at the end.

Click to enlarge; Pinacosaurus Grangeri; Copyright Gregory S. Paul. Princeton field Guide to Dinosaurs, second edition
Ankylosaurs had the same idea, but much earlier. As far as their design was concerned, they went overboard in adding an array of large sharp spikes to their armour.

Click to enlarge; Spinophorosaurus nigerensis; Copyright Gregory S. Paul. Princeton field Guide to Dinosaurs, second edition
Some sauropods may also have had body armour as well as similar thick knobs on the end of their tails. Only one sauropod (Spinophorosaurus nigerensis) apparently sported pointy spikes on its tail, shown here as a juvenile, and drawn by Gregory Paul (I do not think I have to urge dinosaur enthusiasts to get his book 'The Princeton field guide to dinosaurs'). If these long tails were swept at high speed, the transfer of all that kinetic energy should do some real damage. But perhaps a simple threat, along the lines of 'Make my day, punk' would be enough to prevent an actual fight.

The paper in question has the title "The evolution of tail weaponization in amniotes" and is written by Victoria Arbour and Lindsay Zanno. The paper describes which features are the evolutionary precursors of the evolution of tail weapons. The authors performed a thorough statistical analysis of many body traits, and looked separately at four aspects of tail weaponry:  tail lashing, bony terminal tail spikes, a stiff distal tail, and an expanded tail tip.

Click to enlarge. Arbour & Zanno 2018

Here is a figure of the paper, showing these four aspects and the features they are associated with. The result of all this is that you are not likely to find tail weaponry in agile quick-footed predators. If you were designing just such an animal for your speculative biology project, you should probably pause to consider its likelihood. Tail weapons seem to be a last resort for large slow herbivores who already invested in body armour. The authors make the point that equipping heads with weapons occurred much more often. This seems odd because heads are already filled with important structures that should not be damaged, whereas damage to a tail is probably much less risky, so you would expect 'anterior armatification' to be less common that 'posterior armatification'(I could not resist latinising 'weaponisation'). The authors do not speculate why this should be so, but I wonder whether the effective use of weapons requires excellent motor control, something that in turn depends on excellent sensory control, meaning sight. If so, the animal's body may simply be in the way, so it cannot see well enough where to place the sting in its tail.
   At any rate, the authors state that armour in mammals evolved in those animals that are neither small enough to hide nor large enough to deter predators by size alone, and that live in open environments. Close combat with a predator must be a risky business, so the best strategy may simply be running away faster than a predator. And if flight is your main strategy, heavy armour is not going to help. But  a wholly new set of constraints must come into play if you have no chance to outrun your predator to start with. Defensive features such as large size and armour then may become useful, and it seems that active weaponry is the last feature on the list to evolve.

Click to enlarge; copyright Gert van Dijk

So glyptodons, ankylosaurs, stegosaurs  and some sauropods all fit the 'big slow armoured' description to various degrees. And so do Furahan rusps! The image above shows half a rusp from an unfinished painting (for more on rusps, use the blog's search function). From my very first rusp sketch on, rusps were large, had thick hides and used their whips as active weapons. Of course rusps have front as well as hind whips, so the word 'tail' is not applicable at all, but the point is clear; rusp whips are analogous to the 'weaponised' tails of Earth. Those early rusp sketches predated the paper as well the posts in this blog about rusps by many years. I do not remember exactly how much of the rusp body plan came about consciously. I think that I started with a long body shape. Add to that some wondering why many Earth animals are so vulnerable at their rear and sometimes along their middle as well. As the earliest sketches show eyes on middle rusps segments as well, rusps must have started with a weak encephalisation tendency. From there on the double encephalisation seems natural. Note that the posterior whip is well controlled by its own ring brain, with excellent visual information available to direct the strikes. But part of all this may have come about through largely unconscious associations while sketching. Once a design is on paper, it is often hard to say where it came from. Regardless, it is nice that the meme 'rusps have whips' can now be attributed to a firmly established biological principle.

Much as I like the paper, there is a minor matter that might have made it even nicer. Rather than 'tail weaponisation', the authors could easily have used a word that is both relevant and fun: a tail weapon is a 'thagomiser'.

Click to enlarge; copyright

The first use of 'thagomizer' is shown above (this blog uses British spelling, so I assumed the word would become 'thagomiser' in the UK; the rules aren't always clear...).
   It was published as one of Gary Larson's Far Side cartoons in May, 1982. Actually, this colour image stems from a later luxury edition of all Far Side cartoons. Poor Thag Simmons. For 'Far Side' fans, a caveman called 'Thag' occurs at least once more, and one cartoon, taking place in modern times, featured a 'Mr Thagerson'.
  At first glance the word thagomiser seems to indicate 'to turn an object, animal or person into thag', but the real meaning is obviously a 'structure to kill animals or persons, in particular Thag Simmons'. The word has later been picked up in the scientific community to describe the tail weapons of stegosaurs, and apparently of stegosaurs only. I propose to widen its use to all tail weapons.
   As an author of scientific papers myself I realise that the use of humour in scientific papers can be tricky as it is often frowned upon, and you never wish to harm your chances of getting a paper accepted. (I once inserted the phrase 'This resistance is futile' in one of my own scientific papers as an irreverent reference to Star Trek, but I do not think anyone ever noticed).

If we use 'thagomiser' as a word for 'tail weapon', the paper could have been called "The evolution of thagomizers in amniotes", which would be clear, succinct and elegant, but admittedly probably too flippant for a serious paper. Once 'thagomiser' is an accepted word, can we resist to stop there? The tendency to evolve a thagomiser then might become 'thagomiserificability', and the transition process from 'nonthagomiseriness' (not having a thagomiser) to 'orthothagomiserity' (having a proper thagomiser) is 'thagomogrification'. Obviously. 

Wednesday, 27 December 2017

"The Spirally Slanted Spidrid's Mad Dash For Safety!"

Last September I presented part of a painting showing the Mad Sickle, a species of spirally slanted spidrid ('slanties'). The comments quickly gave rise to two new ideas: the first was that the legs and body of slanties might hook up to form a nearly impregnable wall. I should probably do a painting of one. The second was that slanties might well move by cartwheeling. Imagine that as follows: a spidrid's body along with the legs sticking out in all directions forms a disk; now flip the disc onto its edge and roll it along; that's it.  Slanties might use this trick to escape very quickly down a hill.


As usual, life on earth manages to trump anything the speculative biologist can think of. To prove that, here is a short video showing a Namibian spider using exactly that same trick to escaper down a hill, narrated by Sir David Attenborough. There are also spiders that actually do a series of somersaults, head over tails, but that is another type of movement and also another story: here's a video).

Slanties have an additional trick up their sleeves: once flipped on their side, there is nothing to stop them from using the power of their legs to make this an active way of locomotion. Slanties need not be content with passively rolling downhill; they can get out of the way on horizontal terrain too. Actually, they could even roll uphill. I do not think that that would be more effective than normal walking (normal for slanties, that is!), but they could. 

Mind you, I am not saying I am the first to invent this way of locomotion for a fictive animal. I have written about Warren Fahy's 'disc ant' in the past, and there may be earlier manifestations as well.

   
So here is a quick animation of a slanted spidrid moving in this fashion. The legs flex and extend while the body rotates. I suppose it could also move on the other direction with nearly the same movement. We are looking at the dorsal side of the beast.



Here it is again, rolling in and out of view.

I doubt the animal would use this type of movement as part of its normal repertoire, because I do not think it would be able to see well, with the entire world circling around them like mad. In this respect, the movement is a bit like 'cernuation', a term to describe the movement of the 'squibbon' of The Future is Wild. To read about possible visual problems, find the posts here and here. The poor spidrid only sees the world as a blur when wheeling around in this way, and that is why it uses wheeling only as a last resort to escape from predation.

Sunday, 24 December 2017

Run, rusp, run!

I keep coming back to rusps because their basic centipede shape allows me to play with gaits and movements more than I thought at the start. So far, I have only shown very large rusps, 'megarusps', having a mass equalling or surpassing that of sauropods. If you need to brush up on your crambology (yes, I invented a word to describe the knowledge of rusps), start with some earlier posts: one, two, three and four (there are more, but these will do). Of course, you can also learn about rusp gaits on the main Furaha page.  

Now, megarusps are immense, and you should not expect them to hop and jump around a place like a rabbit on speed. Instead, expect them to move ponderously and solemnly. Still, megarusps must have evolved from smaller ancestors, and that by itself suggests there could be lots of medium and small rusp species, and indeed there are. And then I wondered whether their multilegged nature might keep them from running fast?

Click to enlarge; copyright Gert van Dijk

Here is my earliest sketch of small rusps again. I have not done any full paintings of such minirusps yet, but I do envision a fruitful adaptive radiation, including arboreal and burrowing species.  I have finished two paintings showing metriorusps ('metrio-' indicates medium-sized), and to do so I had to think about their gaits and in which way these would differ from those of megarusps.

    
Digging rusp. Click to enlarge; copyright Gert van Dijk
Varkrusp. Click to enlarge; copyright Gert van Dijk
 Here are some sketches of metriorusps, that did not make it to 'evolved' status. I played with the idea of differential leg development, so I could have digging species. That design has not made it to a painting, but running and armoured rusps did make the 'evolved' status, though.     

Millipedes and centipedes on Earth can move pretty fast, but they do not really run. Can rusps run?  The answer lies in what exactly is meant by 'running'. On the one hand you can simply interpret the word as 'walking quickly', but there are more complex biological connotations too.
  Walking consists of cyclical strides, and each stride consists of two phases. In the stance phase, a leg is pushed down onto the ground and backwards, providing upwards and forwards force. In the swing phase, the leg is lifted and moves forwards so it will be ready for the next stance phase. During the lift phase the animal should not fall, and preventing that is usually accomplished by having other legs on the ground at that time. To walk more quickly there are few options: increase stride frequency and increase stride length. The latter can be done by having long legs and by swinging it over the largest distance possible, and to get that working, the time a leg is on the ground will have to be shortened.

copyright Gert van Dijk
 This is precisely what happens on Earth. Here is an old animations of mine showing a horse walking. When walking, each leg is on the ground for more than half the time, so there are likely to be multiple legs on the ground at any one time. The slower an animal moves, the more the situation resembles standing still, and for an animal standing still its centre of gravity must fall within the area described by the feet: that is static stability. The stars in the animations represent the corners of that area. The order in which the leg moves ensures that the area has the shape of a triangle under the body.
copyright Gert van Dijk

For a galloping horse, each leg only touches the ground for a short fraction of its movement cycle. The result is that the chances are low that many legs will touch the ground at any time. In fact, there may well be no legs on the ground at all at some times, so the animal is in fact making a series of jumps. At high speeds static stability gives way to dynamic stability, meaning the animal is kept from falling through inertia and a footfall at the correct time and place.

Running is regularly defined as walking with each leg touching the ground for less than half a walking cycle. On earth, all really fast animals use these principles. Having said that, it is time to go back to centipedes and rusps. Centipedes do not run: their stance phase typically lasts much longer than their swing phases. This increases the chance that there are many legs on the ground at any one time, and, seeing how many legs rusps have, this is almost a certainty. This adds up to there being no jump phases, which seems a bad idea if we want a fast rusp.

   

The answer, I thought, would lie in the gait. The animation above shows a rusp with a slow gait: each foot is on the ground more than half the time. In real life, the animation may have to be sped up for a more realistic effect, but at least the movements are well visible. To support the body well, no region of the long rusp body should be unsupported for a long time, and that is achieved by choosing specific phase differences between the legs. In this case, these seem to work reasonably well. Mind you, rusps have typical 'zigzagzig' legs (see here, here and here for what that means).



The next step, above, is to equip the rusp with a different movement cycle for its legs; the legs now swing further and touch the ground less than half the time. I kept the phase differences the same for comparison. Fortunately for this rusp, its legs do not kick one another with this setting, so the result is not at all bad. There are always legs on the ground though, and that may limit a further increase in speed.



So the gait is the next parameter to tweak. Here, the phase difference between successive legs is much less than before, so the legs on one side move almost in unison. Still, at the moment the last leg on one side leaves the ground, there is already a leg just touching the ground on the other side.            



That can easily be amended. Now the phase differences are almost gone, and there are two periods in the movement cycle when there is no foot on the ground at all. Again, you will have to imagine a proper film speed. This rusp is going so fast, its feet hardly touch the ground!  

So yes, I think there are ways to have rusps run. Actually, they might be able to change phase differences very subtly and continuously, giving them a 'continuously variable transmission', unlike Earth's large mammals, that typically have up to three gaits to choose from (walk, trot and gallop), each with a specific preferred speed.  But that will also depend on energy requirements, something I haven't studied in any detail. 

Click to enlarge; copyright Gert van Dijk

So here is the scale diagram of the runrusp, one of the metriorusps that has already been painted. To close with, it may be interesting to know that I leave hexpods for last, because I am not fully satisfied with the animation of their middle legs yet. But I must say that exploring all the nonhexapod lineages on Furaha is perhaps not a bad idea: it gives more attention to designs that are least Earth-like.  

Sunday, 22 October 2017

The Trench Gobbler

For once I will show a complete painting. Well, more or less. The painting in question is part of a two page spread concerning 'Fishes VI'. The six groups of 'Fishes' are part of the hexapod family tree, with Fishes I, II, III and V as the direct ancestors of terrestrial hexapods, and Fishes IV and VI as parallel aquatic groups. Mind you, I wondered about using 'Fish' instead of 'Fishes', as 'Fish' in English can be both singular as well as plural. A singular language, English.  I found that 'Fishes' can be used to describe multiple species, so that seemed the right choice.

In Fishes VI the third, i.e. the last, pair of flippers have fused to form a horizontal fluke, very much like that of whales. The problem with making 'Fish' alien is the high probability that a torpedo-like streamlined shape is rather likely to evolve as a 'universal' feature. I chose to accept that, so 'Fishes' superficially look much like Terran animals. But they share their world with cloakfish, kwals and aquatic wadudu, so there are definitely some odd shapes to be found too. And Fishes VI are not all that 'earthy': after all, they have four jaws, four eyes, their respiratory system is completely separate from the digestive tract, etc.

The painting combines several themes. I will split it in four panels that show various species of Fishes VI in 'powers of 10', meaning each species is 10 times as large as the previous one, starting at 4.5 cm. Each panel will also show the species eating, so food webs can be illustrated as well.

Click to enlarge; copyright Gert van Dijk
This is the Trench Gobbler; I haven't thought of a binomen yet. This painting forms the second panel of the four. The Gobbler is a typical deep sea species. In this biotope, the only light is that produced by lifeforms, and these are scattered far and wide. This is in fact a very barren ecosystem, which is due to the fact that it is almost entirely based on a slow and sparse trickle of organic material from above. Before anyone asks, I do not know whether there are hydrothermal vents. Animals need to conserve energy here. The water is largely still, and there is no need to swim fast habitually. Hence, there are no fast swimmers here, so there is no overriding advantage in streamlining. If the rare opportunity to catch some fresh food presents itself, it must be jumped upon, because there may not be a second chance anytime soon. These two influences together have resulted in very odd shapes, just as on Earth. The Trench Gobbler has elongated lateral jaws to grab anything possibly edible. In this image, it is attacking a tentacled creature, probably some larval Cthulhuoid. The larva has just emitted a cloud of bioluminescent ink to try to escape, a trick that seems to be working.

Click to enlarge; copyright Gert van Dijk
And here is a detail, for once at full resolution. It is fun to paint such structures, in particular the somewhat glassy structures of the teeth and fins.      

(PS: There is something wrong with my access to the main Furaha website, so I cannot update the loading screen for a while. To check for new posts you should check here directly)

Saturday, 2 September 2017

Spirally slanted spidrids II

The post has the simple purpose of showing that there is progress with The Book. Readers with good memories may remember that I write about spidrid gaits back in 2013. In one post, I toyed with the idea of changing the plane of movement of the spidrid legs from a purely vertical to an angled one. This was inspired by the legs of many crabs and by those of scorpions.

Click to enlarge; from Wikipedia
Here is a nice image of a scorpion from Wikipedia, showing that the plane of the legs is not vertical but at an angle to the ground.

Click to enlarge; from Wikipedia
And here is a 'sally lightfoot' crab (Grapsus grapsus) also from Wikipedia. Note that the hind legs are seen edge-on, so the plane in which they operate is at an angle of that of the surface on which it stands. 

This inspired a very lively discussion in the comments sections why the legs would be slanted. Among the possible advantages were that the animal would be less high, so it could fit in a crevasse among rocks, or it would be less likely to be swept away by tidal waters. Another argument was that the slanted posture allows more muscles to be recruited for propulsion.

Well, I can now add that I found some evidence for the latter argument, in Mantons's Arthopods (There is more on that book in this post). It is difficult to find anything on the biomechanics of arthropod joints. It seems that most of the relevant work was done in the 1960 and 1970's by Manton. In the end I bought a second-hand copy of her book, which proved to be one of the most densely-written science books I have ever read, but it contains an enormous amount of information. She wrote about 'rocking' of arthropod legs, the word she used for what I described as 'slanting', and her reasoning was that it recruited additiopnal muscles for propulsion. No formal proof though! It does not mean the other arguments are invalid though!




In 2013, I produced this quick and rough animation of what a 'spirally slanted sipidrid' might look like.  I recently sat down to do justice to spidrids in The Book, which means doing a few proper paintings with accompanying size diagrams and maps. I chose to add a slanted spidrid to the introductory page showing the variety of shapes spidrid bodies can take. I do that more often: designing various shapes is fun, and it nicely illustrates adaptive radiation. It also allows me to paint various colours and different surface textures.

Click to enlarge; copyright Gert van Dijk
Here it is. It is just a fragment of the original 4200x6000 pixel illustration, and is just meant to give you a taste, not to satisfy your appetite! As you can see, I chose to go with the shiny texture of the sally lightfoot, as well as its riotous colours.  The text introduces it as follows:

"Mad Sickle
This species represents a major spidrid clade. While ‘square spidrids’ move their legs in a vertical plane, the ‘slanted spidrids’ do not: the basic leg joints have tilted. The most likely reason for this is that the flexion and extension muscles can now more easily help with propulsion. Most ‘slanties’ are very flat and live in crevasses. There are clockwise and anticlockwise slanties; the direction is inherited, so each species has its own exclusive direction. It seems that the two types of slanties arose completely indepedently, so ‘clocko's’ and ‘antics’ are not at all related. The mad sickle is very agile. Please do not try to catch one: you disturb them, you are not likely to succeed, but if you should, it will pinch you very forcefully. 
Name Sicilicula insana; Sicilicula (L.): little sickle; insanus (L.): frenzied, maddening"