What do Roman soldiers, trilobites and the Furahan Droodle have in common?

Click to enlarge; copyright Gert van Dijk

Before answering that, you are probably wondering what a Furahan 'droodle' is. Well, one description found in the 'Annals of IFB Field Expeditions' reads as follows: 'The droodle is a slow an silly creature, behaving in its snug little world like the Lord of Creation, notwithstanding its utter insignificance'. Apparently the Annals did not require any semblance of scientific impartiality before accepting contributions, but that is not the point. Further on the author continues: "It can behave this way because it is well protected because of its foul taste and because of the overlapping armoured plates covering nearly its entire body."

An early version of the droodle is shown above. And there we are: the droodle has an armour consisting of overlapping plates, and so did trilobites, and so did Roman soldiers. I came across the subject when I was preparing to paint the droodle anew for The Book. Most of my new paintings have very little to do with the old ones, but I like some old designs enough to go over them again, taking the opportunity to improve them in as many ways as I can. I started wondering how animals manage to move while covered with what seem like very stiff plates. How are these plates attached to one another? Obviously, in arthropod legs the exoskeleton of adjacent parts of the leg form joints that often have just one axis of movement, much like our own knees: we can bend it stretch a knee but it does not move sideways nor can we rotate the leg and foot backwards. I started thinking about whether that also applies to the plates covering the droodle.

Click to enlarge; copyright Gert van Dijk

Above you see the result of simple experiment: I wanted to form successive hoops curving around the animal's back while widening at the sides. I imagined a hinge between two hoops with the axis of rotation about halfway up the animal. Of course, such an axis of rotation would make sideways movement impossible, but so be it. I assumed that the plate in front would slide over the plate in back. I could imagine that in my mind's eye for half-circular hoops, but felt I needed some visual help with hoops that widened at the side: could they in fact slide over one another over their entire length, or would they intersect, making the movement impossible? So I made a rough shape like that in Vue, of which the top surface represents the plate. As you can see, at the centre one hoop can easily slide under the next one while it wants to move over it at the sides. This does depend on the site of the hinge and some other aspects, but it does show that you cannot assume any angle or shape to work. I could of course still paint it the intended way and no-one would be the wiser. But science has preference over art in such matters. So what was wrong?
 

Click to enlarge; Manton, The Arthropods 1977

I then thought of trilobites: their name indicates that their bodies had three lobes lengthwise, with a thick part in the middle and much narrower side flanges, much like the droodle. And trilobites could roll up their bodies, so they solved the problem how to slide one hoop under the other better than I had (weel, they had more time...). I obviously needed expert guidance, perhaps a book called 'Biomechanics of trilobite intertergite movement' (the hoops are called 'tergites', just so you know). I found something close: 'The Arthropoda' by S.M. Manton, 1977. I am not new to reading scientific papers, but this book is as intricate as it is condensed: the reader is assumed to be rather well-versed in arthropod classification and anatomy. The book contains sentences like 'There were no coxal endites or gnathobases.', in its own way as wonderful as 'It was a dark and stormy night'.

Click to enlarge; Manton, The Arthropods 1977

So here is Figures 1.5 from that book: have a good look at the top right in particular: the tergites are connected by a fold of skin, doubling back on itself. There is no hinge to be seen anywhere. If the tergites are indeed connected only by such a fold over their entire length, they would have much greater freedom of movement than if there were just one axis of rotation: this is a good idea.

I then wondered if his is how all armour segments are connected in arthopods, and browsed through the book. As you would expect, there are a myriad adaptations of tergite movement. In species that burrow, successive tergites are kept from sliding over one another and have a built in 'door stop', allowing the animal to push the soil out of its way. In other species there are additional small tergites normally hidden between larger ones. When the body is flexed, the gap that would otherwise appear between the large ones is filled by the small ones. In many cases tergites only cover the back of the beast. There may be other bits of hoops at the belly (sternites) or the sides (pleurites), all of which are connected to one another by the folds of skin.

Click to enlarge; from The Arthopods, SM Manton 1977

Here is an example of the intricacy of the internal anatomy of a millipede. The large top image shows the poor millipede cut lengthwise with its body flexed (the back is at the top). The lower left image is a horizontal section of the body rotated sideways. Complex, aren't they? The feature I would like to call your attention to is the folding of the skin between tergites: I found that in all such plates.

So I learned from all this that arthropod tergites can in fact be connected by 'hard points', but in many cases the skin folds allow flexibility and freedom of movement. So that was one problem solved, but all this did not answer the question how to ensure that the tergites do not 'intersect' while rotating, as they did in my simple model? Or how do you avoid having large gaps form when the animal moves? There may be several answers to these questions. Perhaps the tergites should be flexible.

( video does not seem to work; I will check later...)
Have a look at the YouTube video above, of a millipede flexing its body in all directions: the tergites do not show any gaps at all, and yet they slide over one another in at least two directions of rotation: they must be flexible. But would that work for a big animal, in which you would expect the tergites to be stiff? (but never brittle: the armour must be capable of withstanding blows, and allowing it to deform it a bit should absorb the energy of a blow). 

Another solution would be to forgo tergites that run from one side of the animal to the other; split them up in separate parts instead. These smaller plates could each be tough, and be connected with skin folds. At the top of this post you'll find a simple model I made to see what a droodle designed in this manner might look like. Mind you, this is not what the painting look like: the droodle has already evolved some more and no longer looks like this, but it does still have multiple overlapping tergites.

Click to enlarge; source here

So what about the Romans? Everyone who has ever seen a film with Roman soldiers in it, or who has read an Asterix book, knows that their armour consisted of metal hoops circling the soldier's body. This seemed very similar to the tergites of trilobites or other artropods, so I wondered how the legionnaire's hoops were connected, That was easy to find out: there are books describing actual archeological finds. The image above is from tha reconstruction based on such finds. The Latin word for this particular type of armour is 'lorica segmentata' ( I also leaned that all these films might be wrong: this plate armour type may not have been the standard type of armour; chain mail may well have been more common.) And here is how the loops are connected: not by hinges, but by leather straps on the inside of the hoops.

( video does not seem to work; I will check later...) 
The video above shows the Roman lorica in action (the inside is well visible two minutes into the video). The hoops could slide and rotate a bit with this arrangement, in exactly the same way that the tergites of trilobite could slide over one another thanks to being connected by folds of skin. Only the trilobites had their armour some 520 millions of years before the Romans invented their lorica.

So this is how the droodle came by its armour and by its scientific name of 'Lorica segmentata'. There is a long list of items the Romans did for us, to which I would humbly like to add that they can make you think how exoskeletons work. Not a bad thing at all. 

More cloak and dagger stuff: cloakfish IV

Cloakfish have been discussed here previously; for the latest instalment, go here. Before I go on, I wonder how to call them; the plural of 'fish' is still 'fish' when you are talking about the same species, but as far as I know 'fishes' is correct when dealing with more than one species. So should I write sentences like 'Clown cloakfish are founds in their thousands under floatreefs' and 'The many cloakfishes of all shapes and sizes in the peri-Archipelago seas'?

Anyway, cloakfishes (!) were developed as animations before I painted them. So far, they were animated using MS-DOS, believe it or not, but the result was a bit two-dimensional. I later used Matlab too, but only as a painting aid, not to produce animations. Their bodies were very simplistic and the cloaks themselves were just sheets, without any thickness to them. But when I saw large cloakfishes in my mind's eye, they floated majestically into view, with cloaks as substantial as those of a manta ray. In fact, the one I will show now is a 'shortsleeved cloakfish' so it does look a lot like a ray, but with four-sided radial symmetry, obviously. So how could I realise such a vision?

Click to enlarge; copyright Gert van Dijk

Well, with difficulty... The overall strategy consists of several steps: the firsts relies on Matlab to design the overall shape of a cloak, as shown above. The various curves are combined to form the outline of the cloak as well as of the part of the body -the dagger-  it is attached to.

Click to enlarge; copyright Gert van Dijk

Then, flesh out the form by creating two surfaces for each cloak so it smooths into the dagger. What you see above are two such half cloaks, together making up one cloak. If you were to stick four such ensembles together you would have a full cloak and dagger assembly.

Of course, there is movement to think of, and the shape of the cloak has to be changed over its movement cycle. I divided the cycle into 200 steps to have some temporal resolution. For each stage of the movement there are eight half cloaks, so we are now at 1600 files. All these shapes are written to store as 3D obj files, again, using Matlab.

Click to enlarge; copyright Gert van Dijk

Meanwhile, design a head in a suitable program such as Sculptris. There you are; it is not very detailed, but more details would probably not be visible anyway. Also create an underwater landscape in Vue Infinite with a simple animation to allow the cloakfish to glide through the water. Open the programming language Python and write a script for Vue Infinite; from within Vue, use the Python script to load the eight appropriate half cloaks for each frame, the head too, assign textures, transport the lot to the correct positions, render an image and store it. At a reasonable resolution of 640x360 that will take about 30 hours.

Copyright Gert van Dijk

All that remains then is to create a film, perhaps add sounds, etc. What you see above is a trial version in which the cloakfish is just white. I rather like the movement. For a better view, visit Loncon3, where I intend to show a good version... 


PS 1: this is post #200...
PS 2: I am considering returning to blogging regularly after Loncon3.


(PS 3: this is to stop a particular site from copying my blog: 7InDB4PgQaCddePKQEqA )

Influence of the rostrum linkage system on forage volume in Brontorusps (Brontocrambis brucus)

A Christmas Special!

Ahead of the normal schedule, and with dinosaurs, rusps and biomechanics!

Click to enlarge; copyright Gert van Dijk

The title of this post sounds like that of a proper scientific paper, doesn't it? Something out of the 'Journal of Astrobiological Biomechanics', I guess. It's time to look at rusps again. My big rusp painting is finished, and as it is meant as a double-page spread, it is large: 7200 by 2700 pixels. A spoiler is shown above showing a fragment of a rusp in the background of the painting. The fragment has been halved in size and its area represents just 2% of that of the entire painting. The painting is based on earlier sketches. For more on rusps, either visit the main Furaha site or look at these posts: sketches, anatomy, predation, concept paintings, etc.  

The evolution of new Furahan animals gets more complicated with time. In the beginning I just sketched a pleasing shape and started painting right away. Now, I worry more whether the animal makes evolutionary, mechanical and ecological sense. Well, up to a point; this is science fiction and supposed to be fun, after all. 

Here are some of the steps in rusp 'ontology': they started with some quick sketches, and then the slow evolution began: successive legs were offset medially and laterally to avoid legs bumping into one another, followed by an arrangement for their skeleton. Their fore and aft whips are long and held horizontally rather like the tails and necks of sauropods, and hence have a similar system of internal trusses as compressive elements at the bottom and ligaments at the top to withstand tensile stress. The whip is held up passively by these forces, so avoiding the high cost of doing that with muscle force only. The last stage involved refining the head of the rusp, and in particular its snout, or 'rostrum'. In an earlier post this rusp species was called Mammoth Rusp / Megacrambis, but now it is the Brontorusp / Brontocrambis; yes, that means 'Thunder Caterpillar'!  The Mammoth Rusp still had some intricate limbs functioning as additional feeding aids under its snout. I was not too certain of that arrangement, and my doubts were confirmed by comments on that post. So the Brontorusp no longer has these additional mouth parts. The thing is, now we have a massive animal with a large head. How does it feed itself?

The mouth of the rusp is in its head, which seems obvious but in speculative biology not many things are obvious. Also note that rusps are large herbivores: they need a lot of food and spend much of their time eating. Moving about is costly, so it would be best if they moved the least possible amount to get their food, which does not sound as if there is much room to save energy. Let's tackle that by considering the problem of getting an animal's mouth on vegetation; there appear to be four solutions to do so; rusps use the fourth, but we'll come to that. The first solution, always necessary as vegetation will not come to you, involves walking to the food source.

Click to enlarge; copyright Klein et al; Biology of the sauropod dinosaurs. Indiana University Press 2011

But once an animal arrives at its 'foraging station' a nice way to save energy is to keep most of the body motionless and to have a long neck allowing the head and mouth to move about independently of the gut. For very large animals, needing to feed all day, it pays to divide their anatomy in mouth and guts; the rest is just 'other bits'. Sauropod dinosaurs used that method, and the image above is from a study on how far sauropod mouths could reach, depending on neck length and leg length. The idea is that the neck can move in a horizontal plane 90 degrees to the right and the left, and in a vertical plane straight up and down. If the animal is lying on the ground the volume of space that it can reach is one quarter of a sphere. If the base of the neck is higher up, when the animal is standing, the volume increases. The authors assume that the bottom part of the volume then is cylindrical whereas I would assume that to be spherical as well, but never mind.

Click to enlarge; copyright Gert van Dijk

Swans and geese have very flexible necks and can probably reach every point within that envelope, but if an animal has a neck less flexible than a swan's, only part of the volume is accessible to the mouth. If this is the first time you realised that geese and sauropods might have long necks for a similar reason, good!

The image above shows an adapted 'forage volume' for a sauropod: the outer red sphere is the outer limit of where it can reach, and the inner blue sphere represents the inner limit, assuming that the neck is too stiff for the animal to reach a point closer to its body. The human ('Marlene') is just there to keep the sauropod in its proper place. 

The third solution to get the mouth near food is to use an appendage to shovel food towards the mouth. The best example I can think of is the elephant's trunk, which greatly increases the elephant's reach. The erstwhile rusp mouth limbs were short and not at all good as harvester limbs, and I did not wish to elongate them tenfold; they are gone. I also did not wish to turn the whip into a grasping organ. Rusp whips are not built for that, although in a pickle they can probably be used to knock a branch off a tree. Instead, rusps use a fourth system which is really just a combination of the last two: they carry their mouths towards the food without moving the rest of the head. The 'mouth extender' is extensible and based on a mechanical linkage system. In itself this is certainly not a new idea: Earth fish have such systems in abundance.

Click to enlarge; copyright Gert van Dijk

This image shows a schematic view of the rusp rostrum. Start with the red shape in the foreground: it consists of two V-shapes starting from a vertical axis. All places where elements meet are in fact joints. The pink axis shows that the whole ensemble can rotate, but it can do other things as well: if the two Vs rotate towards one another, the whole shape will become longer and narrower. At its right end, the shape ends in two points on a horizontal line. Now copy the shape, rotate it by 90 degrees, and you get the blue shape in the foreground. The two points where the red shape ends act as connection points for the blue shape. Once connected, some movements from the red shape are connected to the blue one, but not all, and that makes the rusp rostrum quite versatile. In the back you see how the rostrum is formed by stringing red and blue shapes together. In reality the trusses are not formed by straight bones, but by curved ones, so the section of the rostrum is circular rather than rhombic. The cylinder on the right attempts to show the outlines of the bones on a cylinder.

Click to enlarge; copyright Gert van Dijk

And this image shows an as yet unmentioned aspect of movement: if the two starting points are brought closer together, this changes the section of the rostrum as well as its length. The right one is extended, the middle one shortened, and the right one is in neutral position. I expect rusp rostra (yes, that's the plural) to be able to double in length.

Click to enlarge; copyright Gert van Dijk

But we need more flexibility, and that is achieved by rotating the shapes and using the angle between the Vs for additional control. The stylised skeleton in the back shows what can be achieved. So there we are: an extensible and steerable system to get rusp mouths where they would otherwise not reach.

Click to enlarge; copyright Gert van Dijk

Here are two views of an adapted Sculptris model of a rusp head. I take it you will recognise the system of trusses under its hide.

Click to enlarge; copyright Gert van Dijk

And finally, a schematic rusp foraging volume, rather like that of the sauropod (the whip of this model is truncated). Note that the rusp can access a larger portion of the outer foraging volume than the sauropod. The volume itself is smaller though, as rusps are smaller than sauropods, and their rostra extend their reach, bot nearly as much as the sauropod's neck does. Marlene is standing in the forage volume, something I would definitely NOT recommend! In practice, rusps are ground feeders, not bothering about high branches. Have I told you about the ecology of the spotted plains where they live, where post of forests alternate with plains and how rusp feeding habits are to blame for that? No? Oh well, that is another story.  

Hexapod evolution in a twist

Just a short post this time, as I am busy painting. The painting in question involves the early evolution of hexapods, something also discussed in a post titled 'The lateral fin theory and mackerel mode'.  

Click to enlarge; copyright Gert van Dijk

Above you see the specimen of 'Fishes II' that was shown in the previous post. It was digitally sculpted and painted in Sculptris. Such sculpts help define the perspective of the undulating fins. Once you have such a shape in your computer, you can go two ways: the first is to  perfect digital sculpting, which at present probably means mastering ZBrush. That road does result in a 2D image, taken as a snapshot of the model, but do do that the models need to be sculpted with much more finesse that the rough ones I produce. Readers of this blog will know the work of Marc Boulay, who does all this at the expert level.

But I chose to stick with regular figurative painting, because there is something about a painterly look that I like. It is not that easy to define 'figurative painting' in such a way that it excludedes digital sculpting. Perhaps it is creating the illusion of a three-dimensional object by placing colours on a two-dimensional surface. This includes digital painting as well as classical painting using oils or water colours or any such technique (I sometimes encounter a resistance against digital paintings in art circles, which must mean they see it something else than it is: just another technique).

In this process, 3D sculpt programs are aids to get the perspective or the lighting right. As with any technique they have their own unique problems. People will accept any perspective on a photograph or computer rendering, but not on a drawing (see here for an explanation).

Click to enlarge; copyright Gert van Dijk

Anyway, I try to produce a painterly effect. The two images above show two versions of the head of the Fishes II species Vexilloscissus. The left one was based on the 3D sculpt. I thought the painting was finished, and suddenly realised that there was no way that the six protojaws seen here could evolve into the typical four jaws of the basic terrestrial hexapod Bauplan. That design involves upper and lower jaws with two rows of teeth each, and two lateral jaws with one row each.  While sculpting I had forgotten that, so I had rotated the ensemble of six jaws incorrectly, with jaws in the midline in the upper and lower positions, and no jaw in the lateral positions. In world building it is hard to keep tracks of all the details, or at least that is my excuse for the mistake.  

So I had to erase the jaws and paint them again in the correct position. The result is at the right. It's a  pity really, as I rather preferred the left one. Oh well, never mind...      

The 'lateral fin theory' and mackerel mode

I still have no time for posts that take time to read, think and write; well, more than a hour or two. That is a pity, as some ideas need time to do them justice. For instance, there is a post to write on what happens is photosynthesis is less dramatically imperfect as it is on earth (see here); there is also the final chapter of the 'sight is superior series' (see here), and I have at least one other world builder's creations in mind.   

Those will have to wait; instead, here is a short post on where the six limbs on Furahan hexapods came from. On the 'real life' level the answer is easy: 'six limbs will look exotic and therefore help create an alien ambiance'. Within the Furahan world, the logic of science fiction demands an answer that fits within the concept.

 

Click to enlarge; copyright Gert van Dijk

The sketch above is an old one, and the first that showed the first steps in hexapod ancestry. By now, many of the anatomical features are being overhauled, so the number of eyes is incorrect. The overall scheme is still there though: it all starts with a less than impressive little elongated tube with broad fins at its sides. This 'ULF' (unassuming life form) swims by waves that pass from front to back along the fins. Nothing particularly spectacular here: undulating fins may well be a constant throughout the universe. From that start I assumed that the fins might be divided gradually, to provide greater control and flexibility (you cannot suddenly move a part in one direction if it is fixed to parts in front and behind of it). This greater need for manoeuvrability evolved together with jaws; you cold also say that the jaws and the fins helped one another's evolution: without jaws, there is no speed, and without a better propulsion, the jaws do not provide that much benefit. The third stage shows an animal with fully separated fins, just not necessarily six of them; the reduction to six came afterwards.

The origin of hexapod fins therefore lay in a lateral membrane that split up. Many years later I wondered where Earth vertebrate limbs originated. To my very large surprise, the first explanation I came across was something called the 'lateral-fin theory'.

Click to enlarge; Coates MI. The origin of vertebrate limbs. Development 1994; Supplement 169-180 

The images above show an example of what a hypothetical vertebrate ancestor was supposed to look like: it already had unpaired fins along its back and belly, and lateral (sideways) fins along its sides. The theory, apparently first formulated in 1877, states that these lateral fins later gave rise to limbs. I was first a bit irritated, but later pleased that I had stumbled on a principle that apparently was not altogether fictional. That was until I went back for a closer look at current theories regarding vertebrate limbs. It would appear that the lateral-fin theory is now out of date. Other theories held that limbs evolved out of gill branches, which seemed to make sense as the first forelimbs were attached directly to the skull. That theory apparently also now belongs in the dustbin of history.

                   

Click to enlarge; Coates MI, Cohn MJ. Fins, limbs, and tails: outgrowths and axial patterning in vertebrate evolution. BioEssays 20:371–381, 1998

The image above shows an illustration from a recent paper on limb development. It shows that that unpaired fins in the midline ('median fins') existed well before vertebrates had jaws or lateral fins/limb. When lateral fins appeared, the first to appear were the front pair, with as yet no trace of hind limbs. The two pairs did not evolve together, which you would think, given their similarities. Modern discoveries in the field of 'evo-devo' ( embryonic development in light of evolution) centres on hox genes as a sort of overall conductors of embryo formation. A recent theory holds that the genes responsible for limb formation were co-opted from a previous use, one that involved formation of the gut through the 'lateral plate mesoderm'. The paper from which the image above was taken  mentioned the possibility of a third pair of limbs in vertebrates, the kind of nice exotic happening that we like in speculative biology. Here is what Coates and Cohn wrote:

"Finally, the absence of vertebrates with more than two sets of paired appendages has often been used as an illustration of evolutionary constraint. Developmental mechanisms responsible for this anatomical limitation remain unclear. Arguably, the nearest approach to a third pair of lateral appendages may be the lateral caudal keels of certain fishes, such as tuna and various sharks."


So there are in fact three pairs of lateral, well, outgrowths in vertebrates? Fascinating. But the test continues:

"Even the most elongate lateral fins of primitive fishes terminate in front of the anal level. Clearly, lateral caudal keels can and do emerge, but articulated endoskeletal paired appendages require the lateral plate mesoderm, and this is linked intimately to the extent and pattern of the gut."

Curiouser and curiouser. It does not look as if vertebrates will surprises us by evolving a third pair of legs, though. For three pairs of legs, you need to turn to insects, and for big hexapods, there is always the fictional universe.

But does all this mean I should give up on my 'lateral fin theory'. Actually, I see no reason to do so. In fact, it is rather nice that the lateral fin theory remains in place on Furaha, as the explanation of the origin of six legs in Furahan hexapods.

 

Click to enlarge; copyright Gert van Dijk 

To celebrate that I stole another two hours and used Sculptris to sculpt two quick ULFs. The first is shown above: no jaws, four eyes, two lateral undulating membranes and two long gill tubes running along the belly connected to the sea by a number of spiraculae. I still need to name it, and I think I need something that does justice to its pivotal position in evolution. Suggestions are welcome. Latin or Greek only though, please.

Click to enlarge; copyright Gert van Dijk

And here is its successor. As you can see, the membrane has developed indentations and the animal is longer and bigger. It has six claspers in front that can already deal with soft prey quite well. Note that the body is stiff, very unlike the very flexible body in the old sketch. The body can flex up and down, but sideways movement are almost impossible, thanks to he two stiffening rods that lie buried in the body at the root of each lateral fin. The stiffness is a consequence of this early body plane, and is a feature of all later hexapods.

Click to enlarge; copyright Gert van Dijk

I could not resist quickly daubing one in Sculptris with colour to show one in 'mackerel mode' (I still prefer painting, but the 3D process certainly is a very quick way of producing an illustration).    

A marblebill in progress (also known as the becdacier)

No time this fortnight to write anything elaborate, unfortunately. Some posts take much more time than others. The ones that take most time are those that require checking the physical aspect of some matters, not just because finding sources and digesting the content takes time, but usually also because I then need to do some programming of my own or I have to make some specific illustrations. In short, the heavy science bits take a lot of time. Over the years I have written quite a few words on such subjects, and I started wondering whether I should perhaps bundle them, work them over, write some new chapters, and produce a book on the biomechanics of alien life. Something like 'Darwinian creativity in a Newtonian Universe'. The title is probably much too enigmatic for the book to sell, but perhaps it could be a subtitle. Mind you, it would be completely separate from the Furaha book. But would anyone buy it? Let me hear what you think.

Anyone, I have been working on an update of the marblebill. I showed you another such update once before, and the marblebill is on the Furaha website but featured previously on this blog as well. You may recognise some general update principles. The eyes on stalks are now less prominent, but certainly still occur in various species. There is also eye specialisation. The images below are taken from the sculpting program Sculptris, a free programme I recommend unreservedly.

Click to enlarge; copyright Gert van Dijk

The marblebill is an arboreal brachiating predator, and has two forward facing eyes to help it judge distances and fixate its prey. As is the case for dragonflies, the size of the ommatidia (the individual eyelets in a compound eye) depends on where you are in the eye: they are smaller in the part of the eye facing directly forward. This increases visual resolution at the price of sensitivity to light. The marblebill is a diurnal creature, which makes sense I think: you would need impossibly good vision to allow an animal to hurl itself from branch to branch at high speed at night.

Click to enlarge; copyright Gert van Dijk

There is another pair of eyes, the 'oculi posteriores'. Note that these were not posteriorly placed in ancestral hexapods, whose four eyes were placed around the head. What became the anterior eyes were once the bottom ones, and the posterior ones are the former upper ones. Anyway, in the marblebill lineage the upper ones, alresdy in the posterior position, over time migrated outwards, providing an all around vision, not just in the horizontal but in the vertical plane as well. For an animal living in three dimensions this is more important than for a grazing animal. One result is that it would not be easy to sneak up on a marblebill. Not that there is any other predator up there in the trees that would perform such sneakish acts anyway: it would be too dangerous. The marblebill also does not need much vertical vision for its territorial disputes, as these involve no sneaking whatsoever, but are announced frighteningly loudly. But detecting prey is another matter, and for that these eyes are superb.

Click to enlarge; copyright Gert van Dijk

Here is the painting in progress. I used to work out perspective and draw everything completely without any aid except for the occasional ruler, but I now make use of what the digital age has to offer. So I exported the sculpted head into Vue infinite, made certain the lighting came from the correct direction, adjusted the perspective angle and produced two renders. Cut out the head, place them on a separate layer in Painter 12 (to be deleted later), and everything is in place to start painting. Now all I need is the time to do so...

Away until back...

After almost four years of writing posts for this blog it is time for a sabbatical. There are certainly enough subjects left to write about. For instance, there is the issue whether established echolocation can prevent eye evolution taking off (I think not), as well as more on eyes, issues on flight, on camouflage, etc. I find writing posts and interacting with those who react (thank you all!) most enjoyable. It is just there are things I need to take care of, and the blogging batteries need recharging. I do not know when I will resume writing, but a nice time to do so would be sometime around the blog's fourth birthday (that's in April, in case you wonder). That is not a definite promise though.

This does not mean that the Furaha project is in any danger. After 30 years I am not going to drop it now. Far from it, in fact: I intend to devote part of the time I have spent blogging on painting. There's lots of things to do.

As proof that the project is very much alive, I can tell you that Furaha will appear in a film that you can actually see in a cinema. The film is being produced by an independent company and is being shot right now. I cannot say too much about it, but it is not a documentary; it will be about people, right here on Earth, and the Furaha project plays a very interesting role.

The producer recently asked me to make -with two days notice, but such things always seem to work that way- a 3D model of my woolly-haired shuffler, an animal that they had seen in my newspaper interview (here and here). and so I loaded Sculptris, a program I wrote about earlier, and started making one. Sculptris is completely free and a joy to work with. The resulting model is certainly not perfect, but for someone like me with limited experience with digital 3D sculpting programs it did not turn out too bad, I think. Particularly if you consider that this was done in about four hours of time...

Click to enlarge; copyright Gert van Dijk

Here are some screen shots of Sculptris with the model in various colours. It was a bit difficult to get the lateral jaws in there, as Sculptris does not formally accept holes. What i did was to push two extrusions together and then I flattened them where they toch one another. Formally, there are no holes in the model...

Once I had that, it wasn't difficult to export the model to the 'obj' format, import it into Vue Infinite and make a 'turn table animation'. That is what you see above. Not too bad, is it?

With the 'obj' model at hand, I decided to have a better look at a website I had visited before. The site, by the firm 'Shapeways', provides a service through which you upload a 3D computer model, and they then check it, print it in 3D and ship it to you. The instructions on how to check the model and upload it were fairly straightforward, so all was left was to choose a material. You can choose various materials with different qualities, such as the ability to hold detail. I chose a material that promised to allow details and settled for a small size, as you pay for the volume of the material used.

Click to enlarge; copyright Gert van Dijk

The model arrived within in two weeks and looked good. Part of the left maxilla had broken off, not too surprising if you consider how thin it was. The website has lots of information on how to prevent making your models too thin. What I had not foreseen is that the material was transparent, so much of the detail did not show up. I painted it to solve that, and photographed the result. Interesting, isn't it? I was impressed with the details, but would like a larger size next time. You pay for the volume of material that goes into the model, so I will have to learn how to hollow out the model; if I manage that, I should be able to order a much bigger one for the same price.

So, it's off towards the sunset for me, for a while. I intend to keep on replying to questions here and on the Furaha bulletin board in the meantime, so I'm not away altogether.

It's a Fish! (yes, again...; this one's in 3D, though)

Click to enlarge; copyright Gert van Dijk

This is just an extra post. Regular readers may remember that I tried my hand at ZBrush in the past. I still try it from time to time, but found that it, as everything, takes time to master, and digital painting takes precedence. The ZBrush people keep out churning new options, so I will probably never get around to mastering even the simpler elements. Pixologic, the same firm that produces ZBrush, now offers a similar program but completely free: Sculptris. It offers only a few controls, which really helps to learn it. It is very impressive. The controls are the same as those of ZBrush, so experience with one program helps the other. I could not resist trying it, and found it a pleasure to work with. Go to the Pixologic site to see what can be done with it, because my meagre efforts only show what you can do with it in one evening. It is very useful for 2D artists who do not plan to go into 3D, becaue it is easy to sculpt a rough shape to help get the perspective right.

Click to enlarge; copyright Gert van Dijk

So here is a Fish, of the Fishes IV type; I showed one before. I painted four now for The Book, and will not publish these paintings here on the blog. But having done that, Fish IV anatomy came natural to me, and here it is: six flippers, usually attached higher on the body as you go aft, a large head merged without a neck to a stiff body, and three gills on each side with separate inlets but a fused outlet. You knew about the four eyes and the four jaws. As I said, typical Fish IV anatomy.

Click to enlarge; copyright Gert van Dijk

Click to enlarge; copyright Gert van Dijk

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P.S. As Luke remarked in the comments section the Fish shown so far are fairly large. Aren't there smaller ones? Yes, there are. I had realised I had a tendency towards larger ones, so I explored the possibilities of size on purpose.

Click to enlarge; copyright Gert van Dijk

Here is a rough sketch in Painter11. Its smaller size is indicated by relatively large eyes and by having thinner flippers, that as a result resemble fins more (the second pair are probably too large). I also experimented with a general 'fishy' look by giving it a glistening skin. The counter-colour pattern (dark on top, pale below) is probably a universal trick to blend into the background.