Its a bird, it's a plane, it's... a tetropter (tetropters IV)

The nice thing about computer animation is that it allows you to actually see thing that you could only dimly imagine beforehand. One image that has been sitting in my mind for many years is the following: you see a dusty plain, and a herd of handlebars (Latifrons imperator) come galloping in from the right hand side of the image in the distance, and then wheel towards the viewer as if they were performing a well-rehearsed cavalry manoeuvre. I can almost hear them too...

Unfortunately I do not see anyone spending a small fortune to make this a reality, so I will have to content myself with what I can do myself, with my PC, at home. Some visions therefore remain locked in my head, but a few more modest ones do find their way out. Making tetropter flight visible is something I thought I worked on for quite some time; today I can show you a near-final result. Near final, because nothing creative is ever truly finished. In this case, the camera should move, the animals should vibrate in rhythm with the wing beats, there should be more details, there should be motion blur, and there absolutely has to be blurring to mimic a limited depth of field and through that create the illusion of small size.

Still, what I can show you is the principle of the thing. It's not a movie, but an illustration of wing movement in slow motion. Tetropters have been described several times on my blog. A summary of the tasks involved in animating them is found here, and entries on their design and wing movement patterns are here, here and here. In short, they are radial flying animals, whose four wings can do a 'double clap and fling', invented by yours truly, and later also by other people in the flying robot business. By the way, the movement of tetropter wings is not all that different from the complex way in which Earth insects move their wings.

This is an animated scheme to show how it all works: the wings are planes that are warped as they cycle through their movement cycle, so their shape is different depending on were they are. Where they are is governed by rotations along the x-, y- and z-axes, and all these paths can be altered and edited. The Matlab programs that do all this in the end write lots of 'obj' files: those are files describing 3D shapes; one is produced for each wing for each frame of the cycle (there are usually 120 frames in a cycle). A script written in Python then loads in a scene containing a body shape without wings in Vue Infinite, adds the appropriate wings per frame and stores the images. These are then used to form an animation, and those are what you see here.
The 3D shapes of the wings consist of 1600 small triangles, which is more than enough to show supple movement. As they are they do not look like wings at all, but there is another trick to take care of that.

The trick in question is to add transparency and colour. The transparency mainly makes unintersting parts invisible, but it is also useful to make the wing itself partly transparent as here. To create the fly-like animal above (Bombilator musca) I used an image of a real insect wing found on the internet, and used that to create a transparency mask. All of a sudden, the boring rectangular 'wings' produced by the Matlab program take on a biological appearance. Please do not look too closely at the body of the animal: it is a simple shape cobbled together in Vue. As you can see the animal has four legs and two sets of eyes: upper ones, presumably to scan for danger, and lower ones, near the food gathering end at the bottom.

A bit of colour makes a lot of difference, so here is a farfalloid, resembling a butterfly in overall appearance (Farfallapter caeruleus). Indeed, I stole its wings from a real Earth butterfly, albeit with some warping and editing. Mind you, quite a bit is lost in the conversion process.

Click to enlarge; copyright Gert van Dijk

To show that, here is a still of the Farfallapter; better, isn't it? Then again, you can see how crudely the wing is linked with the body...

I guess I now no longer have any excuse to put off work on the 'Flying with...' page. It is probably also time to redesign the site. I have already looked at that, but the days where you could learn HTML in two evenings seem to have gone for good.

Nereus (or how you can have radial flight with an odd number of wings)

As regular readers know, I am always on the lookout for creative projects concerning speculative biology. On places like Deviant Art you will find many interesting alien or alternate animals. Some feature new traits, others rework well-known themes; some are professionally drawn, others are less so. But what interests me most if there is a background: are there biotopes, is there a food web, do the predators match the prey, etc. That shortens the list considerably.

Some large projects have been in existence for very long times, and it does not feel entirely right to discuss them here. But there is one project, Nereus, that is relatively new. Its creator, Evan Black, does not mind, so that helps. Apparently Nereus received its name because humans first thought it was a water world (Nereus is a being from Greek mythology). The earliest post on the Nereus project on the Speculative Biology forum dates from May 2009. Evan has already produced 100 species and aims to achieve no less than 200 species. That is a lot or work: creatures have to be designed and described, and also drawn. I like the way Evan draws animals: while a bit stylised, they are very energetic, and as design they work: what you see are lively animals.

Click to enlarge (VERY much so!) Copyright Evan Black

Here is a start: a rather large cladogram of current Nereid species. Don't be surprised to find that the one on Evan's site differs from the one here, because he might have added a new species by the time you go there...

The Speculative Evolution pages contain discussions and comments on how Nereus develops, but I much prefer to see the result on Evan's own site. There, you can work your way through the menu, clicking on the Latin names of the various groups until you get to individual species, but you do not see what you are aiming for until you get to the species pages. Once there each species has two pages: one with text and a thumbnail, which leads to a much larger image with additional text. But there is another way to browse Nereus that I much prefer, and that is to choose 'world', and then 'cartography and climates'. That will take you to a list of 7 biomes, and clicking on them rewards you with an overview of that biome and small images of the species in it, that you can then pick and read at will.

Click to enlarge. Copyright Evan Black

As an example, here is the 'Sog Basin'. Sog "carpets the landscape like a thick tangle of spongy red veins", which sounds a bit like Well's Martian weeds. Luckily, there are no intelligent aliens around to regard Earth with envious eyes (or not yet). Sog sucks up water from the few available sources, and transports it across the otherwise dry biome. Leaks in the sog create watering holes, on which many species depend. Now that is why I prefer creations with a background: you immediately start to think how that works, how such species might look, etc.

Click to enlarge. Copyright Evan Black

Here is one such species: the kappa (Nothorana pratensis). It is a predator lying in wait in sog ponds, with just its dorsal eyes and its nostrils above the water. Take a good look: the kappa has three legs: two paired front ones and one unpaired jumping leg in the back. The illustration also contains a classification list containing the familiar Linnaean scheme, which starts at the species level and goes all the way up to the phylum Tetrabrachia (that would be 'four arms', if I remember my Greek correctly). One of the nicest things about Nereus creations is that it all fits together. Look up the Tetrabrachia, and you will find a page devoted to their anatomical Bauplan.

Click to enlarge. Copyright Evan Black

And here it is. The four arms in question concern four major nerve trunks emerging from the central brain. One trunks goes upwards, and that one deals mostly with sensory functions, which in modern Tetrabrachia has caused them to develop a head. The other three trunks control movement. In effect, what we are seeing here are radially organised animals, and I like the idea of taking radial animals rather further than they have managed to do on Earth (see the discussion on tetropters here, here, here and you can more on tetropters yourselves; here is something about radial symmetry; if that is not enough, just search for spidrids on this blog). But the kappa does not show radial symmetry; it is blatantly bilaterally symmetrical, and the legend includes information just when that happened.

Click to enlarge. Copyright Evan Black

I cannot resist showing one particular specimen, and that is because Evan and I discussed its s flight mode. Again, this is a radial life form. Most flying forms on Nereus are bilaterally symmetrical, resulting in flight plans that are superficially similar to the ones on earth. Not so the Cliff Whistler (Cadosmilos Aetopsis).

As you can see, it flies a bit like my tetropters. The tetropter discussions may have helped inspire the Cliff Whistler, which is flattering. Anyway, the Whistler flies by beating its three wings horizontally to and fro. Diehards out there may remember that I made extensive use of the 'clap-and-fling' principle to explain tetropter flight. The 'clap' involves two wings beating against one another at the end of their movement, then sweeping back to the other end of their range, where they then clap against another wing. Etcetera. That works with two wings (Terran insects and some birds), four wings (Furahan tetropters) and would work with more wings too, although no-one has yet invented any of those yet as far as I know. Besides offering increased lift through 'clap-and-fling', an even number of radial wings neatly solves the problem of torque: if a wing moves clockwise it pushes the body counter clockwise, which is useless. With two or four wings these forces even out.

Three-winged radial flyers run hnto problems. There is no clap-and-fling mechanism, and the wings move in unison: all three clockwise, and then all three counter clockwise. That leaves torque to be solved. Well, evolution, in the form of Evan, designed an adaptation of the Whistler's mouth parts at its bottom: these evolved into winglets beating in the opposite directions of the main wings, countering to a degree. Enough for the Cliff whistler to be a viable organism, or so Evan and I thought.

Recently I came up with a way to have a clap-and-fling mechanism with just three wings though. It would increase lift but introduce some new problems. Again, Evan and I thought that it might work, but not necessarily better than the Cliff Whistler approach. Perhaps one species will emerge on Nereus with this particular mechanism, we would have to ask Evan. I am not going to tell you how it works, merely that it can be done: each of the wings A, B and C claps against another wing on the extreme ends of its movement range. I wonder if anyone will take the bait...