Epona Reconnaissance Flight (Epona V)

The Epona Project was, or perhaps is, probably the first serious attempt to build an fictional biosphere from scratch. There is still a website, definitely worth watching. Admittedly, the project has stopped in the sense that no new life forms have been developed for a long time, nor is that likely to happen. But the website is being added to, and I return to it from time to time. The last blog entry on Epona is to be found here, while another one that shows the same scene as is shown in the film below is right here. This time, I used Vue Infinite (version 7.5) to produce a film of almost one minute duration.

How does this work? Well, first of all, there were the life forms to consider. Steven Hanly had modelled them in the past, and it proved possible to port some of his models into the Vue environment. The 'uther' you see flying in the scene is entirely Stephen's doing. The plants could not be used directly, as present-day computer imagery requires more detail than was available when he first designed the models. They were therefore designed anew, using XFrog for the large leaves of the pagoda trees and for all small plants. The stems of the large pagoda tress were done in Vue Infinite. The trees were assembled in Vue, and Vue's 'ecosystem' feature was used to create a terrain with a stream running through it. Then just imagine that a 5-second fragment of film may need some 34 hours to render.

After that, a bit of sound was added, a process I have hardly any experience with. I hope the result is not too jarring.

Anyway, there we are: perhaps the film is about a robot drone taking a look on an Eponan archipelago, covered by a pagoda forest. There is a larger version on YouTube. The original film on my computer is much better; I wish I knew more about optimising quality while compressing a video...

These legs are made for walking (Legs II)

In my last post I played with some concepts about leg design, mostly concerning whether it is better to have sprawling legs or ones that function as pillars. It turned out that there is no answer that is always correct: for large animals pillars help minimise energy expenditure in the form of muscle power, and for small animals sprawling legs provide protection against wind forces, something that gets more consequential the smaller you get. Perhaps wind is also one of the reasons why small arthropods are so good at gripping surfaces tightly: I had thought that that was mainly a neat feature to cling to vertical surfaces or even to land on a ceiling, but perhaps simply keeping put where you are if there is a strong wind weighs in too. What do insects do when there is a real gale out there? Does anyone know?

There are still enough problems to play with. I took the Disneius species that had just evolved last time and decided to take its legs one step further, i.e., I tried to simplify their design some more. The reasoning was that legs largely have to move in the body direction, rendering movements in other directions less important. The result is Disneius mechanicus:

Click to enlarge; copyright Gert van Dijk

And here it is. This has taken the idea to an ultimate form: the joints in its legs rotate purely in forwards and backwards directions. Note that this would not work in real life, as the animal would not be able to turn. In real life you would want to make the feet and at least one joint higher up more adaptable.

The legs are built in a zigzag way, like those of its predecessors. Last time I discussed that avoiding bending ‘moments’ becomes easier the nearer the joints are near the centre of gravity. Mind you, zigzagging legs in which the joints zigzag inside and outside are not necessarily worse than ones that do their zigzagging forwards and backwards. The usual explanation for the anatomy of mammal legs is that ‘vertical’ is better, but just suppose you take one of D. mechanicus’ legs and turn it by 90 degrees. If its foot was directly underneath the hip joint to start with, the rotation will not change that. The joint angles do not change either. All this leads me to conclude that ‘verticality’ in limbs depends more on having straight legs than on the direction the joints zigzag in. Legs that predominantly move forward and backwards have the advantage of allowing simpler joints, and simpler joints may allow less muscle strength to control their position: a good thing. I would expect large animals with highly evolved legs to adopt forwards and backwards bending as well. A bit boring, but that is what you get with universal laws of nature.

Luckily there are enough items left that might make alien animals more alien-looking. As you can see, the fore and aft legs of D. mechanicus are exactly alike. This is not what mammal legs look like. From a mechanical point of view fore and aft leg tend to have different effects, with aft legs providing more propulsive force than front ones. Is that also the reason why mammal knees point forwards and their elbows backwards? It seems as if, starting with a newt, its upper arms were rotated backwards and its thighs forwards to turn it into a mammal with fore-aft moving legs.

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Here is a picture from this site that explains just that phenomenon. It explains why the bones in the forearm are crossed while those in the leg are not. But that is just one way to look at things. In the same newt-to-mammal trip, a third large movable segment was added to the newt's two. In the front leg the shoulder blade turned into a movable segment, and in the hind leg foot bones were recruited. If you look at the result from a functional point of view, the first large movable segment is the shoulder blade in the front limb and the thigh bone in the hind limb. Both point forwards, and from that the other segments zig backwards and then forwards. That is what D. mechanicus looks like! Based on this functional view, I feel that identical front and hind legs are theoretically quite possible. Prolonged specialisation for braking and weight carrying (front legs) and propulsion (hind legs) might change some aspects, but I see no need to ‘prescribe’ the typical mammal pattern as the only feasible one.

Click to enlarge; copyright Gert van Dijk

So here is a variant (the left one) in which the upper segments starts the zigzag by pointing backwards, not forwards, as in the righthand side one. Can this work? At present I see no reason why not. Perhaps I should do some animation studies to see if any big problems come up. But if there are none, an animal could have front legs that start with a zig and hind legs that start with a zag, or vice versa. They are in the background of the image above, but a closer look follows.

Click to enlarge; copyright Gert van Dijk

And here they are: we could make up interesting leg formulae, like ‘zigzig’for an animal in which both front and hind legs start with a forwards zig (and in which the other segments follow the lead of the first segment). ‘Zagzig’ denotes an animal with a front leg starting with a backwards zag while the hind leg starts forwards. You can think of what a ‘zigzagzig’ means for yourselves.

Click to enlarge; copyright Gert van Dijk

Just for fun here is a herd of the beasties. How many zigzags should there be? I do not know. If there is a proper foot, in which many segments touch the floor, I would expect all of them to bend backwards to promote ‘rolling’ over the ground. If just one segment touches the ground, as in hoofed mammals, I have no idea. But the majority of long segments will likely zigzag.

Click to enlarge; copyright Gert van Dijk

Here is an animal with more zigzags, along with an ancestor. The giraffomorph looks weak to me. There must be an optimum number of segments to achieve good manoeuvrability and/or good speed, but I do not dare speculate on that, or at least not now. I also do not know why the scapula in mammals is not connected by joints to the vertebral column, in contrast to the hind legs. Does it have to do with shock absorption versus propulsion? Perhaps those are good subjects for later posts.

Legs to stand on

When I sketch a large alien animal, its legs tend to take on the shape of Earth legs with a life of their own. Depending on their general way of life, the animals' legs look like those of mammals, reptiles or amphibians. When the animals are insect-sized, the legs that take shape on the paper are thin and stick out sideways. Apparently the parts of my brain that are responsible for these patterns are so indoctrinated by life on Earth that it takes an effort not to produce them. I am not alone in this, as a glance at websites such as Speculative Evolution will reveal.

Click to enlarge; from 'Primeval'

The wish to 'alienate' the animals can easily result in trickery, such as inflating the arthropod design to the size of a large mammal, or to give the animal tentacles to walk on. The two images above are from the series 'Primeval', a British television series (I like it, by the way!). The heroes encounter some Silurian animals. As you probably know, there were some impressive arthropods around at the time, but they weren't impressive enough for the makers of this series. A pity, as there are enough ways to tell a good story without being silly. There are various reasons such animals could not be that big, and they could no more cling to the ceiling than you can. Effects of scaling are largely to blame, discussed earlier here and here.

But even if you do take physical constraints into consideration, there are thousands of intriguing questions to ask. For instance, if sprawling legs are a bad idea for large animals, why do small animals have them? Why do mammal legs folded in a zigzag manner, with successive bones pointing in opposite directions? Why shoulder blades? What is the optimal number of leg segments? This post presents some -rambling- thoughts on such questions.

Click to enlarge; copyright Gert van Dijk

Let's start with an animal with insect-like sprawling legs. It's not insect-sized though, but mammal-sized. There are four legs, but that is not the point. There are three segments to each leg, but that is not the point either. The joints are all ball and socket joints providing movement around three axes each; that is a bit much, but I will get back to that.

It does not look comfortable, does it? Neither would you if you had to walk around in a similar position: like doing push-ups all day. The poor beast (Disneius salamandris) will have to spend a lot of energy to keep its body from sagging to the ground. In other words, it takes energy to keep the joints in their current positions. To understand how you can minimise that force requires a bit of knowledge about levers, vectors and torques.

Click to enlarge; copyright Gert van Dijk

Here is a drawing of the body with just one leg. Let's pretend the body and parts of the leg are stuck together, so there is just one joint to consider (where blue and brown meet). Gravity pulls at the mass of the animal at its centre of gravity, with a force marked 'W' (for weight). How much 'turning power' does that result in at the joint? Easy: connect the joint and the centre of gravity with a line of distance d. Now, using vectors, draw the component of W that is at a right angle to line d; that force is what turns the joint (marked with a black arrow 'R'). The longer the arrow for R , the higher the force. How much turning power this exerts at the joint is obtained by multiplying d with F: the turning 'moment' or 'torque'.

Click to enlarge; copyright Gert van Dijk

To make that a bit more intuitive I overlaid a wrench on the graph. The wrench grips the joint, and the part where you would put your hand is at the centre of gravity. To use the wrench you would pull or push on it at a right angle to it, right? That would be the force 'R'. The harder you pull, the larger the torque will be. If you were to use a longer wrench with the same force, you would also get more torque. More force and longer handles; that is about all there is to it. Back to D. salamandris; it will have to exert an equally large torque of its own using muscle forces -not drawn- to stop the joint from moving.

Click to enlarge; copyright Gert van Dijk

Here is the same reasoning worked out for another joint. In all cases the torque, the product of multiplying d with R, calls for lots of muscle power. Avoiding all this energy expenditure calls for minimising the torque. You can make d smaller by getting the joints as close to the centre of gravity as you can. Minimising R also works, and to do that you should make the line d as vertically as possible: get the joints underneath the body. I think that this principle also explains why legs tend to bend in zigzag fashion: it keeps the joints more or less close together and minimises gravity-induced torque. So, poor D. salamandris does it all wrong.

Click to enlarge; copyright Gert van Dijk

But before we let D. Salamandris go extinct, let's have a look at what its sprawling stance means for the anatomy of the joints in its legs. Above you see one leg in a few positions, obtained by rotating it around the axis in the joint connecting it to the body. To get a movement suitable for walking, its foot should move in a straight line from front to aft (in reality the foot would stay put but the body would move forwards; seen from the body it is the foot that moves backwards). Getting the foot on the stripe only requires straitening some of the joints a bit. But ensuring that the foot always points forwards also requires that there is a way to rotate some of the bones around a longitudinal axis. If you start to think about this some more, you will find that having legs stick sideways requires rather complex joints; it may seem easy, but is not.

Click to enlarge; copyright Gert van Dijk

Here is an intermediary stage in standing on one's own legs: this animal has brought its feet in underneath its body, and its legs show a zigzag pattern, but mostly sideways (a final stage will appear in a future post). This does not solve all problems, as you may well ask why insect do walk with their legs sprawling to the sides. After all, if bringing the legs in is so advantageous, why do not all animals do so? There may be two answers to that. Sprawling and having bent legs is not advantageous if gravity is a big problem, as such positions require lots of muscle power. As discussed previously in my posts on scaling, such problems increase very quickly as animals get bigger. Make them smaller, and the added energy expenditure hardly counts any more in the overall budget. There is also an advantage for small animals to have sprawling legs: it helps them from being blown over by the wind.

Click to enlarge; copyright Gert van Dijk

Above is a similar drawing as previously, but now with a horizontal force acting on the animals: wind. Wind forces can cause the animal to topple over, and once again the component of wind force that does that is at a right angle to the line connecting the centre of gravity to the point of rotation: where the feet touch the ground. The animal with the lower centre of gravity and the more sprawling legs is better protected against wind forces: the force R is small and directed upwards, meaning the weight of the animal counteracts it. For the upright animal the story is different: R is directed sideways, is not counteracted by gravity, and the animal only needs to tilt a bit before the centre of gravity is no longer above the feet.

Once again, scaling plays a part: when you are very small, wind forces play a relatively larger role than at our human size. The same works when you supplant air with water: walking under water will be very difficult if the water is streaming at some velocity. So, vertical legs become more advantageous when animal mass increases, and the more so on planets with a strong gravity. Horizontal, sprawling legs are better when being blown over is an issue, and that is more likely to happen when animal mass is very low, when the atmosphere is very syrupy or the wind becomes stronger. Which legs are best when you are an animal on a very high gravity world with gale forces howling through its soupy atmosphere? Difficult to say; perhaps it should have vertical weight-bearing legs as well as lateral struts...

Whose alien plants are these ? - bis

'Anonymous' gave the right answer yesterday, when I had already written the first draft of this post. The 'paintings' I showed last week were in reality photographs of glass works of art displayed in natural surroundings. The artist who made them is called Dale Chihuly, whose work I found by traversing the internet looking for alien plants. I rather like the plant shapes he produces: they are very organic looking, and displaying them among real plants provides a pleasing contrast. I thought that showing them in their original form might have made the riddle a bit too easy, which is why I turned them into 'paintings'. I did so with Corel Painter, by the way.

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Above are the three images I had worked over, but now as I found them on Mr Chihuly's website, right here. There are two more I did not work over to give you a further taste of his work. If you wish to see more images of his plant-like creations, you will find many more of them under the column 'temporary' of the 'installations' page; just pick something from the right-hand column and have a look.

After this intermezzo I will be back with a post about legs, discussing things such as why splaying them works for very small animals but not for large ones, and why bones of large animals have a tendency to fold in zigzag fashion.

Alien plants III: whose plants are these?

While the busiest part of the year for me usually lasts from the middle of August to the middle of July, the present period presents problematic peaks. In short: not enough time.

Therefore I will just continue the alien plants theme by showing a few images of otherworldly plants. So who made them? Do you know?

I warn you that I cheated: the images have been altered to prevent any immediate recognition. I will post the answer in a next post, along with the unaltered images.

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Adding oddity (alien plants II)

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I don't write often on alien plants, for a simple reason: there seem to be few of them. I wrote about the -real!- plant life on the island Socotra once, shown you Furahan swamps and showed a few images from the British comic strip Dan Dare. My main post on alien plants was devoted to a computer-generated video. The firm that made it produced another one, as I learned from a site called dexigner.com. The images shown here and the video are taken from that site (the video quality on the site is very good). In fact, there I learned that the previous one was called 'Sixes Last'; there are so many copies of it on the Internet that it is not hard to find it, but it is hard to trace its origin. The 'new' one dates from 2006 and is a commercial for an alcoholic drink. I have nothing against that; in fact, C2H5OH plays quite a role in Furahan biochemistry. As 'advertisement' is not exactly a synonym for 'accuracy', do not expect much in the way of plausibility. Then again, the film does not try to be accurate, just intriguing and humorous. It succeeds well, I think. The computer-generated bits seem to be added to real footage, which may explain why the images look very real.

Click to enlarge

The second reason to show it is to discuss the problem of how to design odd plants. I have this worrying idea that the basic plant design may not allow much creative freedom, at least not if the definition of plant is not stretched too much. The main ingredients of the definition may be photosynthesis and being sessile, with some -arbitrary- limits in that the plants in question are multicellular and that they are land plants. Photosynthesis needs light, and the best way to get much light is with a large area, i.e. thin shapes. Needles are good but planes are better. Basically a blanket-like shape with roots to pick up minerals and water is all you need. But if the blanket gets too large it may be torn by the wind, and an easy way to avoid that is to distribute wind stress over many small leaves. Growing towards the light avoids being in the shadow of other plants. Branching systems and leaves seem unavoidable, and any alien plant with those will look like an Earth plant.

What can be done is to alter the relative sizes of plants: thick stems, enormous leaves, etc. and giving them odd colours. But there are usually reasons for these proportions as well as for colours, so there is no total freedom here. The simplest way to add oddity may be to add elements of animals: give the plants eyes or mouths. That is what happened in the earlier video as well as in the present one. Eyes are there to tell an organism about its environment: where is the prey, where is the predator, are there good-looking potential mates around, etc. Acquiring information is only useful if you can act on it, and the main limitation here may be the sessile lifestyle. Sessile life forms can certainly be interesting; there are quite a few sessile predators: think of anemones. But there may be a limit on how well developed their sense organs and brains can become. Why have fine eyes and precise grasping arms when your reach remains frustratingly limited? Wouldn't an animal that can do the same things but that can move around be vastly more fit in the evolutionary sense? You may counter that by saying that it may be enough to outperform the dumb and blind types of sessile organisms. In evolutionary biology traits always seem to cost something. The price to pay may be a metabolic one: eyes, muscles and particularly brains are very expensive in terms of energy.

In that sense, high class eyes are jetset organs, reserved for high flyers only. So the puzzle remains how to increase the oddity of alien plants...

Strandbeesten and mantis shrimps

Actually, 'Strandbeesten and stomatopods' might have sounded better, but would be even more incomprehensible, and a blog is supposed to attract readers, not frighten them away. Based on how many readers were attracted by previous posts, I should probably use 'The Future is Wild' and particularly 'Avatar' a lot more often in post titles (and no, Furaha was NOT modelled on Avatar; it is much older). Right; now that I've got that out of the way, back to the strandbeesten.

I discussed Theo Jansen's imaginative mechanical walking machines before on this blog. Literally the word is Dutch for 'beach beasts'. If you do not know about them, read that entry and visit Mr Jansen's site, or just enter 'Theo Jansen' into Google or YouTube. His work came up in this blog because of my interest in animal locomotion. The problem he faced was how you can get a foot to move backwards along a straight line when on the ground, after which it has to be lifted, moved forward and put down again for the next step. For real animals this is not a big problem, as the various segments of a limb are all controlled by a nervous system telling each segment when to do what. As Jansen's devices lack a brain, he needed a purely mechanical system to achieve this sort of motion. In the end he came up with an intricate series of interconnected bars: if you start with a rotary motion of one bar, another bar, ending in a foot, produces a suitable movement. Very clever indeed. Such series of connected bars are called linkages. You can take a good look at his design on this particular site, which shows other linkages as well. When I wrote that post I had never seen a single strandbeest yet, and that has now been rectified. Mr Jansen works not that far from where I live, so it was a matter of time before I could visit one of his demonstrations nearby. This was the case last June, on a very cold and windy day. I will show a few videos I made that day.

This is a tiny strandbeest, of which there were three. If its sail is perpendicular to the wind direction, the little beast may walk with the wind. I tried pushing it forward as well, and found that it is not in fact that easy to move. While the 'beesten' are quite light, their joints were harder to move than I had expected. There is no lubrication, but the main problem seems to be that the entire shape deforms enough to put shearing forces on the joints. One result of this is that the poor beest tends to topple over. But never mind that, they are an amazing sight.

Here is a larger one following one of Mr Jansen's assistants.

And this is the major species present at the occasion. Not only did it have two bodies or trunks, an enormous number of legs, but also two waving membranes at the top that I think were designed to help propel it. These sails were reefed that day however, and the force of the wind on the body was enough to prod the beast onwards. Aren't they wonderful?

In my previous post I wondered how often linkages occurred in biology, but did not look up the matter. I have done a bit of research now, and found that there are quite a few examples. Fish jaws are probably the best-known example (see below). Other structures, such as sheep hocks and human knees are also counted as so-called four-bar linkages. In a four-bar linkage four stiff bars are linked together in a sort of circle by pivots. If you hold one bar still, and move another one, the remaining two must move in a fixed way. What that way is depends on how exactly they are connected. I felt that regarding the human knee as a four-bar linkage is bending the rules a bit, as two of the bars are ligaments rather than stiff bars. If you include connected series of bones as well as ligaments there are lots of linkages in biology; what I was looking for was linkages of bones involved in locomotion, but I have not yet seen any. Presumably a system with more mechanical freedom but with a smart nervous system to control it is simply superior. Still, the other ones are interesting.

Click to enlarge; Wainwright et al, Integr Comp Biol 2005; 45: 256-262

Here is an example of what fishes do with a four-bar linkage. The source is mentioned in the caption, and the colours are my addition. Fish use this kind of mechanism to move their jaws forward and to enlarge the volume in their mouths, sucking in water as well as their prey. There is at least one Furahan animal with a similar arrangement, and those are 'Fishes' too. The jaws of the sawjaw are connected, all four of them, by bars linking them to the neurocranium in a kind of circular linkage.

So where are the mantis shrimps, everyone's favourite Terran alien? When searching for linkage mechanisms I found that there is a four-bar mechanism in their 'raptorial appendages' as well! I like that: somehow you expect animals that not just spear or club their prey but can see depth with just one eye to be special in other respects as well, and mantis shrimps never seem to let us down when it comes to, well, weirdness.

Click to enlarge; Patek et al; Nature 2004; 428: 819

Here is a figure from the journal Nature, no less. The first author, Sheila Patek, has a lab where she studies all kinds of biomechanically interesting things, most notably mantis shrimps. Have a look, as there are quite a few videos and photographs. Under 'multimedia' you will find an inspired lecture she gave on 'TED', where she explains the striking mechanism of stomatopod raptorial appendages. Very interesting. She is not the only one interested in stomatopods either; here is another enthusiast.

So now you know why strandbeesten and stomatopods end up in the same post: they are connected by linkage (I could not resist that one). I guess both also score very highly when it comes to their ability to evoke a sense of wonder.



PS. This is post #100!