An aside about rusp insides (Archives IVb)

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

Click to enlarge; copyright Gert van Dijk

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

Click to enlarge; copyright Gert van Dijk

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

Click to enlarge; copyright Gert van Dijk

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

Click to enlarge; copyright Gert van Dijk

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

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

Archives IV: once and future rusps

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

Click to enlarge; copyright Gert van Dijk

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

Click to enlarge; copyright Gert van Dijk

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

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

Click to enlarge; copyright Gert van Dijk

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

Click to enlarge; copyright Gert van Dijk

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

Click to enlarge; copyright Gert van Dijk

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

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

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

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

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

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

A century of thoats

As post titles go, the one above may be a bad choice: it will probably only catch the attention of those who already know what a thoat is. To attract more readers I should perhaps alter the title; the second-highest rating post in this blog, as far as numbers of viewers is concerned, had 'Avatar' in the title, so I should probably learn from that. So here is an alternate title: 'Why do animals such as the thoat in "John Carter of Mars" and the thanator in "Avatar" walk in such an illogical manner?

A thoat is a large eight-legged Barsoomian animal, 'Barsoom' being the native name for the planet Mars in Edgar Rice Burrough's works. Burroughs starting writing Barsoom novels around 1912. I never read any, for the simple reason that there were no Barsoom books in translation around when I was at the right age to enjoy them. I did read his Tarzan books, though, and suppose that I would have read Barsoom novels with equal appetite. The reason Barsoom caught my attention after having ignored it so far, lies in the recent movie 'John Carter of Mars' (JCoM).

Click to enlarge; copyright Michael Kutsche

The wonderful image above is from the DeviantArt account of Michael Kutsche, who designed the thoat for JCoM; the thoat is the eight-legged beast, not the individual sitting on top. Have a look at how Kutsche approached the 'leg problem': where do you put eight legs without them looking odd, if not altogether ridiculous? Kutsche solved the problem by dividing the eight legs in front and hind groups. In build, the legs look a lot like those of a large mammal such as a rhinoceros or an elephant. In fact, the original hind and front legs were simply copied and pasted as close as possible to the original. Where there was one leg there are now two, moving in unison. Being so close together, that is all they can do, as otherwise they would knock into one another. This solution is very reminiscent of the large animals in Avatar, except for the fact that these had six legs, with just the front legs doubled. I criticised that arrangement in a previous post, thinking that it did not make much sense from a biological point of view. It felt it would be easy to learn how six-legged animals could or should move: after all, Earth is literally crawling with insects. For eight-legged creatures you can look at spiders or crabs.

The video fragments above shows a few seconds of thoats walking in JCoM (sorry about the quality), illustrating the 'doubled leg design'. Bt the way, I wonder why the legs are so immensely thick. Their thickness looks about right for an athletic elephant-sized mammal on Earth with just four legs. But with eight legs, each leg can be more slender than if there are four (read here for posts on leg design, gravity and the number of legs). As it is, the animal looks as if it was designed for a planet with a very high gravity, not for Mars, where gravity is just 38% of that of Earth.

Click to enlarge

The Barsoom fictional universe has been around for a century, so many illustrators over the years must have faced the problem how to design a plausible as well as dramatic eight-legged big animal? The drawing above, by John Allen St John, must be one of the first depictions of the Barsoom universe (I found it here). The style of the drawing fits the early twentieth century. This early thoat does not show doubling of the front and hind pairs of feet, but shows tripling of the front feet, keeping one pair of hind legs. There seems to be a generic 'copy and paste legs' solution operating here.

In the late thirties there was an attempt to produce an animation of JCoM. Only a bit can be found now, coming from ERBzine, a very large website on Edgar Rice Burroughs. I woulld like to include it here but am having upload problems; I may rectify that ater, but for now, here is the YouTube version. Look at how the thoat lands on its feet: there is a definite phase offset between the successive pairs of feet, resulting in a jumping gallop. This is one of the very few thoat designs with phase differences between successive pairs of legs.

Click to enlarge

Edgar Rice Burroughs son, John Coleman Burroughs, worked on his father's creations. He produced a wooden thoat model, shown above. I found these images on the Erbzine site. It is a pity that the model cannot be seen better. The legs are so close together on the body, that they must all move in unison on one side of the body, or else they will knock into one another.

Click to enlarge; copyright Frank Frazetta (I presume)

The late Frank Frazetta, famous for his equally but not similarly well-developed heroes and heroines, produced quite a few Barsoom paintings. I found no thoat among them, but there are two banths, Barsoomian lions with ten legs. The ink drawing above shows a banth from the front, a nice trick to avoid looking too closely at its shape. The legs on one side seem to be moving in unison. For the oil painting, Frazetta chose to hide most of the banth's legs from sight. For a painter of Frazetta's skill this is probably no coincidence; did he feel that showing all legs would not work?

Click to enlarge; copyright William Stout

The image above is by William Stout, a well-known painter of palaeontological scenes. His thoat is livelier than most, as can be expected from a Stout design. And the legs? Well, a doubling design again.

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So, what can be concluded from studying a century of thoat design? Some of the best fantasy illustrators worked on the problem, and many gravitated towards the same solution: they doubled or tripled pairs of legs, and as such did not depart too much from the familiar mammal pattern. To me the 'doubling solution' does not seem like a good idea, but if all these wonderful illustrators chose it, I may have been too harsh in my judgement. A good artist or illustrator will have learned human and some mammal anatomy, but that education is not likely to include hexapod and octapod locomotion. In fact, the necessary knowledge is not that easy to find, and has not been adapted for non-specialist use.

Copyright Gert van Dijk

What would you get if you do take such knowledge into account? Well, probably something as in the animation above (adapted from a model designed to study Furahan rusp locomotion). I made no effort to define the body and the legs all have the same shape. The main point was to show an eight-legged gait that can work well. The gait is based on one described in a scientific paper on spidr gaits, and concerns a slow walk. I applied that gait to a model in which the legs are held vertically rather then horizontally, making the design better suited for large animals. Personally, I think it makes more sense than the doubling design.

You could argue that using such a true octapod gait or the simpler 'doubled leg gait' does not matter, as the audience will probably accept doubled legs as easily as a more sensible gait. Maybe; the audience may also feel that the true octapod gait has a more alien feel to it, and that should please the designers. All in all, I probably overestimated how accessible the required biological knowledge is. Well, that is a good reason to continue this blog. What else could be done with it? Phone Hollywood, perhaps?...