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?...