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...
11 comments:
Both are interesting designs, but if I could offer my humble opinion, I would suggest the secondary structure, where the central column sitting lower in the body. It less resembles vertebrate skeletons, allows for greater flexibility, and leaves open spaces for organs to expand - a rusp with this system could support much larger intestines, stomach or lungs. For even greater flexibility, you could offset the angle between the masts and leg arches on consecutive segments, such that when the rusp bends these move into the gap between bones rather than bending right into them, but then you must find a space to avoid squashing the organs...
If you needed even greater weight bearing, you could have an additional column running through the open mast, or perhaps arches extending from the mast to the leg extensions (a combination of both methods). Such a rusp would be almost entirely rigid, however.
Cool, I've been hoping to see the internal anatomy of a few of your creatures. I especially like the flexing joints.
Both designs look good. I suppose the first one might make more sense if the rusps' bones evolved from an exoskeleton, as in the hexapods.
Regarding flexibility: could the rusps have "flex points", like some city buses? http://visual.merriam-webster.com/transport-machinery/road-transport/bus/articulated-bus.php
I just can't imagine you doing this design only "in 2D" You must be thinking of animating this. I am quite curious about how this design would walk as it will be different than the animation you did in 2D feet slightly out of phase on a "normal" caterpillar without a spine. What do you think of a real 3D animation with flexible segments to let the animal go where it wants? :-) Would it be difficult?
Bob(o)
Zerraspace: I think both designs offer ample room for internal organs. I agree that the second design resembles a vertebrate skeleton less than the first one. The thing is that the skeleton needs to combine flexibility with rigidity; so far, I think both designs could do that.
Spugpow: in the rusp case, an endoskeleton was there from the beginning. As for the flex points, these seem like proper joints in which the skin is adapted to fold and stretch around the joint. That suggests to me that such buses are a rare example of technology following nature: all our joints have such features!
Bo: Believe it or not, but I hd not intended to do a full 3D animation of a walking rusp (you did see the ones in the previous posts, I suppose,). I certainly imagined how rusps deal with uneven terrain: the legs deal with most surface irregularities, and only part of the terrain features have to be taken care of by the body itself. You could say that the legs act as a low pass filter, taking care of most small features. I could write a fairly complex program in Matlab to deal with that, and then I would have to write procedures to write scripts for Vue. Not very difficult, but simply a lot of work...
a side note, about a past blog: I re-watched 'John Carter' on the big screen, and the "Barsoom dog" and (to a lesser extent) the thoats, seem to propel themselves more with their ankles and feet than with the rest of their legs.
Another awesome post! I have to admit, I like certain things about both of the possibilities above. The first design would make the rusp more "protected" as the bone basically creates an armor right underneath the skin, but such a rusp would have to sqeeze the other internal organs when the lungs would inflate.
Do you think you could compensate for that by making the "floor" mobile, so the segments could expand and contract like vertebrate ribcages?
The second design would allow a free space for the lungs to expand outwards rather than inwards, but question is if the lungs wouldn't be more vulnerable this way - the internal would be arranged around a central bony structure, while the first design would protect the internal organs very well. I've been thinking of rusps as of living tanks, and the bony arches protecting the animal would add to that feeling, it would make them basically living fortresses.
Fascinating stuff, as usual. The first skeletal design, even if it's internal, seems like it would have similar issues as an actual exoskeleton. It might just be too massive to be supported by the legs at larger scales.
The second design seems to require less mass, and with its structure, I could even see the orange side hinges becoming superfluous. With plenty of connective tissues and controlling musculature along the mast and supporting arch, this design would work great, and possibly even allow for more overall flexibility.
Rodlox: Thank you. It turns out that I took a much better look at the film as well, and noted that the 'dog' analogue seemed to walk with all legs on one side moving in unison.
Petr and Evan: I should probably have added that the design is not overly detailed, so the actual thickness of bones was more or less chosen at random. It is quite possible that the arches could be less thick in reality, or that their cross section should be narrow rather than broad.
As for breathing, I did not intend for the structural skeleton to double as a ventilatory pump; that is another departure from a vertebrate rib cage. You are now probably wondering how the lungs are compressed and expanded , if not by a ribcage, and without externally visible movement. Well, that can be done; I had something like that in mind for hexapods, and unwittingly assumed a similar structure for rusps.
I have wondered about the necessity of the side hinges in both designs. The reason to put them in was that a leg, pushing backwards against the ground, will result in a forwards force at the hip joint. this force should not be wasted by pushing just the local segment ring forwards at one side against the ring in front of it, but should benefit the entire animal. In short, the force should be transferred to the entire skeleton. One way to obtain that was to equip the sides with springs resisting compression as well as extension (the orange side hinges). Another way would be to have the animal walk with both sides in phase, so forwards forces would be symmetrical, and would therefore mostly affect the central column. Is this explanation understandable at all?
"It is quite possible that the arches could be less thick in reality, or that their cross section should be narrow rather than broad."
That may certainly be the case, but I guess what I'm trying to say is that the second design seems like it can afford to be thicker than the first without exceeding the same weight limit. Then again, perhaps the curvature of the bones in the first design allows for more supple, flexible bones. I don't have any math in front of me to support one way or another, and the possibility may exist that the tradeoff of benefits balances out.
"One way to obtain that was to equip the sides with springs resisting compression as well as extension (the orange side hinges). Another way would be to have the animal walk with both sides in phase, so forwards forces would be symmetrical, and would therefore mostly affect the central column."
I hadn't thought of the transfer of force from the leg to the rest of the body. Symmetrical phases may solve that problem, but I also wonder how that would affect overall maneuverability (relatively speaking). A creature that depends on the legs of both sides being able to provide the same force at one time may struggle with uneven ground or complex movement. A spring-like mechanism just may be necessary.
@SN - It deffinitely is. Thank you! ;)
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