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20:49 18-04-2012
SN
DrásResearcher, It is indeed a nice creature. The perspective suggests it is not small, but the size of a horse or larger?
I agree that it must be from a low/gravity planet, with those spindly legs that first angle upwards and away from the body before coming down. There are also more segments in the legs than seem optimal to carry a heavy load, a feature best suited if loads are low. The legs are nearly vertical, something not strictly necessary in a low gravity environment. Then again, they are not splayed either, something useful if the animal has to keep from being blown over by the wind. So I assume that the atmosphere is not very heavy or that winds are not strong. Is it descended from small spiderlike creatures?
I wonder why the toes are splayed to such a degree. That seems a good device for an animal walking on soft ground, as in a marsh, but you would then also expect the toes to touch the ground over a large surface to spread weight. This is not the case, and as said gravity is probably low.

Evan, I found three books by Clement but not Mission of Gravity, so I cannot help. I agree with Jan that an exoskeleton is unlikely. Not only are they generally heavier than endoskeletons for the same strength, but they are also vulnerable to impact. What Mesklinites need is an endoskeleton made of a light material that can withstand extreme compressive forces and is yet resistant to buckling and bending. They should only lift a leg when those around it are on the ground, and take short steps at that. Apparently Clement revised his estimate of Mesklin´s polar gravity from 700g to 275g. It´s still a lot...
15:46 18-04-2012
Evan Black
All in all it's an engaging creature, DrásResearcher, but I'd like to know more about it. Right off the bat I can tell some things about it. First of all, the gravity of the homeworld is low. Also, while it's impossible to determine if this creature is a herbivore, carnivore, or omnivore, it seems like it could get at a variety of foods. Those manipulator limbs could reach the ground with little effort to pick up plants and/or animals located on the desert floor, or even reach into rocky crevices for hiding critters and/or into crevices in protective cases of plant seeds. Are these supposed to be sapient? If so, where's the brain? The head doesn't seem like it can hold much of one, so it must be somewhere else.
15:37 18-04-2012
Evan Black
I got a hold of a copy of Mission of Gravity from my local library, and started reading it again to look for specific dimensions of the Mesklinites. I'm not done yet, so there may be more details addes as I read, but so far they're described as "fifteen inches long and two in diameter;" that translates into 38.1 cm long and 5.08 cm diameter. Furthermore, their "dozens" of legs are described as "stubby," leading me to the conclusion that Barlowe's illustration, while matching the flavor of the creatures I imagined as I read the book, is just too gracile to match the description in the book, let alone withstand the gravitational forces of Mesklin.

I also find it strange that the Barlowe's illustration doesn't even match the textual description in his own book (35-40 cm and 5 cm diameter). Perhaps it's due to some kind of miscommunication with his co-authors.

I also thought about the weight of Mesklinites, and wondered if perhaps their density is significantly lower than the 1000 kg/m^3 you mentioned, Sigmund. This might be possible if they have a biochemistry that allows for a density less than that of water, but there are two points of interest that I think provide even more challenges. First, Mesklinite musculature is quite powerful, such that in the 3g equatorial regions of their world the weakest of them could make a hundred-yard leap (91 m) with "the barest flick of his body muscles." Now, these muscles could be made of light and strong materials, like what Jan is talking about, but if it was light enough to lower the creature's density below 1000 kg/m^3, but still strong enough to behave as in the book, it would be quite exotic. Secondly, the Mesklinites are sapient beings, indicating that they have a complex neurology packed into their tiny bodies. Unless this too is a quite exotic system, it will add weight as well.

Mike, you talked about a branching of clades in your evolutionary description between the "rollers" and "walkers," which I imagine would move like centipedes, caterpillars, or perhaps snakes. This is important to note, because even though the rollers may be possible they're also having to compete with creatures that can move more easily and consequently thrive and diversify into the various ecological niches. Rollers would thus be a unique and novel form of life, and not highly diversified or derived. That calls into question the possibility of sapience.
05:13 18-04-2012
DrásResearcher
Hey everyone! This is a very silly question, but I am designing a world called Drás and am currently working on the sentient species, the Drasa. It is a mostly desert planet that orbits a large gas giant. Anyways, the predominant characteristics of the species overall is 8 limbs and 2 pairs of eyes with many of the species having 3 genders (male, female, neutral). In this picture you see a female Drasa turned slightly away and looking to the side. She has 6 "legs" and 2 arms, however the other arm is not in perspective. I wanted to get some feedback into if it looks good (for a rough sketch!) and possibly how I could make her look more alien (if she doesn't look alien enough )
http://i860.photobucket.com/albums/ab170/sweeneypaz/Drasa.jpg
18:00 17-04-2012
Jan
Speaking of rotating locomotion, there is also a possibility of a belt-like animal moving like a continuous or caterpillar track, maybe with special devices to stick to the ground. I do not know how dis/advantageous it would be.

Thanks for the informations about mesklinites. I do not know how much gravity such an animal could withstand in reality, but the vertebrate bone does not seem to especionally hard and strong material. The toughest biological material is probably the silk of Darwin's bark spider, and organic material studied by material scientists seems to be even stronger http://news.discovery.com/tech/print-body-armor.html
Maybe more challenging would be the right muscle system (some support from hydraulic system?). I do not understand why high-gravity world animals keep to be presented with exoskeleton.
06:39 17-04-2012
Spugpow
A fascinating video of amphisbaenian lomotion: http://www.spiegel.de/international/germany/0,1518,602160,00.html

Very wormlike.
 
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22:03 16-04-2012
SN:
Jan: I saw you had written something just when I posted my own reply, edited that, and the edited version was apparently lost. What I wrote was that your finds were very interesting, particularly the spider, as it flipped on its side before it started to roll. It was new to me.

Evan: I was aware of Barlowe's mesklinites but have always felt that he hadn't fully allowed for the consequences of a gravity of 700 g at Mesklin's poles. Elsewhere I found that mesklinites were supposed to be 35 cm long with a 5 cm diameter. Assuming a cylindrical form and a specific mass of 1000 kg/m^3 (which is low for an animal), you would get a volume of 687 cm^3 and a mass of 0.687 kg. Barlowe's painting suggests 18 segments with 2 legs each, so 36 legs. Each leg thus has to carry 19 grams of mass.
The point is the 700-fold increase in gravity compared to Earth. The pull of gravity on Mesklin can be likened to the same animal on Earth weighing 481 kg; each leg would have to withstand a weight of over 13 kg. I think the animal as painted would be squashed: its legs and body are much too flimsy. I also do not think it could lift one quarter of its body in the air without support (that bit weighs 240 kg!).
Mind you, I am starting to wonder what the mass of leg bones would have to be to actually withstand such forces, and whether there would be any mass left for the rest of the animal. Clement was no fool, so perhaps I should leaf through the book to find a description of mesklinites. Now, where is that book I haven't seen for over 20 years?

Mike: those are creative solutions. And as for starting with a need for them to look cool, you aren't the only one who used that as a starting point. In fact, if I had to adapt all my own creations to make them science-proof, some of the more amusing ones would have to go...

,
18:32 16-04-2012
Mike
I'm thinking they'd walk that way for long distances, but for simply readjusting their stance or walking a few feet, they may awkwardly shuffle using whatever limbs they happen to be standing on. That being said, they manipulate things primarily through the use of their epitokes, so the atokes themselves wouldn't have to walk too often unless they are moving a great distance, and as a result, they would walk primarily through rolling.

As for perceiving the world while spinning, I would agree that it is a surmountable problem. As a test, I just tried walking around my house while spinning at a sufficient speed, and found no problems seeing what was in front of me at any given moment aside from slight blurring. The problem of course was that I couldn't see what was behind me, so I by spinning I was subjecting myself to the possibility of walking backwards into something, but seeing as these creatures have three eyes covering 360 degrees of vision, they wouldn't have that problem. And even so, there is the fact, as I have mentioned, that the atokes don't need to move much, so they wouldn't be at a great evolutionary disadvantage for experiencing motion blur while walking.

As for how the system evolved, I was thinking their aquatic ancestor would have been something similar to a cloakfish, though with several fins, like an anomalocaris as opposed to a cuttlefish. Each of these fins would only have to move up and down as opposed to forward and backward, as that's all that's required for undulation. When the first of these fish made the shift on to land, they couldn't undulate efficiently on land, nor could they drag themselves along, because they lacked sophisticated enough muscles to do so. Instead, they pushed all the limbs on one side against the ground, flipping the organism onto its side, allowing the next set of limbs to do the same, leading to a rolling organism. I figure a few would develop better muscles for dragging, and these would lead to another branch in the tree of life, but of course, this was the less interesting one that I didn't wish to go into.

As for why they don't stop rolling, the best excuse I could come up with is that, if you look, you can see there's always a set or two of legs on the bottom of the organism which are bent so as to lower the organism enough to allow the legs at the side to touch the ground. The fact that the legs are already bent means they can't really walk with these limbs, or at least not well. They could try standing only on the legs at the very bottom, but their legs aren't strong enough to be supported by only two sets. You could say they could strengthen their limbs, but that would be costly, especially considering that their radial nature causes the strengthening of two sets of limbs to lead to the strengthening of four which don't need to be strengthened. Furthermore, you could make it so their legs are longer, so they can have four sets of extended limbs on the ground at any one time, but any legs which are sufficiently long would be cumbersome and structurally unsound. Any intermediary form would face the difficulty of having to carry the weight of their long legs with every stride.

That isn't to say no organism would take this path, but it would face difficulty arising, and would probably stem from smaller, mouse-sized genera with less problems regarding weight, which would then find difficulty gaining dominance over the land considering the already firmly-established rolling megafauna. A mass extinction would allow for such a role reversal to take place, and considering how mass extinctions are inevitable, it's bound that the walkers would one day dominate the land with their superior method of transportation. However, the remnants of the once-dominant rollers would still live on for a while, enough time for this sophont to arise.

Also, I'd like to point out that I believe the rollers would be more likely to develop sapience than the walkers, so I have more justification for choosing them as the intelligent species for this planet than simply "they look cool" (though that certainly was the original reason). My reasoning for this is that the walkers, due to their more efficient walk cycle, wouldn't need to develop their epitokes as well as the rollers, as they can simply walk up to their prey and take a bite from it. The rollers, on the other hand, use their epitokes for practically everything, the atokes are little more than commanders who tell the epitokes what to do. Because of this, they needed more sophisticated means of communication with the epitokes, as well as a better mind for developing strategy. There's little pressure on the atoke to be physically strong or fast, but as a commander, it must be mentally fit. For this reason, there would be greater pressure on them to become intelligent than in the more physiologically adept forms.
15:17 16-04-2012
Evan Black
I always thought that Wayne Douglas Barlowe's illustration of the Mesklinite was pretty much how I imagined them.

http://images2.wikia.nocookie.net/__cb20110321165410/aliens/images/a/af/Mesklinite_%28by_Wayne_Barlowe%29.jpg

A nice real-world example for rotating locomotion is the this Saharan spider:

http://www.spiegel.de/international/germany/0,1518,602160,00.html

If you did a search for it I bet you can find YouTube videos of it cartwheeling down the dunes.

However, I too wonder about OBLIGATE rolling, like you're talking about here. Mechanically, it's certainly possible, but how does it come about, and what makes the organism ONLY move that way?
14:29 15-04-2012
SN
Gabriel: I have read Hal Clement's 'Mission of gravity', and concur with those who label it as a classic. Clement was an astronomer and had thought hard about his subject matter. Unfortunately, I do not think there are many good illustrations of his 'Mesklinites' about.

Mike: Escher's wentelteefjes only use rotation when in a hurry, I think, but depend on six les otherwise. Your organisms use rotary movement all the time, I presume. I like your animation very much.
You asked how plausible it is; well, in the business of designing alien life forms that is to a large extent a matter of opinion. I will have a try though. Mechanically I do not see any problem for an animal to move this way, but you could ask some questions about how efficient it is in terms of energy efficiency. Each leg goes to a cycle of touching the ground pushing back at it, and being swung forward lifted from the ground. The latter part is of course necessary but does not contribute to propulsion force directly. All legs do that, and so does yours, but in your case the lifted part of the cycle takes longer than in a more conventional arrangement. There will also have to be lots of legs, more than necessary in a conventional arrangements. You can say the same for millipedes though, and they thrive.
Another source of problems is in vision (and hearing). The image of the world is constantly rotating on the retina, which poses a problem. In thinking about cernuation I discussed that problem. Here is the last of my three blog entries on that subject: http://planetfuraha.blogspot.com/2010/07/to-cernuate-or-not-to-cernuate.html
Still, this does not seem like an insurmountable problem either.

It would be nice if you could explain two things: one is why the animals do not stop rotating their bodies and use only some of their legs, which would allow better senses and better energy efficiency. The other question is probably the more difficult one: how did this system evolve? Was there a legless ancestor that rolled? Probably not, as rolling does not carry you over uneven ground well. Is there was a legged ancestor, why did it start rolling. I can imagine a being with numerous stalks protruding from its body in all directions, like the tube feet of starfish. Those could evolve into proper legs, but it would seem to make more sense for those on one side of the body only to do so.

By the way, to my surprise Wikipedia has an entry on rotary movement in biology: http://en.wikipedia.org/wiki/Rotating_locomotion_in_living_systems
07:27 15-04-2012
Jan
Mike: It is not so much alien after all
http://www.youtube.com/watch?v=_hqS93Y1cI0
http://www.youtube.com/watch?v=HmLS2WXZQxU
http://www.youtube.com/watch?v=TBXSm7dB484&feature=related
22:12 14-04-2012
Mike
How plausible is rolling locomotion, such as in the disk-ants of fragment or escher's wentelteefje? I ask because I'm thinking of including such an organism in my project (http://yasbp.deviantart.com/art/Triradials-mark-2-295881126) (http://yasbp.deviantart.com/#/d4w8wd2), and I'm absolutely in love with the xenocentricity of such a design.
20:30 13-04-2012
Gabriel
I find this book quite by chance, and is available at Amazon.com
http://en.wikipedia.org/wiki/Mission_of_Gravity
A novel with scientifically-based assumptions on life in high-gravity. This planet rotates so fast that the gravity at the equator is a tiny fraction of that on the poles (yet 3 times higher than Earth's).
Although published in 1953, (Quote)"even today, it is considered one of the definitive examples of worldbuilding". and, "the exploration of what existence might be like in such extreme conditions is detailed, convincing, and persuasive"
10:14 20-03-2012
Jan
Feathers of flightless birds look like "branched hair" even more. http://www.photoforum.ru/photo/60055/index.en.html
I propose more complicated structure, because it offers greater density of hairs. In fact, the ordinary "metafeathers" would be more like the kiwi´s ones but the decorative metafeathers could be similar to plants or their blossoms. Or maybe it could create more effective mimicry. But I think their insulation efectiveness would be more dependent on how they would hang together.
07:50 19-03-2012
Evan Black
Oh, I assumed when you said, "I wonder why there are no 'branched hairs' on Earth," that you weren't seeing feathers as such.

Well, I know that fish scales are derived from dermal cells, and as far as I know hair has a similar origin. I'm not certain about reptile scales, though. Armadillos have developed similar scaly structures (osteoderms) to those found in reptiles like lizards and crocodiles, so perhaps it's ALL dermally derived.
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