Explaining and animating how cloakfish swim

In the two previous posts I wrote about parts of The Book that provide background information about how animals move on Furaha. There will be four double-page spreads showing such themes in The Book, about rusps, spidrids, tetrapters and cloakfish. 

I thought the cloakfish one would be easy, until I decided that it was high time I also made some progress towards a short CGI documentary I wrote about earlier, the one with cloakfish biodiversity as its main subject. That is a very big job and it is quite possible that I will fail on the programming side. But nothing ventured, nothing gained, so I went ahead and put some hours into Matlab programming. My strategy to design diverse cloakfish is to write editors that allow shapes to be designed with ease. The programmes then proceeds to make ‘3d meshes’, the basic working material for 3D design. How to get from meshes to nice photorealistic images is another story altogether. 

Click to enlarge; copyright Gert van Dijk

These are the editor screens. The user places control points here and there, which are then connected by a spline function. This results in nice smooth curves, useful for organic shapes. Panel A shows the body designer with a default shape. The inset shows a separate window controlling cross-sections of the beastie. By changing both shape and cross sections interesting forms can be produced. Panel B is the cloak editor. Apart from determining the shape of the cloak it also allows control over cloak movement, such as number of waves, wave amplitude, cloak curvature, thickness, etc. Panel C does something similar for the four front fins, and panel D shows the resulting output for the default shapes. 

Click to enlarge; copyright Gert van Dijk

With a few minutes’ worth of tinkering, you get this relatively slender cloakfish, probably a reasonably fast swimmer. 

Click to enlarge; copyright Gert van Dijk

Or this short and bulky ‘short-sleaved cloakfish’.

Click to enlarge; copyright Gert van Dijk

Or even this highly derived cloakfish, in which the cloaks are no longer ribbons, but shaped like penguin wings. They function in much the same way. 

 But the main point of this post was to show how the cloaks move. To do that, I had a look at the literature, and I found some papers on knifefish, but to my surprise more papers about artificial robot fish with similar fins. Apparently, people all over the world are working on robot fish, which is nice. Less nice is that some work at defence institutes, so what are they preparing for? Killer fish robots? Must we really? 

Click to enlarge; from: Liu, Curet. Swimming performance of a bio-inspired robotic vessel with undulating fin propulsion. Bioinspir. Biomim. 13 (2018) 056006 1748-3190/aacd26

Anyway, here is an example of robot ribbon fin design. The artificial cloak design followed exactly the same reasoning as my virtual cloakfish designs. Such papers make a distinction between ‘oscillation’ and ‘undulation’. If a cloak, ribbon or fin swings side-to-side as a whole, the word ‘oscillation’ is used, and when waves travel along the length of the cloak, it is ‘undulation’. But the distinction is not all that clear; it depends on the number of waves travelling along the cloak. If there is less than one wave on the cloak or fin at a time, then the movement largely concerns the fin as a whole, so the movement edges towards oscillation. Here is a YouTube film explaining the difference. 

Pure oscillatory sideways movement are useless, because they do not propel the beast forwards. The animation above shows such an almost pure sideways movement of the cloaks. The movement would push water away from the cloak, resulting in a force towards the attachment of the cloak (the ‘dagger’). In knifefish, with just one cloak underneath the body, this force ‘heaves’ the body up. With four cloaks, the dagger will not be going anywhere, so this is just a waste of energy. We want water to be pushed backwards. The cloaks push water backwards when its parts are at an angle to the direction of movement. These parts produce forwards thrust. 

Let’s equip our default cloakfish with exactly one wave per cloak. One half of that wave will be angled towards the left, and the other half towards the right. Both produce sideways forces, but these should cancel one another out. The robot designers reported that the robots swam nicely with just one wave per cloak. Mind you, the robots usually had just one cloak, like the knifefish. 

The animation also shows one other trick: if you look closely, you can see that the cloaks do not sway much at front, and the amplitude of the wave increases towards the back of the animal. I borrowed that from real biology, as at least rays and knifefish do this. 

Let’s now equip our knifefish with 2 waves per cloak. The parts of the wave that are useful for swimming are now at a steeper angle towards the direction of movement, nearing perpendicular to it. I thought that this should increase the propulsive force a lot, but work on the robot fish did not agree. The velocity did not increase much, but the robot was more stable, which is intriguing. Real knifefish have more than two fins on their ribbon fins at one time, so there must be an advantage in that. 

Click to enlarge; from: Blevins, Lauder. Rajiform locomotion: three-dimensional kinematics of the pectoral fin surface during swimming in the freshwater stingray Potamotrygon orbignyi.  The Journal of Experimental Biology 2012; 215, 3231-3241

This image is from a paper about ray fin movement. The fins as a whole move up and down (so they oscillate), while there are ripples along the edges of the fins (so they also undulate). Nature seems to like combinations better than separations. The edges of the fins curl up and down, so they do not move as if there are completely stiff rays in them. 

I decided to build that in too, so here is a ‘curly-cloaked cloakfish’. I like it. One odd thing about these cloakfish animations is that it is not immediately obvious how they work, when you see the movement. It is also not easy to find an angle, when you rotate the objects, from where it is easy to get an immediate overview just how the animal is built. That can be seen as a disadvantage, or, in reverse, as an advantage, because it underlines that we are looking at an alien shape. 

By now, cloakfish ‘evolution’ has progressed to allow a variety of body and cloak shapes. Shapes range from ‘long-sleeved’ cloakfish with long narrow ribbon fins with multiple waves along their surface, to very short star-shaped cloakfish with narrow wings that fly through the water. That is certainly enough material for two explanatory pages in The Book, and should be enough for a short documentary too. But that will depend on me improving my skills as regards merging and smoothing 3D meshes.

Explaining Spidrid walking

 This will be another fairly short post. In the previous post I explained that I was working on pages for The Book that explained some biomechanical tricks of Furahan lifeforms. Other such explanatory pages deal with things such as rusp snouts and gaits (done), photosynthetic spectra (done), cloakfish movements (to be done) and spidrid gaits (done).

I will not show the actual spidrid illustrations, but can show you some of the underlying thoughts by way of animations.  I used the programs -all Matlab- to produce such animations to choose a single frame, which I then rotated this way and that until I was pleased with the composition. The resulting image was then imported into Corel Painter and used as the guideline for a digital painting. But I will not show these here.

 

The first animation shows your typical run of the mill garden-variety spidrid. It is walking slowly, meaning that each leg is on the ground for one half of the walking cycle. With eight legs, it is easy to have enough legs on the ground to provide a stable support platform at all times. The ‘support diagram’ is a polygon connecting all feet that are on the ground at any one time.

The gait used here is what I call an ‘alternating ripple’. Imagine that the legs are numbered 1 to 8, going round the animal. If the phase differences are 1/8, 2/8, 3/8, up to 8/8 in the same leg order, then legs that are close in phase would also be close in space, so many legs on one side of the beast could be off the ground at the same time, so it would tipple over. So, we introduce an additional offset for even-numbered  legs: 1/8, 5/8, 2/8, 6/8, 3/8, 7/8, 4/8 and 8/8. You will probably need some graph paper to get to grips with all this...

The red lines show the path a legs traces in 3D space. Because the ‘camera’ follows the body, the tracer paths are also respective to the body. The effect is like that of the animal walking along on a treadmill.  

The second one is very similar, but the main difference is that the legs are on the ground for less than half the time. Such schemes are typical for fast movements. The animation runs at the same number of frames per second, so you cannot appreciate the speed difference. There are fewer legs on the ground at one time. The polygons of the support diagrams have now morphed into lines or even points, if there is only one leg on the ground.       

  

Now we move to a more specialised racing spidrid. The camera no longer moves along with the beastie, but is fixed in space. The animal has relatively long legs, and runs the risk of knocking them into one another. That has to be avoided by reducing stride length a bit and adapting the gait: adjacent legs should not be at opposite phases in the cycle, as they then will certainly knock into one another. This one is using the ‘slow’ leg pattern at which a foot is one the ground half the time.   

This is the same racing spidrid at high speed. Each leg is now on the ground for less than half the time, more suited to fast movements. The animal changed its gait in two ways: the first is that the phase differences between legs are smaller, and arranged in such a way that at times there is no leg on the ground at all. It is effectively jumping! The second change is that the leading leg could only contribute to forwards movement by powerful and fast flexion movement, and I decided that the flexion muscles are relatively weak, so the animal simply lifts that legs into the air. (It should really move the body up and down as well, but the animation was not designed for complete realism.)

Many of the principles here are quite common for earth animals: walking faster is often achieved by increasing cycle frequency, stride length, reducing the fraction of the cycle that a leg is on the ground and adapting gaits to achieve jumps. Most mammals and reptiles always use all four legs at all speeds, with a few exceptions (kangaroos, probably hadrosaurs; no doubt there are more). But these poor unfortunate creatures have to make do with only four legs anyway, leaving them little choice. Earth crabs do have choices, and when they speed up, they actually use fewer legs, down to just two. Spidrids, not to be outdone by Earth creatures, have similar tricks up their virtual sleeves.

Explaining tetrapter flight (Tetrapters/tetropters X)

Just a short post this time. 

The Book will not only contain paintings of animals, plants, mixotrophs and people, but will also contain explanatory diagrams. These are usually much more boring to produce than texts or paintings, but they still have to be done... I had postponed writing and illustrating the flight of tetrapters for quite some time, and have now decided to get to work and not to look up until it is done. 

The challenge here was how I could capture the complexity of tetrapter flight in static diagrams, although I already had videos dynamically showing how tetrapters move their wings. The two diagrams above form part of a set of eight. Together they depict one complete movement cycle. I decided that I would show the path of the tip of the wing in the diagram, and that a portion of the path would be shown with a bold line, to indicate the movement since the preceding diagram. I hope that works.

Click to enlarge; copyright Gert van Dijk

 

Click to enlarge; copyright Gert van Dijk

The two diagrams show the point in time where the wings are moving apart after the 'clap' phase, when they touch or nearly touch. When they then 'fling' away, they create the 'clap and fling' mechanism that provides part of the lift. For more on that, you may read some older posts indicated by their year of publication: 2009a, 2009b, 2011 and 2018. 

 

Click to enlarge; copyright Gert van Dijk

 By the way, I have started to update the main Furaha website. I will gradually add some new material, but do not want to give away too much of the content of The Book. Still, some newer paintings will creep in here and there. I changed the image on the welcome screen, and do not think I ever published that particular rusp image before. So there you are.

The evolutionary origin of dragon flight

Perhaps some of you know the ‘dragon’ series of books by Marie Brennan. They are very enjoyable fantasy novels, describing the consecutive adventures of a woman in a fictional world resembling late 19-century Earth quite a bit. There are of course disparities, such as the existence of dragons. 

The protagonist is a young woman, or she is at the start of the first book; in later volumes she is older. She wishes to study Natural History, not at all a proper endeavour for a young woman in her rather Victorian world. To find out more about her and her adventures, you should read the books for yourself, because this post mostly deals with the cover art of one the books: 'Within the sanctuary of wings'. 

You can have a look at all the covers on the site of the artist, Todd Lockwood, where you can also buy prints and have a better look at the covers. 

 

Click to enlarge; copyright Todd Lockwood

Here is the cover in question. I think you can guess why it caught my interest, well, other than this being creative and high-quality art. The four creatures form an obvious succession, starting with a six-legged dog-lizard wingless beastie in front. The distance between its hind and middle legs is larger than between the middle and front legs, which is interesting, but the really important detail is the little membrane connecting the hind part of the middle leg to the torso. 

In the next stage, that membrane is a lot larger, and that second 'protodraco' seems to be gliding as much as it is running. The middle legs stick out sideways a bit; do they even hit the ground? The third stage has undeniable wings, and the fourth stage is all about wings. That one is a proper dragon, with four walking legs and two wings. I think this cover is a diagram of the evolutionary history of flight in dragons. 

The covers of all these books betray an obvious biological interest, which is completely in keeping with the content of the books: the heroine builds her career on the scientific study of dragons, and the readers get to hear interesting snippets here and there. When I saw the cover, I was curious whether this apparent evolutionary history also featured on the books, but I did not find that there. 

Would this progression from a running hexapod with six walking legs to a clade with four walking legs and two wings work? Regular readers will know that Furahan hexapods gave rise to flying forms as well, so I had to devise an evolutionary background for them, just as had been done for these dragons. Actually, hexapods did not only gave rise to the four-winged tetrapterates, but also to two-winged bipterates. On paper there is even a third flying clade, but I haven't worked much on that one yet. 

A basic concept in evolution is that an organ or feature will not develop just because some future descendent, a few million times removed, may make good use of whatever the organ does. That structure must convey some advantage in its early stage, or why would it be there? That advantage is unlikely to be true flight. But the future wing could help in gliding down from a tree or a cliff, or it could help the animal to jump higher and longer, or to run better. If you read about the evolution of flight in pterosaurs, birds and bats, you will find such explanations. I think that the winglets in the 'protodracones' on the cover show that, in dragons, flight evolved 'from the ground up', starting with more efficient running. 

Click to enlarge; copyright Gert van Dijk

At present, that is not how Furahan tetrapterates or bipterates got into the air. They took the 'down towards the ground' route. The rough sketch above was my first try at finding a shape for such animals. This is an arboreal species with folding leg flaps on all six of its legs. They crawl up into trees and then jump out of them and glide away, somewhat clumsily. 

Once the evolution of such gliders is jump-started (sorry for that one), the next stage is likely to involve optimization. The animals will probably not be very good at flying in the beginning, so it may pay for them to have an aerodynamically stable body plan. A stable flight scheme would make them less maneuverable, but at least it should keep them airborne without sophisticated neural control. The easiest way to achieve a stable shape would be to have the centre of lift directly above the centre of gravity, and in turn the easiest way to get there is probably to use the middle limbs as the main or only wings. 

There are intriguing other possibilities though, because the hexapod Bauplan in principle allows  not just one, but two or even all three pairs of limbs to be used for flight. With less than three pairs the next question is which pairs of limbs should be used for that? Any such design must also look into how the remaining legs must be adapted, so the animal will make aerodynamic sense while also being able to move about on the ground. 

Such things might be good material for another post, but I would not be surprised if readers run away with these and better ideas long before I will ever get around to writing that post. 

Book Review: Fundamentals of Creature Design

This is not the first book review in this blog (there were at least nine previous ones) and it is also not the first post about creature design. You could say that speculative evolution, the focus of this blog inasmuch it has one, is mostly about creature design, so is there in fact much difference between the two? 

Click to enlarge; copyright 'individual artists'

The book ‘Fundamentals of creature design’ starts with a section 'How to use this book', stating that the book is aimed at those who wish 'to create believable fictional beasts'. Again, that should include those interested in speculative evolution. Still, reading this book made me think that there are differences between the worlds of speculative evolution and creature design. 

But first, the book itself. It has a soft cover and has no less than 286 pages. It is published by 3dtotalpublishing, a company I think consistently combines high production standards with high quality illustrations. The cover mentions four artists whose work is included, but the work of many more is included, whose work is also good to excellent. The book is divided into 7 chapters: research and imagination, functionality and adaptations, anatomy, general design principles, creature design in the industry, design processes and a gallery. 

Click to enlarge; copyright Alex Ries

The chapter on research and imagination is written by Alex Ries, whose work on the Birrin should be well-known. If not, have a look here. The Birrin-project is a long-standing one; I wrote about his work in this blog back in 2009. In the present book, Alex Ries makes the excellent point that nature on Earth provides an endless array of examples that help inspire new creations. He is not the only author in this volume making that point, but I would say that he does something else with it than the others do. He extrapolates, as do the others, but he departs much farther from Earth life than the other authors. In doing so he succeeds in designing alien lifeforms. He alters the Bauplan of his creatures so they are not at all close to that of Earth reptiles, mammals or other vertebrates. The four-jawed and four-eyed heads shown above are a good example of that. (In fact, Furahan hexapods and the Birrin were given a similar head arrangement by coincidence -although the four hexapod jaws evolved from an original six jaws.) Most of the others artists stayed closer to Earth schemes, so their creatures are largely alternate mammals or reptiles rather than alien species. 

Click to enlarge; copyright Brynn Metheney

The next chapter, on form and adaptability, is by Brynn Metheney, whose work has also appeared previously on this blog, in 2011 this time. She makes the point that form should follow function, asking where animals live, what they eat and whether they are male or female. I like her flowing lines and sense of shape as much as I did in 2011. There is an occasional animal with six limbs in here (see above), but most are regular tetrapods, whose legs in particular could easily belong to some real Earth animals: successive segments bend forwards and backwards in the ‘zigzag’ pattern of mammalian legs. Also front and hind legs are easily recognisable as such. 

I do not think think there is an animal with a truly alien leg design in this book; see the last post on zigzag legs here. Admittedly, I am still struggling with the finalisation of just that aspect of Furahan hexapods, and have been doing so for quite some time. And if you do manage to draw unearthly legs, the animal will tend to look ‘wrong’ (but alien). 

This pattern of sticking close to the design of Earth animals is a common theme in the rest of the book. The chapter on anatomy, by Dominique Vassie, makes that point expressly, containing muscle sketches of groups such as primates, dogs, cats, horses, whales, but also myriapods and insects. There was something here that surprised me, and that was advice on how to blend anatomies of different animal groups. I had noticed that tendency in creature design before (see here and here). I was surprised then and now about that, because biological evolution simply cannot mix birds with mammals, for instance, to produce new species. Of course, there is convergent evolution, and that results in similar solutions to similar problems; but evolution does not stitch the front end of a badger to the hind end of a boar, as was done here. Or does that simply mean that creature design is not all that committed to biological evolution? 

The chapter on general design principles focuses on the artistic side of matters, and that is welcome, although one chapter cannot obviously do justice to all the various artistic styles. The chapter gives advice on matters such as a sense of scale and the use of detail at some parts of a painting but not others. The points made here are all valid. Overall, the design principles are not so much aimed at producing the most biologically plausible animal, but more at evoking associations in the humans watching the images. Soft and round shapes help evoke cuddliness, and sharp jagged edges give a more aggressive appearance. There may be a biological truth in that, in that animals with lots of teeth and claws are probably more dangerous than those without. But in biology such messages can be tricky: a cat, or tiger, for that matter, may look all soft and fuzzy at rest, but when it gets angry even a house cat suddenly has more teeth and claws than you thought possible. Such deceiving appearances are absent here: if an animal is to look dangerous, you can tell. Mind you, I have also altered the shape of some Furahan animals to convey a message to human observers. 

This is where my review becomes a bit critical, but please realise that the observations that follow only hold from my peculiar point of view. I am a scientist who happens to be able to draw a bit, and what I like to see are biologically plausible organisms, with a form that makes biomechanical, evolutionary and ecological sense. If the speculation takes place on another planet, the results can indeed resemble Earth life because of convergent evolution, but it is unlikely that the resulting animals could ever be mistaken for Earth mammals or birds. The discussions on the speculative evolution forum, and the often very knowledgeable and insightful comments on this blog, show that people engaged with speculative evolution usually take their biology and plausibility very seriously.

 

Click to enlarge; copyright Dominique Vassie

Click to enlarge; copyright Edin Durmisevic

That may be the heart of the matter: if speculative evolution is like ‘hard’ Science Fiction, then most creature design is like Fantasy, where the laws of nature take a back seat. There is no hard border between the two realms. The inclusion of the Birrin in fact shows that the two worlds fit well together. Mind you, the Fantasy element is much the stronger one in this book. That Fantasy focus explains why the book contains creatures such as a a giant insect-like beast that can carry humans, although its legs are biomechanically unlikely to allow it to stand, or a human-bear hybrid in the form of a were-bear. Both are biologically implausible, but in a fantasy setting, that's fine.

Click to enlarge; copyright Brian Valeza (I could not scan a part of the image at the left; sorry for that)

Click to enlarge; copyright Kristina Lexova

The book is filled with brilliant images such as the ones above, and I enjoyed it immensely. The above examples are random examples. It does exactly what it set out to do. I recommend it wholeheartedly to anyone interested in designing animals for a Fantasy setting. I also recommend it to those who wish to draw better life forms in a Speculative Evolution context, but just remember that it is not primarily a guide on how to design life forms with a systematically different Bauplan and evolution. That would require a different book, one that may not exist yet. I wonder if there would be a market for such a book...

'Ulla sanguisuga' at work on a plant louse (a work in progress)

At some 120 pages, The Book is steadily progressing, slow as ever, but getting there. I thought I would let you have a peek at a recent painting. The Book should show at least some of the myriad small animals that make up the bulk of Furahan animal biomass, and so I painted a few. But after that, the final series of paintings will probably show big hexapods only! 

Click to enlarge; copyright Gert van Dijk

What you see here is just a fragment of a painting, and it is even more limited in that it only shows the head and neck of the most important animal on the painting. I turned the layers containing the other parts of that animal to invisible, so there will be something left for The Book. That head belongs to a 'lice eater', an insect-sized animal of the type usually labelled as 'wadudu'. Wadudu are reminiscent of arthropods, but they have a mesoskeleton, not an exoskeleton. Admittedly, the difference in skeleton type is only obvious for the largest wadudu, the size of mice and sparrows. 

Anyway, this 'lice eater' carries the scientific name of Ulla sanguisuga. It should not be difficult to work out where the inspiration of that name came from. 

Its prey consists of 'plant lice'. That is not a clade, but a simple group designation for all the little animals that make a living by sucking plant sap. The plant is question belongs to a major plant clade called the 'poliochromes'; they have a photosynthetic pigment that absorbs light across most of the visual spectrum, explaining why these plants are generally dark grey. 

To mimic the effect of macro photography, I first painted the entire scene as I would normally do, and then rearranged everything in layers that represent distance to the imaginary camera. I left only one layer in focus, and blurred to varying degrees. We now have depth of vision on an imaginary planet; you would think that photography a few centuries into the future would have done away with such blurring, but no, here we are...

Ballonts IX: Blue Sky Thinking (Part 2)

By Abbydon

The previous article discussed the possibility of using soap bubbles to create small lighter than air organisms. A second possibility is more sophisticated and relies on the wonder material, graphene. It was discovered in 2004 by two scientists at the University of Manchester who were subsequently awarded a Nobel prize for their work.

Graphene is made of a flat sheet of carbon atoms, so it is a little bit like 2D diamond. It has many interesting properties but is most well-known for its high strength (100 times stronger than steel) and low density (less than 0.001 grams per square metre). An amusing illustration of this was provided in the Nobel prize paper. Imagine a one square metre graphene hammock tied between two trees. This could hold a 4 kg cat before breaking yet would only weigh as much as one of the cat’s whiskers.

As impressive as this is, recent work suggests that graphene has another property that is extremely relevant to ballonts. Graphene is also impermeable to gases. With such an amazingly low density it effectively produces a matte-black massless membrane even when a few thousand layers are used.

It would however be extremely challenging for life to produce a graphene balloon with absolutely no defects. A more robust approach is to copy the bubble foam concept and use a mass of small graphene “bubbles” instead. Conveniently, a material extremely similar to this called aerographene has been invented by scientists. It consists of a complex 3D network of graphene and carbon nanotubes where most of the volume is air. For this reason, when measured in a vacuum it has a density slightly lower than helium at 0.16 kg/m3.

Click to enlarge; copyright unknown; source here

While aerographene itself is not airtight it is not inconceivable that a material like it could be produced that contains many small airtight compartments in a similar way to a bubble foam. If these compartments contained a lifting gas, then the entire structure would float. When I mention aerographene below I am actually referring to this possibility and not the real material. The chart below shows that both a 1000-layer graphene membrane and a “solid” aerographene balloon would easily enable small (or large) ballonts.

Click to enlarge; copyright Abbydon

This strongly suggests that an “magic” aerographene like material could be used to enable small ballonts to exist. Since they cannot have a membrane then any aerographene produced would be an external structure grown from the bottom up, like hair, and could not be repaired only replaced. Additional graphene would be produced on the lower surface where the organism was hanging while the top surface would slowly degrade.

It is unfortunately unknown whether life could produce graphene in the first place as it does not appear to be produced naturally by life on Earth. Industrial processes for producing graphene based products typically require temperatures beyond the reach of even the most extreme of extremophiles. However, Shewanella oneidensis bacteria can be used to produce graphene from graphene oxide which is at least a start.

I am not a chemist and this is not the blog to delve deeply into the exact chemical process that life could use to produce graphene at ambient temperatures. There is some justification that it would not be implausible though. Inspired by photosynthesis the direct conversion of carbon dioxide into graphene at high temperatures has been demonstrated. A slightly different approach has even been shown to work at room temperature.

As an example of what is possible, an approximately spherical lump of dark grey aerographene with a 9 cm radius can lift about 3 g. This could support something like a praying mantis that is about 7 cm long though could perhaps be longer and thinner. A cup-like abdomen could contain the graphene and hydrogen producing organs while the four long rear legs partially surround the sphere to maintain a grip. Four independent wings could provide mobility. The long forearms would then provide good reach to gather food. Due to the benefits of aerographene this hanging mantis would be able to float even when small and could grow to a size only limited by other factors. 

Click to enlarge; copyright Gert van Dijk. Note that the graphene 'floating body' is narrower at the tope than the bottom, because the animal grew in-between forming the early top and the more recent bottom graphene.  

The soap bubble and aerographene concepts don’t mean that the small ballont problem is solved as they are really just meant to inspire others to come up with their own ballont concepts. In the absence of any lighter-than-air organisms for comparison on Earth there are still many unanswered questions to be considered and that is all part of the fun of speculative evolution.

For example, why would an organism evolve to be lighter-than-air? Is it always lighter-than-air or is it only temporary? How does it control its movement when floating? How does it protect itself from predators? How does it feed? Can it repair or replace its balloon if punctured? How is the lifting gas generated? How fast does the lifting gas leak from the balloon?

If we were only interested in creature design then this would all be sufficient to inspire a range of organisms based on shimmering soap bubbles or black graphene. Speculative evolution requires more than that though. Demonstrating that physics supports the idea and that there is a plausible way for the organism to implement the idea are both important. To be thorough, it is also important to consider whether the proposed organism could have evolved through a series of plausible steps, rather than just spring into being fully formed.

There are various ways that life on Earth already generates hydrogen, such as through fermentation, so that part is not unusual. The formation of chemical laced water to form longer lived bubbles is also fairly common as fish, frogs, snails and insects are already known to do this. A soap bubble based ballont as shown in the previous article therefore seems reasonably plausible.

On the other hand, the formation of graphene is more challenging to justify in a series of steps and I cannot give a solution to this. Graphene does have the ability to absorb light efficiently at all wavelengths, which is why it is black after all. A plausible evolutionary path could involve algae or plants in low light environments developing graphene for photosynthesis related reasons. Since hydrogen can be produced by algae as part of the nitrogen fixing process perhaps forests of lighter-than-air pitch black plants could feasibly evolve. That is however an idea for another time but perhaps it will eventually appear on my recently created blog. It describes the tidally locked world Khthonia, which orbits twin red dwarfs.

Finally, I am very grateful for the opportunity to share my thoughts on this matter in this blog and I hope that they inspire people to develop their own ideas in this area. Please comment to let everyone know what you think about graphene and its possibilities.