Monday, 14 May 2018

How do tetropters walk? (Tetropters IX)

In a recent post I showed my latest animation of tetropter flight, using a brightly coloured farfalloid species as an example. As I wrote then, the reason to get down to the nuts and bolts of tetropter anatomy and movement was that I am painting a few tetropters paintings.


Click to enlarge; copyright Gert van Dijk
Here is a small fragment of the latest one. I had given most attention to tetropter wing movement, but naturalistic paintings also require details about the rest of their anatomy, such as eyes, mouth and legs. The radial nature of tetropters is very reminiscent of that of spidrids; tetropters obviously share a common ancestor with spidrids. On the whole, tetropters are much smaller than spidrids. Whereas spidrids are in the crab range, tetropters are more like insects in size. The Furahan atmosphere is denser than Earth's, which makes flying easier. The tetropter respiratory system does not wholly depend on passive diffusion, so it does not form a crucial limiting factor. Some tetropters, such as the Red Baron shown earlier, are quite a bit larger than current earth insects. There may well be tetropter species in remote areas that are as large as the giant dragonflies from Earth's Carboniferous era. These areas have not been explored in detail yet: they are far away and travel is expensive.

Tetropters have eight legs, just as spidrids do, and their gaits are in many cases exactly like those of spidrids. There are exceptions though. Tetropter legs differ in some aspects from spidrid legs. The most obvious difference is that the legs of a tetropter need not be all alike. In contrast,  all eight legs of any spidrid are virtually identical. Again, this is a bit like insects' legs, that usually differ markedly in size and shape between front, middle and hind legs. This probably makes sense because these legs have different mechanical roles, whereas tetropters do not even have a front or a back. The asymmetry of tetropter legs takes a shape that is peculiar to their radial nature, and quite fitting: there are four large legs and four smaller ones, and they alternate: big, small, big, small, etc. Over evolutionary time, the differences have become quite marked in some clades. In predators such as the 'Red Baron' the outer ring of legs has gained a grasping function. In most species both the outer and inner rings are used for walking. Some say that the differences came about in response to a need to stop the legs becoming entangled; that sounds good, but spidrids do not seem to suffer from tripping over their own legs! Others say that the small size of tetropters means they needed legs that are splayed very wide to stop them being blown over by the wind. But why should that hold for just four legs? Sometimes we just do not know... (meaning I will shelve the question for later, or perhaps I will leave it unsold. There are many things unclear in Earth biology, so perhaps I do not have to explain everything).



Anyway, here is a schematic tetropter using the 'double table' gait. Its wings are neatly held in their vertical resting position. At any time there are four legs of either the outer or the inner ring on the ground. For a brief moment there are eight. This system is just as stable as the 'double tripod' of insects. There is little or no chance of falling. Note that the body wobbles a bit. I did that just so you could see that there is a joint between the 'corpus' holding the legs and mouth on the one hand, and the cephalothorax holding eyes and wings on the other hand.

   
This specimen proves that the gait can be a bit more fanciful than the 'double table' without destroying overall stability. You may also note that the joints of the legs are arranged in a different way. In the previous species, and in all spidrids, the angles between the three big leg segments always bend in the same direction, so the leg gets curved more inwards and downwards as you progress from the proximal portions near the body to the distal parts at the tip. In this particular species, the first joint bends in the other way. In earth arthropods you can easily find these patterns too.


Finally, here is a walking tetropter in which the joints of the legs of the outer ring all curve inwards, while the inner legs have yet another pattern, starting with a downwards followed by an upwards bend. The gait is somewhat complex as well, which I like, as it gives the animal a more biological feel.

So there we are; now I can safely paint an explanatory diagram explaining how tetropters walk. After that, it's back to 'toe studies' again. I must say I am distracted because I watched season 4 of Game of Thrones again. There is a scene in a giant rides a mammoth. Hang on; as I calculated earlier, such a giant should weigh about 1440 kg! Mammoths are big and probably strong, but that is some weight! How much weight can a mammoth actually carry? That is obviously a very silly question, but also one quite worthy of this blog. I may need to find out...

Thursday, 3 May 2018

Equations I: Drake's equation

People with an interest in speculative biology will probably know Drake's equation well. It describes how many civilisations in our galaxy are at present broadcasting their existence by emitting electromagnetic radiation into the universe. If you are only interested in the purely biological side of speculative biology, then alien intelligence might not appeal to you very much. Still, it makes sense to think that any biological intelligence will be deeply shaped by the specific biological background, so alien intelligence is a part of speculative biology (probably until that in turn gives rise to machine intelligence; would that reflect its maker too?). I aim to write two or three posts on the biological evolution in our galaxy, starting with Drake's equation.

I do not have that much affinity with speculative intelligence. I once started to evolve an intelligent species on Furaha. The creature was derived from hexapod predatory stock, so its forelimbs were not used for locomotion, as an example of centaurism. Most such 'neopredators' evolved their front limbs into clubs or spears, as can be seen on the Furaha website. These modified front legs lost all their toes in becoming spears or clubs, but the proto-intelligent species belonged to a group of small neopredators that had in fact developed the grasping ability of toes on their front leg. This allowed them to radiate into a number of interesting shapes.


Click to enlarge; copyright Gert van Dijk
This old and rather poorsketch shows this putative proto-intelligent species. It evolved on an isolated island and was supposed to have gone extinct shortly before humans came to Furaha, say only 30,000 years before. There would be some evidence of shaped clay or other things suggesting that the use of purposely shaped objects. at the time of human discovery, the island's ecology was supposed to be devoid of large species and to have remarkably little diversity. The idea was based on the presumed history of Easter Island, as described by Jared Diamond in his book Collapse. The story holds that overpopulation caused the inhabitants of Easter Island to cut down all trees and to destroy their environment, and through that their civilisation. Easter Island, seen in this way, holds a mirror to all of Earth, telling us to stop and think what we are doing. While reading up on Easter Island, I found that  these depressing ideas have later been questioned, and the case of Easter Island has even been labelled as a story of efficient adaptation. The trees are still all gone, so I find this rather depressing as successes go. 

I had tucked these proto-intelligent species away on a remote island where they would provide the Furahan equivalent of Easter Island, providing a lesson without ruining the entire planet. I later felt that I did not need such a heavy-handed approach so I erased the story entirely.

Back to Drake's equation. Below is a text taken directly from Wikipedia. The equation describes the number of civilisations, N, with which communication might be possible. It is assumed to be equal to the mathematical product of the following parameters:

R, the average rate of star formations, in our galaxy,
fp, the fraction of formed stars that have planets,
ne, for stars that have planets, the average number of planets that can potentially support life,
fl, the fraction of those planets that actually develop life,
fi, the fraction of planets bearing life on which intelligent, civilized life, has developed,
fc, the fraction of these civilizations that have developed communications, i.e., technologies that release detectable signs into space, and
L, the length of time over which such civilizations release detectable signals.

N = R   fp  ne  fl   fi  fc  L

I confess that I always had trouble understanding why this product represents the number of civilizations that are transmitting signals now. In an interview posted here Frank Drake said he started with the rate of new stars being produced because the equation was based on a continuous production of new planetary systems. As a result, the number of detectable civilizations is proportional to the rate of star formation. That makes sense, but still... Say that 10 stars are formed in the galaxy over one year. The equation ends with the average number of years that a civilisation actually transmit signals, say 300. The product would be 3000, modified by the other parameters. This suggests that the equation results in the total number of 'transmission years' resulting from one year's batch of new stars, and I do not quite understand why that would equal the number of civilisations that are transmitting right now. It seems more logical to start such an equation with the total number of stars in the galaxy and to modify that number. In fact, there are equations out there that do just that, and I found that there are several variants that are also called "Drake's equation".

Regardless of the different versions of Drake's equation, the message is clear enough: any estimate of the number of transmitting civilizations depends on a fairly large number of parameters, most of which rely more on guesses than on facts. The Wikipedia paper discusses that nicely, stating that N can vary from less than one to over 15 million. Drake himself arrived at about 20 civilizations in our galaxy. The more there are, the more you have to wonder why we never heard from them, which is of course well-known as Fermi's paradox. Here is a very thorough and entertaining book discussing 75 possible solutions to Fermi's paradox.    

Something like 20 civilizations distributed over one galaxy is not much. The average distance between such civilizations would be enormous, giving us little chance of hearing them. Note that Drake's equation is about how many civilizations are out there, not about our chances are of detecting them. Any considerations on actually detecting them must take the size of the galaxy into consideration. I could not resist playing with these ideas a bit.

Click to enlarge; copyright Gert van Dijk
The figure above shows a solar system containing a transmitting civilization. This civilisation started transmitting at some point in time, here just 30 years ago. From that moment on the signal travelled into space with the speed of light. For every year of time it obviously travels over a distance of one lightyear. After just 10 years the civilisation stopped transmitting. Perhaps the inhabitants found more efficient ways to contact people on their own planet than wasting energy by blasting a signal in all directions. Perhaps they went the Easter Island way, by cutting down all their trees, by nuking themselves to oblivion, by using creative biological weapons, or perhaps their successors, machine intelligences, decided they did not want pets. Whatever happened, a shell of transmissions with a thickness of 10 lightyears is still expanding outwards at the speed of light. The signal strength will decrease quickly, as it is governed by the square of the distance (see here for an explanation, on sound rather than electromagnetic radiuation, but the principle is the same). I tried to find information about how far the type of unfocused signals earth sends out might be received with current equipment; here is one source saying that 21 light years is optimistic, which is not much at all. Another source, from a senior SETI astronomer, states that detecting Earth from 'a few hundred light years' require an antenna the size of Chicago. That's impractically large...



Here is a simple model of a galaxy with most stars in the middle. The image spans 1,500,000 lightyears horizontally and vertically. Over a span of 100,000 years, civilizations evolve and transmit for a while, in this case for any duration between 0 and 5000 years (as longer as all of human history). The thickness of the expanding rings show the duration the civilisation was transmitting. I assumed their signal could just still be detected at a distance of 25,000 lightyears, requiring fantastically sensitive devices. The brightness of the colour indicates signal strength: at 25,000 lightyears it fades to nothing. Note that signals can only be detected in the coloured rings themselves, not in their blank interiors. The result is clear: the total area of the galaxy that lies in a ring is very small, and those are the only areas where transmissions can be picked up.

 
Here it the same scheme, but with a shorter duration of transmission and a smaller distance over which a signal can be detected. There are thin small shells here and there, but you have to look carefully or you will miss them altogether. This is still a very optimistic vision, I think. If there are just 20 transmitting civilisations that require a ridiculously large antenna to be heard seems to mean that it's not surprising we haven't heard anything yet. But there is Seager's equation:  looks at the problem in another way, so that's one I will have a look at in later post.              

Tuesday, 10 April 2018

Ten years on

The first post of this blog was published on April 22, 2008, or ten years ago. I wrote several earlier progress reports. It is time for a new one, especially because of the festive nature of ten years of blogging. Well, more or less, because the rate of new posts has been low in the past few years. More on that later. 

Let's start with a comparison with 5 years ago, when I also wrote a progress report. Then, there had been 307,000 page views according to the blogger 'stats' page, and now the counter stands at 639,478 views. I am not altogether certain that all these visits represent actual people; perhaps there were bots  as well. What is certain is that I had written 197 posts five years ago, whereas the counter now stands at 233 posts, so it is obvious I wrote more posts in the first five than the second five years.  There were 1638 comments in all, and I must say that I enjoy the interactions. The comments have quite often made me think a bit harder about what the project, and gave rise to new animals on more than one occasion. Thanks to all who read my posts with such enthusiasm!

The 'stats' section also tells me what the most-visited posts were over these ten years. Here they are, with their previous ranking from five years ago between parentheses:

1. (1) Swimming in Sand 1: the Sandworms of Dune; 5 Feb 2011; 8854 views       
2. (5) A future book on future evolution from France; 19 Nov 2011; 6239 views       
3. (4) Avatar's 'Walking with hexapods'; 11 Feb 2010; 4862 views
4. (2) Warren Fahy's "Fragment"; 8 Aug 2010; 4010 views                   
5. (-) Future evolution from France: 'Demain, les animaux...; 30 May 2015; 3327 views
6. (3) A century of thoats; 5 May 2012; 2996 views
7. (-) Create your own planet (using Celestia); 13 Aug 2011; 2717 views   
8. (-) The anatomy of giants in 'Game of Thrones'; 11 Jun 2016; 2661 views           
9. (9) Ballooning animals and Newtonian fitness; 15 Jul 2011; 2338 views   
10. (-) Second part of a review of 'Demain, les animaux...; 13 Jun 2015; 1958 views   

There are four newcomers in the top-10, but it seems that the sandworms of Dune are unbeatable. My French friends Marc Boulay and S├ębastien Steyer will be pleased to learn that their work occurs no less than three times in the top-10: first as an announcement in 2011, and then as a two-part review in 2015. I hope that this signals an immense interest in books on speculative biology, because that would be good more my own project: The Book.

Click to enlarge; copyright Gert van Dijk
Some of you may recall that I had announced that I would spend less time blogging to have more time to work on The Book. The graph above shows the cumulative number of blog posts in red, from 0 in 2008 to 233 now (the present one excluded), as well as the cumulative number of spreads in blue, starting in 2011. A spread is a two-page account of a species, a chapter introduction, or of any topic worthy of devoting two pages to. The number of spreads started in 2011 because I had made the switch to digital painting and started collecting the slowly increasing number of spreads in an InDesign manuscript. I am at present working on the fiftieth spread, so within a short while the manuscript will have exactly 100 pages. Not bad, hey?

But did the reduction of blogging benefit The Book? The two vertical red lines indicate the post in 2014 in which I announced a temporary stop, and the one in 2015 in which I said that I would stop blogging except for the occasional post. Have a look at the rate of increase of the two lines: the total number of posts rose much slower from then on, while the number of spreads rose appreciably faster. The rate of new spreads since then is about nine spreads a year, which is less than the 12 I hoped to be able to manage. But please remember that this is not a job and that each spread takes presumably 20-30 hours to produce. I you ever write a book, do just that: write it; don't paint it! Mind you, The Book does not consist of images only: there are over 32,000 words at present, which is the length of a novella.

I always aimed at something like 125 pages, simply because comparable works have such a number of pages. At present I think the number will be more like 130, but we'll see. The good news is that I expect that the number of spreads per year will increase, so producing the remaining 15 spreads shouldn't take very long. Mind you, 'not very long' should be considered from the perspective that such a project may take a few decades...              
    
Because this is the tenth year of blogging, I also aim to write a few extra posts this year. I think I will finally write the long-awaited post 'What are toes for?' There will also be posts on equations: the Drake equation, the Seager equation and possibly the Nastrazzurro equation...

Friday, 30 March 2018

From freezing the anatomy of tetropters to op art (Tetropters VIII)

Tetropters have been discussed in this blog several times. Eight posts were devoted to them (one, two, three, three bis that doesn't really count, four, five, six, and seven) and they were mentioned more often. In fact, they first featured in the third post ever, published on April 27, 2008. Attentive readers may note that the 10 year anniversary of this blog is coming up, and I intend to write more posts this year to honour the occasion.

Tetropters are flying animals with a radial symmetry, something that was not common at their time of invention, well before they featured in the blog. They fly with a 'clap and fling' mechanism, also used by various flying animals on Earth: the animal brings its wings together over its back and then separates them again, starting at the top. This apparently creates a lower pressure above the animal, which helps the animal to stay in the air. Earth animals, with their two wings, have one 'clap' in each movement cycle of the wings; Wikipedia has a short section on it. Tetropters have four wings and move them in such a way that there are two 'clap' events in every wing cycle. I was delighted to learn, years after their 'evolution' as Furahan animals, that someone had had the same idea but with the purpose of building an actual flying robot using the double flap and wing scheme. I wrote about that in this post.

At present I am working on the second of what will probably be three two-page spreads on tetropters. The first detailed paintings of a specific animal (or plant or mixomorph) always represents a bit of a crisis, as the characteristic features of a group, its Bauplan, have to settled for good: it has to be frozen. Tetropters had  four wings and I knew their movement pattern, but that left many other decisions to be made. How many eyes should they have and where are these eyes placed? They are presumably related to spidrids, so which features should they share? Should they have eight legs or four? If the mouth is placed at the underside of the animal, how does that reach its food? The list goes on. I have frozen the Bauplan of spidrids, cloakfish and Fishes I to VI in the past, so the process is familiar by now. I confess that I have kept one of the most difficult decisions for last, and that is the suspension system and leg anatomy of large hexapods: I wish to avoid a mere doubling of hind legs or of front legs, which is how most illustrators solved the problem of designing animals with six or eight legs (see my posts on Avatar and thoats).

The first decision regarding tetropters was that it dawned on me that I had not considered the etymology of the word well. The word is derived from the Greek roots for four, 'tetra', and wing, which is either 'pterux' or 'pteron'. In biology just the stem 'pter' is used often. So where did the 'o' come from? I guess I just used 'o' to string the two roots together, or perhaps because of an association with 'helicopter' (a combination of 'helikos', meaning winding, rolling, turning, and 'pter'). As an aside, the Lexilogos websites for Latin and Classical Greek are useful for such things). But as 'tetra' already ends in a vowel, no other sound is necesary to connect the two words, so 'tetropters' are now 'tetrapters'. In the posts I will stick to tetropters or other posts will be difficult to find.

Click to enlarge; copyright Gert van Dijk
Readers will be more interested in what the animals look like. Well, here is a drawing from the famous 'Field Guide to Imparian Tetrapters', showing the male and female forms of the 'Red Baron'. These animals are large, for tetropters that is, predatory tetropters that prey on other tetropters, catching them in flight. They have long wings and are very manoeuvrable. You may note that the outer legs have evolved into grasping limbs, leaving just the inner legs as a landing gear and to walk around on.


To help me get a good idea of tetropter wings in flight I dusted off earlier tetropter animation programs, relying on an unwieldy combination of Matlab, python and Vue Infinite. When I first made these programs I dreamed of producing 5 or 6 minutes high quality films; the one above was made with this idea in mind. Later I realised that these required considerable investments in time, time that might be better used working on The Book directly. So I gave up on nice backgrounds with leaves moving in the wind, etc., and just use animations as a scaffolding for the paintings.


This first animation shows a general undetailed tetropter in 'helicopter mode': the wings are relatively long, and when they move through their 90 degree movement from one clap to the next, they do not move down very much. The 'angle of attack', that is the angle of the plane of the wing compared to the direction of movement, is low. One extreme angle of attack would be a flat plane moving at a right angle to the wind, creating maximum drag but no lift. The other extreme has the plane moving exactly parallel to the wind: no drag, but again no lift. The optimum angle of attack should be one that for a given air speed creates the most lift for the least drag. This is also the flight mode for the Red Baron.

I have played with the structure of the wing, which is transparent with some bright red spots. The structure is much like that of insects, with a thin membrane, taut between 'spars' that give it its shape. There are two main spars to help control the curvature of the wings during flight. I tried to envisage completely unearthly spar structures, but all my attempts ended up looking like insects; let me know if you find a workable unearthly design. Note that the speed of movement shown here is not at all the natural one: for earth insects, wing frequency varies between 4 and 250 Hz, with low frequencies for large butterflies (I might write a short post on tetropter wing beat frequency taking air density and gravity into consideration).



This second example shows a 'rowing' mode of flight. Here, the wings beat down over a large angle and the plane of the wings is at a large angle to the direction of movement, somewhat in the way the blade of an oar is at a right angle to the direction of the stroke.  I should probably have made the body a lot smaller in relation to the wings, so the animal can beat its wings like Earth moths or butterflies: slowly, so the colour pattern can be appreciated. Just think of the animations as showing the animal in extreme slow motion.


Still, I could not resist adapting the animation to show a wing movement at 4 Hz, which is really low for Earth insects.  The colours stand out less.


The third and last movement concerns a mixture of the two flight patterns shown above: not too flat nor too steep, but just right. Again, this should be probably a large animal with a smaller body. There is some reasoning behind the bold colours.

I assumed that animal vision in relevant Furahan animals deals separately with colour contrast and with luminance contrast, just as the human visual system does. Generally, if you wish to see detail, use a large contrast between light and dark (i.e., a big luminance difference). You might think that colour differences are more important, but they are not. Designers know such things; here is a nice NASA image that explains the use of both types of contrast from a design point of view.

Click to enlarge; copyright Gert van Dijk
Colours can do strange things: the visual resolution differs between colours, with blue as a particularly poor colour to use for spatial information. Here is a trick to show that: the original is at the top left. I used that to blur two of the three colours red, green and blue, leaving one colour in its original sharp form. You will see that the clarity of the image really suffers f the green channel is blurred, but that the image does not suffer that much if green is unaffected. What this simple experiment shows is that blue and red, mostly blue, have a poor spatial resolution. Interesting things happen if you put two contrasting colours side by side, and tweak their luminance until they appear equally light or dark. This contrast has a poor spatial resolution, making shapes seem to float or flicker. This is just one of the properties of the visual system that op art relied on. Just type in op art in Google and do an image search.

I used such a design for the wings in this tetropter. Each wing has a bold pattern of two colours. Two wings have their colours placed opposite to the other two. The idea was that the wings in a near-clap position would provide a visual shock. Theoretically the to and fro sides of each wings could have contrasting patterns as well, to provide even more dazzle.


Here it is again, manipulated to result in a 4 Hz cycle. Does it work? Such visual effects rely on the properties of the visual system, and those will differ greatly between different animals. One species op art is another species' drabness. I have often wondered whether the colour patterns of some  Earth animals evolved to create a specific visual effect in a specific visual system. For instance, what effect do the stripes of a zebra have on the visual system of a lion, perhaps at night?

I will equip a Furahan farfalloid tetropter with a similar pattern, in the expectation that its colours will ignite at least one visual system, probably those of potential mates, to make it something like 'Wow!'.


Saturday, 17 February 2018

Rusps turn out to follow biological rules about the weaponisation of tails

I recently came across an interesting paper on the evolution of the use of tails as weapons in Earth animals. This turns out to be a fairly rare occurrence, and perhaps that rarity helps explains why animals with tail weapons are so spectacular. After all, we take the common for granted, and it is the departure from the common that attracts attention.

The glyptodont Doedicurus; click to enlarge. https://en.wikipedia.org/wiki/Doedicurus

A nice example on an animal with a tail that is obviously useful as a weapon is the glyptodon genus Doedicurus, a giant armadillo-like mammal, the size of a small car. Doedicurus was encased in strong armour and endowed with a tail with an impressive thickened club at the end.

Click to enlarge; Pinacosaurus Grangeri; Copyright Gregory S. Paul. Princeton field Guide to Dinosaurs, second edition
Ankylosaurs had the same idea, but much earlier. As far as their design was concerned, they went overboard in adding an array of large sharp spikes to their armour.

Click to enlarge; Spinophorosaurus nigerensis; Copyright Gregory S. Paul. Princeton field Guide to Dinosaurs, second edition
Some sauropods may also have had body armour as well as similar thick knobs on the end of their tails. Only one sauropod (Spinophorosaurus nigerensis) apparently sported pointy spikes on its tail, shown here as a juvenile, and drawn by Gregory Paul (I do not think I have to urge dinosaur enthusiasts to get his book 'The Princeton field guide to dinosaurs'). If these long tails were swept at high speed, the transfer of all that kinetic energy should do some real damage. But perhaps a simple threat, along the lines of 'Make my day, punk' would be enough to prevent an actual fight.

The paper in question has the title "The evolution of tail weaponization in amniotes" and is written by Victoria Arbour and Lindsay Zanno. The paper describes which features are the evolutionary precursors of the evolution of tail weapons. The authors performed a thorough statistical analysis of many body traits, and looked separately at four aspects of tail weaponry:  tail lashing, bony terminal tail spikes, a stiff distal tail, and an expanded tail tip.

Click to enlarge. Arbour & Zanno 2018

Here is a figure of the paper, showing these four aspects and the features they are associated with. The result of all this is that you are not likely to find tail weaponry in agile quick-footed predators. If you were designing just such an animal for your speculative biology project, you should probably pause to consider its likelihood. Tail weapons seem to be a last resort for large slow herbivores who already invested in body armour. The authors make the point that equipping heads with weapons occurred much more often. This seems odd because heads are already filled with important structures that should not be damaged, whereas damage to a tail is probably much less risky, so you would expect 'anterior armatification' to be less common that 'posterior armatification'(I could not resist latinising 'weaponisation'). The authors do not speculate why this should be so, but I wonder whether the effective use of weapons requires excellent motor control, something that in turn depends on excellent sensory control, meaning sight. If so, the animal's body may simply be in the way, so it cannot see well enough where to place the sting in its tail.
   At any rate, the authors state that armour in mammals evolved in those animals that are neither small enough to hide nor large enough to deter predators by size alone, and that live in open environments. Close combat with a predator must be a risky business, so the best strategy may simply be running away faster than a predator. And if flight is your main strategy, heavy armour is not going to help. But  a wholly new set of constraints must come into play if you have no chance to outrun your predator to start with. Defensive features such as large size and armour then may become useful, and it seems that active weaponry is the last feature on the list to evolve.

Click to enlarge; copyright Gert van Dijk

So glyptodons, ankylosaurs, stegosaurs  and some sauropods all fit the 'big slow armoured' description to various degrees. And so do Furahan rusps! The image above shows half a rusp from an unfinished painting (for more on rusps, use the blog's search function). From my very first rusp sketch on, rusps were large, had thick hides and used their whips as active weapons. Of course rusps have front as well as hind whips, so the word 'tail' is not applicable at all, but the point is clear; rusp whips are analogous to the 'weaponised' tails of Earth. Those early rusp sketches predated the paper as well the posts in this blog about rusps by many years. I do not remember exactly how much of the rusp body plan came about consciously. I think that I started with a long body shape. Add to that some wondering why many Earth animals are so vulnerable at their rear and sometimes along their middle as well. As the earliest sketches show eyes on middle rusps segments as well, rusps must have started with a weak encephalisation tendency. From there on the double encephalisation seems natural. Note that the posterior whip is well controlled by its own ring brain, with excellent visual information available to direct the strikes. But part of all this may have come about through largely unconscious associations while sketching. Once a design is on paper, it is often hard to say where it came from. Regardless, it is nice that the meme 'rusps have whips' can now be attributed to a firmly established biological principle.

Much as I like the paper, there is a minor matter that might have made it even nicer. Rather than 'tail weaponisation', the authors could easily have used a word that is both relevant and fun: a tail weapon is a 'thagomiser'.

Click to enlarge; copyright

The first use of 'thagomizer' is shown above (this blog uses British spelling, so I assumed the word would become 'thagomiser' in the UK; the rules aren't always clear...).
   It was published as one of Gary Larson's Far Side cartoons in May, 1982. Actually, this colour image stems from a later luxury edition of all Far Side cartoons. Poor Thag Simmons. For 'Far Side' fans, a caveman called 'Thag' occurs at least once more, and one cartoon, taking place in modern times, featured a 'Mr Thagerson'.
  At first glance the word thagomiser seems to indicate 'to turn an object, animal or person into thag', but the real meaning is obviously a 'structure to kill animals or persons, in particular Thag Simmons'. The word has later been picked up in the scientific community to describe the tail weapons of stegosaurs, and apparently of stegosaurs only. I propose to widen its use to all tail weapons.
   As an author of scientific papers myself I realise that the use of humour in scientific papers can be tricky as it is often frowned upon, and you never wish to harm your chances of getting a paper accepted. (I once inserted the phrase 'This resistance is futile' in one of my own scientific papers as an irreverent reference to Star Trek, but I do not think anyone ever noticed).

If we use 'thagomiser' as a word for 'tail weapon', the paper could have been called "The evolution of thagomizers in amniotes", which would be clear, succinct and elegant, but admittedly probably too flippant for a serious paper. Once 'thagomiser' is an accepted word, can we resist to stop there? The tendency to evolve a thagomiser then might become 'thagomiserificability', and the transition process from 'nonthagomiseriness' (not having a thagomiser) to 'orthothagomiserity' (having a proper thagomiser) is 'thagomogrification'. Obviously.