The RETURN Of The NIGHTSTALKER!!

The Nightstalker is, as most readers will know, one of Dougal Dixon’s creations presented in his 1981 book 'After Man', a book that proved fundamental for speculative biology. In that book, he presented completely novel themes, such as penguin whales and terrestrial cephalopods or bats; for more on the 1981 setting, see an earlier post here.

Click to enlarge; copyright Dougal Dixon

The image of the nightstalker in the 1981 version of After Man was later changed by Dixon, who did not like the original one very much. The new version is shown above and is published in recent editions of 'After Man', such as the '40th anniversary edition' (which has new information too!).  

The nightstalker descended from bats that were among the first animals to arrive on the newly emerged volcanic Batavian Islands in the Pacific. Facing no serious terrestrial competition, the bats lost the ability to fly, became fully terrestrial and diversified. Once other mammals arrived as well, a bat species started to hunt them and evolved into the nightstalker, a formidable bipedal predator of one meter and a half in height, or as tall as an 11-year old child.

Nightstalkers are blind and use echolocation to find their prey in the night, ‘screaching and screaming through the Batavian forest’. This may mean that the nightstalker uses echolocation at sound frequencies we can hear too, although the text does not literally say so. The screeches might also be used for communication within the pack, leaving ultrasonic sound for echolocation. In either case I wondered whether its prey can hear the echolocation sounds too, which would make life more difficult for the nightstalker.  I have compared the relative merits of vision and echolocation in three posts (one, two, and three). It turned out that echolocation is like someone shouting at the top of their voice ‘WHERE ARE YOU!?’. Provided the prey can hear the sounds used in echolocation, echolocation is the opposite of stealth.

The nightstalker is bipedal, with the interesting twist of walking on its front legs. That makes sense in that the wings of bats are much larger and stronger than their hind legs. The animal uses claws on its hind legs to help overcome it prey, to which end the hind legs pass the front legs on the outside. In my 'review with hindsight' of After Man, posted in 2018, I wondered whether it would make more sense if the hind legs moved forwards between the front legs. I asked Dougal at the recent 2022 TetZooCon if he would mind me writing a blog post about this particular revision of the nightstalker. He did not, so here it is. I could not help myself thinking some more about terrestrial bats. I do not doubt that bats could evolve to walk efficiently again, as there are bats alive today that not only walk, but run too. 

Researchers managed to get vampire bats to run on a treadmill, and the animals obliged by using a unique hopping run. That is the video above. That odd gait must be due to the extreme difference in size between front and hind legs, which poses an unusual problem. During walking, legs that are on the ground at the same time must all propel the body over the same distance in the same time, or else the shoulder would walk faster or slower than the hip. From this it follows that the shorter leg will be on the ground for a shorter period than the longer leg, so the shorter leg only supports the body for a short time. That may be impractical, which suggests three different evolutionary solutions.

The first and weirdest solution is to have the hind legs move twice in the time the front legs move once. That is definitely possible, at least in theory. I know that because I was once requested to program such a gait to help visualise a terrestrial shark, posted here. The videos above show the result. This solution does not seem the most likely one though...

Click to enlarge; copyright Marc Boulay / Jean-Sébastien Steyer

 The second adaptation would involve quick enlargement of the hind legs, which appears altogether sensible and straightforward. the result would be very similar to the Steyer/Boulay terrestrial bat shown in ‘Demain. Les animaux du futur’ (and discussed on this blog here and here).
 
The third possibility means the animal no longer uses its hind legs for locomotion, so they can be used for something else, such as being weapons. If front limbs are liberated from their walking role, I would call that ‘centaurism’ (see here for the first mention of the principle). But the nightstalker freed its hind legs, so we probably need another name than centaurism; 'reverse centaurism'?

Click to enlarge; copyright Gert van Dijk

Of the three, the second option seemed the most straightforward one, and I considered stopping alternate evolution right there. Then again, the result wouldn’t be a proper nightstalker! I suppose a bipedal animal can still evolve from the enlarged hind limb version, so there you are: a bipedal terrestrial erstwhile bat with reverse centaurism.

What else did I change?

• I made the ears smaller than in the original. When animals species increase in size, organs do not necessarily scale linearly with body size. Eyes, for instance, are relatively small in large animals. Beyond a certain size an organ's function may not improve noticeably, so there is no point in making the organ larger than necessary to do its job. I am not certain this also holds for echolocating ears but assumed this to be the case.
• The skull and face are less bat-like than the original, because I assumed that the larger size would require a sturdier build. Bats have many pointy needle-like teeth, useful to catch insects. But an animal the size of a large dog would need teeth that can handle larger stresses.   
• I kept the leaf-based nose because it is part of the basic package of vampire bats. However, it seems very vulnerable.
• The eyes are still there because eyes seemed much too useful to abolish altogether. They are still small though, but useful for unforeseen circumstances.
• There are no fingers, just thumbs. Bats fold their fingers, that support a large part of the wing membrane, out of the way when roosting and walking. They use their big thumbs to hang from. What will happen to the fingers if the wing atrophies during evolution? I foresee the fingers disappearing completely, and not coming back as toes. The thumb has grown and now extends towards the midline to support the body underneath the centre of gravity. Normally animals place their feet close to the midline for that purpose, but the nightstalker needs room under the body for the hind legs. The thumb could help support the body directly under the centre of gravity by extending towards the midline. The two stubs you see on each hand do not have nails or claws, because they are not fingers! They are pseudo-fingers, supported by former wrist bones.                
  

So here we are: an alternate nightstalker with its hind legs between the front legs. When I look at the result, it looks much less like a bat then the original, which may not be good from a didactic point of view. The image serves to illustrate an evolved bat, so people who see it should immediately associate it with bats. My revised version probably does that less well than the original. Mind you, my first version had smaller ears, no leaf nose, a longer snout and sturdier teeth, so it looked even less like a bat than the one you see now. The version shown above was 'batified' on purpose, but it still doesn't shout 'bat'. That raises the interesting question of balance between  presumed biological underpinning and what the image is supposed to evoke. It is fun to play with both aspects, and adds another layer of speculation to speculative biology.

Epilogue

The above was all seen by Dougal. His response to reading the text was this:

"I claim it is an example of speciation in the Batavian archipelago! A new species on one of the newer volcanic islands in the "hot-spot" conveyor belt island chain. Shared ancestor with Manambulus perhorridus rafted across from the Big Island at a time of its early appearance along with its potential prey species."

And so it shall be; the new species deserves a new name though, and I think the differences are too large to use the same genus.  I therefore present Condylovador terriloquus! (from condylus: knuckle; vadere; to go or to walk;  terriloquus: uttering frightening words)

'After Man', by Dougal Dixon; a review with hindsight

The book 'After Man' is arguably the best-known book in Speculative Biology. It first appeared in 1981, so you may well wonder why I should choose to discuss a book everyone knows already, 37 years after its publication.

Well, a shiny new edition came out. It is a facsimile edition of the 1981 version, but with some changes. I still own the copy I bought in 1981 and could easily compare the two. The new version faithfully copies the monochrome sections at the beginning and end of the book that explain basic concepts such as the nature of evolution. These, printed on a somewhat coarse type of paper, enclose the heart of the book like slices of bread in a sandwich. That heart consists of 90 pages filled with illustrations in full colour, printed in much better quality on glossy paper. Even the page numbers match up perfectly.

The few changes are interesting. The introductory text has been updated in a few places, and these are indicated with a slightly different font, a nice touch for the bibliophiles among us. For instance, the old version states that early amphibians already had 5 toes on each foot, whereas the new version says that that pattern only emerged as the standard pattern after earlier experiments with other numbers.

Click to enlarge; copyright Dougal Dixon, with permission

The middle part of the book describes animals using ecological zones as a guiding principle, but Dougal Dixon has made two changes to the illustrations. These were originally done by professional artists and were based on sketches by Dougal. That process was not always easy, as Dougal explained in an interview with Darren Naish. I own some photocopies of early sketches for Greenworld that Dougal was kind enough to send me a long time ago, so I can say with confidence that he knows what he is doing when he sketches animals. I discussed Greenword, still only available in Japanese, here, here and here. Dougal gave me permission to use the drawing above to illustrate his own skills. These are of course predatory descendants of rats (falanxes) attacking a rabbit descendant, the rabbuck. Dougal was generally happy with the illustrators' work, except for two interpretations. In the new book he replaced the drawings of the reed stilt and the night stalker with his own drawings, and they indeed look better, in particular the reed stilt, that now is a lightweight and slender creature. I will not show them here; but leave them as an incentive to buy the book.         

I could stop here and consider the job done, but I have seen some critical discussions of Dixon's works, including 'After Man'. I sometimes think these criticisms are overly harsh and would like to add a bit of background to 'After Man', meaning the time in which it appeared.

Click to enlarge; Granada Publishing 1981

Everyone is obviously free to form his or her opinion on the matter, and let me stress that I have my doubts here and there too. As an example, let me discuss the night stalker in some detail. It is a fierce predator, descended from a bat that has given up flight and is a nocturnal terrestrial hunter, using sonar to find its prey. It walks on its front legs and uses its hind legs to catch prey, for which they arch over and outside of the front legs. The image above was copied from the dust cover of the 1981 edition, showing Dougal with a model of the night stalker. Dougal is very good at making such models by the way: I saw several of them for myself on the occasion of the Loncon3 science fiction convention (discussed here by Darren Naish and here by me).

Let's follow the scenario of evolving a land-living bat with specialised grasping legs. I would not expect all those features to evolve at once, but that one would set the stage for the next. (Whales did not evolve baleens the minute they entered the water, but had to become proficient swimmers first.) I expect the first step in that process to be that the bat gives up flight and becomes an animal walking on all fours. That will force quick changes to both the front and hind legs. I would expect that freeing one pair of limbs to catch prey and using the other legs to walk on to evolve only after that. (That, by the way, would be an example of 'centaurism'; see earlier posts here and here). Which pair of legs would become grasping limbs? My guess would be the front legs, because they are closer to the prey. But if the hind legs would be used for some reason, would they reach forward on the outside of the front legs, or in between, where the entire hind part of the body might also be swung forward to extend the reach?

My second doubt concerning the night stalker is that I do not think that sonar works well for a ground-based predator, as I explained in a series of earlier posts (here, here and here). Basically, using sonar is the opposite of stealth. I would therefore expect the animal to redevelop its eyes, keeping its extraordinary hearing as a passive sense. So my personal variant of a bipedal terrestrial predatory bat descendent would walk on its hind legs and not use sonar. I think it would be fairly likely, but it would also be much more conservative and also more boring than Dougal's night stalker...  

By now you may feel that all this criticism of what is probably the most famous creation of 'After Man' is a very odd way to defend Dougal's work. But there is a point here: it is very unlikely that anyone would have been able to raise such specific and detailed considerations in 1981. Such a person would at the time have to have been a professional biologist, not a member of the general public. I am not a biologist, and I can only raise such criticisms now because of several reasons. The first is having ideas; even though I thought hard about the use of sonar for a land-living predator, someone had to have to come with that idea first, and that certainly wasn't me; it was Dougal. The second reason is that you need knowledge to think matters through; to learn, there must be something to learn from.

Suppose you find yourself in 1981 wanting to know more about some biological subject, say sonar, the evolution of whales, or any specific animal group such as 'mudskippers'. You go to a book store or ask your local librarian, who will probably come up with the same one or two books every time, leaving you both frustrated and ill-informed. Anything specific would require access to something like a university library, and even there you would on some subjects find less information than you find on Wikipedia now. There was hardly anything to fill the gap between a general interest and professional levels. The information that is readily available now with a few clicks was either non-existent or almost completely inaccessible in 1981. So what could someone interested in biology, palaeontology and science fiction find in 1981? Well, disappointingly little:

• On the dinosaur front, you would not be happy. There were stirrings of the coming 'Dinosaur Renaissance' (Bakker's paper from Scientific American from 1975 can be found here). But Robert Bakker's book 'The Dinosaur Heresies', that spread the message that dinosaurs were lively, athletic and interesting was still five years into the future in 1981. The most spectacular book on past life that you could own at the time was probably 'Life before Man', illustrated by Zdenek Burian. It had been around at least since 1973.
• Speculative biology did not really exist as such. An early work such as Stümpke's 'Snouters' (1957) would remain unknown to you, unless someone book dealer would decide to distribute a new printing, so you could find out about it, by chance, by browsing a book store. I found one in 1983 (under its original German title of 'Bau und Leben der Rhinogradentia'). I later wrote about them here, here and here.            

That's about it. There was no information at your fingertips. If you wished to learn something from an author, you wrote them a polite letter and hoped for the best. No internet, no Google, no computers (well, except for the Sinclair ZX-81 with a 1Kb memory). The lack of information back then would now feel like a near vacuum, and as a result even the most interested people could not possibly become as well-read as many people on the forums now are. It was in this vacuum that Dougal Dixon used his knowledge of evolution and zoology to come up with not just one odd animal, but a whole book full of them. He in fact largely defined speculative biology with 'After Man'. It was an extraordinarily creative production at the time of its first appearance, and that is the only time to judge originality and creativity.