Friday 27 January 2023

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)

10 comments:

Davide Gioia said...

I just finished reading my copy of the 40th anniversary edition, what a coincidence.
It's interesting to note that the most terrestrially proficient modern bat species, the vampire bats and the mystacinids, already sort of show two alternative modes of locomotion: while vampire bats (specifically the common vampire bat Desmodus rotundus) engage in wing-powered run, the reverse of the other tetrapods, mystacinids do not, and indeed their hindlimbs, although short, are quite strong and equipped with wrinkles and grooves that are thought to aid in gripping on the ground, together with their needle like claws.
Indeed, there are quadrupedal terrestrial bats on Batavia too.

Sigmund Nastrazzurro said...

Funny; I read that book again in order to write this post. I should probably have mentioned the New Zealand bats in the posts, as they provide additional evidence that bats can and will walk, if circumstances are favourable.

Keenir said...

Most enjoyable; this is an awesome post.

I'd be curious how you'd tackle the Reedstilt redesign (as compared with the two _After Man_ versions, as well as the Nyx redesign)

As to the Nightstalker -
> Once other mammals arrived as well, a bat species started to hunt them and evolved into the nightstalker,
This suggests that, at least for the initial period where the proto-Nightstalkers are turning carnivorous (maybe they're already bipeds, or at least flightless, by this point?)...and don't have to worry about the non-bat prey being able to hear much or any of the echolocation.

(and even if the prey *can* hear echolocation, probably 90% of all the mammalian fauna of the Batavian Islands *also* produces echolocation)

-Anthony C. Docimo.

Sigmund Nastrazzurro said...

Anthony: thank you. I never thought about the Reedstilt much, other than than that Dougal's design looked nimbler and much more slender than the one published in 1981. Its feet caught my attention though, but not to the extent that an alternate form immediately came to mind.
You make an interesting point about the nightstalker having an initial advantage if the prey simply did not hear them. I have always wondered about the consequences of echolocating predators shouting their presence and intentions to their prey. If all predator and prey species detect predators with ease, as you suggest, what does that mean for hunting success?

Keenir said...

Here is Nyx's Reedstilt: https://nixillustration.com/science-illustration/not-paleoart/2021/spectember-2021-reedstilt-redesign/#more-1627

>I have always wondered about the consequences of echolocating predators shouting their presence and intentions to their prey. If all predator and prey species detect predators with ease, as you suggest, what does that mean for hunting success?

My apologies, I was not clear in what I was suggesting. What I meant was that all the predators *and most prey* on Batavian Islands, is "shouting their presence" as you phrased it.

Imagine that its not just the carnivorous hunters on the savannas - the lions and cheetahs - who are shouting, but also the elephants and antelope and warthogs shouting as well...suddenly the odds of picking out the specific hunting calls of a leopard or Nightstalker (by a bat-descended or non-bat-descended herbivore) drops to extremely very low.

-Anthony C. Docimo.

Sigmund Nastrazzurro said...

Anthony: Aha! Now I understand what you meant: the nightstalker's sound would be drowned in all the noise. I wonder, though. Just think of what human hearing can do in similar circumstances, and human hearing is not the best possible version of all hearing. Even in an environment with a large number of other humans, closely packed and speaking at a similar volume and pitch, we still manage to pick out what the person across us is saying (until you are over 40, when the sense of hearing is apparently past its sell-by date). You can even pick up your name from among all the words going on around you, showing that a lot of automated analysis is going on. In short, I expect that directional hearing and smart sound analysis would negate effects of surrounding noise to a large degree.
As for the Nyx reconstruction: I had not seen that, but it looks like solid work. He has a good point about the seven cervical vertebrae (although there may be workarounds to achieve greater flexibility). I will have to think about that. The number of the other types of vertebrae does not seem as fixed; odd indeed.

Keenir said...

Another detail for your _Avatar 2_ post(s) is this:

At the 2:19 mark in https://youtu.be/9E_0-qbpmsg this interview by Bobby Chiu with one of the artists who did _Avatar 2_, there is an aquatic predatory organish (a "fish" of sorts) whose jaw doesn't just open vertically like all the other backboned animals of Earth and Pandora...but also horizontally at the front of the jaw.

About an hour later, I realized the Sarcastic Fringehead of Earth gives the appearance of a similar split...but I don't know - to my eyes, it seems this involves more of the skull than just "lips" or something along those lines...it struck me as being as structural as the multiple jaws of _Minecraft_ Creepers or your own hexapods of land and sea.

Just thought to bring it to your attention.

Have nice days and be well.

-Anthony C. Docimo.

Sigmund Nastrazzurro said...

Anthony: I am writing a post about Avatar TWOW; it may turn into two posts, with one entirely devoted to the skimwing. I have bought a book 'The Art of Avatar TWOW' because it offered dgood looks at variousanimals. I noticed that predator too, and wondered how such a basic departure from the Bauplan of other animals would fit into the evolution of Pandoran animals.

Sockmonkey said...

I would think that early on, before the hind limb lengthened, that it would have a bounding gait like a gorilla.
It apparently works well as they're scary quick over short distances.
Long forelimbs with a hook on the end would also seem to favor an arboreal existence.
Getting around by casual brachiating like orangutans do.

Sigmund Nastrazzurro said...

Sockmonkey: the bounding gait is a definite possibility! It would also be interesting to see these animals crawling back into the gtrees again. Perhaps Dougal has already thought of this type of speciation.