My question is basically about what a gliding mammal that can magically produce thrust would look like, whilst meeting these criteria:

  • Can use tools to a sufficient level to develop civilisation
  • Is adapted to life in the mountains
  • Its gliding ability is useful for life in the mountains (this is perhaps more related to the amount of thrust it can produce and for how long, but the skin flap design also plays a part)


In the fantasy world I am working on, plants and non-human animals will sometimes develop "magical" adaptations. These will develop similar to evolution where a magically ability will sometimes randomly develop, and can be passed on to offspring. Magical abilities require higher energy use but not necessarily proportional to the amount of energy the physics of the ability requires. For that reason a "useless" ability is unlikely to become pervalent.

I am working on a gliding mammal that has developed some kind of limited ability to produce thrust and has a similar intelligence to humans.

For the sake of argument let's say they can produce a jet in a direction they choose for a limited amount of time per day. Let's say the jet produces a maximum thrust of 0.2 times their body weight, but add the limitation that using the jet at maximum force is strenuous so they would be able to do it for a shorter time.

I am open to other forms of generating thrust if you think they would work better.


Gliding seems to be a common adaptation that has independently developed many times. In mammals, this adaptation seems to develop in arboreal animals. A possible evolutionary explanation for this evolution is energy efficiency when gliding. Another possible explanation is the ability to avoid predators. It seems to make sense to say that this sapient gliding mammal evolved from some kind of arboreal glider before developing powered flight through their jet ability, allowing their ancestors to live in more mountainous regions over time. Another possibility is that the jet ability developed first in some mountain primate, rodent, or marsupial before the gliding membranes evolved. The jet ability may have been selected for to allow for better jumping.

A common feature of these gliding mammals, as far as I can tell, is that they are bad at locomotion compared to their brethren who have no patagium.

The colugo is supposedly the best adapted glider, so it seems like a useful reference to use. According to Wikipedia, they reach lengths of 35 to 40 cm (14 to 16 in) and weigh 1 to 2 kg (2.2 to 4.4 lb).

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Wingsuits may also be a useful reference. The electric wingsuit developed by BMW might be a good illustration of the physics involved. The device puts out 20hp for around 5 minutes, but I am not sure how those numbers relate to my earlier suppositions about the creature's jet ability.

Current thoughts

I am not particularly attached to any of these ideas, but they are the ideas I have reached after my research and hopefully they provide a good starting point.

  • Height and weight: The creature is 1 - 1.2m and weighs 15-18kg. The greater height should be useful for agriculture and animal husbandry, whilst the higher density allows for a sturdier creature design with potentially better locomotion. Given how humans can fly with a powered wingsuit I think this creature's density could be even higher if that is useful.
  • Hands: The hands have opposable thumbs and are webbed. Potentially the thumb isn't webbed for better dexterity. The webbing is a feature colugos have and seems to be useful for gliding. Their hands are likely relatively larger than a colugo's hand, for better tool use. I am not sure if this creates issues for flight, since flying squirrels supposedly have smaller hands to avoid "wing loading", but I hope the webbing and jet ability will offset any issues. The hands potentially have small vestigial claws from their arboreal ancestors.
  • Legs and feet: Unlike all flying mammals I have found in my research, this creature's legs are not attached to the gliding membrane. This allows for better locomotion, bipedalism, and the ability to ride animals. I envisioned the feet as capable of gripping, similar to an eagle's claw. This is for two reasons: first I imagined that their evolutionary ancestors used their flight ability to swoop in and grab eggs or small animals with their feet as birds do. The second reason is for gripping the ground so they are not blown away by the winds at high altitudes. The legs and feet I imagined are part of the reason I gave them a higher density than colugos.
  • Gliding membrane: also known as patagium. This is one of the parts I am very iffy about but I will mention my current thoughts. To make up for the membrane not being attached to the legs I imagined it going from the wrists to a bifurcated, or trifurcated, tail. There would also be a membrane in between the tail parts. My main concern is having sufficient arm mobility for tool use whilst still having enough membrane for useful gliding. Arm mobility could potentially improve if the membrane is attached to the elbows.
  • Tail: As mentioned above I imagine it as being bifurcated or trifurcated. This would, in theory, allow for sufficient membrane whilst allowing the legs to be detached. I also imagine that the tail can be moved in such a way that the membrane attached to the wrist is loose enough to give the arms a good amount of mobility.
  • $\begingroup$ How is this "tiny" amount of thrust delivered? Can it be applied to tiny objects instead of the body? If so, its most useful function will be to turn your arboreal into a flying predator, as they fire bolts, spears or even bullets at prey, then enemies. I might suggest that your species has LEARNED gliding, with gliders, and doesn't have flaps. Large animals are going to be increasingly challenging to make fly. If you want them big, they might recapitulate pterodactyl or bird evolution, rather than being giant flying squirrels. This is a comment because I need feedback to follow your needs. $\endgroup$
    – DWKraus
    Sep 12, 2021 at 14:50
  • $\begingroup$ I would like them to be flying creatures already at the point they start developing cvilisation. My current supposition for thrust is the ability to create one jet, maybe two if necessary, in a direction they use. I assume the jet fluid is air. Regarding weaponisation, I do think the ability would be useful, but I think they would likely develop this as their civilisation develops with the ability primarily being used for mobility by their evolutionary ancestors. $\endgroup$
    – katrite
    Sep 12, 2021 at 15:14
  • $\begingroup$ Is this at all helpful? worldbuilding.stackexchange.com/questions/210739/… $\endgroup$
    – DWKraus
    Sep 12, 2021 at 15:16
  • $\begingroup$ It is helpful to look at a similar question but the focus is a bit different. I am more interested in some of the physical details such as ideal patagium placement, hand size, webbing, foot design, and how all of this is adapted for both flying/gliding with a jet ability as well as mountain life. I suppose a bat origin could work but it is a bit of a different aesthetic than my desired gliding mammal. $\endgroup$
    – katrite
    Sep 12, 2021 at 15:27
  • $\begingroup$ Since such a large bipedal gliding animal hasn't evolved, the biomechanics are going to be fairly speculative (especially for mammals, since the closest analogs will be birds and raptors). Since thrust is a function of mass, to optimize the usefulness of this ability your species will have pressure to get larger (and thus become increasingly awkward fliers). Thus my question about alternative functions (especially weaponizing, which would radically affect selective pressures). As weaponizing and tool use happen, glider tools and weapon tools will reduce natural flight characteristics. $\endgroup$
    – DWKraus
    Sep 12, 2021 at 15:39

2 Answers 2


They are bats.

baby bat


You are already thinking about colugos so I will take this in a different direction. Your creatures are bats. Just as humans have been on the ground a long time but our own bodies have evidence of adaptation for life in the trees, your sentients have been using agriculture and animal husbandry (probably more the latter if in the mountains) for a long time - maybe longer than humans.

The wing has more fingers than the single bat finger - more like a hoatzin or a pterodactyl. In the remote past these creatures could fly. Their close relatives (chimpanzee equivalents for us) can still fly and those things are out there. Tool use, intelligence and a different lifestyle selected for larger bodies in your sentient bat people and although their wings remain useful for gliding, these creatures are now too big to fly.

As adults. Little kids can still fly. Kindergarten is in three dimensions.


I think that you have the basic plan down. I'd suggest a magical ability to speed up the air flowing over their back(like an airplane wing). And then have them evolve from a normal Calugo that lives in the forested mountain valley's. Because of the magic needing more energy the creature evolved to be bigger. Then it moved up the mountains as it could sustain longer flights and oversee a larger hunting ground. The management of this magical ability and the necessity to hunt larger prey in groups drove the creature to become smarter and more social. If the magical ability is powerful enough then they may loose the palagium between the back legs and the tail. Allowing for a free tail that trifurcates near the end to create a hand of sorts. (the pokemon aipom)

This would keep the patagium between the arms and legs though. But in the mountains there are often winds going up and down. Smart creatures could use those natural currents to their advantage. By going down to catch a prey. Cut it up in pieces to store in a marsupial pouch. Then use those currents to get back up to their cave/home.

The ability to ride other animals is severely overrated. First of all the mountainous terrain is difficult to navigate. A flying mount is unnecessary for obvious reasons. And flying is plenty fast so you wouldn't need it for travel. for longer distances without pause then it may be useful. But a smart creature could easily invent a cart.

  • $\begingroup$ I do like the more detailed ideas on how the evolution happened. Regarding riding, I considered the idea because when looking at ancient Andean civilisations I read they had no riding because Llamas could not carry the weight of an adult human. However, a lighter species could presumably ride something like a llama or a mountain goat. $\endgroup$
    – katrite
    Sep 13, 2021 at 12:24
  • $\begingroup$ Getting a creature to to the point where it would allow you to ride it takes a large amount of effort. The benefits for doing so would therefore have to be equally as large. Consider horses. It took thousands of years to make them able to be used as a mount. $\endgroup$ Sep 13, 2021 at 21:09
  • $\begingroup$ True, but a civilisation like this would likely practice pastoralism on the mountain plateaus, so they will be motivated to domesticate these animals anyways. $\endgroup$
    – katrite
    Sep 13, 2021 at 22:56

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