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A long time ago, Yi Qi diverged into three main groups: Cockatrices, Drakes, and Wyverns. Some characteristics of Wyverns include:

  • They are tetrapods/quadrupeds
  • They are covered with feathers
  • The males have horns
  • They have bat like wings
  • They have swan like necks
  • They are roughly the size of quetzalcoatlus (some are slightly larger)
  • have dolphin level intelligence
  • The males gather shiny objects in their nests to attract mates
  • They have small tails
  • They are carnivorous
  • They can support the weight of ONE unarmored human
  • They store a flammable liquid in a gland of some kind, which they then ignite and release onto their victims

Given these characteristics, could such a beast realistically exist?

NOTE: Magic does not exist in my story

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  • $\begingroup$ I’d just like to know, did these Wyverns survive the dinosaurs extinction? $\endgroup$ – Daikyu Maryu Feb 8 at 19:38
  • $\begingroup$ Wyverns are bipedal winged dragons. Two legs, two wings. And they have long tails. Please don't call your short-tailed quadrupeds wyverns; you will obtain nothing but confusion. Wyverns are often met with as heraldic charges; it is quite important to understand what the herald means when he blazons "gules, a wyvern or" (that is, in common parlance, a golden wyvern on a red field). $\endgroup$ – AlexP Feb 8 at 19:56
  • $\begingroup$ @AlexP ok just don't know what else to call them $\endgroup$ – icewar1908 Feb 8 at 20:02
  • $\begingroup$ Icewarbeasts? Holoptiles (= all feathered)? Ptilotheres (= soft-feathered beasts)? $\endgroup$ – AlexP Feb 8 at 20:12
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    $\begingroup$ While it is true that in heraldry, the Wyvern is always shown with a long tail, the only consistent distinction fantasy writers usually make between wyverns and other dragonoids are the appendages. A wyvern being one with 2 wings and 2 feet vs a dragon that has 2 wings and 4 legs or a drake that has no wings and 4 legs. While smaller tails are atypical in art, it actually makes wyverns much more believable for a flying creature not to have a big meaty tail. $\endgroup$ – Nosajimiki Feb 13 at 21:56
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I know this one already has an accepted answer, but I think the flight mechanics part deserves a bit more science.

Flight is all going to come down to two factors: the wyvern's profile and the square-cube law. We do not know very much about quetzalcoatlu; so, the best place to start is to look at the most powerful pound-per-pound flying animal we have alive today, and see if we can make it work. For this I will be using the crowned eagle which is an 11kg bird able to carry prey up to 20kg back to its nest.

A mid-sized quetzalcoatlus is about 20 times the mass of a crowned eagle. Thanks to the square cube law, we know that it is unreasonable to expect it to perform to the same ratios as the eagle, because mass cubed can only carry a squared capacity.

Why quetzalcoatlu size does not work

  • The combined mass of a crowned eagle carrying large prey is about 31kg
  • A mid-sized quetzalcoatlus weighs about 220kg.
  • The maximum lift capacity of a quetzalcoatlus sized eagle like animal would be ((20^-3)^2)*31 = ~228kg

This means that even mimicking the most powerful pound per pound birds we have today, your wyvern would be just barely able to fly for fairly short distances under its own strength, and could absolutely not carry a rider at all.

Is there a more optimal size?

After running a number of calculations, I found that the ideal size for a bird to maximize its total carry capacity is about 75-80 kg with a total carry capacity of ~37kg. 37kg is pretty darn impressive, but not enough to carry almost any adult humans. However, children in the 8-12 year old range (or adults with significant dwarfism) would be small enough to ride an 80kg wyvern for short distances.

Would a more optimal shape help?

Perhaps... larger animals almost always have adaptations to help support their greater size that smaller animals do not. Lower bone density, less mobile joints, more complex circulatory systems, etc. The square-cube law assumes that you are just taking the eagle and making it proportionally bigger in all three directions. The Eagle is an aggressive predator meaning it has a certain amount of brawniness it could do without if you want an animal that focus on pure flying efficiency. If instead of making it ~1.91 times the size of the eagle in all directions, what it you made it ~1.5 times as thick (or similar proportions, just 30% less dense) and ~2.16 times as wide and long. Then you would have an animal ~77kg with ~4.67 times the lift area of the eagle giving you ~68kg of lifting power which is the approximate weight of an average pre-industrial grown man.

The takeaway here is that making a rideable avion like creature may just barely be doable as long as you build it to pretty specific specifications. Ideally, it should have a wingspan of ~25.5 feet, and a length of ~13.5 feet with very broad wings like an eagle, owl, or flying fox and weigh in at ~77kg. Its peripherals would all need to be pretty minimal in size too; so, I would shy away from horns or a long reptile like neck or tail. Instead, you might want to give it horn and tail like feathers (which some birds have). This way you can get more of the look you want without compromising the carry weight.

As for fire breath... there is no example of this is nature, but... dragon breath is so mainstream in our fiction that most people will not question it.

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  • $\begingroup$ Given we have solid reasons to believe giant azhdarchids like quetzalcoatlus could fly at weights exceeding 200 kilos, it seems odd to argue for a smaller size. This doesn't help ridability at all, which I'm afraid just isn't going to happen with this sort of anatomy, it does allow for a more impressive animal. Ref: markwitton-com.blogspot.com/2018/05/… $\endgroup$ – Myrdden Wyllt Apr 17 at 15:38
  • $\begingroup$ @MyrddenWyllt Quetzalcoatlus could fly under its own weight, but just barely. The smaller size is better able to carry its own weight and then some. A ant can carry more in proportion to its weight than a human because it is smaller, but being bigger, we can carry more total weight, but this is not a linear relationship. There are optimal sizes for every body plan at which the weight of your own body begins to lead to a lower total lift capacity as you scale it up. $\endgroup$ – Nosajimiki Apr 17 at 16:17
  • $\begingroup$ Ah, fair enough. With that in mind, have my upvote. $\endgroup$ – Myrdden Wyllt Apr 17 at 16:19
  • $\begingroup$ So a quetzalcoatlus could carry itself and just itself, but a smaller flying animal can carry itself plus prey/rider. $\endgroup$ – Nosajimiki Apr 17 at 16:19
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Most Plausible

Being a proper tetrapod, evolving from an actual creature that resembled a wyvern, having feathers, a short tail, and an avian behavioral trait are all very solid and plausible.

Feasible

Horns can be pretty heavy and not aerodynamic, but if they’re hollow or otherwise lightweight it certainly isn’t a deal breaker, and sexual selection has definitely led to suboptimal flight profiles in nature (see peacock tails). Fire breathing has the classic answer of the bombardier beetle, so it’s not absurd that something else in nature could evolve a similar trait. Maybe it evolved from a sprayed venom.

Stretching it

Quetzalcoatlus was the biggest flying animal ever, and it was very specialized for this distinction. Your wyvern is definitely packing some extra weight. Consider having it weigh a little less? Carrying an unarmored human would be pretty hard on the wyvern, unless it was a small human.

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    $\begingroup$ I would move the "breathe fire" into "stretching it". Bombardier beetles' spray isn't like a flamethrower or even an oxidization reaction, it's more like throwing hot acid. Doing so (shooting acid, toxin, or other fluid) is feasible, but igniting it to be an actual flame is stretching it. $\endgroup$ – Dragongeek Feb 13 at 10:46
  • $\begingroup$ @Dragongeek Fair Point $\endgroup$ – NixonCranium Feb 14 at 2:44
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I'd say these wyverns could exist, except for the flammable liquid, as it would make more sense if they used methane stored in its air-sacs, which not only would allow fire-breath, but would also provide lift.

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