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Last year, the Adult Swim program Primal treated us to perhaps the most Halloweenish episode yet, "Terror Under the Blood Moon", in which our two unspoken protagonists--the caveman "Spear" and the tyrannosaur "Fang"--come across a flock of giant red bats. The fact that this is the same world in which giant pterosaurs also live only amplifies the show's pulp fantasy atmosphere.

But what if this were in real life?

An Australian scientist had decided to terraform a recently discovered Earth-like planet with a more extensive list of organisms than Serina's:

  • All 800 species of Australia's orchids
  • All 57 species of Australia's palms
  • All 3 species of Australia's southern beech
  • All 75 species of Australia's mistletoes
  • All 37 species of Australia's seagrasses
  • All 39 species of Australia's mangroves
  • All 69 species of Australia's cycads
  • All 39 species of Australia's conifers
  • All 390 species of Australia's ferns
  • All 44 species of Australia's fern allies
  • All 10-12k species of Australia's algae
  • All 1,000 species of Australia's mosses
  • All 800 species of Australia's horn/liverworts
  • All 250,000 species of Australia's fungi
  • All 3,238 species of Australia's lichens
  • All the species of Australia's invertebrates
  • All of Australia's prehistoric freshwater fish
  • All of Australia's prehistoric amphibians
  • All of Australia's prehistoric reptiles
  • All 357 species of Australia's mammals (including the 76 species of bats)
  • All of Australia's non-avian dinosaurs
  • All the pterosaurs of the clade Azhdarchoidea

In this long list, let's focus on only the two candidates--the bats and the pterosaurs. Both groups had evolved from different ancestors yet looked similar to each other because they had similar problems. In our timeline, bats evolved after pterosaurs, but putting the two groups in the same world will be the focus of the question.

Sooner than later, there will be a mass extinction that would drive away the biggest species. In the case of the bats and the pterosaurs, only the smallest and most adaptable species will survive. But this raises the question--in a terraformed world without birds but still plentiful food, would both the surviving bats and pterosaurs fly the same skies, perhaps grow bigger to the extent presented in Primal?

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    $\begingroup$ You really have a lot of unexplained (though perhaps irrelevant) background here, starting with WTF is "Primal". However, the basic question seems to be whether bats and pterosaurs could coexist. The answer seems an obvious yes, since bats and birds manage to do so. $\endgroup$
    – jamesqf
    Oct 4, 2020 at 16:38
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    $\begingroup$ In the current world, bats and flying dinosaurs coexist just fine. There are over 10,000 extant species of dinosaurs, most of them volant, a few secondarily flightless; and over 1,400 species of bats -- Chiroptera is the second largest order of mammals after Rodentia. Why would you believe that Chiroptera would find it so hard to coexist with Pterosauria when they don't seem to be bothered by Dinosauria? $\endgroup$
    – AlexP
    Oct 4, 2020 at 17:18
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    $\begingroup$ This is what the site calls a high concept question. High concept questions are off-topic because, without substantial inclusion of details, conditions, limitations, and requirements, the question is too broad and too opinion-based. As is the case here, the only valid answer is, "yes, if you want it that way." In short, the question is too speculative and lacks too much foundation information. Can you edit it to make it (a lot) less speculative? $\endgroup$
    – JBH
    Oct 4, 2020 at 18:05
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    $\begingroup$ @JBH High concept? Not so. It only takes a reading of previous comments to show the question is answerable. A basic understanding of ecology is all that is necessary. Plus knowing that resource rich environments animals become bigger. The question could be streamlined to be more to the point, but that's a trivial issue. $\endgroup$
    – a4android
    Oct 5, 2020 at 1:21
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    $\begingroup$ Asking to do this with one set of species that are completely undefined (huge bats) and one that are known only indirectly (pterosaurs) is totally impossible and belies a fundamental misunderstanding about how ecology works, both in terms of our level of ignorance as humans but also inherent limits of the data. To suggest this is "basic ecology" is not only absurd, it's insulting to professional biologists! $\endgroup$
    – cereal_killer
    Oct 5, 2020 at 2:14

2 Answers 2

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Yes it is possible for them to coexist.

Birds and pterosaurs coexisted there is no reason bats and pterosaurs could not. In fact birds evolved while pterosaurs were dominant. The existence of fliers does not prevent the evolution of other flight. flying animals is to broad a category which group fits each individual niche is what matters and that is not a given.

Also consider Yi, a dinosaur with Bat-like wings. So not only did flight evolve in other groups while pterosaurs were around it happened multiple times reinforcing the idea that it is not an impediment.

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Now for size and ecology.

Bats with echolocation would certainly have a huge advantage at night so you may see a split along day/night. Or you may see a niche division, since bats have rotated hind legs, allowing attacking with the hind legs to evolve. live birth vs egg laying might favor one or the other in certain conditions. Hollow bones might provide a big advantage for size with pterosaurs so will likely see more large pterosaurs. Note pterosaurs were likely pushing the limit on the size for a flier in earths gravity so don't expect anything noticeably bigger.

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  • $\begingroup$ I have misread. $\endgroup$
    – JohnWDailey
    Jan 8, 2021 at 22:25
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Pterosaurs are far more advanced flyers than bats. So they would have relations exactly as birds and bats has now: pterosaurs rule the sky and bats are "hiding" in some marginal niсhe.

If conditions would allow pterosaurs would grow bigger.

But bats would have a chance to do it only in some isolated areas. And I doubt they would ever become as effective flyers as ornithodira are. They just have no lots of very special improvements and couldn't have many of them. So any invasion of pterosaurs would shrink bats both in size and numbers.

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  • $\begingroup$ "Pterosaurs are far more advanced flyers than bats" What is the basis for this claim? $\endgroup$
    – DKNguyen
    Oct 5, 2020 at 14:07
  • $\begingroup$ Bats are not "hiding" anywhere. Bats are a very successful mammalian order, with over 1,400 species, ranging in size from the diminutive Craseonycteris thonglongyai (wingspan 150 mm or 6 in, weight 2.5 g or 1/16 oz) to the megabat Acerodon jubatus (wingspan 1.7 m or about 6 feet, weight 1.5 kg or 3 1⁄2 lb). They live all over the world and are very common. True, in most places they are much less common than birds, but they are in no way rare. $\endgroup$
    – AlexP
    Oct 5, 2020 at 20:24
  • $\begingroup$ @DKNguyen, basis is hundred of millions years of pterosaur's evolution and millions of year of pterosaur coexistance with birds. Just read article in wikipedia - see how complex their wing was compared to bat's $\endgroup$
    – ksbes
    Oct 6, 2020 at 8:54
  • $\begingroup$ @AlexP, bats are "hiding" - becase they are leaving in marginal hiches. Feeding mostly at night and keeping away from any birds spacial and/or time areas. And never ever try to "fight"(in any sense) with birds . Exactly like "successfull" mammals were living in dinosauros times. And btw, compare your bat's numbers with those of bird's. You will clearly see who is "hiding" from whom. $\endgroup$
    – ksbes
    Oct 6, 2020 at 9:00
  • $\begingroup$ Bats are already better fliers than birds, with better performance (more lift, less drag, greater maneuverability, faster speed, more efficient). Birds have the advantage of a decoupled flight mechanism which makes them better at most everything not related to flight $\endgroup$
    – John
    Jan 6, 2021 at 21:11

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