Worldbuilding Wednesdays: Aerial Adaptations
Welcome to Worldbuilding Wednesdays! Every Wednesday, we spend what is probably far too much time walking through our worldbuilding process. In this week's post, we discuss the peak of evolution: the sugar glider.
What We Have So Far
Our world is starting to take on a definitive shape. Distances are massive, the weather is always kind of wet and mild, the sky seems to go on forever, the map is dotted with hyperforests and megasavannas, and the sky is dominated by the Lantern and its kin, the red and blue moons. A calculator is needed to determine the tide at any given moment, there's an even chance that fog has rolled in, and you should be careful not to stand near a smashfruit tree.
To this, we're going to add aerial critters, but first, we should discuss a little of Mother Nature's design philosophy, by which we mean evolutionary biology.
Aeronautics for Avians
One reason birds are shaped the way they are is that their main method of locomotion is flight. This sounds straightforward, but has ramifications we need to consider. For example, enlarged pectoral muscles are needed to launch birds into the air, and skeletal structures that minimize weight while still providing sufficient support are selected; a bird has to be light enough to take off without being so frail that it breaks its wing bones in the process.
However, that's on a planet with 10 times more gravity. On our world, a bird of the same shape would be a (pound-for-pound) several times stronger flyer. Or, perhaps it would be a several times larger bird with the same ratio of dimensions. Perhaps it would be a bird the exact same size but with solid bones, since hollow ones aren't necessary to be light enough for flight. Perhaps the bird, with less effort needed to fly, can spend its developmental energy on other things, like defensive and attack mechanisms. Four-legged birds are a real possibility, as are birds with multiple sets of wings.
This is only considering those birds that are true flyers. With a much larger hang time, a lower terminal velocity, and a whole lot more space, the real winners will be the gliders. Most animals won't need special features to climb, since they're pulling ten times less weight up a tree than they would be on Earth. Earth creatures that jump can expect to get several times the maximum height and an even greater maximum horizontal. All of these aspects of our world indicate that gliding would be incredibly advantageous, to the point where it may well be the default form of locomotion. Even if it isn't, gliding will certainly be more common on this world than on Earth.
Sidebar: Dress for Success
A note: Don't quote us on this, because we didn't have a wind tunnel handy to confirm our calculations with, but a typical human with a large but not comical trench coat should be able to survive a fall from any distance. When we calculated the gliding area necessary to drop a human-ish weight's terminal velocity below lethal falling speeds, it came out to about 6 extra square feet. We don't guarantee the integrity of their legs after such a fall, but they should live.
Looking at Logical Extremes
Getting back to our world's aerial life, we're able to draw some conclusions.
Earth Birds Will Work Here. This is an important note. You can quickly fill the air with two types of creatures: Earth-standard birds, which will be more powerful flyers than on Earth, and Earth-standard-but-bigger. Suppose we assume that the Square-Cube Law is the limiting factor, rather than aerodynamics or similar factors. In that case, you can further safely assume that any Earth bird could be about 2.5 times larger in every direction with no real issue. This, of course, applies to other creatures, like bats and insects, as well.
"Flying Wings" and "Cloud Whales" are Possible. Generally speaking, lift requirements scale directly with weight. This means that a creature the size of a golden eagle, say, (weighing 10 lbs) would need wings 1/10 the size of a golden eagle's. Take that in the opposite direction, and wingspans for gliders in particular- creatures that don't have to worry about the Square-Cube Law because they won't be flapping their massive wings- can be up to ten times larger than similar creatures on Earth. That's ten times the area, not ten times the length, but still... look at it this way. The largest gliding animal ever was the Quetzalcoatlus, which had a 40-foot wingspan. A similarly built creature on our world could have a wingspan of a bit more than 100 feet, meaning we could have creatures comparable in size to the largest whales (dimensionally, not in terms of weight) flying through our skies. Such animals would have to constantly glide or use thermals and updrafts to take off, since there is no way their bones could withstand the torque of flapping, but still.
Everyone and Their Cousin Will Have Skin Flaps. We made that note about trench coats for a reason: to highlight the fact that it will be absurdly easy to become a semi-aerial creature. All most animals would need is some extra skin that can stretch out or unroll during a jump. This particular adaptation is seen most commonly on Earth in little arboreal scamps like the flying squirrel and the sugar glider, but those animals have it because their weight is so low that a small amount of skin is all that's needed. On our world, the same amount of skin will permit a creature ten times heavier to glide equally well.
On Earth, one of these could glide across a field; on our world, these guys could engage in limited flight.
This will lead to scenarios that you wouldn't see on Earth. The most obvious: small ambush predators that glide down onto their prey from the trees. House-cat-sized predators would definitely work, and with the proper adaptations, larger ones would be possible. Something large enough to try and attack a human (say, the size of a leopard) might be a little too heavy... but just in case, keep one eye on the branches above.
Faux Wings, Gliding Blades, and Extra Limbs. Because gliding/flight is so advantageous on this world, and because the relative cost for gliding and/or flight is so much lower than on Earth, we'll see some creatures that evolve psuedo-wings the same way that creatures on Earth evolved limbs. Normally, the skeletal structure and musculature necessary to have true wings in addition to other limbs would be too complicated and expensive... but we already know that four-limbed creatures are capable of evolving fins. It wouldn't be that much of a stretch to say that some creatures evolved horizontal fins that, over time, at least assumed a more wing-like shape, even if they aren't true wings.
Like this, but two of them, and oriented for gliding.
Even creatures that couldn't manage true gliding or true flight might end up with such adaptations as a way of lengthening their already prodigious leaps. For example, a rabbit can leap up to 10 feet. A regular rabbit on our world will be able to leap maybe 80 to 100 feet, which is already ridiculous. A rabbit with skin flaps couldn't put as much power in its leap, due to the limited range of motion caused by those flaps. A rabbit with specialized, oversized shoulder blades, on the other hand, could create a partial gliding surface that significantly improves that distance.
This all presumes that creatures won't have other reasons to have more than four limbs, of course. Creatures with six limbs could easily transition one pair of limbs to wings on our world. Of course, there aren't exactly many terrestrial animals with six limbs to start with.
...
Those of you who have read enough of these will recognize that as foreshadowing.
Conclusion
We won't go back to the hilltop just yet, since we have more animals to look at. We will, however, note that if we're still under the rollstone tree, we should spare a few nervous glances skyward. Not just because a rollstone to the head would be just as nasty as a coconut to the head; because the rustling of branches could signify that there's a skyforest stalker up there. It might be too small to eat an adult human... but you aren't entirely sure that they know that.
Next time, we'll look at Creatures of the Land. Fair warning; if you thought predatory sugar gliders were weird, you haven't seen anything yet.