#ectothermic is what cold blooded animals are btw

[trashcreatyre]

He’s actually very comfortable

[annoyedbritishperson]

Alien Anatomy

I’ve kinda been thinking about alien anatomy and here’s some vague conclusions I can come up with.

Insect: so there’s the idea of insect type aliens and if they’re anything like earth insects then their size would be limited by the amount of oxygen (or whatever they breathe) is around. So larger bug aliens could only exist with high breathable concentrations so their planets atmosphere must be a minimum of 30% of their preferred breathing gas. Also, exoskeletons can only be thick to a certain extent before they can’t breathe so larger sized insect aliens would have a thin (compared to smaller insects) exoskeleton; but that doesn’t mean that they can’t have the biological equivalent of steel making up their exoskeleton, they’d still need support if they’re on the larger size, flight could also get a little tricky if they’re on the larger size (basically they might have to go into different methods of it but idk, I’m not a professor on insect flight)

Reptile: so like insects their size would also be limited, but not by air/atmosphere composition but by temperature. The closer to the equator (on earth) the hotter the temperature, and, if you haven’t noticed, the bigger the reptile species. Only the largest reptiles live in the hottest places, you don’t exactly see a saltwater crocodile in Norway. To put it simply, it’s because of their heat regulation; they’re ectothermic. If they live/ evolved on a world with similar temperatures to ours then largest they could be would be a large monitor lizard. And don’t ask “what about dinosaurs? They were lizards”; taxonomically yes but their living descendants (birds) are exothermic, suggesting some sort of transition along the evolutionary line.

Mammalian: size can obviously stay the same maybe bigger/smaller than what we know (for mammals it’s mostly gravity and pregnancy limiting our size) whether they evolved on a planet with more/less gravitational pull. Mammal variations such as marsupials might get around the pregnancy issue since their young are born around the size of a jellybean and monotremes just lay eggs (btw the pregnancy issue is basically that the bigger the mammal the longer the pregnancy and the longer the pregnancy the more time you’re vulnerable to predators) though if you’re a pack hunter, pregnancy might be less of an issue since you are the predator and those in your pack could bring you food so that you wouldn’t be in any danger by hunting (the prey could choose to attack as a form of defense).

Birds: now you can bring in your dinosaur anatomy since they’re technically one in the same (though velociraptors were likely not unnaturally intelligent). This isn’t a rule based off of fact but if you base the bird/dinosaur design off of Jurassic park dinos then you’re out (THE THERAPODS (carnivorous bipeds: velociraptor etc) SHOULD’VE HAD FEATHERS! T. rex might’ve been the exception as they could’ve been big enough to regulate their temperature without insulation but I digress) they would also be able to get around mammals size issues as they don’t have to worry about since they typically lay eggs and have a lighter structure meaning larger size (have you ever held a bird? They’re strangely light, as if they’re constantly inhaling helium instead of oxygen)

Fish: all I know of their physiological limits is that it’s a little similar to the insects limits as oxygen concentrations (or any gas really) is almost always in higher concentrations in the atmosphere than it is diffused in the oceans. As long as they have some sort of propulsion and streamlining to a degree there would be less rules with this one ¯\_(ツ)_/¯

Amphibians: they would have to be heavily reliant on the liquid they evolved from and their skin would be weak to infection (at least ones they haven’t evolved against) they might be able to metamorphose like bugs through their life too.

Mollusks: for those who don’t know mollusks include things like octopuses (yes its octopuses not octopi) and snails. Due to the lack of set bones you could have as many appendages as you please, ones around the mouth are likely as it would help with eating. Early in their evolution basically all mollusks had shells so it wouldn’t be unheard of for your alien to have one too though they could also have lost them (like squid or octopuses) or chosen to adapt them into a bone like structure (like cuttlefish) though that would prevent their awesome ability to squeeze into anywhere. Their skin could also be used to communicate or camouflage as they’re notoriously good at changing their colour and even shape to fit their surroundings.

Plant based life: by this I basically mean a moving plant. If they regularly photosynthesise then their need lots of leaves or their equivalent, they’d likely have a bark like exoskeleton to keep them from flopping about as they move, if they don’t, they’d likely stay small; like bowtruckles from fantastic beasts. If active then they would get rid of rooting into the ground as a method of nutrient extraction for something else, they could have a mouthpiece to transfer water directly to a xylem and have some sort of digestive system equivalent for minerals etc.

Planet: I need to put this in because it sorta affects all creatures. If they evolved on a planet with less gravity then they could potentially become space faring sooner as they wouldn’t have as much of a problem reaching escape velocity. There’s also more potential for flight and bigger “mammals” on these planets. Their orbiting star can affect them too; if they’re around a red dwarf then they’d have more time to develop but their planet could be tidally locked meaning there could be limited habitability on their planet, either too hot on one side and too cold on the other but there’s a small line between the two where liquids could exist and life could evolve, it would also bring in the fun concept of them being like “WOAH, NIGHT AND DAY? WHAT IS THIS?!” Since all the time it would look like twilight/dawn on their planet. If they’re orbiting a supergiant star then they’d have to evolve quickly since supergiant stars don’t live that long before going supernova; this could suggest that they’d have super short lifespans, a year (for us) might be super old to them and they could think were immortal since we live so long (even by our standards) their planet would also have to be much further away to be in the habitable zone so their star may be dimmer from their perspective and, as a result might not evolve eyes. Life on a planet orbiting a supergiant star could also survive with less of a magnetic field (they’d still need one though, but life could still exist with a weak one) so life on their planet could have less geographic activity, therefore less volcanoes and less earthquakes. Other mainstream stars like our own might not differ much when it comes to development and lifespans, it just matters how long they’ve been there/ how long through the stars life it is.

Blood: the colour of an animals blood depends on its needs. Since all animals we know of use oxygen I’m basing the colour on what we know of oxygen breathing life. Hemocyanin (blue blood) would be better used in cold climates so if your creature evolved on an icy planet it’s blood would likely be blue. It gets its blue colour from copper instead of iron. Remember, evolution works as survival of the good enough so if the planet was extremely cold in life’s early emergence then they’ll likely gain this colour and stick with it regardless of whether their planet is cold later in its life. Haemoglobin (red blood) is overall more efficient so if the planet isn’t that cold then red would be more likely to occur. Hemerythin (violet blood) is a simpler structure compared to the first two; going along with the rule of ‘survival of the good enough’ a lot of creatures could possibly have violet blood due to its simplicity. Biliverdin (green blood) is a pigment, it doesn’t carry oxygen and occurs when haemoglobin breaks down but makes animal more resistant to disease meaning that it would be more likely to occur if they evolved in a disease infested environment, likely as a result of lack of predators since disease would replace them in culling their population.

Limbs and organs: limbs such as arms and legs have no real set boundaries though it’s a good idea to make sure that they keep the same amount of limbs or less of them based on the creature they and other creatures on their planet have evolved from (e.g. we have four limbs in total because the first terrestrial vertebrates had four, animals like snakes etc have lost theirs over time but none have gained any limbs because you’d need to have severe evolutionary stress to specifically gain limbs or die: otherwise it’s too much effort for extra limbs). Organs you can go crazy with, you can have as many eyes as you want and in insect like aliens you could even forgo the need of a heart (or heart equivalent) due to their different respiratory system (you could get rid of lungs then too :P) you can have as many sensory organs as you want though you should take into account their planetary surroundings to make sure each organ is necessary (e.g. little to no constant light could mean no eyes/eyes that detect different wavelengths than us)

This has been an unnaturally long 1:30 am shitpost but I felt like I had to say something. Thanks for reading, laters.