I’m basing this analysis on the Mothra figures, so they may not be accurate. Also I’m not an expert on arthropods (or an actual expert on anything because I’m only 17).

Mothra’s monarch file doesn’t state much besides her bioluminescence and part of the natural order. So this will mostly be about her morphology. But let’s start with her power first.

Mothra’s thorax can emit beta waves (electricity from the brain) that can activate bioluminescent patterns oh her wings. Insects have ganglia across their bodies, and the largest are in their thorax. Ganglia are kind of like second brains that help process and transmit information. So Mothra’s ganglia can transmit powerful signals to her wings that can activate specialized cells that can generate luminescence. I’m not sure how she can refine it into a ‘god ray’ but maybe the scales on her wings act as mirrors that can direct the light.

Now onto her morphology.

Mothra’s larval form is different from the little toilet log we all know and love. Her larval form is decked out in heavy chitinous plating. She has a short abdomen (for a caterpillar, which normally have abdomens that take up most of their body) with only six pseudopods. Most of her body is actually taken up by her thorax, which also stands upright. Now I can’t really tell if she has six legs or eight in her larval form. They could just be another pair of pseudopods, but if those are legs then that’s incredibly unusual, because Mothra is explicitly stated in her file to be a lepidopteran. AKA a moth (butterflies also are lepidopterans but they’re a family of derived moths so they technically count) and thus an insect. Insects only have six legs (although technically antennae and some mouthparts are derived from legs) so if Mothra’s larvae has eight legs then that’s incredibly unusual. Maybe her kind have a weird mutation where one of the leg pairs were duplicated in their larval form? Or maybe it’s exclusive to this specific Mothra and is not natural for her kind.

Again though, they could be pseudopods.

Now for her imago form.

Starting off with her head we can already see that her anatomy is ever so subtlety weird. Mothra has eyelids. No I’m serious, you can see them move during the close-up of her very menacing face during the trailer. But, if Mothra's limbs are all scythes that have no cleaning fuzz then I guess that's a necessary adaptation for cleaning her eyes. Something that big moving that fast is going to accidentally get some creatures splattered on her eyes. Mothra’s mouth is also equally weird. She seems to only have one pair of palps and her labium and labrum are either vestigial or completely absent (the bottom palps are attached to the labium so that probably explains why they’re not present). Her mandibles aren’t visible so it seems like her maxilla have taken up the job. The top palps are attached to the maxilla so that’s how I could tell they were her maxilla.

This is completely different from any other moth, because the only mouthparts present for them are their maxilla and its palps. But the maxilla of moths are also fused to form a tongue (there’s also moths with no mouths in their imago phase).

Next is her limbs.

Mothra definitely has six legs in her imago form, but her first four pairs of legs all end in very large and menacing raptorial appendages. It’s worth noting that only extremely carnivorous insects ever evolve raptorial appendages. Her first four limbs appear to only have three segments. I’m only seeing the coxa, femur, and tibia. So I guess her species have completely lost their tarsus, which are crucial for walking. Mantids, for example, may have seem like their claws only have three parts, but even they have a tarsus as well, because they can’t walk on their claws or they’ll get worn down and dull. So Mothra’s species either spends little to no time on the ground at all, or they only walk on their hind legs. Speaking of hind legs, it seems like hers do have a tarsus. Unusually though, while her first four legs are attached to her thorax, it seems like her legs are attached to her abdomen... or so it seems. We can see something very similar in beetles, where it seems like the hind legs are attached to the abdomen, but they’re really attached to the very back of the thorax. So it only looks like their hind legs are attached to their abdomen. And while it looks like there’s a very clear divide between Mothra’s thorax and abdomen, that’s really just a part of her thorax that’s pinched. Some Hymenopterans like ants also have a pinched thorax as well. It also looks there’s parts of here exoskeleton that look more like plated armor or scales that an actual exoskeleton, so she might have both an exoskeleton and bits of an endoskeleton. But then again, I could be reading the blurry pictures of the figurines wrong.

As for her placement in the tree of life, it seems like her kind evolved from very primitive moths, and diverged from the rest of the lepidopteran order before their maxilla fused into a tongue.

Now, I want to go back to her arms and mouth again. Past Mothra incarnations have had small mouths and stubby little legs (that oddly ended in three claws despite all arthropods only having two), but the legendary incarnation is different.

She has raptorial limbs, and a very big and threatening mouth.

This is not the cute and adorable Mothra we know.

This Mothra is a predator, and not just any kind of predator.

We see her diving from the sky with her raptorial claws outstretched and ready to stab in the trailers. You know what other kind of predator dive bombs it’s prey and strikes it with such devastating speed?

Peregrine Falcons.

Skullcrawlers only have two well developed limbs. Adults also have weird extensions of the elbows that look like spines. Their limbs aren’t adapted for burrowing, but because they originally came from subterranean ecosystems, they probably use their head as a wedge and brute force their way through cave walls.

The head of the skullcrawler is where they get their name. Their head has a large keratinized surface with two “fenestra” that are actually just two holes in their keratinized head. I’m not sure if there’s actual fenestra in their skull or not. Skullcrawlers have no nostrils, which supports my theory of them using their head as a wedge since having dirt in your nostrils isn’t fun.

A skullcrawler’s mouth houses hundreds of teeth. The whole structure resembles the mouth and throat of leatherback sea turtles. While these teeth may look like the keratin spines lining the throats of leatherbacks, these are in fact teeth. This means that all skullcrawlers have hyperdontia, and it’s probably not unusual for teeth to grow where they’re not supposed to. In the middle of their bottom jaw is two ridges that their tongue rest between to avoid being impaled by their hundreds of teeth. They seem like fleshy ridges, but as someone who’s family owns snakes I can tell you with certainty that those ridges are extra rows of teeth. Boas and pythons have four rows of teeth on their upper jaw, and those ridges on the bottom jaw of the skullcrawler looks very similar to the middle rows of teeth in a python.

The tongue of a skullcrawler is a little extravagant for what it’s really used for. Their tongue is triple forked instead of normal forked like a normal varanid or snake. Skullcrawlers use their tongue to pull small prey into their mouth, but instead of evolving a chameleon tongue or a forked tongue that can function like a claw, they just wrap their tongue around the prey item and suck it into their gullet. This is an incredibly inefficient means of using a long tongue. Also their tongues are connected to their stomach. I can’t really explain that so I’ll chock it up to how they’re supposed be biological mistakes. I’m not even sure if they’re tongues at that point if they’re not connected to their mouth.

Next is their anorexic torsos. Apparently skullcrawlers are hypervores, which means that they’re like the Deviljho from monster hunter in that their metabolism is so high that they have to eat near constantly. So being starved is essentially the normal state for the species. There’s some places on the torso that are actually translucent, particularly the back. Now, I’m not exactly sure if skin and muscles can be translucent at that size. Probably not, but there is a species of fish who’s name eludes me that are transparent for a reason scientists aren’t quite sure of yet so maybe skullcrawlers are doing something similar. There’s also little to no muscle mass at all on their torso. Unfortunately that scene where the adult skullcrawler jumps onto Kong and in an impressive feat of core strength it flexes its stomach to bring its tail around Kong’s legs would not have been able to happen due to the lack of muscle. Also their torsos are very short and their tail actually makes up the vast majority of their bodies. Skullcrawlers are obviously based on varanids and snakes, but unlike skullcrawlers they’re mostly torso. Because of this they can get a ton of nutrients out of their food. Skullcrawlers might actually be hypervores because of their short torsos. With such little space for a digestive system and much of their body mass comprising of a thick muscular tail, it’s no wonder why they’re always so hungry.

They also throw up the bones of their prey like owls.

Also, because they’re hypervores with extreme metabolisms, they produce a ton of heat. There’s no obvious way for them to vent their heat. Something that large and active without a proper way of venting heat would immediately die via its proteins breaking apart and its tissues melting. And that actually might be what’s going on inside a skullcrawler and that might explain the lack of muscles in their core and why when Kong ripped out the adult’s stomach it came out in a jumbled mess of fused organs. Skullcrawlers insides might be in a perpetual state of melting and trying to regrow, but end up becoming a mess.

Skullcrawlers might have some capacity for learning and problem solving. The adult noticed something was wrong when one of the characters walked up with a grenade, but at the same time it didn’t notice that Kong was going to whap it with a tree despite having time to notice that.

The adult skullcrawler is also shown clearly having fun causing suffering in others, so it probably has sadistic personality disorder just like Ghidorah.

Finally

Okay so after taking a quick look through Rodan’s monarch file, here’s the important things to note.

1) internal combustion system of magma

2) rock-like scales that act as geothermal armor

3) skeletal structure similar to that of a Pteranodon

4) wingspan big enough to create a sonic thunderclap capable of leveling entire cities as it flies overhead

5) skin is not made of rock, but does have an outer dermis of sharp volcanic sediment collected from centuries of dormancy

6) vulcanized appearance of its skin may be an evolutionary trait developed as a form of camouflage against mountain or large rock formations

Okay so obviously what we’re dealing with is a rock bird with a magma jet engine that has wings big enough to level cities.

In all seriousness though, it seems like Rodan’s species is adapted to hibernate in volcanically active areas and stockpile geothermal energy, and then quickly fly to new feeding grounds when volcanic activity stops. Alternately, Rodan might have bacterial colonies that can process elements found in volcanoes and produce organic compounds as waste, like creatures living near hydrothermal vents. It’s camouflage would help it hide from other kaiju in the area whilst hibernating, and it might have relied on volcanic sediment to build up on its body for extra protection. It’s also stated that the sediment is sharp, which means that there could be an extreme buildup of obsidian. Obsidian is the sharpest naturally occurring thing on the planet, which would be useful in cutting through the tough skin of other kaiju. Rodan’s skin is tough, and is a good protective barrier between his softer flesh and literal molten rock.

I’m no expert on aerodynamics and extremely weird physics, so I can’t really say anything about the whole leveling cities thing other than the fact that Rodan is definitely flying at least above Mach 1.

The internal jet is interesting. It seems weird and even counter intuitive to use magma, which is liquid rock, as a means of achieving flight, but I digress. Rodan must have some kind of organ that can store all of it. I’m also a little skeptical of the whole internal jet engine thing. Magma can be seen leaking out of the back ends of his wings, so Rodan’s species might be using it to heat up the air and create updrafts to make flying easier.

And then there’s Rodan’s skeleton. It’s said to resemble a Pteranodon’s so it would seem pretty cut and dry that he’s a pterosaur, right?

No not necessarily.

He’s definitely related, yes, but I don’t think he’s a pterosaur. His legs are located directly underneath his body. Rodan’s feet are also exactly like those of a bird of prey, i.e. a theropod dinosaur. From what I’ve seen of the screenshots and toy models, Rodan’s fourth finger looks less like a finger and more like a big styliform.

All of these are pretty strong evidence that suggests that Rodan’s kind are actually kaiju scansoriopterygids related to, if not descended from the genus Yi.

King Ghidorah is an interesting one.

Following the format for my Rodan analysis, I’ll list everything important.

1) unknown origin

2) can be frozen and still survive

3) divergent frontal lobe density in the brains of the three heads, denoting each head has disparate levels of cognitive functions, and possibly even independent thought

4) dermal layer is gilded with trace amounts of aurum (gold)

5) Metallurgical studies theorize the scales act as a conductor capable of carrying bioelectrical currents through the creature’s body

6) Muscle tendons on the wings are so hyper-tensile that their massive aerodynamics could generate hurricane-force winds when in flight. Coupled with its body’s electro-receptor molecular biology capable of conducting electrical currents, water vapor in the air would be heated at extreme levels creating its own localized storm system as it travels

Okay let’s start with the electricity. Electroreceptors are a type of organ that can sense electricity (also we can forget about the molecular part because that’s just nonsense), but can’t produce it and aren’t great at conducting. However, they are used in electroreception. Ghidorah probably has organs containing stacks of electrocytes (cells that can actually produce electricity) in specialized organs in his body, and probably has a way to store electricity extracted from lighting as well. Ghidorah can probably subsist on other forms of energy as well since he was shown draining nuclear power from Godzilla. The whole personal thunder storm seems reasonable though.

Hyper-tensile basically just means that something is incredibly resistant to breaking under tension (being stretched). This means that Ghidorah’s wings are pretty tough and powerful, and they have to be considering his skin is made of gold and is thus really really heavy. Each of Ghidorah’s wings are also supported by three ribs as well.

Ghidorah has gold on the surface of his scales. His body is too big to say that he just coats himself in the stuff, so he probably produces it naturally or occasionally consumes gold and his body repurposes it and incorporates it into his scales. The gold in his skin helps conduct electricity. his makes sense because gold is the third most conducive metal; with the second most conducive being copper and the first being silver. Now why Ghidorah’s species decided that gold was the best option instead of the much more conducive, common, and lighter copper is beyond me.

Ghidorah has been frozen in ice for thousands of years and lived. This suggest that he might have antifreeze compounds in his body.

Ghidorah has three heads, and thus three brains. And each one has its own conscience. The center head is the one in charge, and the right head is more aggressive and likes to stay focused on a task at hand. The left head is more curious an aloof, and was nipped and pulled by both the center and right heads when it got distracted. It’s also worth noting that, aside from his brains, Ghidorah’s entire nervous system is largely decentralized. Severed pieces of Ghidorah’s body (like heads for example) will continue to move despite being separated from the rest of the body. Eventually they still die though.

I’m not sure how Ghidorah’s gravity beams work. Despite their name, they’re really just lighting bolts that come from his mouth. Ghidorah is basically a flying tesla coil so I guess he can direct his electricity wherever he wants.

Ghidorah has incredible regenerative abilities, and was shown to regrow an entire head and half a neck in only a few seconds. Massive amounts of stem cells flooded the wound and began growing into tendrils of muscle and bone that twisted themselves into a new head.

Mutos are a large species of endoparasitic radiotrophs, but they have a mouth so they probably still need the occasional source of protein. They implant their young into the bodies of kaiju so their young can have a steady source of radiation.

We’ve seen that the mutos are very curious, emotional, and intelligent creatures. They’ve demonstrated this on multiple occasions. The female was shown mimicking and investigating interesting sounds. The male was shown figuring out how to escape traps. And the female showed loss over her eggs and fury when confronting their murderer.

They can emit electronic frequencies for long distance communication, but these frequencies can also disrupt electrical devices. These same EMP pulses are also said to disrupt the atomic breath of Godzilla’s species, but we never see the mutos do this in the movie so I guess they were just too horny to do it.

Mutos are also a sexually dimorphic species with a body plan that isn’t found anywhere else in nature.

Their head is triangular, with a mouth that has two smaller mandibles on the side of the bottom jaw. These mandibles have limited mobility, and are more pronounced in the male. Mutos also have a row of lens structures in their bioluminescent face patches that function to focus the light coming from said patches to get a slightly focused image of things of interest, like people on a train bridge or that one asshole who killed all your babies. They have a large jointed plate behind their head that goes over their back and is connected to an accordion-like structure that plays a large role in producing vocalizations. That same plate, as well as their shoulder plates, are very smooth and flat. This makes it hard for creatures like Godzilla to grab onto them. These plates also give mutos a distinct echo profile. So if there’s actually more than one species of mutos, then they probably have different shaped back and shoulder plates.

Mutos have eight legs, with the first three pairs having five joints (counting shoulders). The first pair of legs in the male support large wings. These wings do not connect to the body and are instead supported by a large rod. The shape of these wings are very close in shape to the wings of many fast flying birds, being optimized for speed. The second limb pair seems to be responsible for emitting the mutos electromagnetic pulses, and the third pair of limbs are small and used for carrying and grasping objects. These first three limbs end in “claws” which are actually hardened points. These points are used for stabbing and slashing. When not in use, the mutos walk on their “knuckles” to avoid wearing down these sharp points. The hind legs of the mutos are normal digitigrade limbs that end in three toes. These toes have actual claws.

Mutos apparently form monogamous, loving pairs that defend each other. The mating habits of mutos are probably much like that of salmon, with the female laying the eggs and the male fertilizing them externally (so it’s probably likely that the black stuff we saw covering the muto eggs was muto jizz). They only breed once... if they breed at all.

The mutos are said to be the offspring of ‘MUTO Prime’ and are mistakenly thought to be a different species.

I asked some of my friends what they thought the true connection between prime and the normal mutos was. My friend @theload suggested that prime is merely a very old female, and this is likely the case.

But I think the connection is weirder.

We never actually see the mutos mate. The male just gives her a nuke, they nuzzle, and the female just digs a hole and lays the eggs. Plus, those eggs were already pretty far in development. There was little tiny cute mutos visible inside the eggs.

So if they don’t mate, then why is there a male? Well I think these aren’t the actual true adults. They’re smaller than the true adult form, prime, and the two different types of mutos serve as protection for the eggs that will grow up to become primes.

They’re prime dispersal units.

And honestly, there’s weirder life cycles in nature, so it’s plausible.

As far as taxonomic placement goes, most people seem to agree on them being weird placoderms. I think that they’re actually tardigrades. Tardigrades also have eight legs, three main pairs, and one pair at the end of their body. Tardigrades are already slightly radiation resistant. I propose that a group of tardigrades developed complete immunity to radiation, and then eventually capitalized on an energy source that few other organisms would dare go near. Tardigrades have been around since the Cambrian, so that gives them more than enough time to evolve bigger bodies with more complex limbs, organs used in vocalization, electroreception and projecting electronic frequencies, and even endoskeletons. Mutos are explicitly stated to not be arthropods, but tardigrades aren’t necessarily arthropods either. They’re panarthropods, so they’re only distantly related.

Uuuhhh.... shit.

It’s an alien that can travel between planets via green lightning. Reproduces asexually. It eats blood and flesh. It’s incredibly intelligent and probably is sensitive to the electrical signals in our brains in order to learn. It might make pheromones to lure people to it. Probably transfers memories to young before they separate from their body considering that the little baby buds were fully conscious and singing in the climax. Has molars for grinding bones to get to the bone marrow. Has both cells with walls and cells without walls.

Mother Longlegs

Going back to my normal format of listing everything important first.

1. All female

2. It’s a harvestman

3. Vascular bundles of woody xylem found within the the appendages of the mother longlegs suggests that trace elements of actual bamboo are within its physiology, as though the flora of its natural habitat has become infused within its DNA.

4. Evolved razor sharp spines at the end of its legs

5. Poisonous spurs on spikes immobilize prey

6. Drink up liquids from victims through feet like a straw

7. Underbelly releases muscular tendrils that drag prey up into its open stomach

Okay this one is gonna be hard.

Usually I save taxonomy for last, but that’s honestly the easiest thing to do this time. Mother Longlegs are simply a giant parthenogenetic member of the Opiliones, and despite their appearance Opiliones are actually more closely related to scorpions than they are to spiders. And honestly it’s nice to see them taking the spotlight instead of the very overused Araneae. Also, considering that their cephalothorax and abdomen haven’t fused suggests that they diverged from other harvestmen before that happened… and I guess became harvestwomen.

They’re parthenogenetic because they’re basically stationary in their adult phase so they can’t really go and find mates. Although if my florafauna theory holds water then this has to be something recently evolved or else they wouldn’t be so seamlessly merged with their plant parts. Parthenogenesis basically results in clones and doesn’t make a lot of genetic variety, and thus slowing down the process of sorting out the new plant genes generation after generation.

Instead of retaining the normal foot of an arthropod, Mother Longlegs have legs that end in a single sharp point. While this is useful for what they use their legs for, those points are going to dull down very, very quickly. They’re constantly impaling their legs deep into the ground to get a strong footing so they don’t fall over via wind or the clumsiness of a large animal, but because of this and how thin their legs are they’re most likely going to snap their legs if they attempt to walk anywhere. And harvestmen legs don’t grow back, and they’re going to need all the legs they can get to support their body, which looks to be pushing half a ton in weight, without an endoskeleton. Their legs probably support them through both a complete muscular system and hydrologic system (somewhat like spiders). They also apparently have venomous spurs on the end of their foot that’s used in immobilizing prey. While this is useful, they still run the risk of snapping their legs, but I suppose the reward in nutrients is well worth it to them.

On a related topic, Mother Longlegs can seemingly suck nutrients and fluids from prey impaled on their feet. Arachnids already partially have some of their digestive tract in the base of their legs, and sea spiders (which might not even be chelicerates at all) have most of their digestive system in their legs and even use the rhythmic pulsing of it to move around. So it’s plausible to evolve leg straws. Speaking of their leg straws, Mother Longlegs have xylem in their legs. Xylem is a vascular tissue in plants that conducts water and nutrients from the root and up the plant using suction and pressure. Xylem also helps form woody elements in the stem of a plant. So this is likely what Mother Longlegs are using to suck fluids up from impaled prey, and their feet mouths might actually be an extension of the xylem that connects to their digestive track. Xylem is also responsible for why their legs look and feel like bamboo.

Mother Longlegs also can release muscular tendrils that pull prey up into their exposed stomach. This simply isn’t going to happen since the stomachs of arachnids are on top of their nervous system and sometimes even their brain. The movie seems to notice this since we never see their underside open, and the tendrils are instead dragging a soldier up towards its mouth. Prey dragged towards the mouth are crushed by the pedipalps of the Mother Longlegs, and are devoured (harvestmen don’t have a filter system or a sucking stomach so they just eat bits of food). Also their chelate are reduced to large fangs. I don’t know what purpose they serve. They have plants on their abdomen that photosynthesize and provide extra energy.

Harvestmen don’t have very well developed eyes and they’re pretty small compared to their body, so that begs to question why Mother Longlegs have such large and well developed eyes. My guess is that they’re hold overs from when they were cave dwelling creatures, and that they eventually came to the surface of skull island through its many cave systems.

On the bottom of their abdomen are two sphincter-like organs. They could be derived from book lungs or the same chemical spraying organs that other harvestmen use for defense.

Speaking of lungs, at this size ordinary book lungs aren’t going to cut it. The Mother Longlegs have to have a well developed respiratory system.

As far as their life cycle goes, I assume that they start off small, and are omnivorous scavengers like normal harvestmen, and as they molt and grow bigger and slower they migrate back to the bamboo forest. Once there they molt one last time and become fully sedentary.

However I am going to say a few things about him.

1. I’ve seen people theorize that he’s descended from many things. From pseudosuchians to labyrinthodonts, but honestly I think he’s probably descended from some kind of early reptilimorph.

2. He’s a radiotrophic organism much like radiotrophic fungus and honestly there’s no shortage of melanin on his gray body. He’s gray all over so it makes sense.

3. His atomic breath is a beam of Cherenkov radiation and he can emit the same glow from his face and dorsal scutes as an intimidation display.

4. Maybe the reason the tail is shorter in the 2019 version in comparison to the 2014 version is because it got cut off and it didn’t grow back quite as long much like how some lizards regrow tails.