Kaiju Biology

I am sorry but Shin-Godzilla is not the most scientifically plausible kaiju, that would be Monsterverse Godzilla.

Shin Godzilla evolves like an anime/video game monster/villian. Cancer cells may mutate rapidly but are hardly a good example for shin's video game/anime psudo-evolutionary stages. Also Shin-Godzilla needs to be green (Chlorophyll) in order to conduct photosynthesis and also isn't shin godzilla originated as a deep sea animal before becoming godzilla?

Monsterverse Godzilla evolved naturally through the generational process of natural selection. Godzilla is an archosaur, the animal group that gave rise to crocodilians, pterosaurs, and dinosaurs/birds.

Mouths evolve for eating, if shin godzilla has no digestive system, he would have no need for a mouth and would use something other vector for self defence.

While I can't comment on the ability of an animal to reach such sizes, the Monsterverse Godzilla probably has the most well-explained and realistic Atomic Breath in terms of how it functions and why it could do what it does.

Official background info describes the process as him using his bio-nuclear circulatory system to draw out power that, when activated, causes a neutron flux to travel up his backspines to nucleosynthetic throat chambers that explodes into the Atomic Breath.

If you look up how real-life nucleosynthesis works, you'll find that the immense amount of blue plasmatic heat energy of the Atomic Breath is consistent with its properties. It involves the fission of nuclei via the flow of additional neutrons that can produce explosive aftermath effects, like a nuclear bomb or the reactions in a solar star.

It's essentially the creation of new elements that result in immensely energetic reactions. While the ability to naturally wield it may not be that realistic, the conveyed medium certainly is close.

According to calculations done by folks over at the Spacebattles Forums, a yield of several kilotons of force at minimum would be necessary to send the 141k-ton Ghidorah flying away in the way the Atomic Breath did. And lo and behold, according to the official MONARCH Sciences website, Godzilla's projected yield does indeed reach the 40-kiloton range within 4 seconds, approximately 10-KT/sec.

TL;DR

Godzilla has a portable on-demand nuke with all the science checking out for how it's produced and why it's so powerful.

@Xenotaris 

While I respect your opinion I disagree. I never said he photosynthesizes, I said he does something similar. In the movie it is mentioned he intakes elements from around himself, to gain energy. So no he would not have to be green. Another thing yes he was a deep sea animal. I beleive when exposed to radiation he developed a cancer like tumor which spread across his entire body and became a new organism. Mouth did evolve for eating, but only in animals and some plants, (not going to mention cells.) As seeing that shin is something completely different, it would have a different purpose, It might not even scientifically be a mouth. And Legendary Godzilla is not and Archosaur, he existed in the Permian period, which did have archosaurs, but he was active at this time, suggesting he evolved before archosaurs. Yes I know that they evolved into reptiles and birds. Yes I agree on the fact that cancer cells cannot divide fast enough, as cellular division takes hours to take place. 

Sorry, while legendary Goji may LOOk realistic, he is far from it. Biologically he doesn't work. He doesn't have any explanation on how he is able to absorb Gamma ray Radiation, which is a type of light, which would imply he needs photosynthesis. He may get radiation from prey, but it doesn't seem that he actively hunts. His eating of Ghidorah was to humiliate it. His skeleton cannot support his weight, and his heart isn't nearly large enough.

Animals cannot grow to that size. And it's hard to accept, Shin Godzilla is not an animal.

P.s I think Gojiverse is cool. Very well done.

Garteth Edwards said Monsterverse Godzilla is a dinosauromorph which is a type of Archosaur

Thanks, although I kind of went a little overboard in the second half of the gojiverse or phase 2 as I call it here on scified. I have the expanded version on SpaceBattles.com

Cool, I'll check it out, The archosaur thing is inconsistent, because Goji is stated to have lived throughout the Permian period when archosaurs first appeared in the early Triassic. 

Yeah, I think the people in hollywood don't do their research properly because dinosauromorphs made their first appearance in the fossil records in the middle triassic although scientists believe they may have first appeared in the early triassic but so far there is no dinosauromorph fossils were ever recovered from that epoch.

Out of interest, do you know what specific type of dinosauromorph Legendary Goji could be? His skeletal structure hints that he is a theropod. He has theropodic hips but he drags his tail, which makes him clearly not one. He also has a similar sternum to many large theropods but he still drags his tail. 

Does it have to be Godzilla?

No. Any kaiju you think could be plausible. I think biollante could also work because its a plant.

although technically theropods are dinosauromorphs via clade but generally dinosauromorphs are the ancestors of the dinosaurs themselves. Monsterverse Godzilla wasn't specially labeled as a dinosaur but rather a dinosauromorph meaning the ancestral group were dinosaurs originated from.

Dinosauromorph = which contains the basal dinosaur-like ancestors of dinosaurs and the more advanced Dinosauriformes.

Dinosauriformes = which contains to various linages of near-dinosaurs as well as true dinosaurs.

Dinosauria = true dinosaurs which includes the theropods, sauropods, orinthosaurs, hardosaurs, stegosaurs, pachycelphosaurs, ceratopsids, and ankylosaurs

With that out of the way, he could may have evolved from dinosauromorphs along the lines of the Lagerpetidae. However most dinosauromorphs discovered were either from the middle triassic and late triassic so it would be hard to say what specific linage of dinosauromorph Monsterverse Godzilla would have evolved from since we have yet to fully uncover early triassic dinosauromorphs.

In my own Gojiverse, I simply retconned all the godzillas including zilla into being dinosaurs, highly derived descendants of the Gojirasaurus quayi. I built out a hypothetical godzilla evolutionary family tree.

First I took Gojirasaurus which itself a Coelophysoids (Late Triassic flexible tailed basal neotheropod). Its descendants became burrowers (reference to G98 and Mothra vs Godzilla) called Microgojiras. They evolved to be smaller since most surviving basal neotheropods were out competed by the newly evolved Averostra. The Microgojira would hide off in burrows to escape predators and would spit a foul smelling mucus at its predators (which would be the progenitor of its atomic breath)

In this scenario the microgojiras would survive and evolve into a new branch of theropods called Gojirasauria. Pretty much the gojirasaurians resembled a bulkier coelophysis-like theropod with dorsal spines on its back with long whip-like tails.

The Gojirasaurians would eventually lead to the semi-aquatic Godzillasauroids. They resemble Godzilla98 to a certain extent with their biggest member barely reaching T. rex size.

Initially earlier Godzillasaurids resembled Godzillasauroids but gradually began to adopting a more up right stance as their were forced to retreat in the hollow earth after the K-T extinction. Zilla in my story is more of an evolutionary throwback to earlier godzillasaurids. With all "classic" Godzilla, Monsterverse Godzilla, and Shin Godzilla belonging to the more advanced godzillasaurids.

I just looked at Legendary's skeletal structure, which was clearly designed after a theropod. Do you know how they are going to continue to evolve? Maybe you could make your own designs.

I think legendary should have gone with godzilla is a dinosaur route since they clearly designed godzilla after a theropod. As a stated earlier in my fanfiction, I have godzilla started out as Gojirasaurus quayi; a distant relative to the Coelophysis.  I have thought of some alternate evolutions to godzilla such as a therapsid, a basal archosauromorph (which both existed in the late permian), and even a highly derived tyrannosauroid before settling on the Coelophysoid origins.

Now in the early chapters of the gojiverse (before it becomes an epic crossover fiction) I time skip to all the key members of godzilla's ancestors from the triassic to modern times.

I think that could be accurate as science doesnt know all the missing links. So not knowing every godzilla ancestor is realistic.

well evolution-biologist no longer use the term missing link anymore, its now been replaced with last common ancestor which is what the godzilla's key members are supposed to represent. example: Erectogojiras is the last common ancestor to the Monsterverse Godzilla, Shin Godzilla, and the Classic Godzilla (1954-2004) while the last common ancestor that Erectogojiras shared with Zilla was Eogodzillasaurus

I still stand by my opinion of most realistic Godzilla

That's fine