Is Godzilla a Dinosaur?

Kenneth Carpenter, a retired paleontologist who was director of Utah State University Eastern Prehistoric Museum when we spoke to him in 2019, took a stab at that second question in a 1998 essay he wrote for The Official Godzilla Compendium. Traditionally, the monster has been identified as a theropod dinosaur. All known carnivorous dinos (like T. rex) are classified as theropods. So are birds.

Now, Godzilla's skull looks short and blunt for a theropod. He also tends to be depicted with four fingers per hand, and the beast's got multiple rows of bony, vertically oriented plates running down his back and tail.

Using these features, Carpenter tentatively assigned Godzilla to the ceratosauria, a primitive theropod subgroup. Like our radioactive pal, a few ceratosaurians had backsides that were littered with osteoderms: bony deposits embedded in the skin. Certain species, such as the bull-horned Carnotaurus sastrei, had shortened skulls to boot.

And there was another key feature that helped the ceratosaurians stand out. In an email, Carpenter told us that while some theropods had three, two or even one-fingered forelimbs, the more primitive varieties — like the ceratosaurians — "have four or more digits" per hand.

OK, so Godzilla must be a ceratosaurian theropod, right? Not necessarily, Victoria Arbour told us in 2019. An armored dinosaur expert, Arbour is the Curator of Paleontology at the Royal British Columbia Museum. In a 2014 blog post, Arbour made the case that the King of the Monsters might not be a dinosaur at all. Maybe he's got more in common with crocodiles.

Crocs, alligators and their prehistoric kin form a reptilian clade called the pseudosuchia. As Arbour notes, osteoderms and four-fingered hands are more commonly seen in pseudosuchians than they are in theropods. So perhaps Godzilla belongs to the former group.

Speaking of digits, let's check out Godzilla's feet. In most of the original Japanese movies, the big guy has a plantigrade stance. That means he walks flat on his feet like humans. Conversely, digitigrade animals — such as dogs — walk on their toes while keeping their heels off the ground.

"Living crocodylomorphs are plantigrade, but the jury is still out on whether or not all pseudosuchians were plantigrade, especially those that were bipedal," Arbour said via email. No known dinosaur, theropod or otherwise, was similarly flat-footed.

However, for the 2014 American-made movie, Godzilla's feet underwent a dramatic re-design. "I think you could ... make the argument that Godzilla 2014 has tortoise-like feet, and many tortoises are also digitigrade in a manner similar to elephants, with a large heel pad supporting upright toes," Arbour said. She also pointed out that while "almost all bipedal dinosaurs" only had three weight-bearing digits per foot, this version of Godzilla keeps "at least four toes on the ground."

Truly huge land animals such as the long-necked dinosaurs have column-shaped, digitigrade feet. Those limbs are really efficient at supporting massive body weights. So if Godzilla was a real creature we'd probably expect him to have digitigrade hindlimbs — even though a 2017 study claimed plantigrade animals can swing their arms more forcefully in combat. (And Godzilla sure loves combat.)

But of course, it's doubtful that Godzilla could physically walk on dry land, no matter what his feet looked like. "[Getting] Godzilla to stand upright and still would be a complete non-starter," paleontologist Donald Henderson said in a 2019 email. "Its bones would not be able to support its body weight, and its heart would be unable to pump blood to the head."

This is mostly due to the square-cube law: When you scale up an object, its mass increases more sharply than its surface area. Double the height, weight and length of a wooden cube and you'll have also made the thing eight times heavier than it was before.

So how would Godzilla fare underwater? Henderson works at Canada's Royal Tyrell Museum and tackles physics-related questions about extinct animals. In 2018, he used computer modeling to test the hypothesis that Spinosaurus — a theropod with a large sail on its back — was built for swimming. He found that the deep overall body shape of this fin-backed animal would have made the dinosaur prone to tipping over as it swam.

Would Godzilla's osteoderms put him at the same risk? Henderson doesn't think so. By his calculations, the back plates on Stegosaurus — a Jurassic herbivore who influenced Godzilla's design — only represented 17 percent of that dinosaur's overall body mass.

Meanwhile, Godzilla's plates appear to make up an even smaller fraction of the kaiju's total mass. He'd need to build a new digital model to prove it, but for now Henderson suspects that "the plates of Godzilla would not cause it to tip" during swim sessions.

Still, as a marine animal, Godzilla would face plenty of other problems. Seagoing creatures tend to be streamlined. With his jagged osteoderms and chunky legs, Godzilla is anything but. Therefore, he'd need to expend lots of extra energy in order to propel himself through the water.

"The best option for Godzilla to swim would be to undulate its body and tail to produce waves that travel down the body," Henderson explained. "Think of how crocodiles and salamanders swim when they want to move quickly. They fold their arms and legs close to the body, and use sideways motions ... to push back against the water and get a forward thrust."

By the way, semiaquatic behavior was — and still is — widespread among the pseudosuchians. On the other hand, there's no proof that any non-bird theropod was habitually amphibious. Yet some of them did take the occasional dip. In Utah, there's a series of 190-million-year-old dino tracks made by theropods whose toes barely scraped the ground as they paddled along.

For his part, Carpenter disagrees with the pseudosuchian identity argument. Since theropods could clearly swim, he thinks Godzilla's seagoing ways don't preclude the monster from being a bona fide dinosaur. Furthermore, as we've seen, the kaiju does share a lot of traits with the ceratosaurians. If he's not a member of that group, then his ancestors probably evolved all of those features independently. This scenario is certainly plausible (it's a phenomenon called "convergent evolution"). But Carpenter thinks the similarities between Godzilla and theropod dinos are probably too numerous to be coincidental.

"We already know that Dr. Yamane [a character from the 1954 movie] declared the original Godzilla a dinosaur," Carpenter says, "and since he was on site, I'll take his word."