Having monsters that big possess .... problems.
Remember the movie "THEM!" with the giant ants? James Arness fried their sorry butts with flame throwers in the L.A. sewers in that '50s movie.
But ants can't get that big.
Their respiratory systems are primitive and inefficient. A twelve foot long ant would self-asphyxiate. It also wouldn't be able to move as its mass would increase at a rate far larger than its strength.
Back in 1968 a new Irwin Allen TV series premiered; "THE LAND OF THE GIANTS.". Isaac Asimov wrote a rather clever review of it in the TV Guide. However he pointed out its scientific improbabilities. The show revolved around a suborbital L.A. to London spaceflight in a ship called the "Spendrift," which went through a wierd Irwin Allen style time warp and landed on an earthlike planet where everything is twelve times bigger.
And the gravity was apparantly earthlike.
Well, that would put a nominally six foot human on this planet at 72 feet high.
But being 12X bigger, in order to find his mass would require the cube of the factor; 12³, or 12 X 12 X 12.
Put your calculators away, the answer is 1,728.
Now suppose a human being we're talking about would weigh 180 lbs.
Such a human 12X bigger, weighing 1,728 times as much, would weigh 311,040 lbs.
That's 155.52 tons.
BUT consider that his strength would be increased only by the square of the factor, since the cross-section of his muscles is only a two-dimensional factor. In other words his muscles would exert 144 times the physical power of a normal size human. But, remember, the mass factor increases not by the square but the cube. In short, basically, we have a human being that might have some truly impressive proportions but basically have one twelth the physical power required for normal movement.
Oh, and his lungs -- his respiratory surface? That also increases by the square, so our weak giant becomes asthmatic.... in a fashion, since a surface that is only 144 times bigger must provide oxygen for a mass 1,728 times larger.
Now we know earth in the past has supported some really large impressive critters. During the Cretaceous a nasty beast called Tyrannosaurus Rex prowled around and, depending on whose theories one believes, scarfed up carrion or brought down other larger critters and ate them.
The largest figure I've ever heard for T-Rex is fifty feet, and other figures make him slightly smaller, and about 8 tons in mass.
The movie figure of Godzilla, which should really read Gozira, was represented as being many times larger than our real-life T-Rex.
But here comes that Irwin Allen physics.
It doesn't really work. There has to be some limiting size because giantism only works up to some limiting point. I don't know how large Godzilla--er, Gozira was supposed to be, so doing math on it seems pointless. It wasn't really a Tyrannosaurus Rex anyway, it was a mythical beast never really encountered in real life.
But the physics remain.
Thank you Dr. Asimov.