One Final Hypothesis: Exoskeletons

I'm no expert but I'd expect their legs to have visible joints if it was a true insect like exoskeleton, they might have plating on their back and chest that could explain the insect like why their legs seem to join to their body.

I don't think something with a traditional skelton as big as Godzilla would be able to walk on land, but the trailers show a giant skeleton in a cave, so I guess it makes sense in the context of the film.   Maybe a real animal would need some kind of sparse lattice structure to keep the weight down.

To be honest I think the MUTO's have a bone structure very similar to the Xenomorphs from Alien.

DEADITE KAIJU is right. The Xenos have a peculiar body system. In some areas that are vital (e.g. chest, head) they have hard exoskeletons. In the rest of the body like the legs and arms, are made of a tough skin, for protection and durability.

Well, since no giant monster, including the M.U.T.O.s, could be made out of the exact same stuff as normal animals, and given the bizarre look of those specific creatures, I'd say they have both an exoskeleton AND an endoskeleton. Neither are quite as developed as a respective vertebrate and invertbrate, but working together, along with whatever comprises Godzilla and the M.U.T.O.s, makes allows a stable and surprisingly mobile structure.

Yes, they every well could have exoskeletons. The latest looks at them we have got suggest it actually. Great observation and imagination SOMETHING REAL

The thing about science fiction is that you can do anything.  There is no NEED to do, or a NEED to have.

How does Bruce Banner gain weight when he's transformed into the Hulk.  What happens to Mr. Fantastic's bones, brains, heart and penis when he stretches. 

Who cares??

Stan Lee once said, while standing next to me,  "I can do anything with an out of control imagination."

So, except the MUTOs as they are.....  Someone's imagination.

Interesting thread, gonna feature it.