Theory: The eight-legged Mutos will grow from juveniles to adults

So, I just recently realized something about the SDCC 2013 trailer: all of the descriptions by people who saw the trailer said that the monster attacking the airport was absolutely dwarfed by Godzilla, but people who saw both the 2012 and 2013 trailers said that, when the 2012 trailer was shown again before the new one, the dead multi-armed reptile monster was replaced by this new spider-like creature. Now, anyone who saw the leaked 2012 trailer before it was taken down everywhere may remember that the dead monster was massive, easily the size of a Heisei Godzilla monster... but, wait a minute, isn't the new Godzilla, by all accounts, only slightly taller than the Heisei incarnation? It seems like, if the size of the monster in that shot is accurate, it shouldn't be that much smaller than the Big G, but the one from the airport scene couldn't be more than a third his size according to the descriptions. It then occured to me that maybe, like the Gyaos in the Heisei Gamera trilogy, these eight-legged Mutos will be juveniles when they first start emerging, and some of them will survive long enough to grow into adults, becoming large enough to have a real fight with Godzilla and the "winged Muto" (assuming that, as I'm hoping, it will be something separate from the eight-legged Mutos and not a second form or "queen" of them). What do you think? Could we be seeing monsters both young and old in the upcoming movie?