I just noticed

That would be cool, but I don't think that would even fit with the timeline that Gareth Edwards has created. Don't get me wrong, but most of these Godzilla movies are too farfetched, which is why many of them don't really make it to Hollywood and are low-budget. With that said, I don't think that any of the monsters we have seen previously could appear. However, I don't think that necesarily destroys the chances of their making it to the movie...someway. Maybe future enemies could incorporate traits of those monsters, but they just wont be those monsters.

i actually this is how it will go down. most of godzillas enemies will be reimagined version of the older monsters but with new origins similar to godzillas

That was basically the door for any potential sequels. If G and the MUTOs exist, there are probably other beasties. With the movie potentially doing as well as it's looking to do, we may very well see them.

MRFIFTY5IX i wasn't really saying this mentioning their possibilities in sequels, but that would still be pretty nice. I mentioned that to give off an idea on how that ancient ecology could have been like

That would be great, but not with the toho monsters! If they created a whole roster of new monster species that were cool, realistic and menacing then that would be great!

yeah i was thinking the same thing, it would be cool to see anguirus and titanosaurus join in on the cgi, that is if there will be a sequal. :)

Yeah, that's true! There can be millions of other species out there!