User blog comment:Kogath/Monster Hunter X Discussion/@comment-26836109-20150918001749/@comment-184612-20150918194842

Since Jurassic Forest isn't even the official name (the Japanese is Ancient Forest if you actually look at it. Jurassic was put on the TGS cards as a quickie Engrish name for non-Japanese people), this is moot.

If anything, I'd say it's closer to the Cretaceous era.