65000000 B.C. (CTP)
The structure for Singing Mountain can be seen in the Prerelease's 65000000 B.C. map, as well as a non-functioning village below. Even before the Prerelease, a sort of Tyrano meat banquet was supposed to be held on the overworld. Graphics depicting roasting meat, a stew, and dinosaur bones or chains were created but scrapped before the Prerelease was shipped. They are still in the ROM (both pre and final), and can be revived through editing subtiles.
From: Locations (CTP)