From Game Spot:
Rare’s canceled game Dinosaur Planet, which was actually later converted into a completely different game on GameCube, has leaked in its original state online. The game was planned for the Nintendo 64, and much of its DNA still exists in Star Fox Adventures–hence that game’s major differences from the rest of the series. This version, however, has never been available to the public to play before.
Shared by the Nintendo historian Forest of Illusion on Twitter and spotted by VGC, Dinosaur Planet is fully playable via this leaked version, though the account said it won’t run perfectly on emulators. The build appears to be from after Nintend