Hi there, thank you for playing! The fearsome critters (as well as some other characters) can be found inside smaller caves located throughout the desert, like this:
A few of them are blocked off by rocks until you start the quest to find them, but after that you'll be able to go inside. As for the large disk on the floor in the last area, try jumping on it a few times and it'll break, allowing you to go deeper into the cavern.
Thanks again for playing, please let me know if you have any other questions or comments!