Tweet of the Day: Dear Procrastination
This is a world building trope.
The Precursors, those that came before. Also known as Ancients, Ancestors, and even Gods. A common enough trope in speculative fiction. But this particular sub-trope doesn’t appear on the page so we are breaking new ground (as far as you can break new grounds with tropes, of course). The Scaly Precursors are either a form of lizard, dinosaur, or fish people that once inhabited the setting in the Ancient past (for a give value of ancient) and ruled it. As with many Precursor races they tend to have fantastic magic and/or technology. And like most variations of those that came before, they are now long gone, leaving only mysterious and dangerous ruins to explore.
I lay the reason for this trope on the feet of the Theory of Evolution. Lizards and dinosaurs evolved before mammals, so it stands to reason that if civilization rose before the Anthropocene, then it might take the form of a civilization of reptilian creatures. This makes them alien enough to be different but because of the Intelligent Gerbil trope, remain familiar enough that you can apply other familiar tropes such as Reptiles are Abhorrent for those Precursors (or their degenerate survivors) to fill the role of villain in your story. The fans, scales, poison and carnivorous disposition of many reptiles adds a touch of nastiness that, say a a giant talking bear, lacks.
Since reptiles and fish are also associated with the tropics (be they the tropical rain forest or desert regions) it is also a way to introduce a Fantasy Counterpart Culture, perhaps modeled on the Egyptians or a Pre-Columbian Mesoamerican civilization. Talking of fantasy, dragons seem to be the number one reason for the existence of Scaly Precursors. Either dragons fill the role or are related to the civilizations in questions, as mentors, or rivals.
So, if your spinning the Wheel of the Ancients it might well land on Scaly Precursors.