What is a thought to be the evolutionary precursor to feathers?

The evolutionary precursor to feathers is believed to be structures known as "dino-fuzz" or proto-feathers, which were likely simple filaments or hair-like appendages found on the skin of some theropod dinosaurs. These structures may have originally served insulation, display, or other functions before evolving into more complex feather forms. The transition from these primitive structures to the sophisticated feathers seen in modern birds illustrates an example of evolutionary adaptation and diversification.