>I'm not sure that fossils can provide evidence of this, but I'll ask
anyway; is there any indication of possible symbiotic relationships
among dinosaurs (or dinosaur/ mammal, etc.)?
I'm not sure if any fossil evidence exists, but it is quite probable (deriving it from recent niches) symbiotic relationships existed among dinosaurs and insect-eating early birds and/or pterosaurs.
Beri's Dinosaur World