This is still not something we can answer with certainty. For a couple of years there, paleontology thought that psittacosaurus had feathers on its tail - and as a ceratopsian, on the complete other side of the dinosaur ‘tree’, that would suggest the base form for dinosaurs must have feathers and any that didn’t have them lost them at some point in their lineage (and thus could potentially regain them if the DNA was deactivated rather than lost). Now the feathers are disputed again, as “something else” - spines of some sort unrelated to feathers.
No doubt lots of dinosaurs were scaly, but I don’t think anyone would say with certainty that feathers were limited to late theropods.
From what I know, most raptors had feathers and that’s where birds came from.
The broader group of theropods, including the T-Rex, had a precursor to feathers literally called “Dinofuzz”.
All other kinds of dinosaurs I believe are actually scaly like we thought.
This is still not something we can answer with certainty. For a couple of years there, paleontology thought that psittacosaurus had feathers on its tail - and as a ceratopsian, on the complete other side of the dinosaur ‘tree’, that would suggest the base form for dinosaurs must have feathers and any that didn’t have them lost them at some point in their lineage (and thus could potentially regain them if the DNA was deactivated rather than lost). Now the feathers are disputed again, as “something else” - spines of some sort unrelated to feathers.
No doubt lots of dinosaurs were scaly, but I don’t think anyone would say with certainty that feathers were limited to late theropods.