What part of evolution would give them feathers in a warm, humid jungle-like climate?
First, not all dinosaurs lived in "humid, jungle-like climates". Earth has always had a wide range of climates, even when it was on the whole warmer or colder than it is now.
Second, ectotherms ("cold-blooded" animals, although that term is now out of favor) always have problems with regulating their temperatures. Anything that helps keep a more *steady* internal temperature is an advantage, since fluctuating temperatures cause all sorts of problems, biologically. Even in a warm climate an "adjustable insulation" like feathers would help increase heat retention when the temperature drops, and allow more heat out when the temperature rises.
Besides, we find dinosaur bones in Alaska and Atarctica.
I got your point. ;-)
think camouflage, not thermal insulation.
highly invaginated and densely layered surfaces disrupt an object's outline and eat up light far more effectively than do smooth surfaces with the same pigmentation and pattern.
I believe these folks are missing a trick when they jump straight to thermal insulation for an explanation.
Also color communications giving rise to focusing on mates to create subspecies, new species.
What bird living in a warm climate does not have feathers.?