It is now known that feathers first evolved in dinosaurs. So-called protofeathers serve an insulation function, which would have been important to poikiotherms/ectotherms such as dinosaurs whose internal sources of heat would have been negligible. This is not such a problem if you are a very large dinosaur, but it can limit body mass decrease as heat is lost through surface area… As reported by Marie-Claire Koschowitz, Christian Fischer, and Martin Sander (2014; “Beyond the rainbow: dinosaur color vision may have been key to the evolution of bird feathers”), the interesting twist is that dinosaurs also had excellent color vision – much better than mammals – even primates with trichromatic vision. Dinosaurs were tetrachromats and capable of distinguishing red, green, and blue (like humans and other catarrhine primates) as well as ultraviolet and turquoise because of a 4th (short wave-length) cone cell type. Protofeathers would have obscured color signaling and display from the skin. The evolutionary trade-off? Evolve pennaceous feathers containing pigment in the form of melanosomes!! Check out this post by GrrlScientist and read more from Koschowitz et al (2014) vol 346.