 The first of these were initially described as simple filamentous "protofeathers", which were reported in dinosaur lineages as primitive as compsognathids and tyrannosauroids.However, feathers indistinguishable from those of modern birds were soon after found in non-avialan dinosaurs as well.A small minority of researchers have claimed that the simple filamentous "protofeather" structures are simply the result of the decomposition of collagen fiber under the dinosaurs' skin or in fins along their backs, and that species with unquestionable feathers, such as oviraptorosaurs and dromaeosaurs are not dinosaurs, but true birds unrelated to dinosaurs.