I just watched a podcast interview with one of the scientists behind this study. They looked at diplodocus scales that were incredibly well preserved and they were able to identify a variety of melanosomes. They were only able to study four scales so far, because the way the scales were preserved means that they contain a lot of information, but it is relatively difficult to extract that information. In fact, in the interview, they mentioned that initially they thought the melanosomes we’re simply not preserved, and they suspect that some of the techniques that they were able to apply in order to eventually find them might help identify melanosomes in other well-preserved specimens where an initial search had failed (for example, Borealopelta).
What is really interesting is that they were expecting to find both oblong and rod shaped melanosomes, which are known from other non avian Dinosaurs; but instead of rod shaped melanosomes, they found disc shaped ones, which were, until not very long ago, assumed to be unique to feathers.
These disc shaped melanosomes are associated with very bright, iridescent colors in birds. They aren’t nearly as concentrated in diplodocus scales as they are in bird feathers, at least in the scales they tested so far, but they are still found in a clade where they weren’t expected at all, and it does mean that diplodocus had some kind of multicolored pattern, even if it wasn’t particularly vibrant.
In the interview I listened to, the researcher suggests to possibilities: that feathers containing these bright color producing melanosomes were present in early dinosaurs or even animals ancestral to them, or that sauropods or their ancestors evolved these melanosomes on their own for some reason. And the interviewer brought up a third possibility, that dinosaur ancestors may have had these types of melanosomes in their scales, and they carried them through as scales evolved into feathers.
Either way, it’s very interesting! I love that we are learning about dinosaur coloration now; when I was a kid, that was the textbook example of a thing we will never know about dinosaurs. Science is incredible!