least its imprint on the rock

Sometimes a piece of skin is preserved, or at least its imprint on the rock. In these fossils you can learn a lot about the appearance of animals; it is known, for example, that some large dinosaurs were covered with scales Princess Hair, and that smaller ones had feathers.

And it has been discovered that certain pterosaurs, at least, had hairs. By the way, it is also assumed that many dinosaurs had feathers and were homeothermic, but that is another matter.