Many drawings are unfinished, just have been experiments or occasional stuff on any white surface I've seen. Herein I compiled many sketches of variable stages of progress. It's for showing how much more imagination exists in mind than could ever led to a completed picture. Using your fantasy you might see much more in this but simple lines or shading …
Voigt, S., Fischer, J., Schindler, T., Wuttke, M., Spindler, F. & Rinehart, L. (2014): On a potential fossil hotspot for Pennsylvanian – Permian non-aquatic vertebrates in central Europe. – Paläontologie, Stratigraphie, Fazies (22), Freiberger Forschungshefte, C 548, 39-44.