At first, the downward-pointing tail bones were hard to interpret. Then, later in the 19th century, a remarkable find was made. Some specimens of "Mixosaurus" and "Stenopterygius" were well preserved in the black mudstones of Germany. These fossils were preserved in such fine sediment that the fossils were almost perfect, with only a few bones disturbed or missing. The outline of the body shape could be seen as a thin carbon film. Even though the soft parts had rotted away long ago, they left their imprint behind. For the first time, scientists could see clearly that the tail of ichthyosaurus was shaped like the tail of a fish. And on its back, like a shark, there was a dorsal fin.