Scientists hypothesize that so many fossils have been preserved in the Messel shales in Germany, as a result of tectonic activity in the area during the Eocene. "Periodic subsurface shifts caused earth quakes that might have released large volumes of poisonous gas (such as carbon dioxide and hydrogen sulfide) trapped beneath the lake water, into the lake water itself and into the surrounding forest ecosystem, killing nearly all living organisms in its wake." (6) These animals were then preserved as they lay on the bottom of the deep lake. Fossils that have been found in the Messel shales have been so well preserved that one can even see the outlines of their fur as well as the remains of their stomach content. (6)
The Messel Pit was declared a UNESCO World Heritage site on 9th December 1995.