The Messel Pit has provided a wealth of fossils that have greatly increased understanding of the Eocene Age. It is a small site approximately 1,000 m long (north to south) and 700 m wide (east to west).
The Eocene ('dawn of new times') epoch (57-36 million years ago) was a remarkable period in the evolution of life on Earth. This was the time when mammals became firmly established in all the principal land ecosystems. They also reinvaded the seas (e.g. whales) and took to the air (e.g. bats). During this period of geological time, North America, Europe and Asia were in continuous land contact and the partial explanation of current distribution patterns is provided by the Eocene fossil record.
The Messel Pit provides the single best site which contributes to the understanding of the middle part of this period. Messel is also exceptional in the quality of preservation, quantity and diversity of fossils. Messel offers fully articulated skeletons and the outline of the entire body as well as feathers, hairs and stomach contents.
The sediments of the Messel formation lie on deposits of 270-290 million-year-old Red Sandstone and crystalline magmatic primary rock outcrops.
During the Eocene epoch, subsidence along faults in the Earth's crust led to the formation of a lake basin. The gradual subsidence of old sediments resulted in the formation of new sediments above them, and over time immense deposits accumulated. The oil-shale bed at Messel originally extended to a depth of 190 m. The subsidence of the deposits preserved them from erosion. Outcrops of older seams from the Eocene succession are found on the slopes of the pit. The location of the Eocene Lake Messel lay south of its present position. This accounts for the site appearing to have had a tropical to subtropical climate.
The fossils found here are providing a unique insight into an early stage of mammal, evolution when many of the basic steps in diversification were being achieved. But mammals were not the only component of the fauna - birds, reptiles, fish, insects and plant remains all contribute to an extraordinary fossil assemblage.
In terms of fossil localities which provide a window into the Eocene Age, Messel is the best and most productive example discovered to date. In contrast to other fossil sites that are marine, Messel can be considered as the single best 'classic' locality snapshot of life as it was in the Eocene. It has been identified as one of the four most significant fossil sites in the world by several senior palaeontologists.