The Messel Pit (German: Grube Messel) is a disused quarry near the village of Messel, (Landkreis Darmstadt-Dieburg, Hesse) about 35 km southeast of Frankfurt am Main, Germany. Bituminous shale was mined there. Because of its plethora of fossils, it has significant geological and scientific importance. After almost becoming a landfill, strong local resistance eventually stopped these plans, and the Messel Pit was declared a UNESCO World Heritage site on 9 December 1995. Significant scientific discoveries are still being made, and the site has become an increasing tourism site as well.
Brown coal, and later oil shale was actively mined from 1859. The pit first became known for its wealth of fossils around 1900, but serious scientific excavation only started around the 1970s, when falling oil prices made the quarry uneconomical. Commercial oil shale mining ceased in 1971, and a cement factory built in the quarry failed the following year. The land was slotted for use as a landfill, but the plans came to nought, and the Hessian state bought the site in 1991 to secure scientific access. In the few years between the end of mining and 1974, when the state started preparing the site for garbage disposal, amateur collectors were allowed to collect fossils. The amateurs developed the “transfer technique” that enabled them to preserve the fine details of small fossils, the method still employed in preserving the fossils today.
Due to the extraordinary fossils, the pit was declared a UNESCO world heritage site in 1995, the only place to be placed on the list exclusively due to fossils.
Many of the known specimens from the site have come from amateur collectors, and in 1996, an amnesty on previously collected fossils was put in effect, in the hope of getting privately owned collections back into public ownership and available to science.
The current surface of the Messel pit is roughly 60 m below the local land and is about 0.7 km² in area. The oil-shale bed originally extended to a depth of 190 m. 47 million years ago in the Eocene when the Messel deposits formed, the area was 10° further south than it is now. The period was very close to the Paleocene–Eocene Thermal Maximum, and the climate and ecology of the site were very different. A large series of lakes, surrounded by lush sub-tropical forests supported an incredible diversity of life. The Messel lake bed was probably a center point for drainage from nearby rivers and creeks.
The pit deposits were formed during the Eocene Epoch of the Paleogene Period about 47 million years ago, based on dating of basalt fragments underlying fossilbearing strata. Oil shale, formed by the slow anoxic deposition of mud and dead vegetation on the lake bed, is the primary rock at the site. Its sediments extend 130 m downward and lie atop an older sandstone foundation. The fossils within the shale show a remarkable clarity and preservation due to the unique depositional characteristics of the lake. The upper stratifications of the lake most certainly supported a variety of organisms, but the bottom was subject to little disturbance by current, spawning a very anoxic environment. This prevented many epifaunal and infaunal species from inhabiting this niche, and thus bioturbation was kept at a minimum. Overturn of the lake layers (caused by seasonal variations) lowered oxygen content near the surface and led to a periodic “die-off” of aquatic species. Combined with a relatively low rate of deposition (0.1 mm/yr), this provided a prime environment for the preservation of fauna and flora.
The Messel Pit provides the best preserved evidence of Geiseltalian flora and fauna so far discovered. Most other sites are lucky to contain partial skeletons, but Messel boasts extensive preservation of structural integrity, even going so far as to preserve the fur, feathers, and “skin shadows” of some species. Unusual preservation has sparked some closely-reasoned interpretations. The symptomatic “dumb-bell”-shaped bite marks on either side of the leaf vein on a fossilised leaf have been identified as the death-grip of a carpenter ant terminally parasitized by a fungus that, apparently then as today, comandeered its behavior, in order to release its spores from a favourable location; it is the earliest concrete sample of fungal behavioural manipulation.
The diversity of species is no less astonishing (thanks in part, perhaps, to the hypothesized periodic gas releases). A brief summary of some of the fossils found at the site follows:
- Early primate fossil with anthropoid (i.e. non-lemuroid) characteristics (discovery made public May 2009), (see Darwinius masillae)
- Over 10,000 fossilized fish of numerous species
- Thousands of aquatic and terrestrial insects, some with distinct coloration still preserved
- A plethora of small mammals including pygmy horses, large mice, primates, ground dwellers (hedgehogs, marsupials, pangolins), aardvark relatives, and bats.
- Large numbers of birds, particularly predatory species.
- Crocodiles, frogs, turtles, salamanders, and other reptiles or amphibians
- Remains of over 30 distinct plant species, including palm leaves, fruits, pollen, wood, walnuts, and grapevines
Exhibits from the pit may be seen in the Messel town museum, the Museum of Hessen in Darmstadt (5 km from Messel) and also the Senckenberg Museum in Frankfurt (some 30 km from Messel). Casual visitors can park close to the pit and walk around 300 m to a viewing platform overlooking the pit. Entrance to the pit is only possible as part of a specially organized tour.