The Messel Formation is a geologic formation in Hesse, central Germany, dating back to the Eocene epoch (about 47 Ma). Its geographic range is restricted to the Messel pit. There it unconformably overlies crystalline Variscan basement and its Permian cover (Rotliegend) as well as Eocene volcanic breccias derived from the basement rocks. The formation mainly comprises lacustrine laminated bituminous shale (‘oil shale’) renowned for its content of fossils in exceptional preservation, particularly plants, arthropods and vertebrates (e.g. Darwinius masillae).

Messel Pit Fossil Site

UNESCO World Heritage Site
Location	Darmstadt-Dieburg, Hesse, Germany
Criteria	Natural: (viii)
Reference	720bis
Inscription	1995 (19th Session)
Extensions	2010
Area	42 ha (100 acres)
Buffer zone	22.5 ha (56 acres)
Coordinates	49°55′03″N 8°45′24″E / 49.9175°N 8.7567°E / 49.9175; 8.7567
Location of Messel Formation in Hesse Show map of Hesse Messel Formation (Germany) Show map of Germany

The Messel pit (German: Grube Messel) is a disused quarry near the village of Messel (Landkreis Darmstadt-Dieburg, Hesse) about 35 km (22 mi) southeast of Frankfurt am Main, Germany. Bituminous shale was mined there. Because of its abundance of well-preserved fossils of the Messel Formation dating from the middle of the Eocene, it has significant geological and scientific importance. Over 1000 species of plants and animals have been found at the site. 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 about the early evolution of mammals and birds are still being made at the Messel pit, and the site has increasingly become a tourist 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 mining 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 began 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.

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 (200 ft) below the local land and is about 0.7 km (0.27 sq mi) in area. The oil-shale bed originally extended to a depth of 190 m (620 ft). 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 Early Eocene Climatic Optimum and the climate and ecology of the site were very different, characterised by a mean annual temperature of 22°C and a large series of maar lakes surrounded by lush sub-tropical forests that 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 13 m (43 ft) 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 and so the Messel pit represents a Konservat-Lagerstätte. 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 (0.0039 in) per year, this provided a prime environment for the preservation of fauna and flora.

The area around the Messel Pit is believed to have been geologically and tectonically active during the Eocene. Leading scientists hypothesize that events much like the 1986 volcanic gas releases at Lake Nyos, Cameroon, could account for the large deposition of non-aquatic species (Franzen & Koster, 1994). Periodic subsurface shifts possibly released large concentrations of reactive gases (such as carbon dioxide and hydrogen sulfide) into the lake and adjoining ecosystems, killing susceptible organisms. During these releases, birds and bats might have fallen in if near the lake surface and terrestrials could be overwhelmed when near the lake shore. Since the lake was very deep, animals that fell in it drifted downwards into oxygen- and bacteria-poor water, where they were preserved remarkably well, being overlaid by successive layers of mud that petrified later, thus producing an aggregation of fossils of exceptional quality, quantity, integrity, and variety. However, other hypotheses have been postulated as well, and have suggested a Cyanobacteria bloom origin resulting in the poisoning of the animals. This last one was considered to be necessary in order to explain the occurrence of excellent fossils throughout the entire sedimentary sequence (Koenigswald & others, 2004).

Exhibits from the pit may be seen in the Messel town, the fossil Museum in Messel, the Hessisches Landesmuseum in Darmstadt (5 km (3.1 mi) from Messel) and also the Senckenberg Museum in Frankfurt am Main (some 30 km (19 mi) from Messel). Casual visitors can park close to the pit and walk around 300 m (0.19 mi) to a viewing platform overlooking the pit. Entrance to the pit is only possible as part of a specially organized tour.

The Messel Pit provides the best preserved evidence of Geiseltalian flora and fauna so far discovered, with over 1000 species identified. 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 the fungus Ophiocordyceps unilateralis, that, apparently then as today, commandeered 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 remarkable partly as a result of the hypothesized periodic gas releases. A brief summary of some of the fossils found at the site follows:

• Nine mating pairs of fossil turtles have been found. The turtles, Allaeochelys crassesculpta, were in coitus (in the act of having sex). They are male-female pairs, with the male's tail tucked under the female, which is how they copulate. Their death must have been rapid. It is supposed that the turtles had started mating in the aerated surface waters of the ancient lake. As they sank into deeper water, they were overcome by the release of toxic volcanic gas. They were then buried in the lakebed sediment. Turtles belonging to this clade are still living. They have lost their reptilian scales, and their skin absorbs oxygen from the water. Normally, this is an advantage: it helps them stay submerged for long periods. However, under anoxic conditions it is a disadvantage, because carbon dioxide and dissolved poisons are absorbed as well.
• Over 10,000 fossilized fish of numerous species
• Thousands of aquatic and terrestrial insects, some with distinct coloration still preserved
• Innumerable small mammals including pygmy horses, large mice, primates, ground dwellers (hedgehogs, marsupials, pangolins), aardvark relatives and bats. The fossilized bat specimens have provided insights into the evolution of echolocation.
• 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

The following is only a partial list:

Darwinius masillae, identified in 2009 as an adapiform primate

Kopidodon, an extinct arboreal cimolestan

Leptictidium, an extinct omnivorous hopping mammal (of the leptictid family)

Propalaeotherium, an early relative of horses

Ailuravus, a rodent

Peradectes, a metatherian

Palaeochiropteryx, a bat

Lesmesodon, a small hyaenodontid

Eomanis, an early pangolin

Eurotamandua, a scaleless, anteater-like pangolin

Europolemur, a primate

Hyrachyus, ancestor of rhinoceroses

Paroodectes, an early carnivorous mammal

Messelogale, an early carnivorous mammal

Pholidocercus, an early hedgehog

Macrocranion, an early long-tailed hedgehog

Masillamys, an early rodent

Messelobunodon, an early artiodactyl

Godinotia, an early primate

Buxolestes, a semiaquatic, otter-like cimolestan

Palaeotis, an early struthionid

Strigogyps sapea (formerly Aenigmavis) a cariamiform

Eocoracias, an early coraciiform with known coloration

Messelornis, the Messel-bird; a species of gruiform

Masillastega, a freshwater sulid

Lapillavis, a possible trogonid relative

Cypseloramphus, a basal apodiform

The Messelasturidae (Messelastur and Tynskya), carnivorous relatives of modern parrots

Palaeoglaux, an early owl with enigmatic breast feathers

Paraprefica, an early potoo

Paraortygoides, a galliform

Masillaraptor, an early falconiform

Parargornis, an early apodiform

Messelirrisor, a tiny bucerotiform closely related to hoopoes and wood-hoopoes

Selmes (an anagram of "Messel"), a mousebird with stubby toes

Gastornis (formerly Diatryma), a large, flightless galloansere

Hassiavis, a member of Cypselomorphae

Quasisyndactylus, a member of Alcediniformes

Vanolimicola, a possible charadriiform

A currently unnamed lithornithid, a sandpiper-like paleognath, the first record of its kind in Middle Eocene Europe.

Asiatosuchus, a large crocodile

Diplocynodon, an alligator

Hassiacosuchus, a durophagous alligator

Bergisuchus, a sebecosuchian crocodiliform

Eoconstrictor, 2-m snakes related to Neotropical boas, Boinae

Messelophis, a tiny, live-bearing or viviparous boa

Messelopython, the oldest known relative of pythons

Cryptolacerta, a lizard with affinities to amphisbaenians

Geiseltaliellus, a lizard with affinities to Corytophaninae

Allaeochelys crassesculpta, aquatic turtles related to Carettochelys

A bowfin, variously described as Amia (the modern genus) or Cyclurus

Amphiperca, an early perch

Palaeoperca, another early perch

Atractosteus, a gar

eel

Hemiptera

• Wedelphus dichopteroides Szwedo & Wappler, 2006

Hymenoptera

Family Formicidae (ants)

• Casaleia eocenica Dlussky & Wedmann, 2012
• Cephalopone – Cephalopone grandis and Cephalopone potens
• Cyrtopone – Cyrtopone curiosa, Cyrtopone elongata, Cyrtopone microcephala, and Cyrtopone striata
• Gesomyrmex pulcher Dlussky, Wappler, & Wedmann, 2009
• Messelepone leptogenoides Dlussky & Wedmann, 2012
• Pachycondyla eocenica Dlussky & Wedmann, 2012
• Pachycondyla lutzi Dlussky & Wedmann, 2012
• Pachycondyla? messeliana Dlussky & Wedmann, 2012
• Pachycondyla parvula (Dlussky, Rasnitsyn, & Perfilieva, 2015)
• Pachycondyla petiolosa Dlussky & Wedmann, 2012
• Pachycondyla petrosa Dlussky & Wedmann, 2012
• Protopone – Protopone? dubia, Protopone germanica, Protopone magna, Protopone oculata, Protopone sepulta, and Protopone vetula
• Pseudectatomma – Pseudectatomma eocenica and Pseudectatomma striatula
• Titanomyrma gigantea
• Titanomyrma simillima

Family Apidae

• Protobombus messelensis Engel & Wappler, 2003

Family Megachilidae

• Friccomelissa schopowi Wedmann, Wappler, & Engel, 2009

Describing the Messel Pit Fossil Site as 'richest geosite in the world for understanding the living environment of the Eocene, as it includes exceptionally well-preserved fossils', the International Union of Geological Sciences (IUGS) included the site's Eocene record in its list of 100 'geological heritage sites', published in October 2022. The organisation defines an IUGS Geological Heritage Site as 'a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history.'

• Lagerstätte
• List of fossil sites (with link directory)
• List of fossiliferous stratigraphic units in Germany
• Paleofauna of the Messel Pit

• Smith, Krister T.; Schaal, Stephan; Habersetzer, Jörg; Herlyn, Hendrik G.; Senckenberg Gesellschaft für Naturforschung (2018). Messel : an ancient greenhouse ecosystem. Stuttgart. ISBN 978-3-510-61411-0. OCLC 1054359916.{{cite book}}: CS1 maint: location missing publisher (link)
• Harms, Franz-Jürgen; Schaal, Stephan (2005). Current geological and paleontological research in the Messel Formation. Stuttgart: E. Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller). ISBN 3-510-61381-3. OCLC 64571829.
• Mangel, Gerd (2011). Faszination Welterbe Grube Messel zu Besuch in einer Welt vor 47 Millionen Jahren (in German). Stuttgart. ISBN 978-3-510-61398-4. OCLC 698592675.{{cite book}}: CS1 maint: location missing publisher (link)
• Kächler, Ernst Rudolf; Grube-Messel-Verwaltungsgesellschaft (2000). Window to primeval times Messel Pit, world heritage site in the State of Hessen (in German). Wiesbaden: Grube-Messel-Verwaltungsgesellschaft c/o Hessisches Ministerium für Wissenschaft und Kunst. OCLC 174602085.
• Schaal, Stephan; Ziegler, Willi (1992). Messel : an insight into the history of life and of the earth. Oxford: Clarendon Press. ISBN 0-19-854654-8. OCLC 25747250.
• Gruber, Gabriele; Micklich, Norbert; Hessisches Landesmuseum Darmstadt (2007). Messel : Schätze der Urzeit (in German). Stuttgart: Theiss. ISBN 978-3-8062-2092-6. OCLC 600404474.
• Gruber, Gabriele; Sandrock, Oliver; Wappler, Torsten (2018). "DARMSTADT: The Paleontological Collections of Hessisches Landesmuseum Darmstadt". Paleontological Collections of Germany, Austria and Switzerland. Natural History Collections. Cham: Springer International Publishing. pp. 157–164. doi:10.1007/978-3-319-77401-5_14. ISBN 978-3-319-77400-8. ISSN 2510-1862.
• Aubert, Hans-Joachim; Deutsche Unesco-Kommission (2010). UNESCO-Welterbe in Deutschland [eine Publikation der Deutschen Unesco-Kommission und des Auswärtigen Amts der Bundesrepublik Deutschland] = UNESCO world heritage in Germany (in German). Bonn. ISBN 978-3-940785-14-5. OCLC 612325291.{{cite book}}: CS1 maint: location missing publisher (link)
• Various Contributors to the Paleobiology Database. "All datasets matching the term 'Messel'". Paleobiology Database. Retrieved 1 December 2019.