The Messel Formation is a geologic formation in

Hesse Hesse or Hessen ( ), officially the State of Hesse (), is a States of Germany, state in Germany. Its capital city is Wiesbaden, and the largest urban area is Frankfurt, which is also the country's principal financial centre. Two other major hist ...

, central

Germany Germany, officially the Federal Republic of Germany, is a country in Central Europe. It lies between the Baltic Sea and the North Sea to the north and the Alps to the south. Its sixteen States of Germany, constituent states have a total popu ...

, dating back to the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...

(about 47 Ma). Its geographic range is restricted to the

Messel pit The Messel Formation is a Formation (geology), geologic formation in Hesse, central Germany, dating back to the Eocene Epoch (geology), epoch (about 47 Ma). Its geographic range is restricted to the Messel pit. There it unconformably overlie ...

. There it unconformably overlies crystalline Variscan basement and its

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

cover (

Rotliegend The Rotliegend, Rotliegend Group or Rotliegendes () is a lithostratigraphic unit (a sequence of rock strata) of latest Carboniferous to Guadalupian (middle Permian) age that is found in the subsurface of large areas in western and central Europe ...

) as well as Eocene volcanic breccias derived from the basement rocks. The formation mainly comprises lacustrine laminated bituminous shale (‘

oil shale Oil shale is an organic-rich Granularity, fine-grained sedimentary rock containing kerogen (a solid mixture of Organic compound, organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general compos ...

’) renowned for its content of

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

in exceptional preservation, particularly plants, arthropods and vertebrates (e.g. '' Darwinius masillae'').

Messel pit

The Messel pit () is a disused

quarry A quarry is a type of open-pit mining, open-pit mine in which dimension stone, rock (geology), rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some juri ...

near the village of Messel (

Landkreis Darmstadt-Dieburg Darmstadt-Dieburg is a Kreis (district) in the south of Hesse, Germany. Neighboring districts are Offenbach, Aschaffenburg, Miltenberg, Odenwaldkreis, Bergstraße, Groß-Gerau, and the district-free city of Darmstadt, which it surrounds. Hist ...

, Hesse) about southeast of

Frankfurt am Main Frankfurt am Main () is the most populous city in the States of Germany, German state of Hesse. Its 773,068 inhabitants as of 2022 make it the List of cities in Germany by population, fifth-most populous city in Germany. Located in the forela ...

, Germany. Bituminous shale was mined there. Because of its abundance of well-preserved

of the Messel Formation dating from the middle of the

, it has significant geological and scientific importance. Over 1400

taxa In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...

of plants, fungi and animals have been documented 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 World Heritage Sites are landmarks and areas with legal protection under an treaty, international treaty administered by UNESCO for having cultural, historical, or scientific significance. The sites are judged to contain "cultural and natural ...

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.

History

Brown coal and later

was actively mined from 1859. The pit first became known for its wealth of

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

s 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 A landfill is a site for the disposal of waste materials. It is the oldest and most common form of waste disposal, although the systematic burial of waste with daily, intermediate and final covers only began in the 1940s. In the past, waste was ...

, 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.

Depositional characteristics

The current surface of the Messel pit is roughly below the local land and is about in area. The oil-shale bed originally extended to a depth of . 47 million years ago in the

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. Kopidodon Senckenberg 2007-01

The pit deposits were formed during the

Epoch of the

Paleogene The Paleogene Period ( ; also spelled Palaeogene or Palæogene) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period Ma (million years ago) to the beginning of the Neogene Period Ma. It is the fir ...

Period about 47 million years ago, based on dating of basalt fragments underlying fossilbearing strata.

Oil shale Oil shale is an organic-rich Granularity, fine-grained sedimentary rock containing kerogen (a solid mixture of Organic compound, organic chemical compounds) from which liquid hydrocarbons can be produced. In addition to kerogen, general compos ...

, 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 downward and lie atop an older

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

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, per year, this provided a prime environment for the preservation of fauna and flora.

Volcanic gas releases

The area around the Messel Pit is believed to have been geologically and tectonically active during the Eocene. Some scientists, especially Jens Franzen, have hypothesized that events much like the 1986

volcanic gas Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities (Vesicular texture, vesicles) in volcanic rocks, dissolved or dissociated gases in magma and lava, or gases emanating from ...

releases at Lake Nyos,

Cameroon Cameroon, officially the Republic of Cameroon, is a country in Central Africa. It shares boundaries with Nigeria to the west and north, Chad to the northeast, the Central African Republic to the east, and Equatorial Guinea, Gabon, and the R ...

, could account for the deaths and preservation in the lake of non-aquatic species. Periodic subsurface shifts possibly released large concentrations of toxic 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. Other scientists, especially Wighart von Koenigswald, have hypothesized that cyanobacterial blooms could account for the rich faunal assemblage of Messel, with animals succumbing after drinking water contaminated with cyanobacterial toxins. This hypothesis drew support from the occurrence of gravid and or copulating animals at Messel, which supposedly reflect a dominant season of death. Others explored the null hypothesis of accidental death. In particular, Krister T. Smith and colleagues found that the annual number of fossilized bats in Messel is comparable to the number of bats that drown in modern swimming pools. That is, bat mortality is not actually elevated at Messel, which fails to support the "mass mortality" hypotheses above. Regardless of the manner of death, the exceptional preservation at Messel (e.g., mostly complete skeletons) indicates that the lake was very deep. Animals that fell in it drifted downwards into oxygen-poor water without scavengers, where they were overlaid by successive layers of mud that petrified later, thus producing an aggregation of fossils of exceptional quality, quantity, integrity, and variety.

Access

Exhibits from the pit may be seen in the Messel town, the fossil Museum in Messel, the Hessisches Landesmuseum in

Darmstadt Darmstadt () is a city in the States of Germany, state of Hesse in Germany, located in the southern part of the Frankfurt Rhine Main Area, Rhine-Main-Area (Frankfurt Metropolitan Region). Darmstadt has around 160,000 inhabitants, making it the ...

( from Messel) and also the Senckenberg Museum in

(some from Messel). Casual visitors can park close to the pit and walk around to a viewing platform overlooking the pit. Entrance to the pit is only possible as part of a specially organized tour.

Fossils

The Messel Pit provides the best preserved evidence of

Geiseltalian The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', 'Dawn') an ...

flora and fauna so far discovered, with over 1400 taxa identified. Most other sites are lucky to contain partial

skeleton A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fra ...

s, 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 Carpenter ants (''Camponotus'' spp.) are a genus of large ants (workers ) indigenous to many parts of the world. True carpenter ants build nests inside wood, consisting of galleries chewed out with their mandibles or jaws, preferably in dead, ...

terminally parasitized by the fungus ''

Ophiocordyceps unilateralis ''Ophiocordyceps unilateralis'', commonly known as zombie-ant fungus, is an entomopathogenic fungus, insect-pathogenic fungus, discovered by the British naturalist Alfred Russel Wallace in 1859. Zombie ants, infected by the ''Ophiocordyceps unila ...

'', 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 In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

are still living. They have lost their reptilian scales, and their skin absorbs

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

from the water. Normally, this is an advantage: it helps them stay submerged for long periods. However, under

anoxic Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved ox ...

conditions it is a disadvantage, because

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

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 (

hedgehog A hedgehog is a spiny mammal of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are 17 species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introduction. The ...

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

pangolin Pangolins, sometimes known as scaly anteaters, are mammals of the order Pholidota (). The one extant family, the Manidae, has three genera: '' Manis'', '' Phataginus'', and '' Smutsia''. ''Manis'' comprises four species found in Asia, while ' ...

s), 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,

salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...

s and other reptiles or amphibians * Remains of over 30 distinct plant species, including palm leaves, fruits, pollen, wood,

walnut A walnut is the edible seed of any tree of the genus '' Juglans'' (family Juglandaceae), particularly the Persian or English walnut, '' Juglans regia''. They are accessory fruit because the outer covering of the fruit is technically an i ...

s and grapevines The following is only a partial list: Darwinius masillae PMO 214

Mammals

:'' 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 Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

:'' Peradectes'', a

metatherian Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well ...

:'' Palaeochiropteryx'', an early bat :'' Lesmesodon'', a small hyaenodontid :'' Eomanis'', an early

:'' Eurotamandua'', a scaleless,

anteater Anteaters are the four extant mammal species in the suborder Vermilingua (meaning "worm tongue"), commonly known for eating ants and termites. The individual species have other names in English and other languages. Together with sloths, they ar ...

-like pangolin :'' Europolemur'', a primate :''

Hyrachyus ''Hyrachyus'' (from ''Hyrax'' and "pig") is an extinct genus of perissodactyl mammal that lived in Eocene Europe, North America, and Asia. Its remains have also been found in Jamaica. It is closely related to ''Lophiodon''.Hayden, F.V''Report of ...

'', ancestor of rhinoceroses :'' Paroodectes'', an early carnivorous mammal :'' Messelogale'', an early carnivorous mammal :'' Pholidocercus'', an early

:'' Macrocranion'', an early long-tailed

:'' Masillamys'', an early

:'' Messelobunodon'', an early

artiodactyl Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other t ...

:'' Godinotia'', an early primate :'' Buxolestes'', a semiaquatic,

otter Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic, or marine. Lutrinae is a branch of the Mustelidae family, which includes weasels, badgers, mink, and wolverines, among ...

-like cimolestan :'' Hassianycteris'', an early bat :'' Archaeonycteris'', an early bat :'' Tachypteron'', a possible emballonurid or miniopterid bat

Birds

:'' 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 Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

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 Potoos (family (biology), family Nyctibiidae) are a group of birds related to the nightjars and frogmouths. They are sometimes called poor-me-ones, after their haunting bird vocalization, calls. The family Nyctibiidae was formerly included with ...

:'' 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 An anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once. For example, the word ''anagram'' itself can be rearranged into the phrase "nag a ram"; which ...

of "Messel"), a mousebird with stubby toes :'' Gastornis'' (formerly ''Diatryma''), a large, flightless galloansere :'' Hassiavis'',Mayr, G.. (2004). New specimens of Hassiavis laticauda (Aves: Cypselomorphae) and Quasisyndactylus longibrachis (Aves: Alcediniformes) from the Middle Eocene of Messel, Germany. CFS Courier Forschungsinstitut Senckenberg. 252. 23-28.
/ref> a member of

Cypselomorphae Strisores ( ), sometimes called nightbirds, is a clade of birds that includes the living family (biology), families and order (biology), orders Caprimulgidae (nightjars, nighthawks and allies), Nyctibiidae (potoos), Steatornithidae (oilbirds), P ...

:'' 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

Europe.

Reptiles

:'' 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 ''Cryptolacerta'' (Ancient Greek and Latin for "Hidden lizard" – κρυπτς or ''crypto'' meaning "hidden" and ''lacerta'' meaning "lizard") is an extinct genus of lacertoid lizard which lived during the Eocene epoch (Lutetian stage, about ...

'', a lizard with affinities to amphisbaenians :'' Geiseltaliellus'', a lizard with affinities to Corytophaninae :'' Allaeochelys crassesculpta'', aquatic turtles related to '' Carettochelys''

Fish

:A bowfin, variously described as ''Amia'' (the modern genus) or '' Cyclurus'' :'' Amphiperca'', an early perch :'' Palaeoperca'', another early perch :''

Atractosteus ''Atractosteus'' (from Greek ''atraktos'' (ἀτρακτὀς), 'spindle' and ''osteon'' (ὀστέον), 'bone') is a genus of gars in the family Lepisosteidae, with three extant species. It is one of two surviving gar genera alongside ''Lepisost ...

'', a gar :eel

Insects

;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

IUGS geological heritage site

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 The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to global cooperation in the field of geology. As of 2023, it represents more than 1 million geoscientists around the world. About Fo ...

(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.'