The Konservat-Lagerstätte Menat (French pronunciation:[məna]) is a Konservat-Lagerstätte located in France dating to the mid-late Paleocene. Though the fossiliferous beds of the sites have been known for a long period of time, with the first large study being published in 1940, Menat has had much less study than other similar deposits. Since the 1980s, a number of excavations have been done by various museums. However, due to the loss of the original sites, most of this is a result of multiple excavations done in the area. The fauna of the lagerstätte is largely made up of insects however, various vertebrates such as mammals, reptiles, and birds have been described from the sites. These fossil were preserved in what was a volcanicmaar lake surrounded by a forest with evidence of common forest fires.
Before the area was known for the Konservat-Lagerstätte Menat, the area nearby was known for its diatomite quarries which were mined until 1873. After this point, a factory was built outside of the town to avoid intoxication associated with the fumes produced. A number of things were produced using this sediment including abrasives and pigments, and later dynamite. In 1940, Piton would publish the largest study of the fossils which laid the groundwork for others in the future. However, similar to a number of other specimens, a large amount of the fossils he described would be lost in World War II with holotypes being found in a number of different collections today.[1]
By the 1950s, mining of at the quarries concluded with the factory later closing in 1964. Even before the mine closed, various people were collecting fossils from the mines associated with the factory. Around this time, the main quarry (known as “Les Grelins”) was turned into a pond with another quarry (known as “La Mer”) was filled and overlain with a road. Even though the main quarry was turned into a pond, a number of fossil collectors would travel to the site to collect specimens. This happened so often that in 1979, municipal council prohibited the collection of fossils to protect the site with a local museum being created soon after. During the 1980s, some excavations of the main site were done by the Muséum National d’Histoire Naturelle though this would not last very long. In 1988, the site would become a Regional Natural Reserve with no excavations happening at “Les Grelins” since then.[1]
More work would be done in the late 1990s-early 2000s the paleontological association Rhinopolis would begin more work at the quarry. During this time, the group also would open a new site known as “Maison de retraite”. In 2009, the village would work with Paléovergne to preserve the paleontological heritage of the area. By 2010, “Maison de retraite” was closed to open a retirement home and a new site known as “Les Lavandes” was opened in 2011. In 2012, a test pit titled "Menat 1" was opened with the main purpose of studying the stratigraphy of the site with another test site known as "Menat 2" being opened in 2013. The most recent site to be excavated is the "Stream site" in 2014 which has much better preservation than the two test pits.[1]
Geology
The Konservat-Lagerstätte Menat is known from three more recently excavated sites that these being the main source of more recent geological descriptions. The more well-known and oldest bed, referred to as "Menat 1", is located on the eastern region of the maar lake that was preserved at the site. Menat 1 has a total thickness of 5.82 metres (19.1 ft) and is made up of nine greyish to white silicifiedclaystone beds which range in thickness from 3–20 centimetres (1.2–7.9 in). The upper clay beds are weathered at the top, fossils are still present in these beds though the preservation is worse than in the silicified beds. During excavations that took place in 2013 and 2014, a second site referred to as "Menat 2" was first worked on. This site is located near the eastern entrance to the nearby village of Menat and has a thickness of 6 metres (20 ft). Similar to the first site, the upper clay beds were weathered though the clay differs more throughout the site. Based on the differences in lithology under these weather beds, Menat 2 has been split into three intervals being A,B, and C.[1]
Interval
Thickness
Lithology
A
1.68 metres (5.5 ft)
Dark grey to black in color that is finely laminated with strata from this interval only being weakly weathered.
B
1.37 metres (4.5 ft)
Grey to dark grey in color with the lowest section of the interval being made up of claystone that is a few centimeters in thickness that are not a result of diatomites.
C
0.95 metres (3.1 ft)
Nondescript with noticeable lamination.
The third site, known as the "Steam Site" was first referenced in the literature in 2018 and has been noted to have better preservation than the other two sites. The beds that make up the site are made up of dark, organic clays and is suggested to be correlated to the “Les Grelins” and “La Mer” quarries. Both charcoal and soot have been found at every horizon of Menat.[1] Fossils found at these sites are preserved on what has been labeled as spongo-diatomites however a more recent study that looked into the composition of these layers found no evidence of diatom sclerites or sponge spicules being present.[2]
Dating
The original dated of Menat was the mid to late Paleocene, with this being based on the presence of a fossil primate. Later palynological studies have suggested either a Thanetian or Selandian age. However the more recent dating based on basalts and tuffs near Menat gave an "average age" of the Thanetian-Ypresian boundary. This age has been referenced as the age of the fossil maar lake itself though this has faced criticism due to the lack of correlation between the lake deposits and the sediments being dated.[1] The most recent papers referencing the date of the site place the age as 59 mya based on pollen. In contrast to this however, macrofloral fossils suggest a slightly older age of 60-61 mya.
Paleoenvironment
Konservat-Lagerstätte Menat represents a volcanic maar lake that has been estimated as measuring 1 kilometre (0.62 mi) in diameter. Based on the algae found at the sites, there would have been no inflow from rivers with there seemingly only being a few shallower areas on the coasts. Outside of these small areas around the margins, it is most likely the maar lake would have been relatively deep.[3] This lake would have been surrounded by a largely deciduous forest, climate in the area would have been temperate to subtropical with cool winters being present.[4] Though humid, the amount of charcoal and soot found at Menat suggests that forest fires would happen often in the surrounding forest.[1][5] Based on the amount of insect trace fossils found on leaf fossils, the ecosystem was already healthy, even with it being only a few million years after the mass extinction event. This suggests that regions further away from the asteroid impact recovered faster than those in regions like North America.[6]
An indeterminate bird known from a specimen of legs and tail feathers that is the largest bird found at Menat. Similar to other birds, the preservation of the material is too poor to assign it to a genus.
An indeterminate bird known from a specimen with a skull, neck vertebrae, and the right wing. The preservation of the specimen is too poor to identify it to genus level.
A possible songziid known from a specimen lacking parts of the hind limbs. Unlike its possible close relative, the bird does not possess the greatly elongated toes.
A messelasturid or halcyornithid known from an almost complete specimen, the skull is large for the bird's size with a beak that was tall towards the base. Though largely complete, the poor preservation of the specimen does not allow for it to be assigned to a genus.
A choristodere known from a well preserved specimen with soft tissue preservation. The specimen was not assigned to a specific species due to in not differing from either much because of the other species having much less material.
A specimen known from a complete, articulated skeleton with soft tissue preserved that was originally placed as in "insectivore". The current placement under the genus is questioned that a reevaluation of the material has yet to be done.
A plesiadapid known from an incomplete skeleton with fur preserved found at the site. When originally described, the material was placed under its own genus, Menatotherium.
A squamate originally assigned to Proiguana loevidens known from a now-lost specimen made up of an incomplete skull that has been compared to what is now Plesiolacerta.
Specimens from softshell turtles found at the site with morphology dissimilar to multiple genera in the family. The affinities of the specimens, represented by shell and limb material, has yet to be determined.
A staphylinid known from a complete specimen with a body length of 5.4 millimetres (0.21 in). Based on the specimen, the beetle would have been dark green or shiny-blue.
A chrysomelid known from two fairly complete specimens, the beetle has a body length of 14 millimetres (0.55 in). It was the oldest sagrine beetle at time of publication.
A cupedid known from a fairly complete specimen with a body length of 7.2 millimetres (0.28 in).
M. orbiculatus
A cupedid known from a single specimen that was originally described as within the genus of Cupes,the body length of the beetle was 9.1 millimetres (0.36 in).
A brentid known from a mostly complete female specimen that is similar to the modern P. antiquum though it is slightly larger and has a straight rostrum.
An ithycerid known from a mostly complete specimen which has been suggested to possibly be male. The genus is the only known Cenozoic member of the subfamily Chilecarinae found outside of North America.
A bibionid known from a specimen lacking an abdomen, the forewing of the fly has been measured to 4.9 millimetres (0.19 in). The exact species could not be determined due to the lack of preserved genitals.
A mydid known from a mostly complete specimen, the forewing of the fly has been measured to 15.8 millimetres (0.62 in). Modern members of the family are only found in warmer, though drier regions unlike the fossil genus, with adults that feed on flowers.
An apid known from a female specimen with wing shapes similar to the modern genus Habropoda. The length of the forewing measures 9.4 millimetres (0.37 in).
A vespid known from a poorly preserved specimen with a body length of 21 millimetres (0.83 in). At the time of description, the genus was the earliest vespine found.
An aulacid known from a mostly complete specimen, being the oldest crown group member of the family at time of publication.
Probombus
P. hirsutus
A megachilid that was originally described as a relative of bumble bees. It has been suggested that the species may be actually a species of the genus Ctenoplectrella.
A small epigomphid known from two forewings and a hindwing attached to a thorax, the forewing of the dragonfly has been measured to be 25.7 millimetres (1.01 in).
A dysagrionid known from a specimen in which only the legs and head are missing; the forewings of the damselfly have bees estimated to be 27.0 millimetres (1.06 in).
A lestinoid placed within a monotypic family known from an almost complete specimen, the fore and hindwings are both about the same length being 28.7 millimetres (1.13 in) long. Based on the presence of an ovipositor similar to what is seen in the family Lestidae, the damselfly most likely injected its eggs into plants.
A synlestid known from a specimen made up of all of the wings, the thorax, and part of the abdomen. The forewing of the damselfly have been measured to 25.4 millimetres (1.00 in).
A tettigoniid known from a specimen made up of hindlegs and wings that are attached to the thorax. Though assigned to the genus, it has been noted that it isn't possibly to fully assign it to the genus.
An indeterminate grylloid known from a mostly complete female specimen. Due to features of the female, it has been suggested that the males of the species would have been able to stridulate.
A possible gryllid known from a mostly complete female specimen. Due to other members of the family being known by wings, it is unknown how the genus compares to those of a similar age.
An orthopteran known from a hind femur originally published under the genus Eremobiites, which was already used at the time and no type species was given.
A Polyneoptera known from the front half of the tegmen, it is unknown if the material actually represents the genus or an orthopteran with it originally being assigned to the family Acrididae.
A possible orthopteran known by a specimen with wings, though it is known which are fore and hind wings. More recent publications suggest that it is most likely either a member of the order Orthoptera or Mantodea.
Pollen assigned to the family Betulaceae, the morphology being the most similar to Corylus and Palaeocarpinus with the more likely genus being Palaeocarpinus due to the presence of macrofossils.
A member of Pentapetaleae known from a flower with in situ pollen. Though the exact placement of the plant is unknown, the pollen does resemble that of the modern genus Kalmia.
Pollen assigned to the family Cupressaceae. The pollen assigned to the family cannot be assigned to a genus, the genera Sequoia and Glyptostrobus are commonly found at the sites.
Gymnosperm macroflora of the Konservat-Lagerstätte Menat
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