The fossil material from the lignite of the Geiseltal is very rich and includes the remains of plants and animals. The floristic material is present in the form of micro and macro remains. The fauna is represented by invertebrates and vertebrates, of the latter there are also a large number of complete skeletons. The good preservation of soft tissue, which is very poorly preserved in fossil form, should be emphasized. Despite the good preservation conditions, a large proportion of the fossils are not autochthonous, but were transported during fossilization, caused by the flow of water. This applies mainly to the finds from the mortuary fields and the streams. The depositional conditions of the fossils can generally be regarded as parautochthonous to partly allochthonous. The exact number of finds is unclear, the inventory of the former Geiseltalmuseum of the University of Halle comprises around 50,000 objects, most of which are vertebrates. During the intensive excavation phase of the 1960s, the collection grew by more than 5830 objects per year. An analysis of more than 10,000 vertebrate remains revealed that almost half of them were
mammals (5,000 pieces), while
reptiles were the second most frequently represented with 2,000 finds. The scientific evaluation of the entire fossil record is still ongoing, and numerous fossil creatures were first described on the basis of the material found in the Geiseltal. The vertebrates alone comprise more than 120
taxa.
Flora Among the quite common plant remains are
pollen and
spores as microflora, which alone occupy more than 100 stratigraphically relevant taxa, the macro-remains are particularly important. These include leaves, twigs, branches, bark and stems as well as fruits, seeds and inflorescences. At least 18
families can be identified from the fruits and seeds alone. In total, more than two dozen families with around 40
genera are known. In addition to
algae,
mosses, primordial
ferns - some of these in concentrated enrichments of ribbed ferns and
climbing ferns, among others - predominantly remains of the more highly developed
seed plants occur. The
gymnosperms are represented by palm ferns, some with whole
fronds, and
conifers with cones and branches. The latter include
pines and
redwoods, some of which occur in clusters. The latter are classified in the
cypress family, of which the extinct genus
Doliostrobus has also survived. The remains of the
angiosperms are much more extensive. Here the
dicotyledons are the largest group with around 20 families. These include
laurel and
beech families. The latter sometimes also form dense leaf layers, such as in the genus
Dryophyllum. Gale shrubs, predominantly fern myrtle, are very common. Plant remains from lime family,
Icacinaceae and
myrtle family, of which
Rhodomyrtophyllum is dominant, are found in large numbers. The long narrow leaves of
Apocynophyllum from the dog poison family are also characteristic. Several up to 44 cm long bark remains with the so-called "monkey hair", fossilized milky sap tubes, attached to them are also assigned to this plant family. Monocotyledons have less diversity. Among these, mainly the
Arecaceae occur in large numbers and are represented by
Sabal and
Phoenicites, among others. However, the frequently transmitted palm tribes cannot be precisely classified taxonomically. Other representatives of the monocotyledons have also been described, for example from the
lily family and the screw tree family.
Fauna Invertebrates Invertebrates were first mentioned in 1913 and are very numerous.
Molluscs, which include
mussels and
snails and which sometimes occurred in masses, are represented by around 20 genera and are ideal for the reconstruction of small biotopes. The same applies to the
ostracods, the
bivalve crustaceans with 10 genera. Further finds of
arthropods are assigned to the
decapod crustaceans. However, these are extremely rare with only 15 specimens and usually only the remains of the armor are preserved. The most frequently found invertebrates are
insects. The
beetles dominate here, with jewel beetles accounting for 28%. The genus
Psiloptera is recorded with eight species, but belongs to the black beetle group. There are also several other beetle families, including the leaf-horned beetles, the
hook beetles and the
leaf beetles. Since the insects are preserved almost exclusively with their backs, the sometimes magnificent coloration of the animals has been preserved, but the exact species assignment cannot be made with certainty in all cases. Flying insects such as
mayflies and
dragonflies have also been detected, but
damselflies only via tiny egg clutches measuring just a few millimetres. These are deposited in double rows on the leaf of an angiosperm and are similar to those left by pond damselflies today ("lestid" type). The group of flying insects also includes fan-winged insects, whereby a
larva of
Pseudococcites from the excretions of a beetle, only 140 μm long and 90 μm wide, forms one of the few examples of this developmental stage of the insect group worldwide. Very small numbers of
spiders and
millipedes occur. The discovery of a stringworm of the genus
Gordius parasitizing on insects is a special feature, as such parasites are extremely rare in the fossil record.
Fish and amphibians The
fish fauna is very extensive with around 2000 specimens, including many complete skeletal individuals, but comprises a total of only 5 families with just as many genera. The most common are the
bony fishes, represented by
Thaumaturus and
Palaeoesox. The former belongs to the
salmonid family, the latter to the pike-like family. Another bony fish is
Anthracoperca, a relative of the perches. With
Cyclurus, there is also a representative of the bony ganoids. Among the
amphibians, the
frogs and
salamanders are the most important, with 200 to 300 specimens of each, plus numerous individual bones. The articulated skeletons of the frogs are all very fragile, with larger skeletal elements close to the body prevailing over smaller ones far from the body. The remains also include a large number of
tadpoles. Quite common is
Eopelobates from the family of European shovel-footed toads, to which today's
spadefoot toad also belongs. Like the latter,
Eopelobates lived largely terrestrially. In contrast, the equally common
Palaeobatinopsis was an
aquatic animal from the
Palaeobatrachidae family, a now extinct group of frogs. Further fossil material may well belong to a closely related representative. Of the newts,
Palaeoproteus is particularly numerous. It is an amphibious
olm that grew up to 25 cm long and had very short limbs.
Tylototriton occurs less frequently. This genus, known as crocodile newts, is still found in East and Southeast Asia and its representatives belong to the
true salamanders. Reptiles and birds Reptiles are among the most common fossil finds and can be assigned to almost a dozen families with around 20 genera. Due to the humid environment, numerous
turtles have survived, especially their shell remains, which are usually flattened by the sediment load. All turtles known from the Geiseltal can be counted among the
Halsberger turtles and include around 500 specimens. These include the genus
Geiselemys from the group of
Old World swamp turtles with a well ossified shell around 18 cm long. Similar dimensions were reached by
Borkenia, which used to belong to the genus
Chrysemys and was thus closely related to the ornamental turtles. At the other end of the size range is
Geochelone (also known as
Barnesia), a land tortoise, which had an average shell length of 50 to 60 cm, possibly up to 120 cm. Another, rather smaller form is
Hummelemys, however, their exact systematic position is disputed.
Palaeoamyda is one of the
soft-shelled turtles, whose shell reached a length of around 30 cm. The animal was well adapted to a life in fresh water. Scale crawlers are recorded with almost 300 complete specimens plus numerous individual finds.
Eolacerta was quite a large animal, reaching a length of 60 cm, with several complete skeletons and additional moulting remains. It was originally counted among the real lizards, but some special
anatomical characteristics, however, led to the establishment of the independent family of the
Eolacertidae, which in turn forms the sister group of the true lizards. A largely complete but heavily fragmented skull is the only evidence of
geckos to date. It belongs to the genus
Geiseleptes, for which in turn a closer relationship to today's European leaf-fingered gecko can be considered. The
iguanas include
Geiseltaliellus, a slightly built lizard with an extremely long tail and fine skin scales, which was probably an arboreal dweller. Due to the short forelimbs, it is assumed that Geiseltaliellus, like today's
basilisks, could occasionally only move on its hind legs. Ophisauriscus can in turn be assigned to the slithers and is related to the glass slithers. The snake-like animals still had rudimentary forelimbs and hind limbs. More than 20 finds have been documented, ranging in condition from almost complete skeletons to disarticulated individual finds and remnants of skin armor. The individual bone plates of the former scales differ markedly in shape and ornamentation from today's forms. Only rarely do relatives of today's
monitor lizards occur. A poorly preserved partial skeleton of
Eosaniwa has a 19 cm long skull, making this lizard one of the largest in the Geiseltal. A good 60 complete specimens can be counted among the
snakes, including two genera of giant snakes from the
Boa family.
Paleryx was up to 2.3 m long, a total of 243 vertebrae could be recognized in a largely complete specimen. Furthermore,
Palaeopython occurs, as well as some rolling snakes. Crocodiles are also documented in large numbers, with around 120 complete skeletons, as well as countless isolated bones and teeth. The
alligators are represented by
Allognathosuchus, which was only about 0.8 m long and had a rather narrow snout.
Diplocynodon is one of the most common forms of crocodile in the Geiseltal and is classified in the extinct group of the Diplocynodontidae. It lived in smaller bodies of water and reached a good 1.3 m in length. A special find includes an almost complete skeleton with bone armor and five eggs in close proximity; it is one of the world's rare examples of brood care in fossil crocodiles. At a good 1.7 m in length,
Boverisuchus, a representative of the
true crocodiles, is somewhat larger and also numerous. Due to its relatively long limbs and hoof-like spread end phalanges of the toes, this crocodile is assumed to have a more terrestrial lifestyle. The largest predator in the Geiseltal was
Asiatosuchus with a body length of around 3 m. It was ecologically similar to today's
Nile crocodile and preferred open waters. It is documented with several complete skeletons. In contrast,
Bergisuchus appeared extremely rarely with only a few lower jaw fragments, a possibly also more land-dwelling animal that was small in stature at 1.5 m in length. In contrast to the other forms,
Bergisuchus represents a primitive and more distant crocodilian relative from the
Sebecosuchia group. Detailed investigations revealed that all crocodiles in the Geiseltal occupied different
ecological niches. There are also fragments of crocodile eggs and numerous
gastroliths (stomach stones), which prove the presence of crocodiles even without fossil preservation. Rather rare are the remains of birds, which have been identified with more than half a dozen families and a good twice as many identifiable genera. Complete skeletons were rarely observed; disarticulated parts and limb remains are more common. In the latter, the joint ends are sometimes missing. Part of the bird fauna is therefore interpreted as food remains of crocodiles and large snakes. In addition, the proportion of female animals is quite high, which can be recognized by the formation of medullary bones, a
calcium-rich bone substance on the medullary tubes of the long bones, which is formed during the development of the eggs. The
Palaeotis is a relatively small representative of the prehistoric jawed birds, which has been identified by its rear extremities and also by a partial skeleton. It was originally considered to be related to the
bustard, but later considered to be in the ancestral line of today's Ostriches. In addition to the clear characteristics that
Palaeotis has in common with the ancient pine birds, some characteristics of the hind legs are more reminiscent of today's cranes. With a total height of up to 1.8 m,
Gastornis (also called
Diatryma). There are over three dozen finds of this large ground-running bird, including several leg bones, but also skull remains and parts of the wings, which represent the largest collection of all sites in Europe. For a long time,
Gastornis was considered a carnivore, but
isotope analysiss on some bones from the Geiseltal showed that the bird was mainly vegetarian. Eocathartes was originally counted among the true carnivorous birds. This was supposed to represent the
New World vultures in the Geiseltal and has been described on the basis of parts of the body skeleton as well as feathers. Furthermore, as a member of the
hornbills, Geiseloceros had an exotic status. It was documented by leg bones and connected wing remains, on which the shimmering blue wing feathers are also recognizable. Today, both taxa are classified as
Strigogyps from the family
Ameghinornithidae, a group of larger ratites with closer relationships to the
seriemas. A large foot bone, which can probably be attributed to
Dynamopterus, also belongs to a similar relationship. There is also evidence of
Aegialornis, a fossil sailor, via an upper arm bone. Smaller representatives of the birds are found with the mouse birds, of which several partial skeletons are available, such as those of
Eoglaucidium and
Selmes. With
Plesiocathartes, identified by several limb bones, a fossil predecessor of today's
courols living on Madagascar is documented. Individual bone elements also refer to
Messelirrisor, which represents the hornbills and hops. In addition, hawk-like species were present, but these can be determined with less certainty, but possibly belong to
Masillaraptor.
Mammals The very extensive
mammal fauna comprises remains from around two dozen families with more than 50 genera. Among the most primitive representatives are the
marsupials, which are represented by
Peratherium and
Amphiperatherium. There are several skulls and lower jaw remains of
Peratherium in particular. Both genera are ancestors of the South American
opossum. Taxonomically difficult to classify is
Microtarsioides, as a relatively complete skeleton has survived, but it comes from a juvenile animal. The Higher mammals are considerably more extensive and diverse. A few characteristically strongly shaped long bones are assigned to
Eurotamandua. Originally considered a member of today's
anteaters, but according to further investigations it represents a basal form of the
pangolins with a similar way of life. The Small Mammals include
Heterohyus, an
Apatemyid characterized by two elongated fingers and circular-arched incisors. The enlarged front teeth were used to gnaw tree bark, and the long fingers were used to drill into crevices and cracks for insects. In its way of life,
Heterohyus thus resembled today's
pinniped of Madagascar. A partial skeleton and a lower jaw of the
Leptictidium have been found. This predatory animal moved by jumping on its hind legs, which indicates the basal position of the
Leptictida, as this no longer occurs in modern insectivores. The rarely occurring
Buxolestes, on the other hand, was a stocky, semi-aquatic animal from the
Pantolestidae group, whose appearance and way of life corresponded roughly to today's
otters. The Paroxyclaenidae are directly related, but only a 12 cm long skull of
Vulpavoides and a 5 cm long lower jaw fragment of
Pugiodens are documented. The short-snouted animals were probably arboreal. Their remains were originally classified as "
Creodonta", later as "
Condylarthra". The insectivore
Saturninia from the group
Nyctitheriidae is also very rare, but with several, partly completely toothed lower jaws. Rodents are rare and occurred in only a few forms.
Ailuravus was very large, around one meter long, and resembled modern
squirrels. Few dentition remains come from the again much smaller
Masillamys, the
Messelmaus named after the
Messel Pit with a very long tail and a total length of 40 cm. Also significant are the remains of
bats, of which 25 complete skeletons with parts of the wing skin are known. They can largely be assigned to the genera
Matthesia and
Cecilionycteris. They belong to the
Palaeochiropterygidae family, whose representatives already hunted with
echolocations of 30 to 70 kHz due to the structure of the ear ossicles. Remarkable remains also come from the
primates. Particularly important here are the
Adapidae, of which several genera occurred in the Geiseltal and which may have been precursors of today's
lemurs.
Europolemur has survived with several skulls and mandibles. One of the few almost complete skeletons of an adapid primate in the world is
Godinotia. This early primate, which was closely related to the
Darwinius known from the Messel Pit, had a distinctly short facial skull and large eye sockets, indicating a nocturnal lifestyle.
Nannopithex is very diverse with several species, but belongs to a more modern family of primates
. The now extinct "Creodonta" were more predatory animals. These include above all the
Hyaenodonta with around 50 finds, including mainly lower jaws, but also some skulls, upper jaw fragments and isolated remains of the locomotor system. These include
Eurotherium,
Matthodon,
Prodissopsalis and
Leonhardtina, the latter two being the most common and each comprising around a dozen fossils. Overall, all creodonts found in the Geisel Valley were relatively small, with a complete skull of
Eurotherium measuring around 12 cm in length. A crushed skull and a single posterior upper
premolar represent the true
carnivores and were originally classified as
Miacis, but are now classified as
Quercygale. The fossil material of the
even-toed ungulates is comparatively extensive, with around 170 finds from around 60 individuals. The artiodactyls of the Geiseltal were all characterized by a very ancient physique with an upwardly arched back, very long tails and short front and long hind legs. They were all smaller than today's relatives and reached a maximum of
piglet size. One of the most primitive cloven-hoofed animals was
Diacodexis from the
Diacodexeidae group, although only a few bone remains have survived. The
Eurodexis from the closely related group of the
Dichobunidae is somewhat more developed, as evidenced by a crushed skull. Its closer relatives include
Messelobunodon and
Aumelasia, both of which are also documented with a few finds. The representatives of the somewhat more developed
Choeropotamidae, which are more closely related to the
hippopotamus and were
endemic in today's Europe, have been observed most frequently. An almost complete skeleton is available from
Masillabune, while
Hallebune is only represented by a few fragments of teeth. Several skeletal remains, including seven almost complete ones, can be attributed to
Amphirhagatherium. This approximately 70 cm long and about 4 kg heavy animal was not only the most common, but also the largest cloven-hoofed animal of the Geiseltal and is widely distributed over the Lower and Middle Coal. In addition, a few remains of other even-toed ungulates such as
Haplobunodon or
Rhagatherium are known. The
odd-toed ungulates have the most extensive finds. These also had an ancient physique with an arched back and four toes on the front feet and three on the hind feet, which today only occurs in
tapirs. Over 310 lower and 120 upper jaw remains, including two complete skeletons, come from the horse relatives from the
Palaeotheriidae group. Of particular note is the well-known prehistoric horse
Propalaeotherium, which is represented by several species. A complete skeleton with a 56 cm long torso, a 20 cm long skull and a shoulder height of 40 cm was discovered in 1933. Other genera that occur are
Lophiotherium,
Hallensia and
Eurohippus. There are only a few teeth of the very rare
Plagiolophus. With almost 180 individuals,
Lophiodon, a tapir relative with a body length of 2.5 m and a shoulder height of 1 m, is also very common and represents the largest representative of the mammals from the Geiseltal. On an area of 131 m2 alone, 110 individuals were discovered, probably the remains of a crocodile feeding ground. Fossil finds of
Lophiodon are known from all fossil-bearing seams, whereby the genus underwent a significant increase in body size from bottom to top. In addition, its relative
Hyrachyus appeared rarer and was found with about 75 dentition remains and some parts of the body skeleton.
Hyrachyus was more modern in construction than
Lophiodon and stands at the base of the evolution of rhinoceroses and tapirs.
Soft tissue, chemofossils and food residues Remains of
soft parts have also been preserved in the lignite of the Geiseltal, which is extremely rare. Fossil soft tissues were first discovered in the Geiseltal in 1934, making them one of the very first such finds from the
Eocene. The discoveries were only made with the development of the lacquer film method. This made it possible to recognize the fine scale relief in individual fishes, for example in
Thaumaturus, as well as in pangolins and more rarely in crocodiles. The skin of numerous frogs could be examined, the individual layers of which, the epidermis and
dermis, can be recognized down to the individual
cells. Feathers have been found on some remains of birds, some of which were colored; the flight skin of
bats has survived. In mammals, such as
Amphirhagatherium and more rarely
Propalaeotherium, parts of the hair coat have been found. It was also possible to document muscles, cartilage and the like, right down to
blood cells. In addition, the original coloration of certain soft parts, especially the skin, could be identified. For example, the fish palaeoesox had a zebra pattern on its body and a dark-colored back, while a greenish skin tone could be observed in frogs. In insects, the color shades of the animals are preserved, in plants the
chlorophyll has survived. Such chemofossils also include "monkey hair", which is often found in large quantities. These are fibrous, light-brown structures flattened by storage in the lignite, which have been preserved through natural
sulphur volcanization. They represent fossilized milky sap tubes of rubber-producing woody plants from the dog poison family, of which leaves of the genus
Apocynophyllum are present from the Geiseltal. According to the recent genus
Couma, however, the "monkey hair" is referred to
Coumoxylon as a
form taxon. Other finds are mainly the food remains of numerous animals, which were also discovered early on, for example in 1935 in the tapir relative
Lophiodon as a greenish plant mass. They have also been found in other mammals such as the prehistoric horse
Propalaeotherium and the even-toed ungulate
Amphirhagatherium, also of the ostrich-like bird
Palaeotis. At least 100 specimens of
coprolites and additional fragments have also been documented. They are mostly in ovoid or sausage-like form with lengths ranging from a few millimetres to a decimetre and sometimes contain remains of bones, claws or plants. Various reptiles and mammals can be assumed to have caused them. Some of the fossilized faecal remains also contain
gastroliths, possibly from crocodiles. Crocodiles have occasionally left bite marks on mammal bones and turtle shells.
Dating The faunistic remains, especially of mammals, are important for the exact age classification of the lignite of the Geiseltal, which also allows a comparison with other sites and outcrops. This
biostratigraphic This biostratigraphic age determination is largely based on the changes in the dental morphology of certain mammal groups, which allows the chronological occurrence of extinct species and genera to be determined. The first vertebrate finds discovered at the beginning of the 20th century, tooth remains of the tapir relative
Lophiodon, led to the classification of the lignite in the geological epoch of the Middle
Eocene. This also determined the more precise relative age of the lignites, which had previously only been suspected. The Middle Eocene is dated to an age of 47.8 to 41.3 million years and consists of the lower stage Lutetian and the upper stage
Bartonian. The exact age of the Geiseltal lignites can be determined relatively precisely by the occurrence of certain mammal forms. This places the rich finds of the Lower Coal up to the Upper Middle Coal in the Geiseltalian zone, a stage within the stratigraphy of European land mammals (
European Land Mammal Ages, ELMA). The Geiseltalian serves as a reference for the Geiseltal fauna and also forms a middle section of the Lutetian. The few finds of the Upper Coal are referred to a younger zone, the Robiacium. The beginning of the Geiseltalian is accompanied by the appearance of early forms of the prehistoric horse
Propalaeotherium, but also its relative
Lophiotherium or the primate
Europolemur, while the end is indicated by the first appearance of primates such as
Adapis. Absolute dating using
radiometric measurement methods are not available from the Geiseltal. However, they have been carried out at sites of approximately the same age. For example, data determined using
potassium-argon dating originate from the important
Messel Pit in
Hesse, which from a biostratigraphic point of view corresponds to the lower coal section of the Geiseltal, and yielded an age of 47.8 million years. As the
basalt examined originates from an area beneath the fossil-bearing lake sediments of the Messel Pit, the age value is to be regarded as the maximum age, meaning that the finds there are somewhat younger (
terminus post quem). The
Eckfelder Maar in Rhineland-Palatinate represents a biostratigraphic equivalent to the upper Middle Coal. Data from
pyroclasts obtained there using the same measurement method, also below the find layer, yielded a value of 44.3 million years. This is also to be regarded as the lowest age. This means that the age classification of the Geiseltalium, to which an age of 47.4 to 43.4 million years is attributed today, and thus of the finds from the Geiseltal, can be regarded as quite reliable.
Landscape reconstruction The numerous plant and animal remains, as well as the large amount of geological data, allow a fairly accurate reconstruction of the former landscape conditions. According to this, the Geiseltal in the Middle Eocene was a water-rich moorland landscape that extended in a north–south direction over a length of four to five kilometers and was located near the coast at a bay that penetrated far inland. This land incision, known as the Central German Estuary, was at least temporarily exposed to the
tides based on pollen finds of the palm genus
Nypa from the Middle Coal, formed numerous bays and local depressions and basins, especially in the middle section of the
Eocene (more precisely in the Lutetian), which promoted the formation of lignite, such as the Helmstedt lignite field in the northwest or the lignite deposits of
Egeln and
Edderitz further south. This branched system also led to the formation of
marine, brackish and
fluviatile and limnic deposits in the Geiseltal deposits (the main agents) as legacies of the
estuary. The subtropical climate at that time contributed to the formation of numerous bogs, ponds and pools with a rich vegetation on the edge of the estuary. The onset of coalification of the dead plant material led to the formation of thick lignite seams over a period of six to possibly eight million years. The area was bordered to the south by a shell limestone plateau with steep slopes sloping down to the north. The plateau itself was partly
karstified. The
chemical weathering created limestone water which penetrated the moorland and ensured the excellent preservation of the fossils. The bog area was interspersed with numerous small pools and ponds, around eight to ten meters in diameter, which are indicated by collapse funnels and served as drinking places for the fossil fauna.
Acrostichum,
Myricaceae and
Restionaceae plant communities grew in the adjacent bank area. In the wider area there were shrub and forest landscapes of palm-pine forests, interspersed with
sequoias and other
conifers and
deciduous trees, which were rich in herbs and light and had several growth levels. These forests were crisscrossed by a network of
meandering watercourses that periodically overflowed their banks. Towards the south in the direction of the Muschelkalk range, these forests merged into a dense
primeval forest of
laurel plants. Due to the relative proximity to the coast, the altitude at that time probably did not exceed 50 m above sea level. The climate was generally subtropical with frost-free and dry winters with an average temperature of at least 5 °C and humid summers with a growing season of up to nine months and an average of 25 °C in the warmest month, as determined by the numerous fruits and seeds. The annual precipitation was probably around 2070 mm. Due to the significant differences in temperature during the summer and winter months, the landscape was subject to an annual periodicity of rainy and dry seasons, which can also be demonstrated by tree rings and a fine warve of the lignite. As a result, leaf fall can be regarded as probable, so that the leaves formed a loose litter layer on the ground. From the lower to the middle coal, however, an increasing dryness of the climate could be determined. This diverse landscape was inhabited by numerous animals. Leaf- and fruit-eating mammals such as
Lophiodon,
Propalaeotherium and
Amphirhagatherium lived mainly in the forests. The rich insect fauna in turn provided food for numerous other animals, such as frogs, frogs and pangolins, but also
leptictids, bats and some primates. The ponds and pools were home to aquatic or amphibious animals. Of particular note are the numerous crocodile forms, which, like today, preferred a much warmer climate and thus also represent an important climate indicator. The richness of the
ecosystems and the long depositional period of around 3 million years also reveals certain networks of relationships that go beyond pure food chains. This can be seen, for example, in
Lophiodon and
Propalaeotherium, which represent the two most common mammal forms and probably had a special ecological relationship due to the use of the same food resources. However, while
Lophiodon increased in body size over time (averaging 124 kg in the Lower Coal and 223 kg in the Upper Coal),
Propalaeotherium decreased in weight (averaging 39 kg in the Lower Coal and 26 kg in the Upper Middle Coal). This is possibly an example of the gradual adaptation to different ecological niches to avoid too strong
competition with each other.
Comparison with regionally and nationally significant sites From the regional neighborhood of the Geiseltal, the equally old lignite outcrops from the
Leipzig area (the Weißelster basin) or the
Helmstedt area are of particular importance. Although there are no vertebrate remains here, countless floristic finds are known. For example, macro-remains in the form of conifer cones and palm leaves are found in the open-cast mines near Helmstedt, while numerous leaf finds of dicotyledonouss come from the Profen open-cast mine. The general vegetation history determined on the basis of the microflora largely corresponds to that of the Geiseltal. Vertebrate sites of the same age are not known from the immediate region. However, the
Walbeck Fossil Deposit in the northwest of Saxony-Anhalt is one of the most extensive mammal communities in the world from the Middle
Palaeocene period almost 60 million years ago. The fauna, comprising several thousand bone and tooth remains, differs from that of the Geiseltal in the dominance of prehistoric mammals from the groups of Procreodi, "Condylarthra" or Leptictida, while representatives of more modern, still existing lineages such as the primates occur rather rarely or are completely absent, as in the even-toed ungulates and odd-toed ungulates. Walbeck thus represents an important testimony from the early phase of
radiation of mammals shortly after the extinction of the
dinosaurs. The
Messel Pit in Hesse and the
Eckfelder Maar in Rhineland-Palatinate are of outstanding importance in a supra-regional comparison. Both represent sites in former
maars, whereby Messel is roughly contemporaneous with the Lower Coal of the Geiseltal, Eckfeld with the Upper Middle Coal. In addition to plant and invertebrate finds, a large number of vertebrate remains are known from both sites, currently comprising around 130
taxa in Messel, whereas the number of finds from Eckefeld is comparatively smaller. While the composition of the mammal fauna generally shows similarities, there are clear differences in the details. For example, rodents and bats are underrepresented in the Geiseltal and in Eckfeld, but are more common and more diverse in Messel. In contrast, Messel is characterized by a smaller number of primate and even-toed ungulate forms, which in turn are well and diversely documented in the Geiseltal and Eckfeld, with striking differences reflected in the occurrence of different genera. Similar differences can also be identified for individual mammal genera, such as
Lophiodon from the odd-toed ungulate group, which is one of the dominant forms in the Geiseltal, but in Messel was only found with a young animal and individual tooth finds, in Eckfeld with a lower jaw and also a few tooth remains. Remarkable in Eckfeld is the previous absence of ancient mammal groups such as the "Creodonta" and "Condylarthra", which occur to a small extent at least in Messel and in the Geiseltal. Differences can also be seen in other groups of finds. For example, the jewel beetles are relatively common in the Geiseltal with more than a quarter of all beetle finds, whereas in Messel they are rather rare with less than a tenth, although there is a generally higher diversity of forms of beetles overall. The fact that only a few forms of jewel beetles occur simultaneously at both sites indicates significant ecological differences, which are also reflected in the sometimes differing diversity of the various plant and animal groups and shows that the individual fossil deposits each represent only a section of the rich landscape at that time. == Research history ==