Walbeck fossil deposit
Coordinates: 52 ° 17 ′ 16 ″ N , 11 ° 3 ′ 51 ″ E
The Walbeck fossil deposit is an important site in the western part of Saxony-Anhalt . It is located near the village of Walbeck in the Aller Valley . Numerous fossil mammal and bird remains were found in a karst fissure in the limestone , which, due to the composition of the mammal fauna, can be found in the Middle Paleocene around 60 million years ago. The mammal fauna is dominated by numerous, sometimes primitive, small mammals and by the larger, now extinct arctocyonids , hovering predators and omnivores. Among the birds, in addition to the high diversity, one of the world's oldest records of the giant ratite Gastornis is remarkable. The Walbeck find complex is one of the most extensive of all and is also the only known one in Germany from this geological epoch. It is an important testimony to the first development of mammals shortly after the dinosaurs became extinct .
Geographical location
The Walbeck fossil deposit is located in the northern Harz foreland just a few kilometers south of the village of Weferlingen in the Aller valley in the north west of Saxony-Anhalt . The next largest city is Helmstedt 8 km southwest in the neighboring Lower Saxony . The small town of Walbeck , which gave its name to the site to the north of it, borders on the Lappwald .
geology
The find area itself is on the southwest edge of the Weferlingen-Schönebeck-Scholle (also called Weferlingen-Schönebecker-Triasplatte). The Weferlingen-Schönebeck-Scholle is a 10 to 12 km wide and around 110 km long inguinal floe , which is generally inclined to the south-west and directed from north-north-west to south-south-east. It is broken down several times by numerous longitudinal and transverse faults . The red sandstone that formed 251 to 243 million years ago is mainly deposited here ; only in the north are the remains of the underlying Zechstein . Further south, towards the edge of the Allertal valley , the rocks of the overlying shell limestone follow from 243 to 235 million years ago and then the Keuper , the youngest rock unit of the plaice.
The Lower Muschelkalk of the Jena Formation near Walbeck is largely made up of thin-plate corrugated limestone from the oolite bank and interspersed with yellow-colored, dolomite-like limestone. These were exposed to strong karstification and are now characterized by numerous crevices. The crevices mostly follow rock fissures in the shell limestone and so often point into the subsoil at an angle of 45 °, they often cross each other, and they are also filled with a wide variety of sediments . One of these crevices was directed north-south and reached about 14 m deep into the shell limestone. It was filled with a weathering tone , in which a lens made of initially marbled , but later strongly loamy sand was embedded in the lower area . The numerous bones and tooth remnants of a richly shaped fauna of the Middle Paleocene were found in the spatially narrowly limited sand lens .
Finds
The faunistic finds from the sand lens include more than 10,000 objects that can be assigned to amphibians , reptiles , birds and mammals . These include more than 6000 mammal fossil finds, as well as more than 450 bird remains. Above all, the bird remains represent one of the largest complex of finds from the Paleocene and show a high degree of diversity compared to other sites of the same age . The storage in a karst fissure indicates that the finds from the Paleocene were relocated. The fossils are partially unrolled and badly shattered, only more compact bones such as the petrous bone of the skull or the joint ends of long bones and teeth are completely present. However, numerous bones could be put back together. Based on the overall findings, it is assumed that the fossil material was embedded in the karst fissure as a common unit during a one-off event.
In addition to the unequivocally Paleocene finds, fossilized remains of nautilids and sea lilies from the shell limestone were also found. The appearance of fossils of land and aquatic animals, such as the shoulder blade of the primeval whale Basilosaurus from the Lower Oligocene, suggests that the Paleocene finds were embedded in the karst fissure around the time - probably with the Rupel transgression around 33 million years ago when the then north-western European Tertiary Sea expanded far south into what is now Saxony-Anhalt. The numerous broken bones of the Paleocene fauna may be due to the effects of the ocean surf.
Remnants of the flora of the Paleocene are not known from the karst fissure. In a small, halokinetisch incurred edge of the sink Allertals in Walbeck but a rich macroflora with fruits, seeds and leaves has been preserved that the rare European plant fossils from the Maastrichtian of the Upper Cretaceous include above 72 to 66 million years ago.
Amphibians and reptiles
The numerous fossil remains of the amphibians include fragile vertebrae of several forms of the tail amphibian , including newts such as Woltersdorfiella and Geyeriella , but also the bones of frogs . Reptiles are less common, but occur with some crocodile skin bone plates , such as Diplocynodon and Pristichampus , and several remains of the jaws and vertebrae of scale creepers , including representatives of agamas and iguanas .
Birds
The bird fauna is represented by elements of the musculoskeletal system and the skull and can be assigned to at least five species. At the moment, however, it is only possible to a limited extent to bring them closer to one of the higher groups of birds living today. Almost all birds found in Walbeck are flightless forms. This includes one of the world's oldest records of the giant bird Gastornis (sometimes also called Diatryma ), which was determined on the basis of a 7 cm long raven leg . Fissure avis also contains only a few skeletal elements, such as individual wing bones and a raven bone . This bird possibly belongs to the closer relationship of the cocktails and was first described on the basis of the Walbeck fossils . Almost a third of the avine finds can be attributed to Walbeckornis , although a large part of the body skeleton has survived. The genus resembles the claw-like Messelornithidae from the Messel Pit in Hesse, which dates back to the Middle Eocene , and occurs in Walbeck with three species, including the dominant W. creber . The second most common bird shape in Walbeck is Gradiornis from the broader relationship of the long-legged Seriemas in today's South America , which only includes a little more than two dozen objects. With Berruornis a very primitive representative of the owls could also be discovered. Its fossil material amounts to an approximately 5.7 cm long tarsometatarsus and a 3.1 cm long, bird of prey-shaped intermaxillary bone . Other bird finds have not yet been classified more precisely.
Mammals
The very extensive mammal fauna consists of representatives of around 16 genera from at least 7 orders . The most primitive members of mammals include insectivore-like forms such as the bustylus , which is only covered by two posterior molars. Closely related or possibly identical to Bustylus is the more common Afrodon , of which postcranial skeletal elements are present in addition to tooth material . Both genera are characterized by five pointed enamel cusps on the molars , which suggests that they are mainly insect food. With an assumed body weight of 7 to 8 g, determined on the basis of the average 1.4 mm long molars, these animals belonging to the Adapisoriculidae belong to the smallest mammals of Walbeck. The Adapisoriculidae represent so far little investigated representatives of the early higher mammals , but were in part also considered members of the marsupials . Diaphyodectes had a comparable tooth morphology , which was also similar to today's insectivores, and of which around a dozen finds, mainly remains of teeth, have come down to us. This small animal from the now extinct group of the Leptictida , probably only around 40 g , is a phylogenetic predecessor form of Leptictidium , which has excellently preserved fossils from the Messel pit and is still known from the Geiseltal . The Leptictidae were characterized by short front and long hind legs and lived predatory, with the prey jumping on the hind legs. The Cimolesta were probably closely related to the Leptictiden and are also extinct today. Aboletylestes and Pagonomus in Walbeck could be identified from this group . From Pagonomus however, are only a few teeth.
Plesiadapis represents the primates as a very primitive representativeand belongs to aside branch of the apes that became extinctin the Eocene . The finds from Walbeck, which include around 300 objects such as skull remains and parts of the body skeleton, are among the oldest known finds of this group of mammals. Overall, the animal weighed just under 390 g, about as much as today's shrew and, due to the shape of the molar teeth, probably mainly fed on insects . Much smaller and represented with only a few skeletal elements, including a humerus , is Saxonella , but it represents a different line of early primates. To the ancestors of today's elephant shrews are Walbeckodon and Prolouisina . The former is documented through numerous, around 1.5 cm long and relatively gracefully built lower jaw finds and postcranial skeletal parts, which include around 600 objects, of the latter significantly less dentition material came to light. Both are part of the Louisinidae group, which is the basis of the phylogenetic development of the elephant. The same applies to Adapisorex , which is very numerous with over 1200 finds. Originally it was placed among today's real insectivores and formed an ancestor of today's hedgehogs . A peculiarity is marked by a few upper molars, which can possibly be referred to a sister taxon of today's bats and thus belong to the earliest records from this family group. So far, however, the finds have not yet beenassigned to aspecific taxon .
The largest representatives of the mammals in Walbeck are the Procreodi and Condylarthra , which today represent extinct lines. Above all, the Procreodi, crouching and sometimes predatory animals, take up almost half of the total mammal finds. The medium-sized genera Arctocyon and Arctocyonides from the Arctocyonidae community are of particular importance here . They each combine around 1100 and 1950 found objects, which belong to a total of 250 individuals. The approximately German shepherd-sized animals are more likely to be omnivores due to the nature of the rear teeth. On the other hand, the Mentoclaenodon, which specializes in meat nutrition, occurs rarely . Due to the skull length of 15 cm, this can be considered the largest mammal in Walbeck. Characterized is Mentoclaenodon by long, curved saber-like fangs in the upper jaw and a massive lower jaw with strongly developed chin area. This feature was also the inspiration for the scientific generic name, which means "magnificent chin". In addition to a few remains of the body skeleton, two almost complete lower jaws have survived. From the heterogeneous group of the condylar arthra , the relatively large paratricuspiodon, comprising a few remains of teeth, should be mentioned.
Smaller mammals weighing less than 400 g predominate. More than half of the identified genera can be counted here. Another interesting aspect of the composition of the mammal fauna is the juxtaposition of numerous archaic forms of the early higher mammals such as the Adapisoriculidae, Leptictida and Cimolesta to some pre-forms of lines still existing today, such as the primates and the insectivores. It is noteworthy that the very primeval mammals are missing, including the Multituberculata , which otherwise spread beyond the Cretaceous-Tertiary boundary around 65 million years ago, often well into the Paleocene . The unusual composition of the mammal fauna with a high proportion of arctocyonids is probably a result of selection processes during the relocation through the Oligocene Sea.
Dating
Due to the storage of the fossil-bearing sands in a karst fissure, a relative stratigraphic age dating is not possible. The composition of the mammal fauna enables a biostratigraphic assessment of the age. Already at the beginning of the discovery of the Walbeck fossils, Johannes Weigelt recognized the great age of the fauna and dated them to the geological epoch of the Paleocene 65 to 56 million years ago via the appearance of the Procreodi and the early primates . Later analyzes suggested a position within the Thanetium level in the Upper Paleocene, which was determined with the help of the occurrence of the insectivore-like Afrodon , which also occurs in such ancient sites as Adrar Mgorn in Morocco and Cernay-lès-Reims in France . In more recent investigative approaches, however, a somewhat older age is assumed, so that Walbeck is now classified in the level of the Seelandium about 60 million years ago. The reason for this is the occurrence of more primitive features in some mammals compared to the findings of Cernay. The tooth features of, among others, the elephant-type Adapisorex and the Adapisoriculiden Bustylus , but also of the Procreoden Arctocyonides, resemble the older finds from Maret in Belgium , which can clearly be assigned to the Seelandium, while the finds from Cernay appear phylogenetically more recent.
Landscape reconstruction
Only a few conclusions can be drawn about the former landscape. Due to the common occurrence of smaller and larger animal species, it is concluded that the existing fossil material will be fully recorded during the recovery. Since land-living animals predominate and no evidence of clearly tree-dwelling birds was found, the researchers assume a more open habitat . However, the presence of the primates indicates the presence of trees and bushes.
Research history
The shell limestone north of Walbeck served as a raw material source for a limestone quarry. There the fossil-bearing crevice, which reached under the quarry floor, was discovered by a worker in February 1939. A find report reached Johannes Weigelt , who was in charge of the excavations in the Geiseltal at the time, via the teacher and director of the Gardelegen museum . Based on the first finds, which included the lower jaws of the primate Plesiadapis and the Procreoden Arctocyonides , Weigelt recognized the old age of the site and immediately initiated investigations on site. The entire remaining contents of the column, around 33 t or 16,5 m³ has been in several load trains to Hall for Martin Luther University of Halle-Wittenberg spent and screened there and slurried to also win the smallest bone particles; the sandy find layer material amounted to around 8 m³. However, another 4 m³ had already been transported to a spoil dump and covered with further material. These deposited remains of the find layer were searched for fossils on site in a two-month excavation campaign, during which the overburden material, over 100 m³ in total, had to be removed. Based on this work, the Walbeck fossil deposit is considered to be almost completely investigated. Hoped for further fossil-bearing karst crevices could not be discovered in the following period. The finds are now in the geoscientific collections of the University of Halle.
Individual evidence
- ↑ a b c d e f g Johannes Weigelt: The discovery of the oldest tertiary mammal fauna in Germany to date. Nova Acta Leopoldina NF 7, 1939, pp. 515-528
- ↑ a b c d Walter Steiner: Europe in the primeval times. The geological development of our continent from prehistoric times to today. Munich, 1993, pp. 1–192 (p. 161)
- ^ Karl-Heinz Radzinski, Gerhard Beutler, Hans Joachim Franzke and Bodo-Carlo Ehling: Northern Harz foreland (Subherzyn). In: Gerhard H. Bachmann, Bodo-Carlo Ehling, Rudolf Eichner, Max Schwab (eds.): Geology of Saxony-Anhalt. Stuttgart 2008, pp. 385-408.
- ↑ a b c Gerhard H. Bachmann: Upper Palaeocene of Walbeck. In: Gerhard H. Bachmann, Bodo-Carlo Ehling, Rudolf Eichner, Max Schwab (eds.): Geology of Saxony-Anhalt. Stuttgart 2008, pp. 336-337.
- ↑ a b c d e f Kenneth D. Rose, Gerhard Storch and Katrin Krohmann: Small-mammal postcrania from the middle Paleocene of Walbeck, Germany. Paleontological Journal 2013
- ↑ a b c Gerald Mayr: The birds from the Paleocene fissure filling of Walbeck (Germany). Journal of Vertebrate Paleontology 27 (2), 2007, pp. 394-408
- ^ Lutz Kunzmann and Dieter Hans Mai: The first record of fossil Metasequoia (Cupressaceae) from continental Europe. Review of Palaeobotany and Palynology 164 (3), 2011, pp. 247-250
- ↑ Volker Wilde: Paleobotanical fossil deposits. In: Gerhard H. Bachmann, Bodo-Carlo Ehling, Rudolf Eichner, Max Schwab (eds.): Geology of Saxony-Anhalt. Stuttgart 2008, pp. 343-345.
- ↑ Johannes Weigelt: The new discoveries of Walbeck. Angewandte Chemie 54 (11/12), 1941, pp. 141-142
- ↑ Gerald Mayr: An owl from the Paleocene of Walbeck, Germany. Communications from the Museum für Naturkunde Berlin, Geoscientific Series 5, 2002, pp. 283–288
- ↑ Emmanuel Gheerbrant and Donald E. Russell: Bustylus cernaysi nov. gen., nov. sp., nouvel Adapisoricvulidé (Mammalia, Eutheria) Paléocène d'Europe. Geobios 24, 1991, pp. 467-481
- ↑ a b Eric de Bast, Etienne Steurbaut and Thierry Smith: New mammals from the marine Selandian of Maret, Belgium, and their implications for the age of the Paleocene continental deposits of Walbeck, Germany. Geologica Belgica 16 (4), 2013, pp. 236-244
- ^ A b Eric de Bast and Thierry Smith: Diversity of the adapisoriculid mammals from the early Palaeocene of Hainin, Belgium. Acta Palaeontologica Polonica 57 (1), 2012, pp. 35-52
- ↑ a b Gerhard Storch: Skeletal remains of a diminutive primate from the Paleocene of Germany. Naturwissenschaften 95, 2008, pp. 927-930
- ↑ Jerry J. Hooker and Donald E. Russell: Early Palaeogene Louisinidae (Macroscelidea, Mammalia), their relationships and north European diversity. Zoological Journal of the Linnean Society 164, 2012, pp. 856-936
- ↑ Jerry J. Hooker: A primitive emballonurid bat (Chiroptera, Mammalia) from the earliest Eocene of England. Palaeovertebrata 25, 1996, pp. 287-300
- ↑ Johannes Weigelt: The Arctocyoniden von Walbeck. Freiberger Forschungsungen C 77, 1960, pp. 1-241
- ^ Emmanuel Gheerbrant and Donald E. Russell: Presence of the genus Afrodon [Mammalia, Lipotyphla (?), Adapisoriculidae] in Europe; new data for the problem of trans-Tethyan relations between Africa and Europe around the K / T boundary. Palaeogeography, Palaeoclimatology, Palaeoecology 76, 1989, pp. 1-15