Amphirhagatherium
| Amphirhagatherium | ||||||||||||
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Live reconstruction of Amphirhagatherium |
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| Temporal occurrence | ||||||||||||
| middle Eocene to early Oligocene | ||||||||||||
| 48 to 34 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Amphirhagatherium | ||||||||||||
| Depéret , 1908 | ||||||||||||
Amphirhagatherium is an extinct genus of early even-toed ungulates that lived from the Middle Eocene to the early Oligocene , mainly in Europe north of the Alps . Although the species of the genus were relatively small, they were among the largest cloven-hoofed animals of the Middle Eocene. Particularly well-preserved finds, which include not only complete skeletons but also remnants of the soft tissues, are known from the Geiseltal near Halle in Saxony-Anhalt and enable a comprehensive reconstruction of the animals.
features
The representatives of Amphirhagatherium were small compared to most of the recent cloven-hoofed animals. The head-torso length was about 50 cm plus a tail up to 20 to 25 cm long, the shoulder height was 25 cm. The highest point of the animal was in the area of the lumbar vertebrae and reached 30 cm here. The weight is reconstructed to 3.7 to 4.8 kg. Thus, the species of this genus belonged to the largest pair of ungulates of the middle Eocene . Particularly noteworthy is the long tail, which makes up a quarter of the entire body length and is so atypical for today's artifacts. Overall, the skeletal anatomical structure was therefore rather primitive and from today's perspective is comparable to that of some of the current representatives of rodents .
The skull was elongated and had a low cranial roof, in length it measured about 11 to 13 cm. The occiput was short and square, while the nasal bone was narrow and pointed. The lower jaw had a wedge-like shape with a pointed symphysis and had low jaw branches. It was between 9 and 10 cm long. In both the upper and lower jaws there was the complete dentition early mammals, which amphirhagatherium following dental formula had: . The molars were bunodont with approaches of selenodont (crescent moon-shaped) enamel cusps . The last two premolars were large and clearly molarized, the front ones were much smaller in shape and had only singular cusps. In some species there was a small diastema 5 mm wide between the first and second premolar . Another large diastema was towards the front dentition, which was formed from the three incisors and the canines .
The spine resembled that of today's cloven-hoofed animals and consisted of 7 cervical, 13 thoracic, 7 lumbar and 4 sacral vertebrae, the number of caudal vertebrae was at least 20. Distinctive were the clearly longer hind legs compared to the front legs. At 10 to 11 cm , the shin was again longer than the thigh bone , which was more than 9 to 10 cm in length. The humerus reached a length of 8 to 9 cm, while the radius was only 6 to 7 cm long. All limbs ended in four toes. The central ray , consisting of the third and fourth metapodia, was the most pronounced. In contrast to today's even-toed ungulates, these were hardly overgrown. Two smaller rays, formed from the second and fifth metapodium, were located laterally inside and outside. A fifth, but already significantly reduced, ray was only formed on the front legs. Overall, however, the metapodia were not yet as elongated as in today's artifacts. The last phalanxes of the toes ended in pointed hooves.
Fossil record
Amphirhagatherium finds come mainly from northern Alpine Europe. One of the most important deposits is the Geiseltal southwest of Halle ( Saxony-Anhalt ). Here the genus represents the most common artifacts and has been identified with at least seven almost complete skeletons and numerous isolated individual finds or articulated skeletal elements as well as individual fossilized soft tissues, all of which come from the middle brown coal seams and can be assigned to the middle to late Eocene . Other important finds in Germany come with the first record of the genus from Frohnstetten ( Baden-Württemberg ) and belong to the transition period from the Eocene to the Oligocene . In England , Amphirhagatherium has been found, among other things, from late-Ocene deposits of the Headon Hill Formation with several jaw fragments, and finds from France ( Grisolles and Quercy ) and Belgium ( Mormont ) are also known.
Paleobiology
In particular, the excellently preserved finds from the Geiseltal allow a comprehensive reconstruction of the paleobiology . Originally a pig-like animal was reconstructed, but more recent studies show that the animals were much more graceful and more similar in habit to today's common deer , but the spine was clearly more convexly curved when standing. The short neck and head were also kept much more horizontal. Hair remnants from the coal that have been handed down to us indicate a very short-haired fur, with the woolly hair almost 4 mm long and thus one of the shortest among the ungulates. A antlers or horns had not been trained, possibly started the development of such weapons head later and went with the advent of more open landscapes in the Miocene associated. There were also no other gender-specific features, such as enlarged canines. It is possible that the sexes could only be distinguished on the basis of size.
The legs are clearly angled under the body, the entire structure of the musculoskeletal system suggests agile animals that mastered both slow and faster movements. Since the metatarsals had no extensions, however, they were not persistent runners. The thigh bones show strong muscle profiles for well-developed muscles, which made a quick sprint possible. The turning in and out of the forelimbs was less possible, however, as indicated by the complete separation of the ulna and radius on the forearm. Presumably the animals lived in dense forests as bush hatchers, which quickly disappeared in the dense undergrowth, but were occasionally able to seek out more open areas. The two outer, smaller toes also touched the ground when standing or when they were sitting down, thus creating a larger footprint, which is advantageous for animals that live in landscapes with softer ground, such as swamps or sandy soils. Based on the flora finds from the Geiseltal, an herb and light-rich palm-pine forest with three or four levels of growth, which was interspersed with moist biotopes, is proven.
The wide expansion of the nasal cavity and the structure of the nasal bone on the skull speak for a well-developed sense of smell in Amphirhagatherium . The eye sockets are of normal size and sit on the side of the head. This indicates an animal that is active during the day or at dusk. The auditory region also shows a good development, but some elements are missing that animals with particularly high hearing performance have. Amphirhagatherium probably used the sense of sight for distance orientation , while hearing was used more at close range.
Due to the buno to bunoselenodont molars with low crowns, one can conclude that they specialize in soft plant food. The main diet is likely to come from fruits and leaves that have been eaten from the ground. Fruits predominated, but later representatives of Amphirhagatherium developed significantly more selenodontic teeth, although it is unclear whether this is associated with an increased consumption of leaves or a stronger seasonalization of the climate. Animal protein that was ingested while digging through the topsoil may also have played a minor role. Since the attachment surface on the jaw for the masticatory muscle was significantly widened, a higher chewing force can be assumed, so that even harder parts of the plant could be picked up. Stomach contents from the Geiseltal site could not be examined for preparatory reasons. Analyzes of those from the Messel mine ( Hessen ), which belong to the closely related genus Masillabune , contained a high proportion of laurel plants . Macroscopic traces of abrasion in the form of distinctive grinding surfaces on the raised enamel cusps of the molars of Amphirhagatherium show that the animals chopped up their food with characteristic grinding movements.
Systematics
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Internal systematics of the fossil family Choeropotamidae according to Hooker et al. 2001
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Representatives of amphirhagatherium lived from the middle Eocene to early Oligocene (about 34 million years ago to 48) and died probably related to the Eocene-Oligocene extinction event from event. The genus Amphirhagatherium was first described in 1908 by Charles Depéret . The type species and at the same time the youngest representative in phylogenetic history is A. fronstettense from a late-Ocene to early-Oligocene fissure filling near Frohnstetten . Other species are A. edwardsi , A. louisis , A. weigelti , A. neumarkensis and possibly A. ruetimeyeri . The latter, however, has only survived from a few teeth and a fragment of the upper jaw. A. weigelti and A. neumarkensis originally belonged to the genus Anthracobunodon , but due to the paraphyletic origin of this taxon they were separated and assigned to Amphirhagatherium .
Amphirhagatherium belongs to the extinct and quite extensive family of the Choeropotamidae , the closest related genera are Rhagatherium and Hallebune . The Choeropotamidae are characterized by bunodonte to bunoselenodonte molars, canine-like front premolars and a diastema between the first and second premolar. They are part of the superfamily Hippopotamoidea (formerly also Anthracotherioidea) and are thus placed in the closer relationship of the pig or hippopotamus -like Anthracotheriidae that appear somewhat later . Today's hippos and whales also belong to the wider family .
Individual evidence
- ↑ a b c d e f Jörg Erfurt: Reconstruction of the skeleton and the biology of Anthracobunodon weigelti (Artiodactyla, Mammalia) from the Eocene of the Geiseltal. Hallesches Jahrbuch für Geoswissenschaften, Series B, Supplement 12, 2000, pp. 57–141
- ↑ a b Florian Heller: Anthracobunodon weigelti. gen. et n. sp., an Artiodactyle from the Middle Eocene of the Geiseltal near Halle a. S. Paläontologische Zeitschrift 16, 1934, pp. 247-263
- ↑ a b c d e f Jerry J. Hooker and Katherine M. Thomas: New species of Amphirhagatherium (Choeropotamidae, Artiodactyla, Mammalia) from the late Eocene Headon Hill Formation of Southern England and phylogeny of endemic European Anthracotheroids. Palaeontology 44, (5), 2001, pp. 827-853
- ↑ a b c d e Jörg Erfurt and Hans Altner: Habitus reconstruction of Anthracobunodon weigelti (Artiodactyla, Mammalia) from the Eocene of the Geiseltal. In: Jan Michal Burdukiewicz, Lutz Fiedler, Wolf-Dieter Heinrich, Antje Justus and Enrico Brühl (eds.): Knowledge hunters . Festschrift for Dietrich Mania. Publications of the State Museum for Prehistory in Halle 57. Halle / Saale 2003, pp. 153–176
- ↑ Meinolf Hellmund: Excursion: Former Geiseltalrevier, southwest of Halle (Saale). From the Vita of the Eocene Geiseltal. In: Jörg Erfurt and Lutz Christian Maul (eds.): 34th meeting of the working group for vertebrate paleontology of the palaeontological society 16.3. until March 18, 2007 in Freyburg / Unstrut. Hallesches Jahrbuch für Geoswissenschaften BH 23, 2007, pp. 1–16
- ↑ Ehrhard Voigt: The animal finds from the ancient tertiary lignite in Central Germany. Working group Paläontologie Hannover 17, 1989, pp. 35–51
- ↑ Jörg Erfurt: Stratigraphic meaning of the Artiodactyla (Mammalia) in the Palaeogene of Europe. In: Jörg Erfurt and Lutz Christian Maul (eds.): 34th meeting of the working group for vertebrate palaeontology of the paleontological society March 16 to March 18, 2007 in Freyburg / Unstrut. Hallesches Jahrbuch für Geoswissenschaften 23, 2007, pp. 175–182
- ^ Jean Renaud Boisserie: Family Hippopotamidae. In: Donald R. Prothero and Scott E. Foss (Eds.): The Evolution of Artiodactyls. Johns Hopkins University, Baltimore, 2007, pp. 106-119
- ↑ Jonathan Geisler and Mark D. Uhen: Morphological support for a close relationship between hippos and whales. Journal of Vertebrate Paleontology 23 (4), 2003, pp. 991-996