Namatherium

from Wikipedia, the free encyclopedia
Namatherium
Temporal occurrence
Lutetium (Middle Eocene )
47.8 to 41.3 million years
Locations
Systematics
Afrotheria
Paenungulata
Tethytheria
Embrithopoda
incertae sedis
Namatherium
Scientific name
Namatherium
Pickford , Senut , Morales , Mein & Sánchez , 2008

Namatherium is a genus from the now extinct group of the little explored Embrithopoda , whichbelongsto the closer relationship of the proboscis and manatees and the most famous member of which is the giant Arsinoitherium . The genus is currently handed down through a single skull find from the restricted area of Namibia . This dates to the Middle Eocene and is about 48 to 41 million years old, making Namatherium one of the oldest representatives of the Embrithopoda on the African continent. It was a little smaller than arsinoitheriumand was at times regarded as its closest relative. Due to some noticeable anatomical deviations, Namatherium may not have been the direct ancestor of Arsinoitherium . The genus was scientifically introduced in 2008. It's kind of known.

features

Namatherium has so far only been handed down on the basis of a partial and partly severely crushed skull which lacks the front muzzle and which has the complete molar row on the left, and the two rearmost premolars on the right . The most striking feature were the extremely wide cantilevered zygomatic arches , which were up to 36 cm apart. This exceeds the average degree of Arsinoitherium whose zygomatic arches looked more graceful. In comparison, the distance between the left and right posterior molars in Namatherium was 14.4 cm, whereas in Arsinoitherium the skull was only slightly narrower than the greatest width on the zygomatic arch. The anterior arch attachment in Namatherium was also located significantly further forward on the skull near the last premolar. The nasal cavity was relatively spacious and was separated into two parts by a bony ridge. The ascending outer walls of the nasal cavity were characterized by small protruding ribs, comparable to Arsinoitherium , in which the horns, which are basically hollow, were attached at this point. In Namatherium , the horns have not been handed down, however, due to the structure, they may also have been formed. The front part of the nasal bone is also not preserved. The anterior margin of the orbit was above the first molar and thus further forward than in Arsinoitherium , in which the eye window was positioned above the last molar. The same applies to the infraorbital foramen , which was located above the fourth premolar. Furthermore, the glenoid pit in Namatherium had a rather arched and oval shape, whereas in Arsinoitherium it was banana-shaped and slightly dented. In addition, it was significantly lower on the skull in the former than in the latter compared to the occlusal plane of the maxillary teeth.

The dentition has only been handed down in its rear teeth. As with arsinoitherium, the molars were characterized by two transverse ridges with a deep indentation between them, making them typically bilophodontic . The width of the anterior groin compared to the posterior one increased from the first to the third molar. In contrast to Arsinoitherium , the molars of Namatherium were not quite as high crowned ( hypsodont ), typically the tooth crown protruded higher on the outer side of the molars than on the inner. A prominent cingulum, a bulge of enamel at the base of the crown, formed a small, sharp rib on the tooth corner at the front of the tongue. The third molar in each case was shifted slightly inward to the rest of the longitudinal axis of the row of teeth, a feature that also occurs in Arsinoitherium , but is absent in the earlier representatives of the Embrithopoda. In contrast to the molars, the premolars had only one ridge, so they were monolophodontic , which is a striking difference to arsinoitherium . The size of the teeth increased from front to back. The third premolar reached a length of 1.7 cm with a maximum width of 2.4 cm. The rearmost molar measured 4.1 cm in length and width. The length of the entire existing row of teeth (third premolar to third molar) was 14.2 cm, that of the molar row 10.6 cm, with arsinoitherium the corresponding values ​​were 21.5 and 15.5 cm.

Fossil site

The only Namatherium find so far came to light in Black Crow in the northern restricted area of Namibia . Black Crow is a small depression only a few hundred meters in diameter that is sunk into the Proterozoic underground of the Gariep Formation . It is located about 9 km northeast of the ghost town of Bogenfels and 15 km west of the Klinghardt Mountains . The Black Crow carbonates exposed here comprise a 3 to 6 m thick layer of limestones , which are rich in dolomites and represent the layers leading to the found. They are stored on a similarly thick, plate-like limestone, which is characterized by chalcedony and contains only a few fossils. Both strata groups belong to the Ystervark carbonantite formation , which is relatively widespread in the restricted area. In the hanging wall of this formation in Black Crow are two conglomerate consequences on the one hand the Blaubok conglomerate on the other hand, the Gembokstal-Konglomert include. The latter contains numerous phonolites that come from the volcanic Klinghardt massif to the east . Radiometric dating of these phonolites showed a deposition period from 45 to 40, possibly up to 37 million years ago, which roughly corresponds to the end of the Middle to the beginning of the Upper Eocene . The formation of the Ystervark carbonantite formation is thus placed in the course of the Middle Eocene ( Lutetian ) about 48 to 45 million years ago. Black Crow limestones are heavily silicified on the surface . Since this phenomenon is widespread in the restricted area, but only affects certain rock units, one assumes a unique process in the region, which most likely took place in the late Middle Eocene ( Bartonian ). The silicified rocks of the restricted area are covered over a large area by marine deposits that formed when today's Namib was exposed to the influence of the sea in the transition to the Oligocene .

Black Crow has been documented since the mid-1920s, but the paleontological significance of the limestone deposits was only recognized in 2008 during an expedition. This also included some other, similarly structured calcium deposits in the near and far ( Silica North , Silica South and Steffenkop ), of which Black Crow is by far the most fossil-rich. The discovery region of the restricted area is one of the few sub-equatorial landscapes in Africa in which fossil deposits from the Paleogene have survived. The fossil content is extensive and consists mainly of mammals in addition to isolated remains of reptiles , probably from the group of double snakes . Besides Namatherium could, among other Namahyrax an early representative, hyrax , Namalestes , a carnivorous or insect eat skills animal from the now extinct group of Cimolesta , Notnamaia from the group of monkeys and various small mammals such as shrews , hedgehogs relatives or rodents are described. The fauna shows associations with similarly old finds from the northern part of Africa. It also indicates through several fruit-eating forms such as Namahyrax or Notnamaia or the rodent Glibia the predominance of a humid, tropical-warm climate during the time. The elephants, which in Black Crow consist of shapes with significantly low tooth crowns, also show that the region of the then Namib was not yet under the influence of dry climates. This prevailed gradually in the subsequent Upper Eocene and very strongly in the early Miocene .

Paleobiology

It is possible that Namatherium, like its great relative Arsinoitherium, was an inhabitant of damp swampland. The bony horns of the Embrithopoda, which so far have only been fully documented in Arsinoitherium , but can be assumed for Namatherium due to the nasal structure, were hollow on the inside and had formed completely from the nasal bone . Since they formed a very thin-walled structure, they were probably not used in the intraspecific competition. Possibly they acted as a visual signal or served as a resonance organ for sounds. The latter would mean that acoustic signals also played a certain role in Namatherium's behavioral repertoire .

Systematics

Internal structure of the Embrithopoda according to Gheerbrant et al. 2020
 Embrithopoda  

 Stylolophus


   

 Palaeoamasia


   

 Hypsamasia


   

 Crivadiatherium


   

 Namatherium


   

 Arsinoitherium


Template: Klade / Maintenance / 3Template: Klade / Maintenance / 4



Template: Klade / Maintenance / Style

Namatherium is a genus from the extinct group of Embrithopoda . In the Eocene and Oligocene, this group inhabited large parts of what is now Africa and western Eurasia , but was neither particularly diverse nor very numerous. These are relatively large animals, the most important and best-known representative of which is the huge arsinoitherium , which in its time was one of the largest land-living mammals along with some members of the proboscis . The Embrithopoda are often closely related to the proboscis and the manatees , which is suggested by the middle jawbone , which is elongated to the rear and is in contact with the frontal bone . Because of this, the Embrithopoda form part of the group of Tethytheria , which in turn form the Paenungulata together with the snakes . The latter represent part of the parentage of Afrotheria , one of the four main lines within the Upper Mammals .

Within the Embrithopoda, five other genera are distinguished in addition to Namatherium , which are distributed over a total of three families . These include the Stylolophidae , the Palaeoamasidae, and the Arsinoitheriidae . The former two can be regarded as the phylogenetic rather primeval strands of the group, of which the Stylolophidae from northern Africa, the Palaeoamasidae, however, have so far only been passed down from the Eurasian part of the distribution and are mostly only known through remains of teeth. The tooth structure in general and the higher crowns of Namatherium show little agreement with these basal lines. Rather, relationships to the Arsinoitheriidae can be recognized through the design of the palate or the nasal bone, which so far have only been documented from Africa and the Arabian Peninsula, which was then connected to the continent . However, Namatherium shows, for example with the monolophodontic premolars, significant differences to Arsinoitherium , whose anterior molars appear like the posterior bilophodont . The teeth of Namatherium are generally not as high-crowned as those of Arsinoitherium . According to this, Namatherium should represent the somewhat more primitive form from the phylogenetic point of view, which is also supported by the dating to the Middle Eocene . Further differences in tooth construction can be found in the structure of the lasts and their coverage by tooth enamel . Also noteworthy is the different design of the skull with the widely protruding zygomatic arches in Namatherium compared to the much closer fitting ones in Arsinoitherium . Furthermore, the differently designed glenoid pit in both types suggests a different mandibular-skull joint and therefore different chewing mechanics in both types. It is therefore likely that Namatherium is not the direct phylogenetic ancestor of Arsinoitherium . A study of the tribal history from 2016, which is based on tooth morphological features, sees Namatherium outside the Arsinoitheriidae and groups the genus as a sister taxon to the other, then known representatives of the Embrithopoda. Further phylogenetic analyzes, published in 2018 and 2020, do not share this opinion and again place Namatherium in the vicinity of Arsinoitherium .

The first scientific description of Namatherium was in 2008 by Martin Pickford and fellow researchers. The holotype (specimen number BC 13'08) includes the only known skull find from the Black Crow site in the restricted area of Namibia . The generic name consists of the word Nama , which describes the find region in the local language and can be translated as "desert" or "wasteland", and the Greek term θηρίον ( thērion ) for "animal". The only known species is Namatherium blackcrowense . The specific epithet refers to the Black Crow site , which in turn is a reference to the Cape crow ( Corvus capensis ).

literature

  • Martin Pickford, Brigitte Senut, Jorge Morales, Pierre Mein and Israel M. Sánchez: Mammals from the Lutetian of Namibia. Memoirs of the Geological Survey of Namibia 20, 2008, pp. 465-514
  • William Sanders, D. Tab Rasmussen, and John Kappelman: Embrithopoda. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London 2010, pp. 115-122

Individual evidence

  1. ↑ a b c d e f Martin Pickford, Brigitte Senut, Jorge Morales, Pierre Mein and Israel M. Sánchez: Mammals from the Lutetian of Namibia. Memoirs of the Geological Survey of Namibia 20, 2008, pp. 465-514
  2. ^ A b c William Sanders, D. Tab Rasmussen and John Kappelman: Embrithopoda. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London 2010, pp. 115-122
  3. ^ Charles W. Andrews: A descriptive catalog of the Tertiary Vertebrata of the Fayum, Egypt. London 1906, pp. 1–324 (pp. 2–82)
  4. ↑ Martin Pickford, Yoshihiro Sawada, Hironobu Hyodo and Brigitte Senut: Radio-isotopic age control for Palaeogene deposits of the Northern Sperrgebiet, Namibia. Communications of the Geological Survey of Namibia 15, 2013, pp. 3–15
  5. ↑ a b Martin Pickford, Brigitte Senut, Jorge Morales and Israel Sanchez: Fossiliferous Cainozoic Carbonatesof the Northern Sperrgebiet. Memoir of the Geological Survey of Namibia 20, 2008, pp. 25-42
  6. ↑ Martin Pickford: Cenozoic Geology of the Northern Sperrgebiet, Namibia, accenting the Palaeogene. Communications of the Geological Survey of Namibia 16, 2015, pp. 153–193
  7. ↑ Jean-Claude Rage, Martin Pickford and Brigitte Senut: Amphibians and squamates from the middle Eocene of Namibia, with comments on pre-Miocene anurans from Africa. Annals de Paléontologie 99, 2013, pp. 217–242
  8. ^ A b Martin Pickford, Brigitte Senut, Helke Mocke, Cécile Mourer-Chauviré, Jean-Claude Rage and Pierre Mein: Eocene aridity in southwestern Africa: timing of onset and biological consequences. Transactions of the Royal Society of South Africa 69 (3), 2014, pp. 139-144
  9. ↑ a b c Emmanuel Gheerbrant, Fatima Khaldoune, Arnaud Schmitt and Rodolphe Tabuce: Earliest embrithopod mammals (Afrotheria, Tethytheria) from the early Eocene of Morocco: anatomy, systematics and phylogenetic significance. Journal of Mammalian Evolution, 2020, doi: 10.1007 / s10914-020-09509-6
  10. ^ Nicholas Court: The skull of Arsinoitherium (Mammalia, Embrithopoda) and the higher order interrelationships of Ungulates. Palaeovertebrata 22 (1), 1992, pp. 1-43
  11. ↑ Rodolphe Tabuce, Robert J. Asher and Thomas Lehmann: Afrotherian mammals: a review of current data. Mammalia 72, 2008, pp. 2-14
  12. ^ A b Sevket Sen: Dispersal of African mammals in Eurasia during the Cenozoic: Ways and whys. Geobios 46, 2013, pp. 159-172
  13. ↑ Emmanuel Gheerbrant, Mbarek Amaghzaz, Baadi Bouya, Florent Goussard and Charlene Letenneur: ocepeia (Middle Paleocene of Morocco): The Oldest Skull of an Afrotherian Mammal. PLOSone 9 (1), 2014, p. E89739, doi: F10.1371 / journal.pone.0089739
  14. ↑ Ozan Erdal, Pierre-Olivier Antoine and Sevket Sen: New material of Palaeoamasia kansui (Embrithopoda, Mammalia) from the Eocene of Turkey and a phylogenetic analysis of Embrithopoda at the species level. Palaeontology 59 (5), 2016, pp. 631-655, doi: 10.1111 / pala.12247
  15. ↑ Emmanuel Gheerbrant, Arnaud Schmitt and László Kocsis: Early African Fossils Elucidate the Origin of Embrithopod Mammals. Current Biology 28 (13), 2018, pp. 2167–2173, doi: 10.1016 / j.cub.2018.05.032