Arcanotherium

Arcanotherium
Lower jaw of Arcanotherium , holotype specimen
Temporal occurrence
Late Eocene to early Oligocene
37 to 33 million years
Locations
North africa
Systematics
Higher mammals (Eutheria) Afrotheria Paenungulata Tethytheria Russell animals (Proboscidea) Arcanotherium
Scientific name
Arcanotherium
Delmer , 2009
Art
Arcanotherium savagei ( Court , 1995)

The genus Arcanotherium is an extinct representative of the proboscis and lived at the transition from the Eocene to the Oligocene around 35 million years ago in northern Africa . The name is derived from the Latin word arcanus (hidden, hidden, mysterious) and the Greek word θηρίον ( thērion , animal). They are medium-sized proboscis, the size of which mediates between that of the older and smaller Numidotherium and the large barytherium that occurs at the same time .

features

So far, only a few remains of this genus of proboscis have been discovered, whereby the fossil finds available so far are partly highly fragmented. However, these include both skull fragments and remains of the musculoskeletal system and the spine . The lower jaw of the holotype (copy number BMNH M. 82163) is largely complete except for the joint attachments and belongs to a non-adult animal. The holotype also includes single, isolated teeth and postcranial bone fragments. In addition, skeletal elements of adult animals, including further mandibular remnants and individual teeth, are known.

The largely complete juvenile lower jaw was composed of several fragments and has full posterior teeth in the right branch of the jaw. The deciduous dentition consisted of three premolars (p2 to p4) and three molars (m1 to m3). In addition, an incisor (i1) was found, albeit isolated, while a second (i2) could be identified on the basis of the alveolus . Both incisors must have been about the same size due to the formation of the alveoli. A canine tooth was not formed in Arcanotherium , so that there was a large diastema between the front and rear teeth . The tooth formula of permanent dentition is not known, only the rear molars have been handed down in fossil form.

The molars of both the primary and permanent teeth had two transverse enamel ridges ( bilophodont ), but the rearmost one also had a third ridge. However, the formation of the enamel ridges was not so clearly pronounced and they each had a clear cusp at their ends, which gave the teeth a partly bunodontic character (bunolophodont). The structure of the premolars was similar to that of the molars (molarized premolar teeth). Also noteworthy is the symphysis of the lower jaw, which is very short and only protrudes into the p2 area.

Fossil finds

Arcanotherium fossils have so far only been discovered at the Dor el-Talha site ( Libya ). They come from the local evaporite unit from the Upper Eocene and the Idam unit from the Lower Oligocene, where they were collected by British paleontologist Robert JG Savage in the late 1960s. The finds are now kept in the Natural History Museum in London , a few are also in the Muséum national d'histoire naturelle in Paris .

Systematics

Abbreviated internal systematics of the early proboscis according to Tabuce et al. 2019   Proboscidea    Eritherium      Phosphatherium      Daouitherium      Numidotherium      Barytherium      Omanitherium      Arcanotherium      Saloumia      Moeritherium      younger Proboscidea (Elephantiformes)      Deinotheriidae

Arcanotherium is a genus of the order of Rüsseltiere (Proboscidea). Due to the bilophodontic structure of the molars and the simultaneous use of all teeth (vertical tooth change) it belongs to the group of Plesielephantiformes , the most original representatives of the proboscis. An assignment to a specific family has not yet been made. The only recognized species is Arcanotherium savagei . This was first described in 1995 by Nicholas Court as Numidotherium savagei and incorporated into the closer relationship of the "barytheroid" proboscis ( Barytherium and Numidotherium ). The species name savagei honors the English biologist Robert JG Savage, who had already presented the finds at the end of the 1960s and interpreted them as belonging to a small representative of barytherium .

However, the assignment to the genus Numidotherium was revised in 2009 by Cyrille Delmer . The reason for this was the clear tendency towards bunolophodont molars, which connects Arcanotherium more strongly with Moeritherium . Both thus form a rather closed group and set themselves apart from the phylogenetically older "barytheroid" proboscis of the Eocene with clearly lophodontic molars. The third inguinal attachment on the rearmost molar also brings the proboscis closer to the phylogenetically more advanced Elephantiformes, whose basal forms such as Phiomia and Palaeomastodon also had this characteristic. Another reason for the independence of Arcanotherium against numidotherium the structure can of enamel are cited, which is fundamentally different between the two genres.

Further similarities can also be found with Chilgatherium , possibly the earliest representative of the Deinotherien from the middle Oligocene. This proboscis also had bunolophodonte molars, but unlike Arcanotherium it had a fully developed third ridge on the last molar. The later Deinotheria, in turn, had only two ridges on the third molar and characteristic lophodontic molars. The new cladistic investigations now show that due to this combination of characteristics , Chilgatherium is possibly an ancestor of the Elephantiformes, while Arcanotherium is in turn to be placed in its ancestral line. To what extent there is a closer relationship between Chilgatherium and the later Deinotheria is currently unclear.

Individual evidence

1. ↑ ^{a b c d e f} Cyrille Delmer: Reassessment of the generic attribution of Numidotherium savagei and the homologies of lower incisors in proboscideans. Acta Palaeontologica Polonica 54 (4), 2009, pp. 561-580
2. ↑ Rodolphe Tabuce, Raphaël Sarr, Sylvain Adnet, Renaud Lebrun, Fabrice Lihoreau, Jeremy E. Martin, Bernard Sambou, Mustapha Thiam and Lionel Hautier: Filling a gap in the proboscidean fossil record: a new genus from the Lutetian of Senegal. Journal of Paleontology, 2019, doi: 10.1017 / jpa.2019.98
3. ^ N. Court: A new species of Numidotherium (Mammalia: Proboscidea) from the Eocene of Libya and the early phylogeny of the Proboscidea. Journal of Vertebrate Paleontology 15, 1995, pp. 650-671, doi: 10.1080 / 02724634.1995.10011254
4. ↑ RJG Savage: Early Tertiary mammal locality in southern Libya. Proceedings of the Geological Society of London 1657, 1969, pp. 167-171 ( [1] )
5. ↑ Sylvain Adnet, Henri Cappetta and Rodolphe Tabuce: A Middle-Late Eocene vertebrate fauna (marine fish and mammals) from southwestern Morocco; preliminary report: age and palaeobiogeographical implications. Geological Magazine 147 (6), 2010, pp. 860-870
6. ↑ Rodolphe Tabuce, Cyrille Delmer and Emanuel Gheerbrant: Evolution of the enamel microstructure in the earliest proboscideans. Zoological Journal of the Linnean Society 149, 2007, pp. 611-628
7. ^ William Sanders, John Kappelmann and D. Tab Rassmussen: New large-bodied mammals from the late Oligocene site of Chilga, Ethiopia. Acta Palaeontologica Polonica 49 (3), 2004, pp. 365-392