Numidotherium

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Numidotherium
Temporal occurrence
Early to Middle Eocene ( Ypresian to Lutetian )
56 to 44.7 million years
Locations
Systematics
Higher mammals (Eutheria)
Afrotheria
Paenungulata
Tethytheria
Russell animals (Proboscidea)
Numidotherium
Scientific name
Numidotherium
Mahboubi , Ameur , Crochet & Jaeger , 1986
Art
  • Numidotherium koholense

Numidotherium is an extinct genus of early proboscis thatlivedin North Africa in the Early and Middle Eocene 55 to 44 million years ago. The representatives reached the size of a tapir and were probably the earliest members of the Proboscidea with a trunk . They were largely land-dwelling and thereby differed from their relatives Barytherium and Moeritherium , which followed a semi-aquatic way of life. Thegenus was first described in 1986.

features

Numidotherium is one of the earliest representatives of the proboscis and is known from several tooth and skull finds, but also from remains of the body skeleton. It reached a shoulder height of 1 to 1.5 m and was thus significantly larger than its predecessors Phosphatherium and Eritherium . Furthermore, it was characterized by a short trunk and quite long legs. The skull had a length of 37 cm and a raised cranial roof and had widely spreading zygomatic arches . As one of the earliest proboscis animals, Numidotherium had air-filled bones in the roof of the skull, which, due to the increase in size and weight of the animal, offered a larger attachment point for the neck muscles. The rostrum was short and sloped steeply down from the forehead to the nose. The nasal bone was characterized by an elongated outer area of ​​the nasal space ( nares ), while the intermaxillary bone was rather short and high. The shape of the rostrum created a high, but rather narrow, nasal interior. On the side of the upper jaw there was a deep furrow from the intermaxillary bone to the front attachment of the zygomatic arch. In some individuals, the temporal ridges on the parietal bone formed a prominent crest , in others they remained clearly separated. The occiput was also quite short in shape, with a robust occipital bulge. The joint surfaces here for articulation with the cervical spine were comparatively high.

The up to 39 cm long lower jaw had a low bone body, but wide lower jaw branches. The symphysis extended to the second premolar . The mental foramen lay below the third premolar tooth. The ascending branch loomed up and delimited a prominent masseteric fossa . The crown process was oriented slightly inwards. The number of teeth of the dentition was over older forms Rüsseltier further reduced slightly and included for adult animals following formula: . The second incisor in the upper jaw (I2) was significantly enlarged with a length of 4.5 cm and was conical in shape. Furthermore, he only had a thin layer of enamel . In the lower jaw, the first incisor, which protruded obliquely forwards ( procumbente ), was enlarged by 3.5 cm - the first examinations looked at the second incisor as the enlarged one. These enlargements represent the preliminary stages of tusk formation in later proboscis. There was a large diastema to each of the rear teeth , which could be up to 9.5 cm long. The premolars were characterized by a simple construction with a single raised enamel cusp . The molars, on the other hand, had two transversely positioned enamel ridges ( bilophodont ) and were reminiscent of those of the tapirs , but the rearmost molar of the lower jaw had three ridges. The entire posterior dentition can be described as a low crown ( brachyodont ).

The previously known postcranial skeleton comprises individual vertebrae, especially the first and second cervical vertebrae ( atlas and axis ), which differ only slightly from those of other proboscis. The humerus reached a length of 30 cm and was robustly designed. The bones of the forearm, ulna and radius reached about the same length and were fused at the lower end. The upper joint end of the ulna ( olecranon ) was relatively short and oriented backwards. The thigh bone measured 40.5 cm. The latter was clearly narrowed anteriorly and posteriorly, but had a very broad upper joint end and a third trochanter. The shin was significantly shorter at 26 cm. The forefoot and hindfoot had the serial, taxeopodal arrangement of the root bones typical of proboscis . This means that the individual bones of the carpal and tarsus lay in rows one behind the other and not reciprocally to one another. As a result, there was no contact between the lunar bone and the hook bone on the forefoot . The special arrangement of the carpal bones suggests that an os centrale was still formed between the lunar bone, the head bone and the large polygonal bone , which is to be understood as a rather original feature of the proboscis.

Fossil finds

Numidotherium finds come exclusively from North Africa . The first finds of were discovered in El Kohol on the southern edge of the Atlas Mountains in Algeria . They come from the third layer of the El-Kohol Formation and date to the Middle Eocene . The rather extensive finds include a skull as well as the lower jaw and remains of the musculoskeletal system. A much older find from the Lower Eocene is known with a lower jaw fragment from a phosphate mine near Tamaguèlelt in northern Mali . However, this belongs to a much smaller representative and may have to be assigned to a different taxon. Further dental finds came to light in connection with a rich fish fauna from Ad-Dakhla in Western Sahara and can be assigned to the transition from the Middle to the Upper Eocene.

Paleobiology

The construction of the nasal bone with the elongated outer nasal cavities suggests the presence of a short proboscis in Numidotherium . The early proboscis are often associated with a semi-aquatic way of life, as has been demonstrated in the closely related Barytherium and Moeritherium . The fused bones of the forearm support this view, but the plantigrade structure of the forefoot shows adaptations to terrestrial locomotion, just as the low position of the eyes speaks against a water-dwelling way of life. In contrast to aquatic and semi-aquatic animals, the long bones also have a significantly thinner cortex and an expansive pith tube. The low-crowned molars with their typical, clearly formed lophodontic chewing surfaces indicate a specialization in soft vegetable food, which may have mainly included leaves , fruits and twigs . The fiber-containing food was probably looked for on bushes at head height or just above it, characteristic grinding marks on the anterior premolars suggest that the animals wedged them in their mouths and tore them off with rotating movements of the head. Isotope examinations of the teeth confirm this assumed terrestrial way of life. In Numidotherium , compared to Barytherium or Moeritherium, these resulted in more fluctuating ratios of the oxygen isotope 18 O, which in the latter two are significantly more balanced due to their semi-aquatic way of life. It is possible that an adaptation to a life in a partly watery environment arose several times within the proboscis, whereby the question remains unanswered as to whether the proboscis, including today's elephants, actually descended from ancestors, some of which lived in water.

The transmitted postcranial skeleton of Numidotherium allows conclusions to be drawn about the locomotion of the proboscid representative. Due to the arrangement of individual joint surfaces in the shoulder and pelvic area and the fused bones of the forearm, slightly angled limbs can be assumed. The bones of the front and rear feet are also more horizontally oriented, which is suggested by the structure of the ankle bone with a forward-facing joint head. The joint facets of the root bones, which are sometimes clearly positioned to the side, indicate that the individual rays ( metapodia and phalanges ) were rather spread apart. All in all, it can be assumed that Numidotherium has a sole passage . This is in clear contrast to today's elephants, which have column-like limbs arranged under the body, which can carry the heavy weight. The front and rear feet, with their more vertical structure, show a restricted toe walking (which is, however, overprinted by the foot pad).

The cochlea of Numidotherium , which is built somewhat differently than that of today's elephants, turned out to be a further specialty . In Numidotherium , for example, this has one and a half turns, whereas in elephants it has two. In the basal area of ​​the winding, there are deviations in detail, for example in the clear formation of the lamina spiralis secundaria, which is responsible, among other things, for the perception of certain frequencies . Researchers therefore suspect that Numidotherium was more likely to perceive sounds in the higher frequency range, in contrast to today's elephants, which can also communicate in infrasound . The lower number of coils of the cochlea in Numidotherium also suggests a more limited auditory perception.

It is possible that a sexual dimorphism was developed in Numidotherium , with male animals having significantly higher skulls than females, in the latter the rostrum was also markedly longer and the muscle marks on the skull were developed more gracefully. The shape of the cochlea in the inner ear is remarkable, which leads to the assumption that early proboscis were able to perceive significantly higher sound frequencies than today's elephants.

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



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Numidotherium is a genus of the order of Rüsseltiere (Proboscidea). The construction of the anterior molars, each with two enamel strips, makes them one of the Plesielephantiformes , the most original proboscis. This is also indicated by the vertical change of teeth with the simultaneous use of all teeth; the horizontal tooth change typical of today's elephants did not develop until later. The distinct lophodontia of the molars, however, brings the proboscis genus close to the barytheroid forms, to which barytherium in particular belongs. The genus Arcanotherium , which sometimes lives at the same time, and the younger Moeritherium, on the other hand, have less strongly lophodontic molar teeth.

The first significant finds come from El Kohol in Algeria. They were first published in the journal Nature in 1984 and two years later served as the basis for the first description of the genus, which Mohammad Mahboubi and research colleagues presented. The holotype is a nearly complete skull (copy number KA 1-18), which is now kept at the Départment des Sciences de la Terre of the University of Oran in northern Algeria. The name Numidotherium refers on the one hand to the ancient landscape of Numidia , while the Greek word θηρίον ( thērion ) means something like "animal". The only recognized species is Numidotherium koholense , the additional species koholense refers to the place where it was found. Numidotherium savagei , described in 1995 by the Dor el-Talha site in Libya, was assigned to the newly established genus Arcanotherium in 2009 . In 1992, Jeheskel Shoshani and Pascal Tassy provisionally introduced the Numidotheriidae family . This also contained Phosphatherium in parts, but the genus was later transferred to the independent family of the Phosphatheriidae . The position of Daouitherium within the Numidotheriidae is also not certain.

Individual evidence

  1. ↑ a b c d e f g Mohammad Mahboubi, R. Ameur, Jean-Yves Crochet and Jean-Jacques Jaeger: El Kohol (Saharan Atlas, Algeria): A new Eocene mammal locality in northwestern Africa. Palaeontographica Department A. 192, 1986, pp. 15-49
  2. ↑ a b c d Jehezekel Shoshani, Robert M. West, Nicholas Court, Robert JG Savage and John M. Harris: The earliest proboscideans: general plan, taxonomy, and Palaeoecology. In: Jeheskel Shoshani and Pascal Tassy (eds.): The Proboscidea. Evolution and palaeoecology of the Elephants and their relatives. Oxford, New York, Tokyo, 1996, pp. 57-75
  3. ↑ a b Emmanuel Gheerbrant, Daryl P. Domning and Pascal Tassy: Paenungulata (Sirenia, Proboscidea, Hyrocodoidea and relatives). In: Kenneth Rose and J. David Archibald (Eds.): The rise of placental mammals. Origin and relationship of the major extant clades. The Johns Hopkins University Press, Baltimore, 2005, pp. 84-105
  4. ↑ a b c Abdelmajid Noubhani, Lionel Hautier, Jean-Jacques Jaeger, Mohammed Mahboubid and Rodolphe Tabuce: Variabilité dentaire et crânienne deNumidotherium koholense (Mammalia, Proboscidea) de l'Éocène d'El Kohol, Algérie. Geobios 41, 2008, pp. 515-531
  5. ↑ a b c 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
  6. ^ A b William J. Sanders, Emmanuel Gheerbrant, John M. Harris, Haruo Saegusa and Cyrille Delmer: Proboscidea. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, London, New York, 2010, pp. 161-251
  7. ^ A b Nicholas Court: Limb posture and gait in Numidotherium koholense, a primitive proboscidean from the Eocene of Algeria. Zoological Journal of the Linnean Society 111, 1994, pp. 297-338
  8. ↑ Maureen A. O'Leary, Eric M. Roberts, Mohamed Bouare, Famory Sissoko and Leif Tapanila: Malian Paenungulata (Mammalia: Placentalia): New African Afrotheres from the Early Eocene. Journal of Vertebrate Paleontology 26 (4), 2006, pp. 981-988
  9. ↑ 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
  10. ↑ Nicholas Court: A dental peculiarity in Numidotherium koholense: evidence of feeding behavior in a primitive proboscidean. Journal of Mammals, 58, 1993, pp. 194-196
  11. ↑ Salamet Mahboubi, Hervé Bocherens, Michael Scheffler, Mouloud Benammi and Jean-Jacques Jaeger: Was the Early Eocene proboscidean Numidotherium koholense semi-aquatic or terrestrial? Evidence from stable isotopes and bone histology. Comptes Rendus Palevol 13 (6), 2014, pp. 501-509, doi: 10.1016 / j.crpv.2014.01.002
  12. ↑ Nicholas Court: Cochlea anatomy of Numidotherium koholense: auditory acuity in the oldest known proboscidean. Lethaia 25 (2), 1992, pp. 211-215, doi: 10.1111 / j.1502-3931.1992.tb01385.x
  13. ↑ Caitlin O'Connell, Lynette A. Hart and Byron T. Arnason: Comments on `` Elephant hearing ''. Journal of the Acoustical Society of America 104, 1998, pp. 1122-1123
  14. ↑ 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
  15. ↑ Mohammad Mahboubi, R. Ameur, Jean-Yves Crochet and Jean-Jacques Jaeger: Earliest known proboscidean from early Eocene of north-west Africa. Nature 308, 1984, pp. 543-544
  16. ↑ Nicholas 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
  17. ↑ Jehezekel Shoshani and Pascal Tassy: Classifying elephants. In: Jeheskel Shoshani (ed.): Elephants. Weldon Owen Pty Limited, Sidney, 1992, pp. 22-23
  18. ^ Emmanuel Gheerbrant, Jean Sudre and Henry Cappetta: A Palaeocene proboscidean from Morocco. Nature 383, 1996, pp. 68-70
  19. ↑ Emmanuel Gheerbrant, Jean Sudre, Henri Cappetta, Mohamed Iarochène, Mbarek Amaghzaz and Baâdi Bouya: A new large mammal from the Ypresian of Morocco: Evidence of surprising diversity of early proboscideans. Acta Palaeontologica Polonica. 47 (3), 2002, pp. 493-506