Eritherium
| Eritherium | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Paleocene | ||||||||||||
| 60 million years | ||||||||||||
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| Scientific name | ||||||||||||
| Eritherium | ||||||||||||
| Gheerbrant , 2009 | ||||||||||||
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Eritherium is a now extinct genus of proboscis from the Paleocene of northern Africa . It lived about 60 million years ago and is so far the phylogenetically oldest known representative of this mammalian order. Overall, they were relatively small animals. The body weight of Eritherium was reconstructed to 3 to 8 kg and was therefore comparable to that of the large hyrax , which is one of the closest relatives of the proboscis.
description
The holotype (copy number MNHN PM69) is now in the Museum National d'Histoire Naturelle in Toulouse and comprises an upper jaw with attachments of the zygomatic arch and two jaw branches, each of which is the two posterior premolars (P3 and 4) and three molars (M1-3) exhibit. The piece is about 6 cm long, 5 cm wide and a little more than 3 cm high. In addition, the fossils include 15 other objects that include skull bones such as the frontal bones and nasal bones , fragments of the lower jaw and dental finds in the upper and lower jaw (hypodigma).
The fragmentary tradition of the skull allows only a few statements about the appearance of Eritherium , most of the information relates to the structure of the teeth and the morphology of the teeth. In general, Eritherium shared some similarities in the structure of the teeth with other Paenungulata such as the extinct Embrithopoda or early representatives of the manatees , but the teeth are sometimes more specialized than these. The dentition of the lower jaw, which could be reconstructed using two fragments on the left, comprised the complete original sequence of teeth of the permanent set of mammals with three incisors , one canine , four premolars and three molars . The row of teeth was closed and there was no diastema between the canine and the anterior molars. This primeval mammalian dentition is so far unique in the proboscis, since the third incisor in the lower jaw was no longer formed in the somewhat younger forms of phosphatherium and numidotherium and thus indicates the beginning reduction in the number of teeth in the development of this mammalian order. The exact structure of the upper row of teeth is so far unknown, as the incisors are missing, the rear teeth had the same number of teeth as the lower jaw.
The molars generally had a low crown and bunodontic structure (with small enamel cusps on the chewing surface). Between the paired cusps, however, there were approaches to the formation of two transverse ridges on the first two and three on the rearmost, very small molar, which is typical of lophodontic teeth. In general, the teeth had a rectangular outline, the second molar was the largest in both the lower and upper dentition. It reached a length of 6.8 mm at the top and a width of 8.2 mm, at the bottom the dimensions were 7.9 and 6.2 mm respectively. The premolars had only one (in the lower jaw) or two (in the upper jaw) cusps compared to the molars. The clear difference between the molars and premolars underscores the antiquity of Eritherium , as in later proboscis the premolar teeth are very similar to the molars, as was the case with the somewhat younger Phosphatherium . Furthermore, the first incisor in the lower jaw was relatively large and formed with an asymmetrical crown, while the canine was rather small in shape and already showed signs of reduction. Eritherium connects both with other early proboscis. A tendency for tusks to form from the first or second incisors does not appear to have occurred yet. Another primitive characteristic was the short symphysis of the lower jaw, which ended at the second premolar. The reconstruction of the upper part of the skull showed that the upper jaw was relatively high and long, and the nasal bone also showed a certain degree of extension. The eye socket was at the level of the fourth premolar and the first molar and was therefore relatively far forward in the skull. In the case of Phosphatherium this was located further forward, but other early paenungulata usually had the orbit positioned clearly to the rear. The infraorbital foramen was formed about 8 mm in front of the lower edge of the eye . The anterior part of the zygomatic arch started above the posterior molars; compared to Phosphatherium , it was slightly recessed in relation to the infraorbital foramen. It was narrow on the sides and curved upwards.
Systematics
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Abbreviated internal systematics of the early proboscis according to Tabuce et al. 2019
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Eritherium is a genus of the order of Rüsseltiere (Proboscidea). It forms the oldest representative of this order and, as its basal form, is compared to all other members of the proboscis as a sister taxon . Together with Phosphatherium , Numidotherium , Moeritherium , Daouitherium and other early forms, this results in one of the most complete sequences of the early history of a mammalian order. It has not yet been systematically assigned to any particular family within the proboscis. The discovery of this elephant made it possible to trace the development of today's elephants back to the late Paleocene. As a result, besides predators and rodents, the proboscis belong to the oldest “modern” mammal orders that have survived to this day.
According to further cladistic studies, the manatees and desmostylia form the next outer sister group. With these and the Embrithopoda and the snakes, the proboscis form the group of Paenungulata. Their phylogenetically older representatives had partly bunodont to partly lophodontic molars, but there are still considerable gaps in tradition. However, such molars appear to have been the original morphotype in this taxonomic unit. Since it also appeared in the older forms of the trunk , it can be assumed that such a tooth structure was characteristic of early Afrotheria .
Discovery story
The Eritherium finds come from the Sidi Chennane phosphate mines in the Ouled Abdoun phosphate basin in Morocco . These are only 10 to 20 km south of Grand Daoui, from where two very early representatives of the proboscis were described as early as 1996 with Phosphatherium and 2002 with Daouitherium . The fossils were in the lower bone bed of the bed IIa phosphate layer of the local stratigraphy. This find layer also contained an accompanying fauna with the earliest evidence of the carnivorous Hyaenodontidae , but mainly due to the characteristic plate- gill fauna (including Hologlymostoma , Palaeogaleus ) they can be placed in the geochronological phase of Seelandium (61.1 to 57.8 million years ago) .
With the species Eritherium azzouzorum there is only one representative within this genus. The genus and species were first described by Emmanuel Gheerbrant in 2009. The name Eritherium comes from the Greek and means eρυ ( eri , old) and θηρίον ( thērion , animal), while the species name azzouzorum refers to the inhabitants of Ouled Azzouz near the mine Sidi Chennane honors who discovered most of the fossils.
Individual evidence
- ↑ a b c d e f Emmanuel Gheerbrant: Paleocene emergence of elephant relatives and the rapid radiation of African ungulates. In: PNAS 106 (6), 2009, pp. 10717-10721.
- ↑ a b c Emmanuel Gheerbrant, Baadi Bouya and Mbarek Amaghzaz: Dental and cranial anatomy of Eritherium azzouzorum from the Paleocene of Marocco, earliest known proboscidean material. In: Palaeontographica, Department A 297 (5/6), 2012, pp. 151-183.
- ^ Jan van der Made: The evolution of the elephants and their relatives in the context of a changing climate and geography. In: Harald Meller (Hrsg.): Elefantenreich - Eine Fossilwelt in Europa. Halle / Saale 2010, ISBN 978-3-939414-48-3 , pp. 340-360.
- ↑ 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. In: Journal of Paleontology , 2019, doi: 10.1017 / jpa.2019.98 .
- ↑ 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. In: Acta Palaeontologica Polonica. 47 (3), 2002, pp. 493-506.