Eritrea
| Eritrea | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Oligocene | ||||||||||||
| 26.8 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Eritrea | ||||||||||||
| Shoshani , Walter , Abraha , Berhe , Tassy , Sanders , Marchant , Libsekal , Ghirmai & Zinner , 2006 | ||||||||||||
| Art | ||||||||||||
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Eritrea is a now extinct genus of the proboscis from the Oligocene of northeastern Africa and lived about 27 million years ago. Few bones have been found so far; With a reconstructed body height of 1.3 m and a weight of around 480 kg, it was rather a small-stature proboscis. In the case of Eritrea , itis importantthat the phylogenetic history of this animal genus was the first todemonstrate the horizontal tooth change that is characteristic oftoday's elephants .
description
The holotype (copy number DOG 97.1), which is in the National Museum of Eritrea , includes three bone fragments of the lower jaw . The left branch of the jaw has been handed down with two molars (M2 and M3), while the right one has only one (M2). The alveoli of the first molar (M1) are present on both sides, but those of the premolars are not. Furthermore, there is an anterior part of the mandibular arch belonging to the same individual, which has both tusk alveoli. These are oval shaped with a height of 3.5 cm and a width of 2.3 cm. Reconstructed, the entire lower jaw would be more than 50 cm long, 30 cm wide and 20 cm high. The tusks, which were formed from the first incisors , were probably short, a little longer than 20 cm and probably pointed slightly downwards.
The molars are built up bunodont , the second molar has three ridges with two high enamel cusps each , while the third has four ridges. This has not yet developed any roots in the holotype, has not reached the chewing height of the second molar and - assuming a complete lower jaw - is located far in the rear area under the temporomandibular joint. This means that this tooth was not yet in use when the animal died, which also confirms its surface that has not been worn. The position of the third molar is a clear indication of the horizontal tooth change of the later elephants and differs from the phylogenetically older proboscis, which still have a vertical tooth change typical for mammals . The horizontal change of teeth resulted from the shortening of the jawbone, so that not all rear teeth (premolars and molars) were functional at the same time, but were pushed out one after the other depending on the degree of chewing. Based on the eruption of teeth and in comparison with today's African elephant , a subadult age of around 26 years is assumed for the individual (AEY = "African elephant years"; age comparable to the African elephant, but not identical).
Systematics
With the characteristic of the horizontal tooth change, Eritrea belongs to the genealogy of the elephantimorpha, elephant-like proboscis, which are differentiated from primitive proboscis such as the Plesielephantiformes with the Deinotheria and the Elephantiformes with Palaeomastodon and Phiomia through this characteristic and higher tooth crowns . All representatives of these two groups still have the typical vertical tooth change. Eritrea stands as an intermediary between the Elephantiformes and the more highly developed Elephantimorpha. It differs from the former by the more reduced dentition, since both Palaeomastodon and Phiomia still have all - with the exception of the first - premolars. The exact position within the proboscis line, whether closer to the Mammutidae , to the Gomphotheriidae or to an independent family, is currently difficult to determine, as too little finds are available.
Discovery story
Finds of eritreum were previously only Dogali in eastern Eritrea discovered on the banks of Dogali River. The open Dogali Formation there consists of strongly tilted and folded sediments , which comprise shale clays and basalts in alternating layers . Their age has been determined several times with the help of radiometric dating to 26 to 28 million years. The first finds came to light in 1997.
Eritreum was 2006 Jehezekel Shoshani and fellow researchers scientifically described . The only known species so far is Eritrea melakeghebrekristosi . The genus name, eritreum , represents the State of Eritrea, while the species name, melakeghebrekristosi , the local Farmer Melake Ghebrekristos honors, who discovered the finds and their importance was recognized.
Individual evidence
- ^ 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
- ↑ a b c d Jeheskel Shoshani, Robert C. Walter, Michael Abraha, Seife Berhe, Pascal Tassy, William J. Sander, Gary H. Marchant, Yosief Libsekal, Tesfalidet Ghirmai and Dietmar Zinner: A proboscidean from the late Oligocene of Eritrea, a `` missing link '' between early Elephantiformes and Elephantimorpha, and biogeographic implications. PNAS 103 (46), 2006, pp. 17296-17301
- ↑ Jehezekel Shoshani: Understanding proboscidean evolution: a formidable task. Tree 13, 1998, pp. 480-487