Eritreum
- Eritreum melakeghebrekristosi
Eritreum is a now extinct genus of Proboscidea from the Oligocene of northeastern Africa and lived about 27 million years. There only a few bones were found; with a reconstructed body height of 1.3 m and a weight of around 480 kg, it was more of a kleinwüchsiges tusker. Of significance is at Eritreum that in this animal species phylogenetically the characteristic also for Elephants today horizontal tooth change was detected for the first time.
Description
The holotype ( specimen number DOG 97.1 ), which is located in the National Museum of Eritrea, including three bone fragments of the mandible. The left is pine bough with two molars handed (M2 and M3), while the right has only one (M2). The alveoli of the first Mahlzahns (M1) are present on both sides of the premolars not. Furthermore, there is a belonging to the same individual front part of the mandibular arch, which has both Stoßzahnalveolen. These are oval-shaped with a height of 3.5 cm and a width of 2.3 cm. Reconstructed would the entire lower jaw a length of about 50 cm, a width of 30 cm and a height of 20 cm. The tusks, which were formed from each of the first incisors were probably short, slightly longer than 20 cm and probably slightly obliquely downward.
The molar teeth are constructed bunodont, wherein the second molar has two connectors with high enamel two protuberances, while the third four- bar has. This has formed no roots in the holotype, also reached not Kauhöhe of the second molar and was - a complete lower jaw provided - far in the rear area under the jaw joint. For this tooth was the death of the animal is not in use, which also confirmed its not worn surface. The position of the third molars is a clear reference to the horizontal change of teeth, the later elephants and differs from the phylogenetically older animals from trunk, which still have a typical mammalian vertical change of teeth. The horizontal dentition was created by shortening of the jaw bone, which no longer have any back teeth ( premolars and molars ) were the same in function but were subsequently pushed out depending on Abkauungsgrad. On the basis of tooth eruption and compared with today's African elephants, a subadult age of around 26 years is assumed ( AEY = " African elephant years"; -year age comparable to the African elephant, but not identical) to the individual.
System
With the feature of horizontal dentition Eritreum belongs phylogenetically to the beginning of Elephantimorpha, elephant -like proboscis animals that distinguish themselves by this characteristic and higher dental crowns of the primordial snout animals, such as the Plesielephantiformes with the Deinotherien and Elephantiformes with Palaeomastodon and Phiomia. All representatives of these two groups do not have the typical vertical change of teeth. This Eritreum is mediating between the Elephantiformes and the more developed Elephantimorpha. Of the former it differs further by the more reduced dentition, since both Palaeomastodon and Phiomia even all - except the first - have premolars. The precise position within the animal with a trunk line, whether belonging to the Mammutidae closer to the Gomphotheriidae or an independent family is currently difficult to determine because there is still too little archaeological material.
Discovery history
Finds of Eritreum have been discovered only in Dogali in the east of Eritrea on the banks of Dogali River. The local open-minded Dogali lineup consists of strongly tilted and folded sediments consisting of shales and basalts in metabolic status. Their age was determined several times by means of radiometric dating to 26 to 28 million years. The first finds came to light in 1997.
Eritreum was described in 2006 by Jehezekel Shoshani, inter alia, for the first time scientifically. The only known species is Eritreum melakeghebrekristosi. The genus name, Eritreum, represents the State of Eritrea, while the species name, melakeghebrekristosi, the local Farmer Melake Ghebrekristos honors, who had discovered the remains and recognized their importance.