Eritherium
- Eritherium azzouzorum
Eritherium is a now extinct genus of Proboscidea from the Paleocene of northern Africa. It lived about 60 million years ago and is so far the phylogenetically oldest known representatives of this mammalian order. Overall, it was relatively small animals. The body weight of Eritherium was reconstructed on 3-8 kg and thus was relatively large in the hyrax, which are among the closest relatives of mammoths.
Description
The holotype ( specimen number MNHN PM69 ) is now in the Museum National d' Histoire Naturelle in Toulouse and comprises an upper jaw with approaches the zygomatic bone and two pine branches, each of the two rear premolars (P3 and 4) and three molars (M1 -3) have. The piece is about 6 cm long, 5 cm wide and slightly more than 3 inches high. In addition, further comprise the 15 fossils found objects, bones of the skull, such as the frontal bone and the nasal bone, lower jaw fragments and teeth finds of the upper and lower jaw include ( Hypodigma ).
The fragmentary tradition of the skull allows for only a few statements about the appearance of Eritherium, most of the information related to the Zahnbau and teeth morphology. General informed Eritherium some similarities in the teeth structure with other Paenungulata as the extinct Embrithopoda or early representatives of the manatees, but the teeth are partly already more specialized than these. The dentition of the lower jaw, which could be reconstructed on the basis of two left fragments that included the complete original series of teeth of the permanent dentition of mammals with three incisors, one canine, four premolars and three molars. The tooth row was closed and had no diastema between the canine and premolar teeth. This primitive mammalian dentition is unique in the trunk animals, as even with the slightly younger forms Phosphatherium and Numidotherium the third incisor in the lower jaw was no longer formed and thus indicates the incipient reduction of the number of teeth in the development of this mammalian order.
The molars generally showed a bunodonten ie with a small enamel cusps on the chewing surface provided construction. Between these humps but approaches were to form two cross- bars on the first two and three on the rearmost molar very small, which is typical for lophodonte teeth. The premolars had, however, only one ( in the lower jaw ) or two ( in the maxilla) cusps. The significant difference between the molars and Prälmolaren underscores the antiquity of Eritherium as in later proboscidean the premolars strongly the molars same as it was at the slightly younger Phosphatherium the case. Furthermore, the first incisor was designed to be relatively large and with an asymmetrical crown while the canine had a rather small shape and already showed signs of reduction. Both Eritherium connects with other early proboscidean. A tendency to form tusks from the first or second incisors seems to have not yet occurred. Another primitive characteristic was the short symphysis of the mandible. The reconstruction of the upper part of the skull showed that there was the eye socket in the level of the fourth premolar and the first molar and thus relatively far forward lay in the skull. While this was sitting at Phosphatherium even further forward, other early Paenungulata but usually had a clear set-back position of the orbit.
System
As previously oldest representatives of the Proboscidea Eritherium stands at the base of the phylogenetic development of these regulations. Structurally it has not been assigned to any particular family within the Proboscidea. But Eritherium represents the Schwesterklade to develop line of Phosphatherium, Numidotherium and Moeritherium and shapes continue with these and Daouitherium included one of the most complete sequences far from the early history of a mammalian order. The discovery of this animal's snout made it possible now to trace the lineage of today's elephants to the late Paleocene. This includes Proboscidea in addition to predators and rodents of the oldest "modern " mammal orders that have survived until today.
Furthermore, cladistic studies indicate that manatees and Desmostylia form the next outer sister group. With these and the Embrithopoda and the hyraxes the proboscids the group of Paenungulata form. Their phylogenetically older representatives had partly bunodont to partly lophodont built molars, but here there are some cases still considerable gaps tradition. However, such molars of the original morphotype in this taxonomic group seem to have been. Since he also appeared in the phylogenetically older forms of elephant shrews, it can be assumed that such a Zahnbau was characteristic of early Afrotheria.
Discovery history
The findings of Eritherium 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, where in 1996 and 2002 with Phosphatherium two very early representatives of the Proboscidea were described with Daouitherium. The fossils were in the lower bone bed ( " lower bone bed " ) of bed IIa phosphate layer of the local stratigraphy. This is an archaeological layer also contained an accompanying fauna with the earliest evidence of carnivorous Hyaenodontidae, but mainly due to the characteristic Plattenkiemer fauna (including Hologinglymostoma, Palaeogaleus ) they can be placed in the geochronological phase Seelandium ( million years ago, 61.1 to 57.8 ).
With the kind Eritherium azzouzorum there is only one representative within this genus. Were first described genus and species of Emmanuel Gheerbrant in 2009. Eritherium The name appears from the Greek and means eρυ ( eri, old) and θηρίον ( THERION, animal ), while the species name azzouzorum the inhabitants Ouled Azzouz near the mine Sidi Chennane honors, who had discovered the majority of the fossils.