Chilgatherium

Chilgatherium
Teeth of Chilgatherium ; E to G form part of the holotype
Temporal occurrence
Oligocene
27 million years
Locations
East Africa
Systematics
Afrotheria Paenungulata Tethytheria Russell animals (Proboscidea) Deinotheriidae Chilgatherium
Scientific name
Chilgatherium
Sanders , Kappelman & Rasmussen , 2004

Chilgatherium is an extinct species from the order of the trunk animals (Proboscidea). It is within the mammoths for family of deinotheriidae provided which is a very original group of early members of this mammalian order. Chilgatherium is only known from tooth finds from Ethiopia , which are the earliest records of this family. The only recognized species is Chilgatherium harrisi .

features

Chilgatherium is so far only known about a dozen dental finds that belong to both the upper and lower jaw. They include the posterior premolars (P3 and 4) and the molars (M1 to 3). The rear molars had an oval shape with a maximum length of 6 cm. The chewing surface was characterized by transverse and clearly protruding enamel ridges , which, however, were raised again at the respective ends by additional cusps ( bunolophodont ). Each of the three molars had three of these ridges ( trilophodont ), but the third or rearmost was less developed. As a result, these teeth differed from those of Deinotherium , whose ridges were more pronounced and without additional enamel humps, i.e. were strictly lophodontic . In addition, Deinotherium had only two ridges ( bilophodont ) on the last two molars (M2 and 3 ), only the first (M1) was trilophodont. The premolars of Chilgatherium were significantly smaller than the molars and had rather humped enamel cusps on the chewing surface, which gave them a bunodont tooth character than those of Deinotherium .

Systematics

Chilgatherium is considered a genus from the extinct family of Deinotheriidae and is related to the younger and more modern Deinotherium , one of the largest known representatives of the proboscis that lived from the Miocene to the early Pleistocene . The design of the molars in Chilgatherium , which differs from Deinotherium , suggests an origin of Deinotherium in proboscis with more bunolophodontic posterior teeth and three enamel ridges. A large part of the early proboscid animals in question, such as barytherium or numidotherium, also had significantly more lophodontic molars with only two ridges. A possible candidate would be Arcanotherium from Libya , which is known only from a few fragments of teeth, but had bunolophodontic teeth and had two groins on the front molars and three on the last. However, the previous evolutionary models of the proboscis can not adequately explain a secondary reduction of the third bar in Deinotherium . If Arcanotherium should be placed in the line of ancestors of Chilgatherium , an exclusion from the family of Deinotherium would be probable according to today's status.

From the point of view of biological systematics , the exact position of the Deinotherien family within the order of the proboscis was always difficult. As with the genealogically younger Deinotherium, it can be assumed that Chilgatherium had all teeth in use at the same time (vertical tooth change). This is a clear difference to the modern proboscis with their horizontal change of teeth and clearly places the proboscis representative in the first radiation phase of this mammalian order. These earliest proboscis are generally divided into the primitive Plesielephantiformes, characterized by anterior molars with two enamel ridges, and the more developed Elephantiformes with three ridges. Due to the second molar with two ridges in Deinotherium , this is often assigned to the Plesielephantiformes, but since this is possibly a derived and not an original feature (the first molar has three ridges), some researchers also advocate a position within the more modern Elephantiformes. The findings of Chilgatherium could support an assignment of the Deinotheriidae to the Elephantiformes, but a more precise classification has not yet been made.

The first scientific description of Chilgatherium was made in 2004 by William J. Sanders and research colleagues on the basis of finds from Chilga in Ethiopia . The holotype is a row of teeth from the three right and rear two left molars (copy number CH35-3a-e), which is kept in the Ethiopian National Museum in Addis Ababa . Due to the differences in tooth structure, Chilgatherium was assigned to its own subfamily Chilgatheriinae within the Deinotheriidae. So far, one species is known with Chilgatherium harrisi . The generic name Chilgatherium refers to Chilga as a place of discovery, while the Greek word θηρίον ( thērion ) means "animal". The species name harrisi honors John M. Harris for his extensive research into deinotheria.

Discovery story

The Chilgatherium finds were discovered in Gahar Valley in the Chilga region in northwestern Ethiopia , a plateau-like landscape that rises at an altitude of 1950 m above sea level. In numerous outcrops in river valleys, which include at least 70 discovery points and locally up to 130 m thick, the geological deposits leading to the discovery are exposed, which consist of volcanic clasts, coal, and clay and silt stones . Radiometric dating of orthoclase minerals from these fossil-bearing strata showed an age of 27.4 million years; the base area under the find strata is about 32.4 million years old, according to similar studies. Both results date to the Oligocene . The finds of Chilgatherium , which come from the location Chilga 35, are thus the oldest remains of Deinotheria, the next younger come from Kenya and are a little older than 20 million years. The fossils were associated with remains from other proboscis such as Phiomia and Palaeomastodon , but also with those from Arsinoitherium and several representatives of the hyrax . The finds were recovered between 1998 and 2003 during scientific field research.

Individual evidence

1. ↑ ^{a b c d e} William J. Sanders, John Kappelmann and D. Tab Rassmussen: New large-bodied mammals from the late Oligocene site of Chilga, Ethiopia. Acta Palaeontologica Polonica 49 (3), 2004, pp. 365-392
2. ^ 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
3. ↑ Jehezekel Shoshani, William J. Sanders and Pascal Tassy: Elephants and other Proboscideans: a summary of recent findings and new taxonomic suggestions. In: G. Cavarretta et al. (Eds.): The World of Elephants - International Congress. Consiglio Nazionale delle Ricerche. Rome, 2001, pp. 676-679
4. ^ 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, pp. 340-360
5. ↑ John Kappelman, D. Tab Rasmussen, William J. Sanders, Mulugeta Feseha, Thomas Bown, Peter Copeland, Jeff Crabaugh, John G. Fleagle , Michelle Glantz, Adam Gordon, Bonnie Jacobs, Murat Maga, Kathleen Muldoon, Aaron Pan, Lydia Pyne, Brian Richmond, Timothy Ryan, Erik R. Seiffert, Sevket Sen, Lawrence Todd, Michael C. Wiemann and Alisa Winkler: Oligocene mammals from Ethiopia and faunal exchange between Afro-Arabia and Eurasia. Nature 426, 2003, pp. 549-552