Eurodexis

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Eurodexis
Eurodexis skeleton

Eurodexis skeleton

Temporal occurrence
Lower to Middle Eocene
50.7 to 41.1 million years
Locations
Systematics
Higher mammals (Eutheria)
Laurasiatheria
Artiodactyla (Artiodactyla)
Dichobunidae
Eurodexeinae
Eurodexis
Scientific name
Eurodexis
Erfurt & Sudre , 1996

Eurodexis is a now-extinct member of the artifacts thatlived in Europein the Lower and Middle Eocene 51 to 41 million years ago. It is known through several finds from France and Germany, including from the Messel pit and the Geiseltal . In general, Eurodexis was very small and had a long snout. The animals may have fed on insects and mollusks or on fruits .

features

Eurodexis was a representative of the early cloven-hoofed ungulates and, like them, was extremely small with a characteristically arched back and short fore and long hind legs and a very long tail that was at least 22 cm long. The genus is known for an almost complete skeleton and a skull find. The skeleton refers to an animal with a total length of around 50 cm. The skull find is badly crushed and still 7.5 cm long, but in the original state it was probably around 10 cm. However, due to its state of preservation, only a few diagnostic features are recognizable. The palatine bone ended somewhat thickened above the last molar . The orbit was about 1 cm in diameter and sat above the first and second molars. It was also not completely enclosed by the zygomatic arch. The lower jaw had a very slender and elongated structure and reached about 8 cm in length, with it being about 1.2 cm high behind the last molar. The dental formula corresponded to that of the other early Higher mammals and read: . The pin-shaped incisors , which only reached a height of around 1 mm, were characteristic. They did not form a closed row of teeth, but were each a good 2 mm apart. The lower canine resembled the incisors, the upper the anterior premolars . The posterior dentition was separated from the anterior by a 4 mm diastema . However, there were also larger tooth gaps between the first three premolars. The molars were triangular in shape and quite similar in size, so that the length of the individual teeth varied between 5.3 and 5.6 mm. Overall, they had low tooth crowns ( brachyodont ) and a bumpy chewing surface, with the cusps, which consisted of tooth enamel, were relatively pointed.

The body skeleton is known from a largely complete find, the bones of which, however, were badly damaged and partly displaced. The spine is incomplete, but shows a clearly upward curve of the back. The tail comprised a total of 23 vertebrae, the middle ones being very long. The short front and long hind legs, which were built very slim overall, are characteristic. The humerus was about 6.8 cm long, the radius about 6 cm. The dimensions of the bones of the hind legs are accordingly 7.6 cm for the thigh and 9 cm for the shin . A striking feature of the femur was the presence of a third trochanter (rolling hillock) slightly above the middle of the bone as a muscle attachment point, which is generally absent in today's cloven-hoofed animals and was only developed in the earliest representatives, just as it is typical for most odd-toed ungulates . Nothing is known about the number of rays on the fore and hind feet, as these are not fully recorded. The end links of the forefeet were long and claw-like and therefore resembled those of today's deer .

Fossil record

two lower jaws from Eurodexis from the Geiseltal

Finds from Eurodexis are relatively rare and date to the end of the Lower and Middle Eocene between 51 and 41 million years ago (locally stratigraphically Lutetian ). The oldest finds come from Prémontré in the Aisne department in France and include individual teeth, a fragment of the upper jaw and some postcranial elements such as the talus . Similar old finds are also known from the Champagne-Ardenne region, but represent largely isolated teeth. A nearly complete skeleton from the Messel mine near Darmstadt is somewhat younger , but it is clearly dislocated and therefore has partly badly damaged bones. This was first associated with the genus Messelobunodon . The most recent finds so far have come down to us from the Geiseltal near Halle in Saxony-Anhalt. These include a crushed skull, some mandibular fragments and remains of the body skeleton such as a long bone fragment and parts of the ribs. These were found in the Cecilie and Leo opencast mines .

Paleobiology

The long, narrow lower jaw and the elongated snout, which are not known from primitive cloven-hoofed animals of about the same age, are particularly striking. This talk as well as individual tooth characteristics, such as the prolonged fourth premolar and the pointed Kauflächenhöcker, more for animal food. There may be malnourished Eurodexis of insects and molluscs , which went to rummaging in the topsoil. To confirm this assumption, however, the mandibular joints for the reconstruction of the masticatory muscles have so far been missing. In contrast to these anatomical assumptions, remains from the gastrointestinal area of ​​the Messel skeleton indicate a predominantly fruit-based diet.

In the musculoskeletal system, the elongated lower sections of the front and rear legs are particularly noticeable. In this characteristic, Eurodexis roughly corresponds to today's deer or the ibex . This suggests a nimble, running to jumping locomotion.

Systematics

Eurodexis is a genus of the extinct family of Dichobunidae within the order of the cloven-hoofed animals . Together with the Diacodexeidae , the Dichobunidae represent the most primitive forms of the ungulates. They were generally very small with an upwardly curved back and had very long tails, while the front legs were always shorter than the hind legs. Within the Dichobunidae, Eurodexis belongs to the subfamily Eurodexeinae with a close relationship to Eygalayodon and Herbertlutzius . A characteristic of the Eurodexeinae is an elongated snout, which arose from the extension of the premolars and the inclusion of several diastemas . Diacodexis can be assumed to be the predecessor of Eurodexeinae .

There are two types of Eurodexis :

It turns E russelli is the older type. Firstdescribed was Eurodexis in 1996 by Jean Sudre and Jörg Erfurt basis of the finds from the Geisel . The holotype (inventory number GMH Ce IV-305) includes a crushed skull that was described as belonging to the genus Messelobunodon as early as 1980 . The name Eurodexis is derived from the location in Europe and the close relationship to Diacodexis .

literature

  • Thomas Lehmann and Irina Ruf: The appearance of the artifacts. In: Stephan FK Schaal, Krister T. Smith and Jörg Habersetzer (eds.): Messel - a fossil tropical ecosystem. Senckenberg-Buch 79, Stuttgart, 2018, pp. 285–291

Individual evidence

  1. ↑ a b c d e Jörg Erfurt and Jean Sudre: Eurodexeinae, a new subfamily of the Artiodactyla (Mammalia) from the Lower and Middle Eocene of Europe. Palaeovertebrata 25 (2-4), 1996, pp. 371-390
  2. ↑ a b c Jens Lorenz Franzen: A second skeleton of Messelobunodon (Mammalia, Artiodactyla, Dichobunidae) from the "Messel Pit" near Darmstadt (Germany, S-Hessen). Senckenbergiana lethaea 64 (5/6), 1983, 403-445
  3. ↑ a b c d Thomas Lehmann and Irina Ruf: The emergence of the artifacts. In: Stephan FK Schaal, Krister T. Smith and Jörg Habersetzer (eds.): Messel - a fossil tropical ecosystem. Senckenberg-Buch 79, Stuttgart, 2018, pp. 285–291
  4. ↑ a b Jean Sudre and Jörg Erfurt: Les Artiodactyles du gisement Ypresien Terminal de Prémontré (Aisne, France). Palaeovertebrata 25 (2-4), 1996, pp. 391-414
  5. ↑ a b Jens Lorenz Franzen and Günter Krumbiegel: Messelobunodon ceciliensis n. Sp. (Mammalia, Artiodactyla) - a new Dichobunidae from the Middle Eocene fauna of the Geiseltal near Halle (Saale). Journal of Geological Sciences 8 (12), 1980, pp. 1553-1560
  6. ↑ Jessica M. Theodor, Jörg Erfurt and Grégoire Métais: The earliest Artiodactyls. In: Donald R. Prothero and Scott E. Foss (Eds.): The Evolution of Artiodactyls. Johns Hopkins University, Baltimore, 2007, pp. 32-58

Web links

Commons : Eurodexis  - collection of images, videos and audio files