Propalaeotherium

Propalaeotherium

• Germany ( Messel, Eckfelder Maar, Geisel )
• Switzerland
• France, Spain, Great Britain

Propalaeotherium is an extinct mammal species that is classified in the related with the horses family of Palaeotheriidae. This group presented not the direct ancestors of the horse is, but formed a relatively early again extinct side branch.

Features

Propalaeotherium similar in physique to the known Hyracotherium. There are known several species of this genus, of which the greater a total length of about 90 cm had, but which accounted for about 26 cm on the tail. The height at the withers was 43 cm, due to the strong curvature of the spine was the highest point of the hull approximately at the lumbar spine and reached here about 53 cm in height. Characteristic of the genre was the short neck. The skull measured up to 22 cm and was elongated and wedge- like shape in the side view. The occiput was rather short and rectangular in shape, but sometimes vaulted clearly concave in side view. The nose took some with over 10 cm in length almost half the length of the skull. Is noteworthy, however, that the Nasenincisur to form the nasal cavity einragte only about 3 cm and thus was relatively short in contrast to Palaeotherium. The front line was relatively straight forward and was not as strongly curved as in Hyracotherium or Palaeotherium, so that this feature already clearly recalled the modern horse.

The mandible reached a length of about 20 cm and had a poorly trained symphysis, the mandibular rami were relatively low. Both in the upper and in the lower jaw the full Säugetierbezahnung was using the following formula for the duration teeth. The incisors were relatively small and pointed. For each subsequent canine was a small diastema. The canine itself was formed significantly larger than the incisors and conically pointed. Another, this time larger diastema was the posterior dentition. These had only low tooth crowns on ( brachyodont ), while the occlusal surface of the molars were formed from two enamel strips that cross stood and bumpy at the ends surveys had ( bunodont ). The premolars, especially the front, were, however, very little molarisiert and had only single hump on.

The postcranial skeleton is known comprehensively due to the numerous finds. The spine consisted of seven cervical, eighteen thoracic, five lumbar and five sacral vertebrae. The caudal vertebrae reached, a total of nineteen. The spine is characterized by a high curve-like course. The femur achieved an average length of 18 cm, the tibia in a larger species of 15 cm. The fibula was preserved as a separate bone narrow and not reduced as in today's horses, such reduction did not begin until later in the Miocene. The length of the humerus bone was 14 cm on the average. Radius and ulna were fused together, the spoke reached 13 cm in length. The hind limbs ended in three toes, the central beam was most strongly pronounced. As with many early perissodactyls the front legs still had an additionally trained, smaller fourth toe.

Localities

Propalaeotherium lived in the Middle and Upper Eocene and is one of several localities in Europe known. One of the most important is the Geisel valley near Halle in Saxony- Anhalt. The Fund areas of both the lower and the middle and upper Braunkohleflözen come from more than 200 residues this Urpferdes, including numerous bones, teeth and articulated skeletal elements, but also an almost complete skeleton, which was recovered in 1933. Other outstanding discoveries came in the Messel Pit near Darmstadt (Hessen) to days. The site yielded more than a dozen complete, integrated in oil shale skeletons. The third reference in Germany with high quality fossils is the Eckfelder Maar in Rhineland- Palatinate. Here are several related skeletons survived, including one of a pregnant mare.

In addition to these three major sites, there are other in England, France, Spain and Switzerland. Noteworthy is the karst column in Egerkingen (Canton Solothurn ), Switzerland, from which come some of the recent finds of Propalaeotherium. In France, numerous finds from the Paris Basin are known. The finds include but mostly teeth fragments, teeth and isolated bones and rarely belong together skeleton games.

Paleobiology

Male and female animals of Propalaeotherium can be distinguished mainly on the shape of the pool next to the different size of the canines, which are substantially longer in stallions. In mares while the opening of the ilium due to the birth canal is much further, while it is not only smaller in stallions but is concentrated by the projections on the ilium even further. The general appearance of the genus but is characterized by the short neck and high curved topline. Similar body shapes are rare today in ungulates, but come at the duikers, especially the zebra duiker in West Africa before, but which are among the bovids and thus to the even-toed ungulates. Nevertheless, this particular body shape is likely to be a special adaptation to the tropical rain forest with dense undergrowth vegetation and dry terrain. The four-engine front feet of Propalaeotherium enabled additionally a good locomotion in moist to swampy terrain. Rainforests with mehretagigem vegetation structure and interspersed with moist biotopes be reconstructed for the Geisel and Messel.

With regard to the preservation of the soft tissue, the findings of Messel are outstanding, in which the soft tissues are not self but traced by bacterial processes ( Bakteriographie ). In a fossil of Propalaeotherium the rest of the Schwanzbehaarung is depicted as a shadow. In contrast to the tail of today's horse hair but are trained bushy stand-off. Moreover, the shape of the ears is for the related genus Eurohippus handed, which hardly differs from those of today's wild horse, however, was not designed as bag- like, as in the zebra. In a fossil which is also closely related genus Hallensia internal organs could be detected. It turns out that already the ancestral horses showed a greatly enlarged intestinal tract and probably were Enddarmfermentierer even then, that is, that the digestive system of these animals most of the intestine took place. Such early detection of such a digestion process could mean that the development of this particular gastrointestinal tract was developed already in the oldest perissodactyls and had not formed independently.

The niederkronigen teeth and her bunodonter construction generally speak for a specialization in soft plant foods, such as leaves or fruit. The well-preserved skeletal remains with partially intact gastrointestinal contents confirm this assumption. As early as the 1970s were in some fossils from Messel, which today but counted in the closely related genus Eurohippus, leaf debris from twelve different kinds of laurel family, together with five other plant families, as hickory, figs, myrtles and Hundsgiftgewächse determined. Further investigations in Messel countless seeds of vines plants were detected, confirming that even fruits had a significant share in the food spectrum. Early 2000s also managed the study of the digestive tract of the 1933 in the Geisel recovered skeleton of Propalaeotherium. Here numerous leaf debris of heather and belt flowers plants came to light, but also fruit and flowers were, as the existing seeds and pollen show obviously does not disdain. Furthermore, sand and quartz grains were also frequently seen, indicating that Propalaeotherium its food largely AESend recorded in plant debris lying on the ground without hitting it a special pre-selection.

The complete skeleton of the mare with fetus from the corner squares Maar is an added insight into the paleobiology. The presence of a single fetus indicates the characteristic reproductive strategy of today's hoofed animals, which usually bring just a young one, but which is intensively cultivated ( "k - strategy "). Even with the closely related species Eurohippus parvulus are from Messel at least eight mares each with a fetus known, so this method of reproduction is to be regarded as typical of the ancestral horses. This also points out that even the early equine representatives as today's lived in herds, or at least small group associations and so arranged protection of later generations.

Despite numerous outstanding fossil finds few pathological findings have so far been established. One of the few is a different position of a premolar in a mandible from the Geisel. The tooth was rotated by 180 °, which initially resulted that the animal his jaw could not fully close. However, showing the abrasion of the teeth that this did not affect strongly the animal.

System

About the taxonomic position of Propalaeotherium there are different views. Is a widely held assumption that the genus within the superfamily Equoidea ( Equine ) to the family of Palaeotheriidae, the sister taxon of the horses ( Equidae) family belongs. Within the group Palaeotheriidae Propalaeotherium represents the ancestors of Palaeotherium, as noted by the scientific name indicates. Other researchers, mostly from Central Europe, but are of the opinion that Propalaeotherium is a member of the Equidae and there belongs to the subfamily Hyracotheriinae. Reasons for this include the much larger nose cavity while the Palaeotheriiden, the significantly smaller precipitates in Propalaeotherium and equidae, as are the molars at Palaeotherium are noticeably hochkroniger. Another difference lies in the expression of the hand and foot bones, which at the Palaeotheriiden former are significantly elongated than the latter, which is exactly the opposite in the equine and Propalaeotherium but. Due to its takes Propalaeotherium may be more a kind of intermediate position between the two families. Reasons for the different measurement of position of Propalaeotherium and other early Equoiden within the Central European research can be found, according to some experts, partly in Frankfurt's theory of evolution.

Nearly a dozen species have been described by Propalaeotherium, of which five species are currently recognized:

• Argentonicum P. Gervais, 1848-1852
• P. hassiacum Main, 1925
• Helveticum P. Savage, Russell & Louis, 1965
• P. isselanum Cuvier, 1824
• P. voigti Matthes, 1977

The first scientific description of Propalaeotherium was made in 1849 by Paul Gervais ( 1816-1879 ) on the basis of fossils from Issel, which have already been considered in 1824 by Georges Cuvier as the type Pachynolophus isselanus belonging. In 1925, originally performed by Oskar main as an independent species Propalaeotherium fair lense from the Messel Pit in 1986 equated with Propalaeotherium parvulum which Charles Léopold Laurillard had introduced in 1849 (although as Lophiodon parvulum ). In 2006, however, Jens Lorenz Franzen P. parvulum ordered the new genus Eurohippus to which, although related to Propalaeotherium close, but is considerably smaller and differs in individual dental features. Much of the Messel Urpferdskelette, 60, is a thing of the species E. parvulus. The skull fragments from China, the sinense one hand in 1930 by Otto Zdansky as Propalaeotherium, on the other hand in 1944 by Chung Chien Young as Propalaeotherium hengyangensis have been described, recent investigations rather belong to the basal Chalicotherien.

Propalaeotherium made ​​her first appearance at the beginning of the Middle Eocene. It is largely detected only in Europe. The major findings from the Geisel, the Messel Pit and the corner squares Maar each case allocated to a later phase of the dissemination of Urpferdgattung. In the Upper Eocene Popalaeotherium disappeared. The latest finds are those of Egerkingen in Switzerland.