Subhyracodon

Skeletal reconstruction of Subhyracodon

• North America

Subhyracodon is an extinct genus of rhinoceros and lived during the late Eocene to early Oligocene 37-29 million years ago in North America. The genus is one of the earliest representatives of this group of mammals, but possessed, unlike many later forms no horn formation. The animals reached the size of today's cattle and lived in open woodlands or riparian forests, where they mainly fed on soft vegetable diet.

Features

Subhyracodon comprised small to medium sized rhinoceros representatives who strongly their part simultaneously living relatives Trigonias were similar, but have some more modern features. They came to a head-body length of 210 cm and a shoulder height of around 120 cm. The weight is assumed to be 600-830 kg. Originally a value of 250 kg were as for Trigonias adopted, but this figure refers to agents that are currently assigned to other rhino species.

The skull was up to 49 cm long and was about elongated and very flat. In the plan, he was wedge-shaped with slightly projecting and laterally flattened cheekbones. The rear skull area rose less steeply than in Trigonias. The occiput had an only slightly pronounced bulge. It was also pronounced at right angles and had a significant dent in the plan. The nasal bone was poorly developed and elongated, but comparatively shorter than in Trigonias. Signs of horn formation on the surface in the form of roughened surfaces as attachment points are not known. Also the Zwischenkieferbein had an elongated shape and can, as well as the maxillary miss the characteristic reductions of more modern rhinoceros forms. Between these two bones and the nasal bone was a great and extensive nasal cavity. Means jaw bone and nasal bone were not interconnected.

The mandible reached 40 cm in length had a rather delicate structure with a weak, but up to 8 cm long symphysis. The height of the jawbone was more than 4.8 cm. Opposite Trigonias the bit is already clearly reduced, was the dental formula for an adult animal. The incisors were rather small and were vertically in the upper jaw, lower jaw obliquely forward at an angle of 45 °. The exception was the lower, second (outer) incisor, which was conically shaped and considerably enlarged, so that it reached a length of 2.4 cm. A canine was not formed. The diastema to the rear dentition was up to 2.4 cm. The molars were very niederkronig ( brachyodont ), the premolars were similar to the first molars. Here, the second was complete, the two rear strongly molarisiert. The largest tooth of the molar series was the second molar.

Also the body skeleton is well known due to numerous, partly complete skeletons. The spine consisted of 7 cervical, 18 thoracic, 5 lumbar, 6 sacral and 21 caudal vertebrae. The tapirartig curved arrangement of the thoracic vertebrae was offset by the length of the spinous again, forming a nearly straight line. Overall, these were much slimmer than Trigonias. The spinous process of the first thoracic vertebra reaching 16 cm in length. The upper arm bone was also leaner than the related Trigonias and had 30 cm length. The shaft of the 28 cm long storage is significantly curved, while the ulna with 35 cm length exceeding the upper arm. The femur was 37 cm with the largest bones in the skeleton. The tibia and fibula were not fused together. The former reached 28 cm, 26 cm length of the latter. Hands and feet ended in three toes ( tridactyl ), which was much more modern than Subhyraracodon Trigonias. As with all odd-toed ungulates was the main beam of the third, while the metacarpal bone ( metacarpal III) was 14 cm and the metatarsal ( metatarsus III) 13 cm long.

Locations

Subhyracodon has only been found in North America, where Nashornart was found with numerous skeletons in the High Plains. Significant fossils are detected from the Chadron Formation in South Dakota, meaning this is the Badlands National Park. They come there from the "Lower Titanotherium bed" ( Lower Titanotherium bed ), a sequence consisting of volcanic and siliceous sediments formed within by wind and water deposits ( aeolian and fluvial ) who belong to the middle and late Eocene. Here Subhyracodon occurs together with his relatives Trigonias, but often are also finds of the early horse Mesohippus and the huge, almost 2 ton Brontops, which (originally Titanotherien ) belongs to the Brontotherien. Other finds, including a lower jaw and postcranial skeleton parts arrived at Horse Trail Creek Member of the Brule Formation in Logan County, Colorado -a-days. Other sites are located in Saskatchewan and California. From the latter the U.S. state of recent discoveries, which dated to the Lower Oligocene and were discovered in the Vespe Formation in the Ventura County come.

Paleobiology

The findings so far largely come from sites with relative proximity to water. Perhaps Subhyracodon lived in lowland forests or in the transition areas to more open landscapes. The niederkronigen teeth suggest a relative specialization in soft plant foods, but studies also showed a certain amount of hard plant food. It is believed that the rhino species fed on fibrous plant parts and water-containing leaves. Further analysis of isotopes of oxygen in the molar teeth were quite high depending on the water, but the animals were not bonded to a semi- aquatic life. This is demonstrated by parallel investigations carried out on carbon isotopes in favor of a life in more open landscapes, bringing the animals probably preferred low trees and scrub vegetation as a food source.

System

Uintaceras

Teletaceras

Penetrigonias

Trigonias

Amphicaenopus

Subhyracodon

Diceratherium

Skinneroceras

Menoceras

Floridaceras

Aphelops

Galushaceras

Peraceras

Teleoceras

Subhyracodon is an extinct genus of rhinoceros and is provided for within these primitive subfamily of Diceratheriinae. These were mainly used in North America. Within the subfamily, the Rhinoceros genus belongs to the tribe Dicerathini. The namesake for both the subfamily and the tribe is Diceratherium, which was characterized by two horns on the nose.

Several types of Subhyracodon have been described, the following are valid today:

• S. Kewi floor, 1933
• S. mitis Cope, 1875
• S. occidentalis Leidy, 1850

Where s is the occidentalis type shape and was greater than the other two types. The most recent form from the late Oligocene is p Kewi. Other species described as S. Trigonodus, p metalophus, S. and S. gridleyi hesperius are now regarded as synonyms of S. occidentalis. The originally addressed as S. tridactylum rhino representative is now made ​​to Diceratherium.

Originally discovered in North America rhinos were assigned to the genus Rhinoceros by the American paleontologist Joseph Leidy in 1850, the following year, he directed them to Aceratherium. The first description of Subhyracodon was 1878 by the German naturalist Johann Friedrich von Brandt, the taxon but mite as a subgenus of the rhino species Aceratherium and Aceratherium occidentalis at her. The publication was in Latin and was published in a Russian publishing house. In 1881, the American zoologist Edward Drinker Cope Aceratherium pointed to mite the newly named by genus Caenopus; it is assumed that the description Cope Brandt did not know. American researchers use almost half a century the name Caenopus, in 1927 but had Horace Elmer Wood in 1927 indicated that Subhyracodon takes precedence, as it is the older name and raised Subhyracodon on genus level. However, it took some time before the name in North America prevailed because it was viewed largely elected as bad. The name Subhyracodon suggests a close position to the Hyracodontidae, the sister group of rhinos, but Brandt had so clearly described a representative of the rhinos. The name is derived from the Latin prefix sub - ( "under" ) and the scientific name for Hyracodon, which in turn connect from present-day name for the Hyrax ( Hyrax, actually Hyracoidea ) and the Greek word ὀδούς ( Odous "tooth" ) represents. Caenopus other hand, comes from the Greek words καινος ( kainos "new") and πούς ( pous "foot" ) and refers to the more modern, tridactyle hand or Vorderfußgestaltung the rhino species.

Subhyracodon first appeared in the late Eocene, about 37 million years ( lokalstratigraphisch outgoing Chadronium ). It is among the oldest in North America rhinos, older are largely only Teletaceras and Uintaceras. The oldest representative is S. ociidentalis. In the Lower Oligocene ( lokastratigraphisch lower Arikareeum ) before about 30 million years ago died from the rhino species and was replaced by Diceratherium. At that time, it was possibly only with S. Kewi today in the western part of North America spread. This Subhyracodon formed together with Diceratherium likely precursor forms of the later modern Rhinocerotinae to which they belong today's rhinos.