Teletaceras
| Teletaceras | ||||||||||||
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Illustration of Teletaceras sp. |
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| Temporal occurrence | ||||||||||||
| Middle Eocene to Upper Eocene | ||||||||||||
| 41.1 to 33.9 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Teletaceras | ||||||||||||
| Hanson , 1989 | ||||||||||||
Teletaceras is a very primitive, now extinct representative of the rhinoceros , which lived inboth North America and Asia in the Upper Eocene around 40 to 34 million years ago. It was a very small rhinoceros shape and had no horn formations, but so far only a few skulls and teeth as well as small remains of the body skeleton have survived.
features
Teletaceras comprised small representatives of the rhinoceros, which reached the size of today's small tapirs , weights are around 152 kg. The rhinoceros representative is largely known from skull finds; only a few postcranial skeletal elements are available. Only the metacarpus IV of the forefoot is preserved, the upper saddle-shaped joint surface for the attachment of the hookbone (unciform) indicates that the entire hand was probably composed of only three rays and not of four, as in all other early unpaired ungulates . Such a three-pronged hand differs significantly from the four-pronged hands in younger rhino representatives like Trigonias and is to be understood as an independent, derived development within Teletaceras ( autapomorphy ). Only later did the rhinos develop hands with only three fingers. The hindfoot is much more extensively covered with several ankle bones and heel bones , metatarsal bones and individual toe phalanges and, like today's rhinos, typically had three rays. As with most odd-toed ungulates, the center of gravity of both the front and rear foot was most likely on the third one ( Metapodium III).
The skull was about 38 cm long and very elongated, narrow and flat. The zygomatic arches showed only a slight curvature. The occiput was short and right-angled, the occiput showed a deep depression in the middle when viewed from above. The nasal bone was long and narrow and protruded far beyond the median jawbone . The two bones were not connected to each other, but the interior of the nose was not very large, but ended just behind the canine . There were no roughening on the surface of the nasal bone that would indicate the presence of a horn, as is typical of the very early representatives of the rhinos. The orbit sat above the second molar . Beginning above the eye sockets, a slight bony elevation ran over the parietal bones , creating a kind of lower crest marked in the middle by a narrow groove , which is usually missing in later rhino representatives. The forehead line was also slightly curved, which is also atypical for rhinos, but occurred in the related Hyracodontidae .
The lower jaw reached up to 28 cm in length and was very low. The dentition, which had the full number of teeth in mammals, was striking, which resulted in the following tooth formula in adult animals: The incisors of the upper jaw were small and, except for the first, were vertical in the jawbone. The first incisor (I1) pointed slightly forward and was conical and not yet the typical chisel shape of the late rhinos. The lower incisors here were also small, except for the second, the I2, on the other hand, was slightly enlarged, curved and had a triangular to teardrop-shaped cross-section. Like the I1 of the upper jaw, it protruded slightly forward. As a result, the typical "chisel-tusk formation" of the rhinos at Teletaceras was not yet given. Behind the canine, which barely protruded from the smaller incisors, was a small diastema , so that the entire row of teeth was no longer closed. The premolars and molars had low ( brachyodontic ) tooth crowns. The premolars in particular were very primitive and hardly resembled the molars, so they were not molarized. However, the molars already had clearly curved enamel folds on the chewing surfaces.
Fossil finds
Finds of teletaceras are known from both Eurasia and North America . Very extensive finds with five complete skulls, three lower jaws and postcranial skeletal elements are from the uppermost layer member of the Clarno Formation of the Hancock Quarry in the US state of Oregon . An age of 37.1 million years, determined with the help of potassium-argon dating, comes from a tuff underlying the fossil horizon , which is to be regarded as the maximum age of the finds. Other North American fossil remains, including a mandible fragment, come from Titus Canyon in Death Valley National Park in southeastern California. Teeth from Eurasia are mainly known from Artyom near Vladivostok in eastern Russia . Finds that are rather uncertain about Teletaceras have been reported from the Yongle Basin in southern China and from the Pondaung Formation in central Myanmar , the latter being clearly assigned to Teletaceras in a publication from 2006 .
Paleohabitat
On the basis of other finds from the fossil sites, a forested biotope can be identified at the time of the late Eocene , in which Teletaceras largely lived. A subtropical to tropical climate with an average annual temperature of 25 ° C could be reconstructed . It only became cooler in the transition to the Oligocene .
Systematics
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Internal systematics of the North American rhinos according to Prothero 2005
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Teletaceras represents a genus within the family of rhinos represents and belongs beside Uintaceras and Penetrigonias to the phylogenetically oldest representatives. It belongs to the subfamily Diceratheriinae and within this to the tribe Trigoniadini. These include primitive hornless rhinos and contrast with the clade of the two-horned Diceratheriini.
Three types are recognized today:
The first description was in 1989 by the American paleontologist C. Bruce Hanson . Some of the fossils were originally assigned to Eotrigonias , a taxon that was introduced by Chester Stock in 1949 as belonging to the rhinos, but was dissolved again by Leonard Radinsky in 1967 , since most of the material was to be assigned to the Hyracodontidae . Only the finds from the Clarno Formation in Oregon had no scientific description until 1989 and were referred to as Clarno Rhinos in earlier publications and placed at the base of the rhinoceros family tree. The name Teletaceras comes from the Greek words τελετα ( teleta "initiation" or "introduction"; however , teleta in the scientific name is written without "a"), α ( a "not") and κέρας ( kéras "horn"). The meaning refers to the genus very early position of the genus and the lack of horns.
Teletaceras first appeared in the late Middle Eocene around 39 million years ago. It is possible that the early representatives immigrated to North America from Asia . The rhinoceros representative disappeared from Asia 37 million years ago, in North America it persisted until 34 million years ago.
Individual evidence
- ↑ a b c Takehisa Tsubamoto, Naoko Egi, Masanaru Takai, Chit Sein and Maung Maung: Middle Eocene ungulate mammals from Myanmar: A review with description of new specimens. Acta Palaeontologica Polonica 50 (1), 2005, pp. 117-138
- ↑ a b c d e f C. Bruce Hanson: Teletaceras radinskyi, a new primitive rhinocerotid from the late Eocene Clarno formation of Oregon. In: Donald R. Prothero and Robert M. Schoch (Eds.): The evolution of perissodactyls. New York and London, 1989, pp. 379-398
- ↑ a b c d e Donald R. Prothero: The evolution of North American rhinoceroses. Cambridge University Press, 2005, pp. 1-219o
- ↑ Elizabeth I Beljaeva: Sur le decouverte de Rhinoceros tert aires anciens dans la Province Maritime de l'URSS. Vertebrata PalAsiatica 3 (2), 1959, pp. 81-92
- ↑ a b c Pierre-Olivier Antoine, Stéphane Ducrocq, Laurent Marivaux, Yaowalak Chaimanee, Jean-Yves Crochet, Jean-Jacques Jaeger, and Jean-Loup Welcomme: Early rhinocerotids (Mammalia: Perissodactyla) from South Asia and a review of the Holarctic Paleogene rhinocerotide record. Canadian Journal of Earth Sciences 40, 2003, pp. 365-374
- ↑ Patricia A. Holroyd, Takehisa Tsubamoto, Naoko Egi, Russell L. Ciochon , Masanaru Takai, Soe Thura Tun, Chit Sein and Gregg F. Gunnell: A Rhinocerotid Perissodactyl from the Late Middle Eocene Pondaung Formation, Myanmar. Journal of Vertebrate Paleontology 26 (2), 2006, pp. 491-494
- ↑ Donald R. Prothero, Earl Manning and C. Bruce Hanson: The phylogeny of the rhinocerotoidea (Mammalia, Perissodactyla). Zoological Journal of the Linnean Society 87, 1986, pp. 341-366
