Trigonias
| Trigonias | ||||||||||||
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Skeletal reconstruction of Trigonias |
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| Temporal occurrence | ||||||||||||
| Middle Eocene to Lower Oligocene ( Priabonian ) | ||||||||||||
| 38 to 33.9 million years | ||||||||||||
| Locations | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Trigonias | ||||||||||||
| Lucas , 1900 | ||||||||||||
Trigonias is an extinct genus of rhinos and livedin North America during the mid and late Eocene , 37 to 34 million years ago. It is one of the earliest representatives of the rhinoceros and reached about the size of today's cattle , but had no trained horn. The animals lived largely in open forest landscapes and ate a soft vegetable diet.
features
Tigonias represented a rather small representative of the rhinos, which reached a head-torso length of about 200 cm and a shoulder height of 110 cm. The weight is given as 600 kg, sometimes up to 830 kg. Older figures of only 250 kg are based on fossils that are now assigned to other rhinoceros. It is generally described as the size of a bovine . The short, strong limbs were characteristic .
The skull was about 47 cm long, built low and had protruding cheekbones . The forehead line was relatively straight, but the occiput was clearly pulled out so that a distinctive saddle was created in the rear area. Furthermore, the occiput was rather narrow. The nasal bone was poorly developed, but was elongated and narrow. Signs of a horn in the form of roughened surfaces could not be observed. The upper jaw and the intermaxillary bone were also narrow. There was a large nasal cavity between this and the nasal bone.
The lower jaw reached about 39 cm in length, but was built narrow and graceful with a low jawbone. The symphysis was about 7 cm long. Trigonias had very primitive teeth with only a few tooth reductions. Adult animals had the following dental formula . The upper incisors stood vertically in the jaw, the lower ones protruded forward. They were rather small, with the exception of the lower second. These formed tusk-like teeth with a length of 2 cm. The canine was also very small. There was a diastema up to 3 cm wide towards the posterior teeth . The molars had a low crown ( brachyodont ). With the exception of the last , the premolars were hardly molarized and so clearly differed from the molars . The row of teeth increased significantly towards the back in size of the individual teeth. In the upper dentition the penultimate, in the lower dentition the last was the largest tooth with a diameter of about 4 cm.
The body skeleton is very well known due to numerous finds. The spine consisted of 7 cervical, 18 thoracic, 5 lumbar, 5 sacrum and 23 caudal vertebrae. The height of the spinous process on the first thoracic vertebra was 16 cm. The humerus reached 28 cm in length and was therefore extremely short, with the joint head pointing clearly upwards. The forearm bones, on the other hand, were significantly longer and slimmer. The ulna was up to 35 cm long, the radius up to 28 cm. The femur was cylindrical in shape and 34 cm long. The tibia was shorter than the radius and had a length of 25 cm, while the fibula had significant reductions. The front legs ended in four toes ( tetradactyl ), similar to many phylogenetically old rhino groups. The central ray ( metacarpus III) with a length of 12 cm was strongest . The fourth toe (Metacarpus V) was markedly regressed compared to the others. Like today's rhinos, the foot had three toes. Here, too, the central ray ( metatarsus III) was 11 cm more massive than the other two rays lying on the inside and outside.
Locations
Finds of Trigonias have so far only come from North America and were mainly made in the High Plains . Significant fossils come from the Chadron Formation in South Dakota , more precisely the "Lower Titanotherium bed" ( Lower Titanotherium bed ), a series of volcanic and silicate sediments within deposits formed by wind and water (aeolian and fluvial), the middle and late Eocene . Here Trigonias is often identified with the early horse Mesohippus , the rhinoceros Subhyracodon , but also the huge, almost 2 t heavy Brontops belonging to the Brontotheria (originally Titanotheria) . Other finds, some of which include almost complete skeletons, came to light in quarries in Weld County in Colorado . Other sites are in Saskatchewan , Nebraska and California .
Paleobiology
The low-crowned molars suggest a specialization in soft or mixed vegetable foods. Originally, due to the relatively short limbs, a more semi-aquatic way of life similar to that of hippos was adopted. More recent isotope studies on the molars could not confirm this. Accordingly, the rhinoceros species lived in open landscapes, although it cannot be ruled out that the animal spent part of the day in the water.
Systematics
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Internal systematics of the North American rhinos according to Prothero 2005
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Trigonias is an extinct genus of the rhinos and belongs to the primitive subfamily of the Diceratheriinae , which were mainly found in North America. Their character form, Diceratherium , had two small horns on the tip of the nose. Within the subfamily, the rhinoceros genus is the namesake for the Trigoniadini tribe .
Numerous species were originally described, but two are recognized today:
Other species that have been described, such as T. tetradactylum , T. cooki , T. taylori or T. paucidens, are now largely assigned to the species T. osborni . It was first described in 1900 by Frederic A. Lucas , with a partially preserved skull of an ancient individual from the Chadron Formation in South Dakota, which was originally dated to the Miocene . The name Trigonias is made up of the Greek words τρεῖς ( treîs "three") and γωνία ( gonia "angle", "corner") and refers to the triangular shape of the lower incisors.
Trigonias was first detected in the Middle Eocene around 37 million years ago (locally stratigraphically assigned to the chadronium ) and is one of the earliest representatives of the actual rhinos, along with Teletaceras . Possibly the origin goes back even further (outgoing Duchesneum ). The original species was the smaller T.osborni . In the later Eocene T. wellsi developed , which was characterized by a much larger physique. The rhinoceros genus died out in the transition to the earliest Oligocene a good 34 million years ago and was replaced by the closely related genus Subhyracodon .
Individual evidence
- ↑ Christine M. Janis: Evolution of horns in ungulates - ecology and palaeoecology. Biological Review (Cambridge Philosophical Society) 57 (2), 1982, pp. 261-317
- ^ Donald R. Prothero: Fifty million years of rhinoceros evolution. In: OA Ryder (Ed.): Rhinoceros biology and conservation: Proceedings of an international conference, San Diego, USA Zoological Society, San Diego, 1993, pp. 82-91
- ^ A b c d e William Berryman Scott: Part V: Perissodactyla. In: William Berryman Scott, Glenn Lowell Jepsen, and Albert Elmer Wood (Eds.): The Mammalian Fauna of the White River Oligocene .. The American Philosophical Society, Philadelphia, Pennsylvania, 1941, pp. 775-821
- ↑ Wendy A. Schultz: Body size evolution in Leptomeryx and Rhinocerotinae (Subhyracodon and Trigonias) across the Eocene-Oligocene (Chadronian-Orellan) boundary. University of Nebraska, Lincoln, 2009
- ↑ a b c d e Donald R. Prothero: The evolution of North American rhinoceroses. Cambridge University Press, 2005, pp. 1-219
- ↑ a b Erwin Hinckley Barbour: A new rhinoceros mount: Trigonias osborni. Bulletin of the Nebraska State Museum 1, 1934, pp. 299-302
- ^ William K. Gregory and Harold J. Cook: New Material for the Study of Evolution: A Series of Primitive Rhinoceros Skulls (Trigonias) from the Lower Oligocene of Colorado. Proceedings of the Denver Museum of Natural History 8 (1), 1928, pp. 3-32
- ↑ a b Alessandro Zanazzi and Matthew J. Kohn: Ecology and physiology of White River mammals based on stable isotope ratios of teeth. Palaeogeography, Palaeoclimatology, Palaeoecology 257, 2008, pp. 22-37
- ↑ Kurt Heissig and Oldřich Fejfar: The fossil rhinos (Mammalia, Rhinocerotidae) from the Lower Miocene of Tuchorice in northwestern Bohemia. Sborník Národního Muzea v Praze. Acta Musei Nationalis Pragae (series B, Natural History) 63 (1), 2007, pp. 19-64
- ^ Frederic A. Lucas: A new rhinocere Trigonias osborni from the Miocene of South Dakota. Proceedings of the United States National Museum 23, 1901, pp. 221-223