Uintatherium

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Uintatherium
Uintatherium skeleton

Uintatherium skeleton

Temporal occurrence
Lower? / Middle to Upper Eocene (Upper Bridgerian to Middle Uintum )
48.8 to 42.9 million years
Locations
Systematics
Mammals (mammalia)
Higher mammals (Eutheria)
Laurasiatheria
Dinocerata
Uintatheriidae
Uintatherium
Scientific name
Uintatherium
Leidy , 1872
species
  • Uintatherium anceps Marsh , 1871
  • Uintatherium insperatus Tong & Wang , 1981

Uintatherium is an extinct mammal from the Dinocerata group thatlivedin North America and East Asia during the Middle Eocene , 48 to 43 million years ago. It resembled today's rhinos and was one of the first large mammal forms after the dinosaurs became extinct. Its skull, which had three pairs of horns formed from bones, as well as the saber-like canine of the upper jaw, was characteristic. Uintatherium lived on soft plant food. The genus gained a certain degree of familiarity through its history of discovery, which began in 1872 and in the course of which it was described by three different researchers almost simultaneously under different names.

features

Uintatherium was next to Eobasileus one of the largest representatives of the Uintatheriidae , extinct early ungulates . In general, he had a massive, barrel-shaped or cylinder-shaped body and, according to some reconstructed museum skeletons, reached a head-torso length of 3.1 to 3.2 m, with a shoulder height of around 1.6 m. The weight is estimated at 1500 to 2000 kg, whereby it was slightly lighter than Eobasileus . The stocky, elephant-like legs each ended in five rays with hooves.

Skull of the Uintatherium

The skull reached a length of 69 to 85 cm and was very flat, but also very wide. It differed from other large Uintatheria in its general proportions; so had uintatherium a rather short rostrum , but a longer rear skull. The occiput was drawn out and elongated; when viewed from behind, it had a distinctly rectangular to square shape. The nasal bone lay well above the median jawbone and was often directed slightly downwards; compared to the frontal bone it was markedly extended in length. The orbit reached quite large dimensions. The outstanding feature of Uintatherium were three pairs of horns on the skull, which were formed by bony outgrowths. The foremost pair of horns sat on the front tip of the nasal bone and was very low, it consisted of only two slight bones. The middle, often very elongated pair was connected to the posterior end of the upper jawbone and protruded over the diastema between the canine and posterior teeth . The rearmost and also quite high pair of horns, on the other hand, started on the parietal bones .

The lower jaw was very robust, 49 to 54 cm in length, but relatively short compared to the skull. On the underside, in the anterior area, there were partly massive, downwardly protruding and convexly shaped bones. The bone body reached up to 12.5 cm in height, characteristically the joint ends were clearly far apart. The symphysis was strong and up to six inches long. The dentition was characterized by a few marked reductions, so the upper incisors were generally not formed. The dental formula was accordingly: . The lower incisors were only very small in shape, but had two conical cusps one behind the other . The lower canine was also rather small and resembled the incisors. The upper canine, on the other hand, reached enormous proportions. Overall, it was saber-like, flat, up to 6.6 cm long and 2.9 cm wide at the base, and curved backwards. Its total length reached 18 cm, measured over the outer curvature even 30 cm, so that it protruded well beyond the lower jaw. The lower bony outgrowths on the lower jaw served to protect this tooth. The posterior teeth were separated from the anterior by a large diastema measuring up to 11 cm . There were three premolars per mandibular arch ; the foremost was only very rarely found, which was then very small and attached directly to the canine before the diastema. Premolars and molars were comparatively small and low-crowned ( brachyodont ), the last molar was a maximum of 4.5 cm long. The chewing surface was characterized by two transverse enamel folds ( bilophodont ), characteristic was the formation of a V-shaped enamel fold on the upper jaw teeth, which is typical of early mammals .

The postcranial skeleton is largely fully known. The spine in particular resembles that of the proboscis , but the cervical vertebrae were comparatively longer, and the sacrum generally consisted of four vertebrae. The humerus was up to 60 cm long, the ulna up to 58 cm. The basin measured up to 120 cm across the extremities and was therefore very wide and rather low. The femur reached 71 cm in length and characteristically had no third trochanter . The shin measured up to 50 cm. All limbs ended in five rays. Both the front and the rear feet were rather wide and short, and the structure here was also very similar to the trunk animals.

Fossil finds

Skull of the Uintatherium

The majority of the fossil finds come from the US state of Wyoming and came to light in the upper area of ​​the Bridger Formation (sections C and D), which belongs to the Middle Eocene , but finds from the beginning of the Upper Eocene are also known. The Bridger Formation is widespread in the Bridger and Washakie Basins in southern Wyoming and is up to 200 m thick. The first finds go back to the 1870s and 1880s, in this research period alone, which falls into the time of the Cope-Marsh feud , which is important from a research point of view , countless fossil remains were found, including around 20 skulls or skull fragments and hundreds of postcranial bones Skeleton, including complete front and rear feet. From 1893 to 1906, the American Museum of Natural History carried out several expeditions in which the Washakie Basin, but also the Uinta Basin in the neighboring state of Utah, were the focus of investigation. Finds from the latter locality come from the Green River Formation, which is about the same to a slightly younger age . During these expeditions, in addition to around a dozen skulls, skull fragments and lower jaws, numerous parts of the body skeleton came to light. The findings of the United States Geologicals Survey of 1940 are also outstanding, including an almost complete skeleton near Henrys Fork and Sage Creek northwest of Lonetree, Wyoming, which was only missing a hind leg and part of the foreleg as well as the cervical vertebrae. From the second half of the 20th century, numerous investigations were carried out by the Field Museum of Natural History in Sweetwater County in Wyoming, with at least eleven skulls and skull fragments and individual parts of the skeleton being documented. The first finding of a relatively newborn animal should also be mentioned here. One of the most significant recent finds is a nearly complete, barely crushed, 75 cm long skull that was enclosed in a large sandstone block and was found in 1984 at Salazar Butte Quadrangle in Sweetwater County, Wyoming. Remnants of the body skeleton, such as the lower jaw, vertebrae, ribs and parts of the pelvis, which presumably all belong to the same individual, were later found at the original break off point of the block.

Originally regarded only as a genus common in North America, fossils have been discovered more frequently in East Asia since the early 1980s . This includes an almost complete skull from the Lushi formation in the Chinese province of Henan . One lower jaw comes from the Nomogen Formation in the Erlian Basin in Nei Mongol (Inner Mongolia), which originated in the Lower Eocene. In contrast, individual teeth and postcranial skeletal elements from the Üqbulak Formation in Xinjiang came to light, which in turn dates to the Middle Eocene. The first Uintatherium finds in East Asia, including several huge canines, were published in the 1960s from the Sinyu Formation in Jiangxi .

Paleobiology

Uintatherium , drawing by Heinrich Harder

Uintatherium had a physique that was reminiscent of today's rhinos, but was less robust, but it also had much longer legs than these, which also approximated those of proboscis in their structure . The locomotion was more plantigrad (sole walkers) than with today's elephants, which results from the simpler front and rear feet. The elongated skull suggests a rather low head position, so that the rear part of the occiput was more vertical. For this purpose, strong neck muscles are attached to the back of the head. The typical Lophodontic structure of the molars indicates that Uintatherium was a herbivore that mainly fed on soft foods ( browsing ). This is also indicated by the typical transverse grinding patterns on the molars. In addition, the teeth inside had an irregular arrangement of the tooth enamel in order to withstand higher loads. Furthermore, the lower incisors were possibly used to pluck the food, which is suspected due to the often heavily worn out tooth finds. The absence of the upper incisors suggests a strong and long tongue. The extremely wide basin, which in its proportions is also reminiscent of that of the proboscis animals, suggests that a very extensively developed posterior intestinal tract was developed in Uintatherium . This leads to the assumption that the Uintatherien possibly used their food in the rectum, similar to today's odd-toed ungulates . Otherwise, relatively little is known about the way of life. The long bones thickened by pachyostosis are noteworthy, but it is unclear whether this can be linked to a semi-aquatic way of life, where the thickened bones should balance the buoyancy of the body in the water.

The fossils of Uintatherium show a clear gender dimorphism . The canines of the males were much more pronounced and longer than those of the females. In addition, the females lacked the distinctive lower bony outgrowths on the lower jaw. Furthermore, their bony horns were less clearly developed. The combination of horns and pronounced canine teeth is unknown in today's ungulates; attention was first drawn to this fact in the early 1940s. Musk deer and deer have long upper canines used as weapons, but no antlers. Possibly the canines served as weapons in the mating or defensive battle with Uintatherium . Some skulls show broken canines during their lifetime, but these have polished marks and testify to further active use. The function of the six horns is also not clear; here, too, use for defense or display as well as disputes with conspecifics about the mating privilege is acceptable, similar to today's antler-bearing cloven-hoofed animals .

Systematics

Uintatherium is a genus of the Uintatheriidae family . Within the family, Uintatherium was placed in a revision of the Uintatherien by Walter Wheeler from 1961 to the subfamily Uintatheriinae, which are characterized by representatives with a large body in general and three pairs of bony horn formations and to which Eobasileus still belongs. Originally a third genus was described with Tetheopsis , a partial revision from the year 2002 by William D. Turnbull , but left the independence of this open, since at least one of the two species assigned to it is identical to Eobasileus . Opposite the Uintatheriinae are the Gobiatheriinae, which are characterized by the reduction of the upper canine teeth and an ossified nasal septum in the front part . While the status of the Gobiatheriinae as a subfamily was confirmed in the revision in 2002, some researchers see these partly as an independent family within the Dinocerata due to different tooth morphologies.

The Uintatheriidae are placed in the order of the Dinocerata , within this Uintatherium is one of the largest and most famous representatives. Known from North America and East Asia, this group of mammals was among the first giant forms to evolve after the dinosaurs became extinct. A common feature of all Dinocerata is the absence of the first premolar and the upper incisors (with the exception of the earliest representatives). The relationship to other mammals has not been fully clarified; a closer relationship postulated in the early 1980s via Pseudictops with the Anagalidae , ancient tribal small mammals from East Asia that are closely related to rodents today , turned out to be incorrect. This possible relationship was mostly assumed on the basis of common tooth features, but especially also the extremely small molars in relation to body size in the Uintatheria, but skeletal anatomical investigations refuted this assumption. Today the Dinocerata are generally assigned to the extensive but heterogeneous group of ungulates , where they form a very original branch. The Dinocerata are possibly more closely related to the "South American ungulates" ( Meridiungulata ), such as the Pyrotheria or the Xenungulata . The closest relatives living today are possibly the odd-toed ungulates . With these they share the formation of the hooves, the mesaxonic foot position (center of gravity of the axis of the foot runs through the middle (third) ray) and the lack of a deep groove on the talus for articulation with the Shin joint, which is common among Afrotheria , for example .

Originally, Uintatherium comprised almost 30 species in North America, but these were carried under the most diverse, now synonymous generic names, such as Dinoceras , Loxolophodon and Tinoceras . After a revision from 1961, only U. anceps is valid; this type received her in 1871 first description . Due to partly different characteristics in dental construction, U. insperatus is partly delimited as an independent genus in East Asia . The name Uintatherium is composed of the name for the Uinta Mountains in northeast Utah and southwest Wyoming and the Greek word θήριον ( thêrion "animal").

Discovery and naming

Joseph Leidy

The research of Uintatherium has a long and varied history, in the course of which numerous different and partly independently made taxonomic names were made. The discoveries began in the Bridger and Washakie Basins in the south of the US state Wyoming and fall into the Cope-Marsh feud , which led the two paleontologists Othniel Charles Marsh and Edward Drinker Cope over prestigious fossils in the 1870s and 1880s . The first Uintatherium finds were discovered in 1870 by Marsh on Sage Creek in the Bridger Basin of southwestern Wyoming, who became aware of the region through fossil finds by Joseph Leidy in 1868. In 1871, however, he referred them to Titanotherium , a name that had originally been given for the genus Megacerops from the group of Brontotheriidae . It was not until the following year that Marsh established the names Dinoceras (based on a complete skull, shoulder blade and ribs) and Tinoceras (based on a complete skull) for this new form of mammal, based on new discoveries . He also counted those first finds from 1870 to Tinoceras , and in the meantime he also considered a position of these within the mastodons , primeval trunk animals . His book was published on August 20 of the year 1872. Just three days earlier, on August 17, but had already Cope a telegraphic message to the Natural History Academy of Philadelphia sent to face his opponent Marsh quickly as possible publication of his fossilized Loxolophodon from southern Wyoming - these included the remains of five different individuals, including skulls and postcranial skeletal parts - so that they could be published in the Palaeontological Bulletin immediately . However, the transmitter made a mistake , which is why the name Lefalophodon has been handed down to this day. In the meantime, on August 20, Cope established the genus Eobasileus on the basis of the same find material , for which part of the material is now placed, only on August 22 did he correct the name to its originally intended form Loxolophodon . On August 1, 1872, however, Joseph Leidy had already published fossils that had been found by him and an expedition at Dry Creek and Twin Buttes near Fort Bridger in the Bridger Basin almost two weeks earlier , including some skull bones, molars and a humerus, which he assigned the new genus Uintatherium . At that time he assigned a giant, 30 cm long canine tooth that had also been discovered to uintamastix , which in his opinion was more related to the saber-toothed cats .

The first fossil finds from Uintatherium , discovered by Joseph Leidy and inserted into a skull drawing after Othniel Charles Marsh

It was only after the findings were published that Leidy first realized in 1873 that they had each described the same mammal form or closely related genera, and he had to admit that the giant canine, which he first ascribed to a big cat, was part of this bizarre mammal. At the beginning, Leidy's discovery of Uintatherium largely ignored Marsh and Cope; both researchers viewed the names they had given as being valid in their eyes for this new animal species and that of the competitor as synonyms . However, because of the rules of zoological nomenclature, Leidy's description turned out to be scientifically valid, since it was given first. Cope presented his discoveries in his more than 1000-page publication The Vertebrata of the Tertiary formations of the West in 1885, now known as the Cope Bible . Here he saw the finds as early representatives of the proboscis, which was also reflected in some well-known life reconstructions in which the animals were shown with proboscis. In the same year Marsh himself published his monograph Dinocerata, a monograph of an extinct Order of gigantic mammals, on his finds, in which he referred them to the group of Dinocerata , a name that is still valid today, even if the genus name Dinoceras is only a synonym for Uintatherium is; he created the term Dinocerata as early as 1873. It was only after the end of the Cope-Marsh feud and the death of the two researchers at the end of the 19th century that it was reserved for a new generation of researchers to classify the numerous fossils precisely. The following table presents all the Uintatherium forms described in the first publications between 1870 and 1873 , about a further dozen newly described species followed by 1885, which were mainly established by Marsh.

Taxon author Year of description Type specimen Finds Location
Titanotherium? anceps Marsh 1871 YPM 11030 Skull, vertebrae, long bones Sage Creek, Bridger Basin, Wyoming
Uintatherium robustum Leidy 1872 ANSP 12607, 12609-126013, 12619, 12622 Skull and mandible fragments Twin Buttes, Bridger Basin, Wyoming
Uintatherium ( Uintamastix ) atrox Leidy 1872 ANSP 12606, 12608 Maxillary canine, premolars Dry Creek, Bridger Basin, Wyoming
Loxolophodon furcatus ( "Lefalophodon bifurcatus" ) Cope 1872 AMNH 5045 skull Haystack Mountain, (Wyoming)
Loxolophodon pressicornis Cope 1872 AMNH 5042 (No. 3), 5043 Skull, long bones Haystack Mountain, (Wyoming)
Tinoceras grande Marsh 1872 YPM 11040 Skull, cervical and thoracic vertebrae Barrel Springs, Washakie Basin, Wyoming
Dinoceras mirabile Marsh 1872 YPM 11036 Skull, cervical, thoracic and lumbar vertebrae Big Bone Buttes, Bridger Basin, Wyoming
Dinoceras ( Tinoceras ) lacustre Marsh 1872 YPM 11037 skull Bitter Creek, Washakie Basin, Wyoming
Dinoceras lucare Marsh 1873 YPM 11038 skull Big Bone Buttes, Bridger Basin, Wyoming
Dinoceras laticeps Marsh 1873 YPM 11039 skull Spanish John's Meadow, Bridger Basin, Wyoming

literature

  • TS Kemp: The Origin & Evolution of Mammals. Oxford University Press, Oxford 2005. ISBN 0198507615
  • William D. Turnbull: The Mammalian Faunas of the Washakie Formation, Eocene Age, of Southern Wyoming. Part IV. The Uintatheres. Fieldiana 47, 2002, pp. 1-189
  • Walter H. Wheeler: Revision of the Uintatheres. Bulletin of the Peabody Museum of Natural History Yale University 14, 1961, pp. 1-93

Individual evidence

  1. ^ A b c d e f Henry Fairfield Osborn: A memoir upon Loxolophodon and Uintatherium, two genera of the sub-order Dinocerata. Contributions from the EM Museum of Geology and Archeology of the College of New Jersey 1 (1), Princeton, 1881
  2. ↑ a b c d e f g h William D. Turnbull: The Mammalian Faunas of the Washakie Formation, Eocene Age, of Southern Wyoming. Part IV. The Uintatheres. Fieldiana 47, 2002, pp. 1-189
  3. ↑ a b c d e f g h i j Walter H. Wheeler: Revision of the Uintatheres. Bulletin of the Peabody Museum of Natural History Yale University 14, 1961, pp. 1-93
  4. ↑ a b c Bai Bin: New Materials of Eocene Dinocerata (Mammalia) from the Erlian basin, Nei Mongol (Inner Mongolia). Vertebrata Palasiatica 44 (3), 2006, pp. 250-261
  5. ↑ Horace Elmer Wood: The problem of the Uintatherium molars- Bulletin American Museum of Natural History 48, 1923, pp. 599-604
  6. ^ Gregg F. Gunnell, Paul C. Murphey, Richard K. Stucky, KE Beth Townsend, Peter Robinson, John-Paul Zonneveld and William S. Bartels: Biostratigraphy and biochronology of the Latest Wasatchian, Bridgerian, and Uintan North American mammal "ages ". In: LB Albright III (Ed.): Papers on Geology, Vertebrate Paleontology, and Biostratigraphy in Honor of Michael O. Woodburne. Museum of Northern Arizona Bulletin 65, 2009, pp. 279-330
  7. ^ Nature: Fossil skeleton of Uintatherium. Nature 147, 1941, p. 114
  8. ↑ a b Tong Yongsheng and Wang Jinweng: A skull of uintatherium from Henan. Vertebrata Palasiatica 19 (3), 1981, pp. 208-213
  9. ↑ Jin Meng, Yuanqing Wang, K. Christopher Beard, Chengkai Sun, Qian Li, Xun Jin and Bin Bai: New Stratigraphic Data from the Erlian Basin: Implications for the Division, Correlation, and Definition of Paleogene Lithological Units in Nei Mongol (Inner Mongolia). American Museum Novitates 3570, 2007, pp. 1-31
  10. ^ Tong Yongsheng: Some Eocene Mammals from the Üqbulak area of ​​the Junggar basin, Xinjiang. Vertebrata Palasiatica 27 (3), 1989, pp. 182-196
  11. ↑ Chow Minchen and Tong Yongsheng: Notes on some new Uintathere materials of China. Vertebrata Palasiatica 6 (4), 1962, pp. 368-374
  12. ^ Wighart V. Koenigswald and Kenneth D. Rose: The Enamel Microstructure of the Early Eocene Pantodont Coryphodon and the Nature of the Zigzag Enamel. Journal of Mammalian Evolution 12 (3/4), 2005, pp 419-432
  13. ↑ a b L. P .: Professor Marsh's Monograph of Dinocerata. American Journal of Sciences 3, 24, 1885, pp. 173-204
  14. ↑ Spencer George Lucas: Gobiatherium (Mammalia: Dinocerata) from the Middle Eocene of Asia: Taxonomy and biochronological Significance. Paläontologische Zeitschrift 74 (4), 2001, pp. 591-600
  15. ↑ JGM Thewissen and PD Gingerich: Systematics and evolution of Probathyopsis (Mammalia, dinocerata) from the Late Paleocene and Early Eocene of Western North America. Contributions from the Museum of Paleontology The University of Michigan 8, 1987, pp. 195-219
  16. ↑ AH Garrod: On the Order Dinocerata. Journal of Anatomy and Physiology 7 (2), 1873, pp. 267-270
  17. ↑ Donald R. Prothero, Earl M. Manning and Martin Fischer: The phylogeny of the ungulates. In: MJ Benton (Ed.): The phylogeny and classification of Tetrapods, Volume 2: Mammals. Systematics Association, Special Volume 35B, Oxford, 1988, pp. 201-234
  18. ^ Benjamin J. Burger: The systematic position of the saber-toothed and horned giants of the Eocene: The uintatheres (Order Dinocerata). Journal of Vertebrate Paleontology 35 (suppl.), 2015, p. 99
  19. ^ A b Joseh Leidy: On some new species of fossil mammalia from Wyoming. Proceedings of the Academy of Natural Sciences Philadelphia 24, 1872, pp. 167-169 ( [1] )
  20. ^ Walter H. Wheeler: The Uintatheres and the Cope-Marsh War. Sciences 131, 1960, pp. 1171-1176
  21. ↑ a b W. H. Flower: The Uintatherium. Nature 13, 1876, pp. 404-405
  22. ↑ Donald R. Prothero and Robert M. Schoch: Horns, tusks, and flippers. The evolution of hoofed mammals. Johns Hopkins University Press, Baltimore, 2003, ISBN 0-8018-7135-2 (pp. 9-13)

Web links

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