Eobasileus
| Eobasileus | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Upper Eocene (Lower and Middle Uintum ) | ||||||||||||
| 48 to 42.9 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Eobasileus | ||||||||||||
| Cope , 1872 | ||||||||||||
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Eobasileus is an extinct mammal belonging to the Dinocerata group and livedin what is now North America at the end of the Middle and Upper Eocene 48 to 45 million years ago. It was closely related to Uintatherium and, together with it, was one of the largest land-living mammals of its time. Overall, Eobasileus was characterized by a more rhinoceros-like body, the most striking features were the three pairs of horns on the skull and a saber-like upper canine tooth. The main diet of the mammalian form consisted of soft vegetable food.
features
Eobasileus is the largest known representative of the Dinocerata , a group of herbivorous mammals that is now extinct . According to calculations, the body weight was around 2,500 kg, making the shape slightly heavier than the closely related Uintatherium . As was typical of Dinocerata, Eobasileus represented a relatively heavily built herbivore with a large head, strong, cylindrical body and long limbs.
The skull of Eobasileus was between 85 and 94 cm long and was designed rather flat and wide. The occiput showed a clearly drawn back extension, the nasal bone was long and lay above the median jawbone . The nasal cavity between these two bones was not very extensive and reached up to the canine . As with Uintatherium , there were three pairs of bony horns on the skull , but the skulls of the two genera differed in their proportions. The foremost pair of horns was located on the tip of the nasal bone , as in Uintatherium, and presented only slight bony swellings. The middle pair of horns rose on the upper jaw above the premolars and reached 18 to 22 cm in length. The position of this pair of horns was shifted significantly further back than with Uintatherium , which was located just behind the canine. Due to the rear position of the second pair of horns, the rostrum of Eobasileus also appeared to be considerably more extensive than that of its relative. The rearmost pair of horns grew out of the parietal bones and was very close to the occiput . Overall, the middle and rear pair of horns in Eobasileus sat relatively close together, in contrast to Uintatherium with its rear pairs of horns that are far apart.
The lower jaw was very robust and between 52 and 65 cm long, the body of the lower jaw was 9 to 14 cm high. The symphysis reached a very large extent, sometimes up to 22 cm. Some lower jaws had bony outgrowths on the lower front edge. The dentition had the characteristic structure of the developed Dinocerata. Incisors were only formed in the lower jaw, but were clearly small in shape and had two characteristic small cusps. The upper canine, which was greatly elongated and clearly curved backwards and thus saber-like, was striking, stronger than in Uintatherium . It was up to 5.7 cm long and 3 cm wide at the base, the total length without curvature was 18.6 cm. As a result, it protruded far above the lower jaw and was protected by the aforementioned protrusions of the lower jaw bone. The lower canine was rather small and resembled the incisors. The posterior teeth, which were separated from the anterior by a diastema of more than 13 cm in some cases, consisted of three premolars and three molars for each arch . The dental formula of adult animals was characterized as follows: . The molars had low ( brachyodont ) crowns and were rather small, the rear teeth also showed hardly any extensions, the last molar was a maximum of 5 cm long. A characteristic feature of the chewing surface was the design of two transverse tooth enamel strips ( lophodont ), which were separated by a distinctive saddle. The maxillary molars also had a typically V-shaped enamel fold. The extension of the row of teeth from the anterior premolar to the posterior molar is remarkable, reaching a length of 19.2 cm and thus exceeding that of all other Dinocerata.
The postcranial skeleton is well known, but not as extensive as in the much more common Uintatherium . As with all Uintatheria, the sacrum consisted of four vertebrae. The humerus was up to 65 cm long and slightly exceeded that of Uintatherium . The thigh bone was also a little longer than that of its relative at 75 cm in length. Characteristically it did not have a third trochanter . Both the front and rear legs ended in five rays. The front and rear feet were rather broad and short, a feature that is reminiscent of those of the proboscis .
Fossil finds
Finds of Eobasileus come from North America , here mainly from the northwestern part of the USA , especially the states of Wyoming , Utah and Colorado ; in general, however, there are significantly fewer finds than comparatively from Uintatherium . Most of the fossils were discovered in the late 19th and early 20th centuries. They are assigned to the Upper Eocene (locally stratigraphically called Uintum ) and are therefore somewhat younger than those of Uintatherium . Particularly noteworthy is the first find, which also represents the holotype of the genus and, in addition to postcranial skeletal elements, includes an almost complete skull, which is the largest of the genus to date with a length of almost 95 cm. It was found in August 1872 by Edward Drinker Cope and Sam Smith in the Washakie Basin in southwest Wyoming, more precisely on Haystack Mountain. A skull and limb remains come from here, which were discovered in 1876 during work under the direction of Othniel Charles Marsh and which Marsh described in 1885 as Tinoceras latum , a name now synonymous with Eobasileus . From outcrops of the Uinta Formation on the banks of the White River in Uintah County Utah comes another, with a length of 85 cm, quite large skull, which was unearthed in 1910. In the same year, another skull was uncovered in the same county in the Coyote basin, but it was rather poorly preserved, but due to special deviations it can be assigned to a female animal. Ultimately, a large, over 90 cm long skull from the Wash Sand Basin in Moffat County , Colorado was described. Few finds have been reported from the later period, such as a lower jaw that was found on Haystack Mountain in 1942 and, due to the weak symphysis, probably belonged to a female individual. This also includes some isolated teeth from the same location from 1954.
Paleobiology
Overall, like its relative Uintatherium , Eobasileus has a rather stocky build, which is somewhat reminiscent of that of today's rhinos , but was not quite as robust as these. In addition, the limbs were significantly longer in Eobasileus compared to rhinos . Their structure was largely similar to that of today's proboscis . The gait of the animals was probably plantigrad (sole gait) due to the simply built front and rear feet . The elongated posterior skull allows the reconstruction of massive neck muscles, so that the head was held at an incline downwards and the posterior part of the occipital bone was vertical. The Lophodonte dentition shows Eobasileus to be a herbivore specializing in soft vegetable food ( browsing ). Since the incisors in the lower jaw were very small and those in the upper jaw were completely absent, the tongue probably played a decisive role in feeding, possibly in combination with the canine teeth. The long bones thickened by pachyostosis should be emphasized . This can be observed in some terrestrial vertebrates, which have adapted secondarily to life in an aqueous environment, with the thickened bones compensating for the buoyancy in the water. It has not yet been clarified whether Eobasileus lived semi-aquatic.
A, however, poorly preserved skull of an adult animal had only slight bone swellings instead of strongly developed horns, which may suggest a sexual dimorphism between male and female animals. Another indication of deviating anatomical features between the sexes is a more delicate lower jaw with less developed symphysis. Such gender-specific manifestations are also proven in Uintatherium , but here they are more clearly worked out due to the more extensive fossil material. The function of the horns as well as that of the oversized canine is unclear; they may have been used in the dominance and mating battle. Modern mammals do not have such a combination of head and dentition weapons.
The more rare Ichnofossils include finds from Slide Mountain in the northern part of the US state Washington , where more than 200 footsteps of large mammals were found in outcrops of the Chuckanut Formation from the Middle and Upper Eocene . These were rounded, 12 to 18 cm in diameter and about 4 to 6 cm deep, sunk into sand and siltstones , which indicate a previously water-saturated subsoil. In one case, the trail of a single individual could be followed over several meters; overall, the tracks show the presence of several animals, possibly in the form of a herd of related animals. The shape and size of the tracks suggest large mammals with plantigrader locomotion (sole walkers). An assignment to Eobasileus is quite possible, but Coryphodon also lived at that time , a large animal belonging to the Pantodonta and at that time very common with partly semi-aquatic life and also plantigrader locomotion. An age determination from an underlying layer determined by means of fission-track dating gave a value of 49.9 million years and represents the lowest age limit.
Systematics
Eobasileus is a genus of the family of Uintatheriidae represents and referenced within this to the subfamily Uintatheriinae. This subfamily is characterized by representatives with a large physique and three pairs of bony horn formations. She will continue to be assigned Uintatherium . The Tetheopsis originally described as independent is at least partially identical to Eobasileus after a revision by William D. Turnbull . The Uintatheriinae are opposed to the Gobiatheriinae, which are characterized by the reduction of the upper canines and a nasal septum ossified in the front part . Although the position of the Gobiatheriinae as a subfamily was initially confirmed in the partial revision of 2002, some other researchers also lead them as an independent family within the Dinocerata due to partly different tooth characteristics.
The Uintatheriidae belong to the order of the Dinocerata . This group of mammals is largely known from North America and East Asia and was one of the first giant forms to emerge after the extinction of the dinosaurs. All Dinocerata, with the exception of the most original representatives, have the absence of the anterior premolars and the upper incisors. The close family relationships cause some problems. Due to common tooth features and the extremely small molars in relation to body size in the Uintatheria, a closer relationship to the Anagalidae was postulated in the early 1980s , a tribal group of small mammals from East Asia that is closely related to rodents today . However, this turned out to be wrong after skeletal anatomical studies. Today it is recognized that the Dinocerata is a very original branch of the heterogeneous group of ungulates . The possibly closest relatives include the Meridiungulata , ungulates that were once widespread in South America, of which the Pyrotheria or the Xenungulata could be closely related. The odd ungulates could probably be regarded as the closest relatives living today . Common features between the Dinocerata and the odd-toed ungulates can be found in the formation of the hooves, the mesaxonic foot position (the center of gravity of the axis of the foot runs through the middle (third) ray) and in the absence of a deep groove on the talus for articulation with the shin joint, which for example occurs frequently among the Afrotheria .
The genus Eobasileus is monotypical and includes the species Eobasileus cornutus . Genus and species were scientifically described for the first time in 1872 by Edward Drinker Cope . The history of the discovery of Eobasileus falls during the Cope-Marsh feud of the 1870s and 1880s. Originally, a series of fossils that Cope discovered in Wyoming in mid-August 1872, which included at least five individuals, were given the name Loxolophodon . On August 17, 1872, he sent a telegraphic communication of his discoveries to the Natural History Academy of Philadelphia ; Due to a typographical error on the part of the forwarder , these new finds were published on August 19, 1872 as Lefalophodon in the Palaeontological Bulletin . A day later, on August 20, 1872, Cope referred some of the finds of Loxolophodon ( Lefalophodon ) to the new genus Eobasileus , the reason for this being that several cervical vertebrae were very short compared to Loxolophodon . However, on August 22, 1872, Cope changed it back to Loxolophodon , which at the same time corrected the incorrect spelling. In general, Loxolophodon is now regarded as a synonym for Uintatherium , which Joseph Leidy also described in 1872. The genus Eobasileus was not recognized as an independent species for a while, but the name caught on at the beginning of the 20th century. Originally, Cope had worked out two further species with Eobasileus pressicornis and Eobasileus discornatus , an extensive revision of the Uintatheria published in 1961 resulted in Eobasileus cornutus only being a valid species. The generic name Eobasileus derives from the Greek words ηώςα ( ēōs "Morgenröte") and βις ( basileios "king"). The species name cornutus is of Latin origin and comes from cornus ("horn"), so overall the name means "horned king of the dawn". The holotype (copy number AMNH 5040) includes a nearly complete skull, several vertebrae, a shoulder blade, the pelvis and a right femur.
swell
- Douglas Palmer: Dinosaurs & Prehistoric Animals. An illustrated encyclopedia. Könemann, Cologne 2000, ISBN 3-8290-6113-7 .
- 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
- David Rains Wallace: Beasts of Eden. Walking Whales, Dawn Horses, and Other Enigmas of Mammal Evolution. University of California Press, Berkeley CA et al. 2005, ISBN 0-520-24684-5 .
- Walter H. Wheeler: Revision of the Uintatheres. Bulletin of the Peabody Museum of Natural History Yale University 14, 1961, pp. 1-93
Individual evidence
- ↑ 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
- ↑ a b c d e f g 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
- ^ 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
- ^ A b 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, pp. 1-54
- ↑ George E. Mustoe: Eocene Bird, Reptile, and Mammal Tracks from the Chuckanut Formation, Northwest Washington. Palaios 17 (4), 2002, pp. 403-413
- ↑ Spencer George Lucas: Gobiatherium (Mammalia: Dinocerata) from the Middle Eocene of Asia: Taxonomy and biochronological Significance. Paläontologische Zeitschrift 74 (4), 2001, pp. 591-600
- ↑ 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
- ↑ AH Garrod: On the Order Dinocerata. Journal of Anatomy and Physiology 7 (2), 1873, pp. 267-270
- ↑ 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
- ^ 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
- ^ Henry Fairfield Osborn: Cenozoic mammal horizons of Western North America. United States Geological Survey Bulletin 361, 1909, pp. 1-138
- ↑ Anonymous: Eobasileus cornutus. Discover prehistoric times in Giessen, exhibition ( [1] ; PDF; 154 kB)
