Diplacodon
| Diplacodon | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Middle Eocene (Uintan) | ||||||||||||
| 48 to 39.9 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Diplacodon | ||||||||||||
| Marsh , 1875 | ||||||||||||
Diplacodon is a now extinct genus from the Brontotheriidae family. It lived 49 to 42 million years ago in the late middle Eocene , the majority of the fossils were discovered in the northwestern part of the USA . The representative of Brontotherien did not reach the size of the later and more well-known forms, but was equipped with two distinctive bony horns on the snout and fed on soft plant material. The first description of the genus goes back to 1875 and was made by Othniel Charles Marsh .
features
Diplacodon was a large representative of the Brontotherium , but did not reach the dimensions of the later genera such as Megacerops or Embolotherium . Large individuals reached a skull length of 72 cm, smaller ones usually 50 to 61 cm. At the zygomatic arches this was up to 46 cm wide. Typical of horn-bearing Brontotheria, the skull was strongly saddled at the forehead line with the occiput slightly elongated to the rear . There were clear parasagittal ridges laterally. Especially in the area of the frontal and nasal bones , the skull had a large width and was therefore very massive. The nasal bone was stretched out and pointing slightly forward and downward, but mostly ended shortly before the intermaxillary bone , the lateral edges were typically curved upwards. The characteristic, long oval to round, bony horns sat above the orbit , which in turn was located far in front of the skull above the first and second molars . They protruded obliquely forward at an angle of 45 ° and were composed of the rear end of the nasal bone and the front end of the frontal bone. In contrast to other horned brontotheria, these two bones were completely fused. The intermaxillary bone had a clearly downward course. The interior of the nose, which lies between this bone and the nasal bone, was enormous and extended to the last premolar .
The lower jaw is less well known, a complete specimen reached a length of 53 cm. The symphysis , which reached to the posterior premolar, was directed upwards on the underside and thus formed a chin with an angle of 45 °. Overall, the body of the lower jaw was quite massive. Like most Brontotherien also had diplacodon full Säugetierbezahnung so that the dental formula as follows was: . The incisors were small and spherical in shape and formed a closed arch in the lower jaw. There was a small gap between the two frontmost incisors (I1) of the upper incisors. The canine tooth that usually adjoins it - but there was sometimes a small gap in the upper jaw - had a conical shape and was up to 2.5 cm high. To the posterior teeth there was a diastema up to 5 cm wide . The molars had low ( brachyodontic ) crowns, with the tooth size increasing significantly from front to back, so that the front premolar was only around 1.5 cm long, while the last molar was 7.5 cm. With the exception of the first molar, all the teeth of the rear dentition were clearly molarized and thus resembled the molars. The W-shaped course of the tooth enamel on the chewing surfaces of the maxillary molars, which is typical for Brontotheria, was striking. The entire back row of teeth was around 23 cm long.
Fossil finds
The majority of the finds, which include almost a dozen skulls and skull fragments, as well as half a dozen lower jaws, come from the northwestern United States , all of which can be found in the late Middle Eocene ( Uintan locally ) 48 to 42 million years ago. However, the skull and mandible were rarely discovered together. The type locality is the Myton member of the Uinta formation in the Uinta basin in the US state of Utah , where the skull find serving for the first description of the genus was discovered. From the same geographical region and stratigraphic position comes a skull, which was handed down together with some of the only sparsely survived postcranial skeletal elements, which were published together in 1934 and are stored in the Carnegie Museum of Natural History . Another nearly complete skull of an extremely large specimen was discovered in the upper section of the Wiggins Formation of the Absaroka Range in Hot Springs County of northwest Wyoming and was discovered in 1982. Temporally it is also to be placed in the end of the Middle Eocene. A tooth find from the lower section of the Duchesne River Formation in northeastern Utah is classified as younger .
Paleobiology
A gender dimorphism could be worked out on the basis of anatomical deviations . This mainly consists of clearly varying horn sizes and the differently developed zygomatic arches, which were probably more pronounced in males than in females. The canines also had fluctuating sizes, but this dimorphism is not quite as clearly developed here as, for example, in Embolotherium or Megacerops . Using the microscopic examination of signs of wear on the molar teeth, it was possible to determine that the animals ate a soft vegetable diet, which is also indicated by the low tooth crowns. Since the wear pattern differs slightly from today's leaf-eaters, Diplacodon seems to have been very picky about food, similar to other Brontotheria.
Systematics
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Internal systematics of the Brontotheriita according to Mihlbachler 2009
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Diplacodon is a genus of the Brontotheriidae family (originally Titanotheriidae). The Brontotherien are due to their characteristic tooth structure in the vicinity of today's horses . Diplacodon represents a member of the Brontotheriinae subfamily and the intermediate tribus of the Brontotheriita, which in turn belongs to the Brontotheriini tribe, one of the genetically modern branches of the family. The tribe of the Brontotheriini was originally led by Bryn J. Mader as a subfamily of the Telmatheriinae and contained all North American Brontotheriinae that had pronounced horn approaches, but later he renamed them to Brontotheriinae. Matthew C. Mihlbachler put this subfamily in the interpretation of Mader in 2008 on the rank of tribe and separated with the Brontotheriita the largely North American Brontotheria with trained paired and quite widely spaced horns. In the close relationship thus include Parvicornus , Dianotitan and Pachytitan , the latter represents the Schwestertaxon. This Zwischentribus is the Embolotheriita with embolotherium against comprising the rather Eurasian forms and the closely related generally horns or only a single, verwachsenes and partly as Have battering ram trained horn.
Today two types are distinguished:
- D. elatus Marsh , 1875
- D. gigan Mihlbachler , 2011
Other species of this genus were listed by OA Peterson in 1914 with Diploceras osborni , later also as Eotitanotherium osborni , and named in 1934 with D. progressum . Mader referred the latter to the genus Pseudodiplacodon in 2000 . Since the differences were mostly based only on specific horn and tooth variations, both species are now assigned to D. elatus . Another species, D. emarginatum , which was named by John Bell Hatcher in 1895 , is now part of Protitanotherium . The species D. gigan , which was only described in 2011 - the species name goes back to the huge, horned monster "Gigan" from the Godzilla film Frankenstein's Infernal Brood from 1972 - is an extremely large form compared to D. elatus , which increases it by about 20% surpassed.
The first description of diplacodon was made by Othniel Charles Marsh in 1875. It was based on some finds that are in the Peabody Museum of Natural History at Yale University and that Marsh found during expeditions to the Uinta Basin in Utah in 1870. The holotype (copy number YPM 11180) comprises a skull that was broken into two parts and has almost complete dentition.
Individual evidence
- ↑ a b c d e f g Matthew C. Mihlbachler: Species taxonomy, phylogeny, and biogeography of the Brontotheriidae (Mammalia: Perissodactyla). Bulletin of the American Museum of Natural History 311, 2008, ISSN 0003-0090 , pp. 1-475
- ↑ a b c d e Matthew C. Mihlbachler: A New Uintan Horned Brontothere from Wyoming and the Evolution of Canine Size and Sexual Dimorphism in the Brontotheriidae (Perissodactyla: Mammalia). Journal of Vertebrate Paleontology 31 (1), 2011, pp. 202-214
- ^ A b Bryn J. Mader: Details of the Cranial Anatomy of a Primitive Diplacodont Brontothere, cf. Protitanotherium, from the Wiggins Formation of Wyoming (Mammalia, Perissodactyla, Brontotheriidae). Journal of Vertebrate Paleontology 29 (4), 2009, pp. 1224-1232
- ^ A b Othniel Charles Marsh: Notice of new Tertiary mammals, IV. American Journal of Science and Arts 9, 1875, pp. 239-250
- ↑ a b Bryn J. Mader: Pseudodiplacodon, a new generic name for Diplacodon progressum Peterson (Mammalia, Perissodactyla, Brontotheriidae). Journal of Vertebrate Paleontology, 20 (1), pp. 164-166.
- ^ BJ Burger and L. Tackett II: The stratigraphic importance of the brontothere (cf. Diplacodon elatus) in the Brennan Basin Member of the Duchesne River Formation of Utah. Fossil Record 17, 2014, pp. 69-74
- ↑ Angana Homchaudhuri, Matthew C. Mihlbachler and Nikos Solounias: Dental microwear analysis of Eocene Brontotherioidea and implications for paleodietary interpretations of long extinct species. Journal of Vertebrate Paleontology 30 (suppl.), 2010, p. 107A
- ^ Matthew C. Mihlbachler: A New Species of Brontotheriidae (Perissodactyla, Mammalia) from the Santiago Formation (Duchesnean, Middle Eocene) of Southern California. Proceedings of the San Diego Society of Natural History 41, 2009, pp. 1-36
- ↑ Bryn J. Mader: Brontotheriidae: A systematic revision and preliminary phylogeny of North American genera. In: Donald R. Prothero and Robert M. Schoch (Eds.): The evolution of perissodactyls. New York and London, 1989, pp. 458-484
- ↑ Bryn J. Mader: Brontotheriidae. In: Christine M Janus, Kathleen M Scott and Louis L Jacobs (eds.): Evolution of Tertiary mammals from North America, Vol. 1. Cambridge 1998, pp. 525-536