Duchesneodus
| Duchesneodus | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Skull and lower jaw of duchesneodus , Figure B shows the holotype is |
||||||||||||
| Temporal occurrence | ||||||||||||
| 39.9 to 37.7 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Duchesneodus | ||||||||||||
| Lucas & Schoch , 1982 | ||||||||||||
Duchesneodus is a now extinct genus from the Brontotherien familyand livedin North Americain the Middle Eocene 40 to 38 million years ago. It is a relatively large representative of this odd ungulate group with two horns on the nose and a dome-like elevation on the forehead. It is largely only proven through skull finds, which, however, show a clear sexual dimorphism . The most important find areas are in what is now Utah .
features
Duchesneodus was a relatively large representative of the Brontotherien, which however did not reach the enormous proportions of its close relative Megacerops . Like the latter, however, it had two characteristic bony horn formations on the skull and, analogously, had a rather massive rhinoceros-like physique. The skull was 52 to 61 cm long; on the arched and widely spaced zygomatic arches , it reached a width of 41 cm. Some of the arch tips were also massively reinforced. In the side view it had a clear indentation on the forehead line and thus resembled the other horn-bearing Brontotheria. However, there was a special feature on the frontal bone , which had a sometimes massive dome-like bulge. As a result, the skull also had a broad structure with parasagittal ridges that were widely spaced. The occiput was strongly drawn out and constricted; in supervision it was very broad in shape. The nasal bone was also very broad and straight or pointed downwards, but did not protrude beyond the median jawbone . The typical bony horns of the late Brontotheria rose at the transition from the nose to the frontal bone. They were above the orbit , which in turn was positioned above the first molar . The horns had an oval base and were rounded at the top. Usually they pointed slightly outwards, but did not reach the length of the horns of Megacerops . The interior of the nose between the nasal bone and the upper jaw was not very large and extended to the last premolar .
The lower jaw was between 47 and 61 cm long and had a wide symphysis that reached to the first molar. The body of the lower jaw was quite massive and high overall. The dentition showed slight reductions, which was typical for the late and close relatives of Megacerops , but did not occur in the Eurasian lineage around Embolotherium . The dental formula was: . The incisors were small and spherical and stood in a straight row between the canine teeth , which was interrupted in the upper jaw due to the lack of internal teeth. The canine had a conical shape and protruded over 2 cm, but was on the whole rather small. Behind it was a diastema developed only in the lower jaw , which was about 4 cm long. The premolars and molars were built very similarly and had a low crown ( brachyodont ). The size of the teeth increased continuously towards the back, the last and largest molar tooth was up to 7 cm long. Characteristic was the W-shaped enamel on the chewing surfaces of the maxillary molars, a typical feature of Brontotheria.
Only a few remains of the body skeleton are known, including some vertebrae, a humerus and other skeletal elements.
Fossil finds
Duchesneodus is known for numerous finds of the skull, lower jaw and isolated teeth, all of which belong to the late phase of the Middle Eocene 40 to 38 million years ago (locally stratigraphically called Duchesneum ). The remains from the '' Duchesneodus quarry '', 18 km west of Vernal in the US state of Utah, are significant . Here they come from the LaPoint strata of the Duchesne River Formation and include around a dozen skulls and several mandibular fragments. Among the skulls there are also some that belong to non-adult animals, and the little known postcranial skeletal material was found here. Most of the fossil remains came to light on an expedition to the Carnegie Museum of Natural History in 1929 and 1930. A partial skull and a front skull fragment with preserved horns were found in the Galisteo Formation in New Mexico . Two skulls and two mandibular fragments were recovered from the Vieja Formation of Presidio County in Texas . The White River Formation in Freemont County , Wyoming , contained other mandibles that can probably be attributed to Duchesneodus . They date to the Upper Eocene.
Paleobiology
Different strong anatomical deviations occur in the finds , which can be interpreted as gender dimorphism . Male animals are characterized by more massive bones on average, which is particularly evident on the cheekbones, which often have large swellings at the edges for stronger muscles. The size of the horns and the formation of the dome-like bulge on the forehead also vary between the sexes and are smaller in female animals. A dimorphism of the canines that often occurs in Brontotheria, with large in males and small in females, has not yet been demonstrated in Duchesneodus .
Microscopic analyzes of the molars revealed signs of wear that are similar to those of today's leaf eaters. However, the pattern also deviates a little, which suggests that Duchesneodus , like other Brontotheria, was very picky about his food intake.
Systematics
|
Internal systematics of the Brontotheriita according to Mihlbachler 2009
|
Duchesneodus is a genus of the Brontotheriidae family (originally Titanotheriidae). Due to their characteristic tooth structure, these are referred to as being close to today's horses . Duchesneodus represents a member of the subfamily of the Brontotheriinae and the intermediate tribus of the Brontotheriita, which in turn belongs to the tribe of the Brontotheriini. 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. Parvicornus , Dianotitan and Megacerops are thus closely related . This intermediate tribus stands opposite the Embolotheriita with Embolotherium , which includes the more Eurasian forms and which usually have closely spaced horns or only a single, overgrown horn that is partially formed as a battering ram .
The first description of duchesneodus was made in 1982 by Spencer George Lucas and Robert M. Schoch . The genus arose from the taxon Teleodus , which Othniel Charles Marsh had introduced in 1890 , where he recognized a close relationship with Megacerops due to the missing upper, central incisors. The fossil used to determine the genus, a lower jaw, was bought by Marsh from a private collector for US $ 100 , who said he had found it near French Creek in South Dakota . It was only later discovered that during the preparation of this find, two additional incisors had been accidentally fitted into the lower jaw and the original fossil only had four in total. Because of this, the generic name Teleodus was considered invalid. However, four types of Teleodus had already been described, which Lucas and Schoch now equated with Duchesneodus . Today only D. uintensis is recognized as a valid species, which was introduced by Olof August Peterson in 1931 with T. uintensis based on the findings from the Duchesne River Formation . D. californicus , D. primitivus and D. thyboi are considered nomina dubia , but individual finds of the latter species were incorporated into the Brontotherien genus Parvicornus in 2009 . The generic name Duchesneodus goes back on the one hand to the Duchesne River , after which the geological formation and the chronostratigraphic stage Duchesneum is named, from which numerous representatives of Brontotherien are proven, on the other hand the Greek word ὀδούς ( odoús means "tooth") . The holotype (copy number CM 11809) includes a lower jaw with almost complete dentition, only the left incisors are missing.
Individual evidence
- ↑ a b c d Spencer George Lucas and Robert M. Schoch: Duchesneodus, a new name for some titanotheres (Perissodactyla, Brontotheriidae) from the late Eocene of western North America. Journal of Paleontology 56, 1982, pp. 1018-1023
- ↑ a b c d Spencer George Lucas and Robert M. Schoch: Taxonomy of Duchesneodus (Brontotheriidae) from the late Eocene of North America. In: Donald R. Prothero and Robert M. Schoch (Eds.): The evolution of Perissodactyls. New York and Oxford, 1989, pp. 490-503
- ↑ a b c d e f 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
- ↑ Spencer G. Lucas, Robert J. Emry and Matthew C. Mihlbachler: Late Eocene brontotheres (Mammalia, Perissodactyla) from Beaver Divide, Wyoming, and their biochronological significance. New Mexico Museum of Natural History and Science Bulletin 26, 2004, pp. 113-118
- ↑ 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
- ^ A b 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