Eubrontotherium
| Eubrontotherium | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Middle to Upper Eocene | ||||||||||||
| 42.9 to 33.9 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Eubrontotherium | ||||||||||||
| Mihlbachler , 2007 | ||||||||||||
Eubrontotherium is a now extinct representative of the Brontotheria , which lived 43 to 34 million years ago in North America and East Asia . It was a very large member of this odd ungulate group . It is mainly known through some skull finds, which show that it was a well-developed form in ancestral history.
features
Eubrontotherium was a very large representative of the Brontotheria, but did not reach the enormous dimensions of Megacerops . It is known from several skull and lower jaw finds, but only a small amount of fossil material from the body skeleton. The skull was about 65 cm long and was shaped like a wedge when viewed from above by the up to 41 cm protruding zygomatic arches. On the zygomatic arches, however, the lateral bony swellings, which are often found in other late brontotherias, were missing. The forehead line was characteristically saddled, a striking feature of horn-bearing brontotheria, and laterally prominent parasagittal bone ridges appeared. The occiput has not survived in its entirety, but it was clearly extended backwards. The nasal bone had a broad and elongated shape and curved slightly downwards in its free front part. It was spread laterally in the area of the typical horns. As in all Brontotheria, the horns consisted of extensions of the posterior nasal bone and were covered with protrusions from the frontal bone . They sat slightly in front of the orbit and had an oval cross-section at the base and a round cross-section at the top, but were not very high. The eye sockets themselves were above the first molar . The rostrum with the upper jaw and the intermaxillary bone was short, but protruded a little over the nasal bone and was oriented slightly upwards. The interior of the nose, located between this and the nasal bone, extended to the last premolar .
The strong lower jaw was 61 cm long and had a massive, almost 20 cm long, very wide and slightly erect symphysis in the front area . Here the lower jaw was also up to 9 cm wide. The bite was in the upper incisors slightly reduced, only the representatives of spätesten Brontotherien as Parvicornus or megacerops is known, the dental formula was thus: . The incisors were small and spherical and formed a straight and closed row, but in the upper jaw, due to the lack of an inner pair, an open row in the middle. The canine had a conical shape and was very large, up to 3.4 cm in length. There was a short, maximally 3.5 cm long diastema to the posterior teeth . Such short tooth distances are typical of developed North American Brontotheria and were later completely lost in this line. The anterior premolar was small and rounded and had a single enamel cusp, the posterior ones were clearly molarized and resembled the molars. These increased significantly in size, but were generally low-crowned ( brachyodont ). The rearmost molar had a narrow, slender shape, up to 9.2 cm in length. Typically for Brontotheria, the enamel on the chewing surfaces of the maxillary molars was W-shaped. The entire back row of teeth reached a maximum length of 31 cm.
References
Originally, Eubrontotherium was only known from one site, from the Hancock Mammal Quarry in Wheeler County of the US state of Oregon . From the deposits of the Clarno Formation uncovered here , in addition to an almost complete skull with a lower jaw, several other skull and jaw fragments and numerous isolated teeth come from. From the same, very fossil-rich site, the remains of the very early Teletaceras , which belong to the "parent group" of rhinos and are dated to an age of around 37 million years, were reported. In general, the finds from the Hancock Mammal Quarry are assigned to the Middle to Upper Eocene (locally stratigraphically Uintum to Chadronian ). The dwarfed Brontotherien representative xylotitan was reported from somewhat older locations in the same region . Further finds of Eubrontotherium are known from East Asia and came to light in the Ergilin-Dzo Formation in eastern Mongolia . They contain a partial skeleton with a skull and another isolated skull. These finds are from the Late Eocene and, in local stratigraphy, belong to the Ulangochuian .
Paleobiology
As with many Brontotheria, the design of the canines shows a clear sexual dimorphism , which in male animals includes significantly larger teeth that protrude far beyond the incisors, which is not the case in female animals. However, in male animals, the marked swellings of the zygomatic arches as muscle attachment points, as known from Duchesneodus and other late Brontotheria, have not yet been demonstrated.
Systematics
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Internal systematics of the Brontotheriita according to Mihlbachler 2009
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Eubrontotherium is a genus from the family of the Brontotheriidae (originally Titanotheriidae), which are close to today's horses due to their characteristic tooth structure. Within the Brontotheri, Eubrontotherium is 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 Brontotheri which had pronounced horn approaches. in a later investigation he renamed it Brontotheriinae. Matthew C. Mihlbachler put this subfamily on the rank of tribe in 2008 and separated with the Brontotheriita the largely North American Brontotheriita with trained paired horns, which include Megacerops , Duchesneodus or Dianotitan . This is the Zwischentribus Embolotheriita with embolotherium against comprising the general Eurasian forms and which are usually only a single, verwachsenes and partly as a battering ram having formed horn.
Originally, the finds from the Hancock Mammal Quarry called Clarno brontotheres were named as belonging to Protitanops , but some researchers doubted this. The Mongolian finds, on the other hand, were assigned to Metatitan and Parabrontops . In 2007, the genus Eubrontotherium was first scientifically described by Matthew C. Mihlbachler , referring to the finds from Oregon. The only recognized species is Eubrontotherium clarnoensis . The informal name "Eubrontothere" was used for the first time in 1985 by Spencer Georges Lucas and Robert M. Schoch and encompassed all the most recent Brontotheria of North American origin, which were characterized by small spherical incisors, strongly molarized premolars and well-developed horns. Megacerops and Duchesneodus were therefore mainly considered to be "Eubrontotheria" . The species name clarnoensis refers to the first finds from the Clarno formation.
literature
- Matthew C. Mihlbachler: Eubrontotherium clarnoensis, a new genus and species of brontothere (Brontotheriidae, Perissodactyla) from the Hancock Quarry, Clarno Formation, Wheeler County, Oregon. Paleobios 27 (1), 2007, pp. 19-39
Individual evidence
- ↑ a b c d Matthew C. Mihlbachler: Eubrontotherium clarnoensis, a new genus and species of brontothere (Brontotheriidae, Perissodactyla) from the Hancock Quarry, Clarno Formation, Wheeler County, Oregon. Paleobios 27 (1), 2007, pp. 19-39
- ↑ a b c d e 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
- ^ C. Bruce Hanson: Teletaceras radinskyi, a new primitive rhinocerotid from the late Eocene Clarno formation of Oregon. In: Donald R. Prothero and Robert M. Schoch (Eds.): The evolution of perissodactyls. New York and London, 1989, pp. 379-398
- ^ Matthew C. Mihlbachler and Joshua X. Samuels: A small-bodied species of Brontotheriidae from the middle Eocene Nut Beds of the Clarno Formation, John Day Basin, Oregon. In: Journal of Paleontology 90 (6), 2016, pp. 1233-1244 doi: 10.1017 / jpa.2016.61 .
- ^ 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
- ^ 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
- ↑ a b 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
- ^ C. Bruce Hanson: Stratigraphy and vertebrate faunas of the Bridgerian-Duchesnean Clarno Formation, north-central Oregon. In: Donald R. Prothero and Robert J. Emry (Eds.): The Terrestrial Eocene – Oligocene Transition in North America. Cambridge University Press, 1996, pp. 206-239