Megacerops
| Megacerops | ||||||||||||
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Skeletal reconstruction of Megacerops |
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| Temporal occurrence | ||||||||||||
| Upper Eocene ( Chadronian ) | ||||||||||||
| 38 to 33.9 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Megacerops | ||||||||||||
| Leidy , 1870 | ||||||||||||
Megacerops is an extinct genus of mammals from the Brontotheriidae family, which is one of the distant relatives of modern horses . The genus is documented by numerous fossil finds exclusively from North America , which are assigned to the late Eocene 38 to 34 million years ago. Today recognized species are M. coloradensis and M. kuwagatarhinus . Megacerops is one of the greatest representatives of the Brontotheria at all, its systematic allocation within the family has a long research- historical controversy, whichincludesnumerous synonyms ( Allops , Brontops , Brontotherium , Menodus , Menops , Oreinotherium , Titanops , Titanotherium ).
features
Megacerops was one of the largest known representatives of the Brontotheriidae and is passed down through numerous, partly complete skeletons. It reached similar dimensions as Embolotherium and Gnathotitan , all three genera are comparable in body size to the largest rhinos of today. The largest representative was M. coloradensis , which reached a shoulder height of 2.5 m and, according to calculations, weighed between 1.9 and 3.3 t, but there was also a slightly smaller species with M. kuwagatarhinus . The animal was characterized by one sturdy body with short and massive legs and a long skull from which prominent horn formations arose.
The skull had a very elongated shape and reached 62 to 81 cm in length. Laterally, the cheekbones protruded very far apart, the greatest distance was 67 cm. The frontal bone had a saddle that was characteristic of Brontotheria, which was caused by the long drawn out and thereby acute-angled occiput , but some animals also had a slight bulge on the forehead. The occiput was also extremely solid. The orbit was located above the first molar and therefore quite far in front compared to other brontotheria. The horn formations over the muzzle region, which consisted of outgrowths from the posterior nasal bone and were covered or coated by the anterior frontal bone, were characteristic of numerous modern brontotherias ; they differed so from the horn formations from horn substance or keratin of the later ungulates . In the case of Megacerops , these horns could have a very variable shape and be of different lengths, but were generally available in pairs. These horns rose up steeply or were clearly directed forward. In addition, there were both single horns and horns that had grown together through a basal bone ridge. Furthermore, long, blunt horns appeared, some of which were also forked in a Y-shape at the upper end. Other Megacerops representatives also had only a few slight bumps instead of strong horns. The rest of the front area of the nasal bone was still mostly very short and lay over the median jawbone , the interior of the nose was rather small due to the short shape of the nasal bone.
The massive lower jaw was up to 72 cm long. Characteristic was a barely reduced front dentition with a reduced number of incisors . Among the previously known Brontotherien, this modern feature is known only to a few representatives, including Parvicornus or Dianotitan . The rather small and spherical incisors in Megacerops, however, tended to fall out very early in adult animals. The tooth formula was accordingly . Another characteristic feature of the teeth was the missing diastema between the large and conically designed canine and the rear teeth. The premolars, on the other hand, were clearly molarized and thus resembled the posterior molars. Overall, the molars were low-crowned ( brachyodont ) and had enamel loops folded in W-shape on the upper molars , which were a typical characteristic of Brontotheria. The rearmost and largest molar reached a length of more than 6 cm.
In contrast to the often rhinoceros-like reconstruction of the body and limbs of Megacerops and other younger Brontotheria tribes, they had characteristic deviations. The forelegs were massive and long, the thigh bone reached up to 61 cm, the radius up to 51 cm in length. The construction of the knee joint differed significantly from that of the rhinos , which in Megacerops was not as strikingly asymmetrical as in today's rhinos, whose inner joint role at the lower end of the thigh bone is significantly larger than the outer one. Megacerops , on the other hand, had an only slightly larger outer joint role and a smaller inner one, in this characteristic it is more similar to the proboscis or chalicotheria . The hind legs also differed from those of the rhinos and showed similarities in their position to those of the proboscis, which possibly caused differences in the gait between the rhinos and Brontotherien. The massive thigh bone was up to 81 cm long , the shin only about 45 cm long. As with all early unpaired ungulates, the front legs ended in four rays ( metacarpus II to V), the hind legs in three rays ( metatarsus II to IV). The main axis ran through the third ray, the third metacarpal bone reaching 23 cm and the third metatarsal 20 cm length.
References
Finds of megacerops dating largely to the Upper Eocene and come from the Lower titanotheres bed ( Lower titanium othere Beds ) of the Chadron Formation in the catchment area of the White River in the Midwest of North America . The most extensive material, which includes numerous skulls and partially complete skeletons and can be assigned to around 150 individuals, was largely discovered during several expeditions between 1874 and 1886 to Nebraska and South Dakota as well as Colorado . Today these finds are largely assigned to the giant species M. coloradensis . Other finds also from the White River catchment area come from Capitol Rock in Carter County in Montana , which were found in a solid, greenish-colored sandstone and include a skull with teeth belonging to the smaller species M. kuwagatarhinus with characteristic forked horns. This also includes two skulls and individual finds from the Hunter Quarry in Saskatchewan, Canada .
Paleobiology
The often rhinoceros-like representation of the Brontotheria in general, and of Megacerops in particular, requires some detailed changes after recent investigations. The reconstruction of the musculoskeletal system gives conclusions about a slightly different mode of locomotion of Megacerops , since the hind legs, which are similar to the proboscis, suggest that the animal could not gallop like today's rhinos, but that today's elephants could rather run faster than used the most extreme form of transport.
According to recent analyzes, Megacerops preferred densely forested areas with high humidity. Due to the low tooth crowns with selenodont (crescent-shaped) chewing surfaces, a specialization in soft vegetable food is assumed, which was plucked from low-growing plants. This is confirmed by wear marks on the tooth crowns as well as by isotope tests on the molars; both studies indicate that no mixed vegetable diet was included. Furthermore, based on the analyzes, a greater dependence on water is assumed, which is attributed to the type of digestion as a rectal fermenter similar to that of rhinos and horses still alive today .
The differently pronounced and sometimes varied and, according to interpretations, probably covered by a thin layer of skin, are now regarded as sexual dimorphism . Smaller animals had less pronounced and lower horns than larger ones, but a longer nasal bone. There are also differences in the muscle attachment marks on the cheekbones, which are significantly more massive in male animals. Little is known about a possible herd life of Megacerops , but healed rib injuries may indicate rivalry between male conspecifics. The animals most likely did not have any natural predators when fully grown.
Systematics
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Internal systematics of the Brontotheriita according to Mihlbachler 2009
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Megacerops is a genus of the Brontotheriidae family (originally Titanotheriidae). Due to the structure of the teeth, these are placed close to today's horses . Within the Brontotheri, Megacerops 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. Originally, the tribe of Bryn J. Mader was led as a subfamily of the Telmatheriinae and contained all North American Brontotheria that 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 North American Brontotheria with trained paired horns. This intermediate tribus is opposed to the Embolotheriita with Embolotherium , which includes the Eurasian forms and which usually only have a singular horn , partly designed as a battering ram .
Numerous species have been described, the following are valid:
The individual species and genera very early described research historically large and modern acting Brontotherien representative of North America are now largely synonymous to M. coloradensis considered, only that smaller and later defined, Y-shaped split at the upper ends, paired horns supporting M. kuwagatarhinus is listed as another independent species.
Research history
The exact systematic classification of Megacerops has a long and controversial history, the earliest known finds date from the first half of the 19th century. In 1840, Hiram A. Prout received a mandibular fragment with several huge teeth from a friend of the American Fur Company . The Company had previously opened a stagecoach route through the Badlands and along the White River in what is now South Dakota , and the fossils had been collected by company employees in outcrops there. Prout referred to the lower jaw in a brief report published in 1846 because of similarities in tooth construction to Palaeotherium . This actually quite small member of the now extinct equine species, in Prout's opinion and according to the teeth available, must have been huge in this case. The following year he described the lower jaw in more detail in another publication.
Additional finds by the American Fur Company from the White River area were sent to Joseph Leidy . In a report in 1852 he also took it as belonging to Palaeotherium , but due to its enormous size, he chose - rather casually - the name Titanotherium . But only a few years earlier, in 1849, the French paleontologist Auguste Pomel had introduced the now invalid name Menodus , more precisely Menodus giganteum , based on Prout's lower jaw . The lower jaw and thus the holotype of Menodus was believed to have been lost in a city fire in St. Louis that same year ; but it reappears in the United States National Museum in 1957 . With Megacerops (later sometimes also referred to as Megaceratops ) Joseph Leidy created a name in 1870 that he first used for a fragmented front skull from Colorado with preserved horns. The name Brontotherium was introduced by Othniel Charles Marsh three years later, in 1873, with reference to three individuals from the Natural History Museum at Yale University . Almost 15 years later, Marsh described four other genera with Brontops , Titanops , Menops and Allops , which differed largely in the shape of the horns; the underlying material came from the salvage of the second half of the 19th century, much of which was carried out by John Bell Hatcher .
In the course of the 20th century, the majority of these differently described genera and species were synonymous , so that ultimately only Megacerops , Brontops and Menops remained recognized. Here, characterized megacerops by long-designed, soaring, Brontops -faceted through similar but flatter and Menops contrast with rather short horn formations. In 2004, however, Matthew C. Mihlbachlaer united the remaining genera under the generic name Megacerops and referred the different horn designs largely to variations of a shape (with the exception of M. kuwagatarhinus ), which were partially caused by sexual dimorphism. The name Megacerops , first used by Leidy, is derived from the Greek language and means μεγα ( mega , "large"), κέρας ( kéras "horn") and ὤψ ( ōps "face" or "countenance") and refers to the Horn formations on the muzzle.
literature
- Matthew C. Mihlbachler: Species taxonomy, phylogeny, and biogeography of the Brontotheriidae (Mammalia: Perissodactyla). In: Bulletin of the American Museum of Natural History. No. 311, June 2008, ISSN 0003-0090 , pp. 1-475, doi : 10.1206 / 0003-0090 (2008) 501 [1: STPABO] 2.0.CO; 2
- 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. 229-239)
Individual evidence
- ↑ a b Alessandro Zanazzi and Matthew J. Kohn: Ecology and physiology of White River mammals based on stable isotope ratios of teeth. Palaeogeography, Palaeoclimatology, Palaeoecology 257, 2008, pp. 22-37
- ↑ Gregory S: Paul and Per Christiansen: Forelimb posture in neoceratopsian dinosaurs: implications for gait and locomotion. Paleobiology, 26 (: 3), 2000, pp. 450-4.65
- ↑ a b c Bryn J. Mader and John P. Alexander: Megacerops kuwagatarhinus n. Sp., An unusual brontothere (Mammalia, Perissodactyla) with distally forked horns. Journal of Paleontology 69, 1995, pp. 581-587
- ^ A b Othniel Charles Marsh: Notice of New Fossil Mammals. The American Journal of Science and Arts 34, 1887, pp. 323-331
- ↑ a b c d e f g h 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 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
- ^ Matthew C. Mihlbachler, Spencer G. Lucas, Robert J. Emry, and Bolat Bayshashov: A New Brontothere (Brontotheriidae, Perissodactyla, Mammalia) from the Eocene of the Ily Basin of Kazakstan and a Phylogeny of Asian `` Horned '' Brontotheres. American Museum Novitates 3439, 2004, pp. 1-43
- ↑ a b Christine M. Janis, Boris Shoshitaishvili, Robert Kambic and Borja Figueirido: On their knees: Distal Femur asymmetry in Ungulates and its relationship to body size and locomotion. Journal of Vertebrate Paleontology 32 (2), 2012, pp. 433-445
- ^ Matthew C., Mihlbachler: Body size, dental microwear, and Brontotheres diets through the Eocene. Journal of Vertebrate Paleontology 22 (suppl.), 2002, p. 88A
- ^ A b c 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. 229-239)
- ↑ 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
- ↑ a b 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
- ↑ Hiram A. Prout: Gigantic Palaeotherium. American Journal of Science and Arts 2, 1846, pp. 288–289 ( [1] )
- ↑ Hiram A. Prout: Description of a fossil maxillary bone of Palaeotherium, from near White River. American Journal of Science and Arts 3, 1847, pp. 248–250 ( [2] )
- ^ Rachel C. Benton, Dennis O. Terry Jr., Emmett Evanoff, and H. Gregory McDonald: The White River Badlands. Geology and Paleontology. Indiana University Press, 2016, pp. 1–222 (pp. 3 and 165–167)
- ↑ Joseph Leidy: Description of the remains of extinct Mammalia and Chelonia, from Nebraska territory, collected during the Geological Survey under the direction of Dr. DD Owen. In: David Dale Owen (ed.): Report of a geological survey of Wisconsin, Iowa, and Minnesota and incidentally of a portion of Nebraska Territory. Philadelphia: Lippincott, Grambo, 1852, pp. 534–572 (pp. 551–552) ( [3] )
- ^ Matthew C. Mihlbachler, Spencer G. Lucas and Robert J. Emry: The holotype specimen of Menodus giganteus, and the `` insoluble '' problem of Chadronian brontothere taxonomy. In: Spencer G. Lucas, KE Zeigler and PE Kondrashov (eds.): Paleogene mammals. New Mexico Museum of Natural History and Science Bulletin 26, 2004, pp. 129-135
- ^ Joseph Leidy: (Description of a new genus and species, Megacerops coloradensis). Proceedings of the Academy of Natural Sciences of Philadelphia 22, 1870, pp. 1–2 ( [4] )
- ^ Othniel Charles Marsh: Notice of New Tertiary Mammals. The American Journal of Science and Arts 3 (5), 1873, pp. 485-488 ( [5] )
