Parvicornus
| Parvicornus | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Middle Eocene (Upper Duchesneum ) | ||||||||||||
| 38.9 to 37.7 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Parvicornus | ||||||||||||
| Mihlbachler & Deméré , 2009 | ||||||||||||
Parvicornus is an extinct genus of the odd ungulate thatlivedin North America in the Middle Eocene 39 to 38 million years ago. It is classified within the extinct family Brontotheriidae . It was a large animal, comparable to today's black rhinoceros ; In contrast to most of the late Brontotheria, which were characterized by large bony horn formations on the front skull, Parvicornus had only a pair of very small horns. So far only a few finds are known, the majority were discovered in southwestern California .
features
Parvicornus was a great representative of the Brontotherien , known from several skull finds and some remains of the body skeleton. Based on the surviving finds, an adult animal with a shoulder height of 2 m is reconstructed, so it did not reach the massive dimensions of its relative Megacerops . In body weight it resembled today's black rhinoceros , furthermore with a largely robust body structure that of the other known, large Brontotherien.
The skull ranged in length from 51 to 56 cm and was relatively flat. Similar to other American brontotheria, the zygomatic arches were very expansive and reached a maximum distance of 36 cm, but were sometimes very straight. Typical for representatives with horns, the skull was saddled in a side view and had a protruding occipital bone , which showed a buckled bulge when viewed from above. When viewed from behind, it looked rectangular and wide. The nasal bone was clearly curved downwards and was elongated with laterally thickened and also downwardly directed longitudinal edges. The characteristic bony horn formation, which consisted of fused outgrowths of the two cranial bones, sat at the border between the nasal and frontal bones. Here pointed Parvicornus analog other North American Brontotherien two paired-faceted horns, but they were very small and were only slight bulges. They lay in front of the eye window and protruded slightly forward. The eye window itself was located above the first and second molars and thus a little further back than the relative Megacerops . The interior of the nose, which was located between the nasal bone and the median and upper jaw, was very extensive and could extend to the fourth premolar .
The approximately 49 cm long lower jaw was robust and had a high bone body. The flat symphysis extended to the fourth premolar. The dentition was hardly reduced, only the upper external incisors were missing, which made it look a bit more primitive than in Megacerops . The tooth formula was thereby . The incisors themselves were small, rounded in the upper jaw and shaped like a wedge in the lower jaw and stood in a clearly arched row, with a gap between the two inner incisors in the upper jaw. The canine was large, conical in shape and up to 2.7 cm long, but varied in shape. There was a short, maximally 2 cm long diastema to the posterior teeth . The premolars were clearly molarized and resembled the posterior molars, much more clearly than in other Brontotheria. Furthermore, the molars were comparable to the other members of the family with a low crown ( brachyodont ), and the upper molars of Brontotheria had enamel loops on the chewing surface that were folded in a W-shaped manner. The rearmost and largest molar tooth reached a length of up to 8 cm.
The postcranial skeleton of Parvicornus is partly known. The first two cervical vertebrae of the spinal column, the atlas and the axis , have been handed down, but they resemble those of its relatives. The shoulder blade was long and much narrower than that of Megacerops , as was the humerus , which was much more delicate and reached over 40 cm in length. The thigh bone was the largest long bone with a length of almost 50 cm. Characteristic were the only slightly round joint head and the weakly pronounced third trochanter typical of Brontotheria . As with other Brontotheria, the forelegs ended in four ( metacarpus II to V), the hind legs in three ( metatarsus II to IV) rays, with the middle (third) ray being the strongest.
References
Most of the known finds were discovered in October 2001 during earthworks on the premises of the Ocean Ranch in San Diego County in the extreme southwest of California . They camped in the Santiago Formation , more precisely its layer section C, which reaches a thickness of 55 m. The lower 12 m consists of dark brown sandstones that contain the remains of the late Uintum terrestrial fauna. Above it, separated by a hiatus , follow 40 m thick, predominantly cross-layered sandstones, with an only 1 m thick, solid, brown-colored sand and siltstone bank interposed. These sandstones are characterized by the fossils of the late Duchesneum fauna, which is around 39 to 38 million years old and to which the remains of Parvicornus also belong. The latter lay stratigraphically above the siltstone bank in a canal or river depression cut locally into the sandstones and filled with coarse-grained sand. Due to the frequency of the finds, they are referred to as " bone sands " . However, they also scattered further up into the surrounding fine clastic sands. The fossils consist predominantly of individual bones, only partially in a skeletal structure, which include at least four largely complete skulls, one of them with an associated lower jaw, other parts of the skull and numerous material of the body skeleton. The partial skeleton of a juvenile animal is an exception, but it was damaged during the excavation work.
Additional finds were discovered as early as the mid-1960s in the Slim Buttes Formation in Harding County , South Dakota , but originally described as Teleodus thyboi and later assigned to the new genus Duchesneodus ; In addition to isolated teeth, these also include the remains of a juvenile skull.
Paleobiology
Relatively little is known about the paleobiology of Parvicornus , but the fossil record so far shows evidence of a sex dimorphism . The canines in adult individuals are highly variable, which has also been observed in other Brontotheria such as Gnathotitan , although the larger and more robust canines can probably be associated with males. There are comparable findings on the cheekbones and the bony horns, which are also more delicate in female animals.
Systematics
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Internal systematics of the Brontotheriita according to Mihlbachler 2009
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Parvicornus is a genus of the family of brontotheriidae (originally Titanotheriidae), which due to the dental construction in the vicinity of today's horses are provided. Within the Brontotheri, Parvicornus belongs to the subfamily of the Brontotheriinae and to the intermediate tribus of the Brontotheriita, which in turn belongs to the tribe of the Brontotheriini. This tribe originally introduced Bryn J. Mader as a subfamily of the Telmatheriinae and contained all North American Brontotheria with pronounced horn approaches. However, in a later investigation he renamed the family Brontotheriinae. Matthew C. Mihlbachler put this subfamily on the rank of tribe in 2008 and separated within this with the intermediate tribus of the Brontotheriita the North American Brontotheria with trained paired horns. This group is opposed to the Embolotheriita with Embolotherium and Aktautitan , which encompasses the Eurasian forms and which sometimes only have a singular horn up to a "battering ram" shaped horn. Within the Brontotheriita, Parvicornus is a rather early representative, which can be seen in the front dentition with clearly spherical incisors and a row of teeth bent forward. The next related genera were Protitanops and Eubrontotherium .
The genus Parvicornus was first described in 2009 by Matthew C. Mihlbachler and Thomas A. Deméré using finds from the Ocean Ranch in southwestern California . The holotype (specimen number SDSNH 107667) represents an almost complete skull. The only recognized species is Parvicornus occidentalis . The generic name comes from the Latin words parvus ("small") and cornus ("horn") and refers to the little pronounced bony horns. The species name occidentalis (Latin for "western") is due to the very western location in North America. Also included in this species are some finds from northwestern South Dakota , which include the skull of a young animal. Originally these were assigned to the Brontotherien species Teleodus thyboi , in 1982 Spencer George Lucas and Robert M. Schoch incorporated them into the new genus Duchesneodus . Due to the holotype, the skull of the young animal, which was classified as rather unspecific at the time, this species was largely regarded as a noun nudum .
literature
- 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
Individual evidence
- ^ San Diego Natural History Museum: Parvicornus occidentalis. ( [1] )
- ↑ a b c d e f g h i 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
- ^ Philip R. Bjork: Latest Eocene Vertebrates from Northwestern South Dakota. Journal of Paleontology 41 (1), 1967, pp. 227-236
- ^ A b 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
- ↑ 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
Web links
- San Diego Natural History Museum: Parvicornus occidentalis. ( [2] )