Rusingoryx
| Rusingoryx | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Upper Pleistocene | ||||||||||||
| 100,000 to 33,000 years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Rusingoryx | ||||||||||||
| Pickford & Thomas , 1984 | ||||||||||||
Rusingoryx is an extinct species from the group Kuhantilopen within the family Bovidae . It is documented from eastern Africa , where itinhabitedthe present-day islands of Rusinga and Mfangano in eastern Lake Victoria as well as the adjacent mainlandin the late Pleistocene . At that time, the region was a very dry grassy landscape. Rusingoryx is a medium-sized representative of the hartebeest, which reached about the size of today's wildebeest and to which the genus is also closely related. The most striking characteristic of the animals was a comb-like bony elevation on the skull, which stretched from the nose to the forehead andhas so far beenunparalleled within mammals . Due to the internal structure of the bulge, which consists of cavities and the respiratory tract , it can be concluded that Rusingoryx generated infrasound tones that were used for communication in the open landscapes. The structure of the teeth again shows that the animals were highly specialized grass-eaters. Thegenus was first described in 1984 on the basis of incomplete skull material. Because of this, the independence of Rusingoryx was questioned in the 1990s. Only extensive new find material confirmed the independent genus character of Rusingoryx .
features
Rusingoryx was a medium-sized representative of the hartebeest , which was roughly the size of today's red hartebeest ( Alcelaphus ) or the wildebeest ( Connochaetes ). Its skull ranged in length from 35.9 to 44.6 cm and had a number of unusual features. One notable abnormality was the rostrum . A narrow, high bony crest ran along the upper skull, reaching from the intermaxillary bone over the nasal bone to the frontal bone . The interior consisted of individual hollow chambers that took up a larger part of the skull volume. These extended to behind the end of the row of teeth, along the midline a thin septum was formed, which resulted from the paired structure of the skull bones, whereby the exact origin of the septum - whether from the upper jaw , palatine bone or wing bone - is unclear. Due to the pronounced bulging of the front skull, the middle jawbone and the upper jaw were drawn relatively high and thus took up part of the voluminous space. The nasal canal as part of the respiratory tract was in the upper part of the bulge, its base in turn delimiting the cavity at the top. In the area of the frontal bone, approximately at the level of the orbit , the nasal canal reached the inner skull, where it led downwards in an S-curve. As a result, the mouth in the throat was compared to other mammals relatively far back and at the top of the skull. The palatal bone in turn formed part of the lower boundary of the bulge, it was also extended backwards and completely closed and thus did not allow the passage of the inner nostrils ( choane ). However, parts of the palatine bone such as the sphenoid bone were involved in enclosing the descending airway. On the underside of the palatine bone, deep pits indicated the attachment points of the palate and tongue muscles.
In the rest of the cranial structure, Rusingoryx largely followed the other red hartebeest, special features were the relatively graceful zygomatic arch , the bilobed, forward elongated zygomatic bone and the upward stretched tearbone . The orbit was low on the skull, the foramen supraorbital , which is not to be emphasized on the upper, but on the side edge and formed an extraordinarily large opening, the edge of the eye was also very steeply erected. The width of the skull was about 7.4 cm here. Further abnormalities can be found primarily at the base of the skull, for example with the small wing of the lower cuneiform bone, the robust lower section of the occiput and the little developed tympanic bladder . The bony outgrowths of the horns (os cornu) started behind the eye windows and were 12 to 16 cm long, they had an oval to round cross-section around 4 cm in diameter and showed no significant torsion in their course. In their general structure, the horns showed clear differences from the cones of the closely related Megalotragus , which were up to 50 cm longer, more flattened and clearly rotated clockwise (relative to the right horn).
The lower jaw was strong, the horizontal body deep, its lower edge was rather straight and not curved downwards like other hartebeest. The ascending articular branch started at an obtuse angle. The articular and crown processes were oriented backwards, the latter rose higher and ended in a hook shape. The dentition differed from the general structure of the hornbeam and was characterized by an additional reduction of the second premolar in the lower jaw, which is also documented among the recent red hartebeest in the wildebeest and the hunter antelope ( Beatragus ). The tooth formula was thus , which results in a total of 30 teeth. In addition, the third premolar was extremely reduced in size, which made the row of premolars appear to be greatly shortened. Overall, the molars had very high ( hypsodontic ) crowns. The enamel pattern on the chewing surfaces of the molars was less complex and tortuous than that of today's hartebeest and was more similar to that of Megalotragus . Compared to the latter, however, the molars in Rusingoryx were significantly smaller, the second reached a length of 2.2 to 2.7 cm.
Fossil finds
All known fossil remains of Rusingoryx come from East Africa , most of them came to light on the islands of Rusinga and Mfangano in the eastern part of Lake Victoria . Above all, Rusinga is known as a fossil deposit , but the focus of interest is mostly on the rich finds from the Miocene . The much more recent finds of Rusingoryx are stored here in the so-called Wasiriya Beds , deposits from the Pleistocene , which consist of fine-grained silt , mudde and sandstones as well as conglomerates with intervening formations of volcanic origin. They go back partly to fluvial processes, whereby individual weak soil formations also indicate phases of temporarily low accumulation. The Wasiriya Beds cover the edge areas of the island on an area of less than 10 km² and are up to 10 m thick, their age is radiometrically around 100,000 Dated to 33,000 years, which corresponds to the early part of the Young Pleistocene . In total, more than 140 individuals of Rusingoryx have been discovered on Rusinga so far , Bovid Hill near Wakondo is important here , where investigations in 2011 alone on an area of 19 m² have skeletal remains of 15 adult animals, 8 young animals and 3 very old animals came to light. Around a dozen individuals of Mfangano have been recorded so far, they come from the waware beds , which are exposed in the eastern part of the island and represent former river deposits with an average thickness of only 1 m. They are at least 35,000 years old. In connection with Rusingoryx , various other antelope forms have also been discovered on the two islands , such as the extinct and closely related Megalotragus , but also wildebeest , reedbuck and various gazelles such as Thomson's gazelles , Grant's gazelles, Oribis or Dikdiks . The local fauna is also enriched by zebras , aardvarks , warthogs and hippos . All in all, however, Rusingoryx is the most frequently registered mammal form in both groups of finds. The composition of the fauna suggests that the landscapes were much more open and drier at the time the deposits were formed than is the case around Lake Victoria today. Another skull of Rusingoryx addition of the eastern Homa Peninsula handed where this along with other cloven-hoofed animals radicals in Luanda Beds was salvaged. The layers of the Luanda Beds have a comparable origin to those of the islands of Rusinga and Mfangano and are also likely to be of a similar age.
Significant in connection with the faunistic remains are stone artefacts of early humans, which comprise several hundred pieces and consist of chert , quartz or various types of volcanic rocks of local provenance. The inventory is characterized by Levallois cores and flakes as well as blades and isolated bifacial devices or simply retouched, pointed pieces. Above all, the levalloid shapes and the blades imply a position in the Middle Stone Age ( corresponding to the European Middle Paleolithic ). The different raw materials that were used result in partly strongly varying artefact sizes, which on the one hand can be related to the available raw material and on the other hand to the intensive use of higher quality rocks. In addition to the stone artefacts, individual bones manipulated by cutting marks can also be observed. According to this, at least part of the faunal material can be interpreted as slaughterhouse waste, while another part shows strong bite marks that can be traced back to carnivore damage. The area excavated on Bovid Hill in 2011 is interpreted as a catastrophic event due to the mass accumulation of Rusingoryx remains, but the influence of humans is unclear.
Paleobiology
Rusingoryx shows characteristics in the structure of the skull that are not known from other horn-carriers or higher mammals . The distinct bony bulge of the fore skull, the function of which was long considered unknown, should be emphasized. Initially and using incomplete skulls with a broken or damaged snout area, it was assumed that the animals had a trunk-like extension of the nose, as is known from some Dikdiks or the Saiga . However, complete skulls showed that this bulge extends over the entire length of the front skull, creating a narrow, comb-like structure. The nasal ridge is mainly developed in adult animals, although it is still unclear whether it is more developed in males than in females. In young animals only a slight bump above the nose can be detected, which over time expands backwards towards the forehead and becomes larger. Since a similar structure in mammals is not known, the function can only be assumed. An intended support for thermoregulation is excluded with reference to the structure of the bone ridge, since the entire structure prevents the breathing air from circulating through a lack of connection or opening to the nasal tract. Also, due to the very fragile construction of the bone ridge, it is unlikely to be used in turf and dominance battles or as a visual indicator. The shape of the structure is reminiscent of comparable formations in Parasaurolophus and some other representatives of the Hadrosauridae , a group of herbivorous dinosaurs from the Upper Cretaceous around 70 million years ago. In this it is assumed that the distinctive bony crest on the skull was used as a modulation element in the communication, which is also in the nose comb structure of Rusingoryx could have been the case. The strong palate muscles, which are indicated by deep pits on the palatal bone, made it possible to raise the larynx more strongly towards the nose and thus to involve the nasal canal in the sound modulation. The sounds produced in the larynx were modified by the nasal tract, which is elongated due to its high position on the skull and additionally stretched by the S-shaped curvature in the interior of the skull, whereby a longer nasal tract correlates with lower frequencies. This enabled Rusingoryx to produce comparatively low tones, which were calculated to be between 248 and 746 Hz . Taking into account a further extension due to the soft tissue that has not been handed down , around 20 Hz would also be possible, which is well in the infrasound range. The function of the cavities in the front area of the nasal ridge is not fully understood; they may have acted as a resonator , similar to the horn-like attachment of the hornbills . Loud expressions are very extensively documented for social communication in horned people. Although no known representative has a bony, elongated nasal canal, the saiga, for example, can produce low-frequency tones with a base frequency of 37 to 53 Hz and a dominant frequency of 370 to 460 Hz during the rutting season by stretching its extremely muscular, trunk-like nose by 20% produce. The goiter gazelle in turn is able to produce sounds with basic frequencies around 91 Hz and with dominant frequencies around 546 Hz via the nasal canal by means of its enlarged larynx, also during the mating season. With regard to the hartebeest , communication takes place between individual individuals, for example in dominance and mating contests, in partner recruitment or between young and mother animals and between herds. Especially at night, the calls are often lowered to a lower frequency range and then often serve as a warning signal. The advantage of communication in the low-frequency range such as infrasound is that sounds are transported over long distances - in comparison with elephants in open landscapes up to more than 10 km after sunset - which is extremely important for herding animals. Predators can usually not perceive sounds in infrasound, which in the case of Rusingoryx allowed secure communication over long distances.
Another striking feature of Rusingoryx are the special features of the dentition structure. This affects, among other things, the extremely hypsodontic molars, which are among the highest in relation to other hartebeest. High tooth crowns and the accompanying massive lower jaw body are usually an adaptation to hard grass forage in ungulates , which also applies to the hartebeest, as they inhabit open landscapes. The loss of the second lower premolar is noteworthy in this context . Something similar occurs within the hartebeest in the wildebeest ( Connochaetes ) and in the hunter antelope ( Beatragus ). In contrast to the two present-day representatives, however, the premolar row in Rusingoryx is also greatly shortened compared to the molar row, it reaches less than a third of the length of the molars together. An extended row of premier teeth often offers the advantage of being able to consume softer plant material such as leaves or flowers under certain circumstances. In principle, Rusingoryx represented an extremely specialized grass eater that hardly consumed any softer parts of the plant. This is also supported by the largely round grinding marks on the molar teeth that are created when chewing the hard grass, while softer leaves tend to leave sharp edges. Preliminary results of isotope investigations also confirm this view, just as the very dry landscape determined on the basis of the paleontological findings supports the high specialization of Rusingoryx . It can also be assumed that during the Pleistocene in the dry grasslands of East Africa a similar feeding regime prevailed within the ungulates as can be observed in today's Serengeti . Under this condition, Rusingoryx represented a consumer of mostly medium-high grass stands with average nutrient content, which roughly corresponds to the feeding behavior of the wildebeest. These follow the very large ungulates such as the Cape buffalo and plains zebras , which, due to their size, require considerable amounts of food and are therefore hardly selective, which means that they mainly consume the high, nutrient-poor grass stands. The end of the sequence is formed by small ungulates such as the lyre antelopes or various gazelles , which, as selective food specialists, graze only the most nutritious, low grass stands.
Systematics
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Internal systematics of the hartebeest according to O'Brian et al. 2016
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Rusingoryx is an extinct species from the family of the Bovidae (Bovidae). Within this it is placed in the subfamily of the Antilopinae and the tribe of the hartebeest (Alcelaphini). The hartebeest are medium-sized to very large antelopes , with both male and female animals wearing horns. Typical of hartebeest is the very high position of the shoulder compared to the rest of the trunk, the long, sometimes horse-like tail, as well as the presence of glands only on the front feet and the absence of glands in the groin area. In the cranial structure, there are special features, among other things with the large cavity in the frontal bone between the horn base, with the wide contact of the middle jawbone with the nasal bone , additionally with individual characteristics at the skull base and with the design of the chewing surface of the generally high-crowned ( hypsodontic ) molars. Within the hartebeest, Rusingoryx can be referred to the sub-tribus of the Alcelaphina, which, considering today's representatives, includes the red hartebeest ( Alcelaphus ), the wildebeest ( Connochaetes ) and the hunter antelope ( Beatragus ). Opposite them are the Damaliscina with the lyre antelopes ( Damaliscus ). Taking into account the fossil forms, Megalotragus forms the closest relative of Rusingoryx , the genus was introduced by Egbert Cornelis Nicolaas van Hoepen in 1932. This is an extremely large form of the hartebeest known from the Pliocene and Pleistocene of eastern and southern Africa and has been handed down at important sites such as Koobi Fora and Olduvai as well as Awash . The most closely related red hartebeest today represent the wildebeest. Together with these two genera and also the extinct Oreonagor , Rusingoryx forms a closely related group within the Alcelaphina.
The first scientific description of Rusingoryx was made by Martin Pickford and Herbert Thomas in 1984 on the basis of finds from Wakondo on the island of Rusinga in Lake Victoria . The holotype (copy number KNM RU 10553A) consists of a partial skull with both horns but a damaged part of the snout and missing zygomatic arches . The generic name Rusingoryx is made up of the name of the island Rusinga as a reference to the place where it was found and the Greek name oryx ( ὄρυξ for the "antelope" or a "wild animal"). The only recognized species is Rusingoryx atopocranion , whereby the specific epithet consists of the Greek words άτοπος ( atopos "unusual") and κρανίον ( cranion "head" or "skull") and refers to the special skull shape assumed at that time (the first description was based on a From today's point of view, the skull was squashed by sediment; the authors suspected at the time that Rusingoryx carried his head very high in relation to the configuration of the occiput , in contrast to the typical low position of the head with the face pointing down in today's hartebeest). Only a few years later, in 1991, John M. Harris equated Rusingoryx with Megalotragus due to the general shape of the skull - but determined on incomplete specimens , which Elisabeth S. Vrba confirmed in 1997. A phylogenetic study from 2011 came to the conclusion, after examining better preserved skulls and the lower jaw, that Rusingoryx is an independent genus. Arguments for this were found, among other things, in the much smaller horns of Rusingoryx compared to Megalotragus , in the lack of torsion in the former and also in the construction of the teeth, such as the sharp shortening of the premolar row compared to the molar row as a characteristic of Rusingoryx . A connecting element of both genus is the clear bulging of the nasal area, which does not appear to be so advanced in Megalotragus .
Tribal history
According to the fossil record, the genus Rusingoryx has so far been restricted locally to the area on the eastern edge of Lake Victoria , namely on the islands of Rusinga and Mfangano and on the Homa peninsula to the east . Lake Victoria is a geologically young formation that originated about 400,000 years ago. Little is known about its development, however, during the course of the Pleistocene there were various transgressions and regressions of the water level. Initially it was discussed whether Rusingoryx might represent an island form of the hartebeest, but the very dry climatic conditions, the character of the deposits and the only shallow water depth in the eastern part of the lake with sometimes less than 5 m speak against it and support that Rusinga at the time of the Existence of Rusingoryx was connected with the mainland. It is therefore unclear why the genus has not been documented at other sites of the same age, such as Lukenya Hill or Lainyamok (both located in Kenya). Possibly this results from confusion with Connochaetes and Alcelaphus , since the two forms are similar in size to Rusingoryx and resemble it in the postcranial skeleton. The extinction of Rusingoryx is unexplained, the genus disappeared at the end of the Pleistocene, like numerous other large grass-eaters from Africa. This event, which is part of the Quaternary extinction wave, took place gradually in Africa and may be related to the decline in the very dry grasslands in Africa.
Individual evidence
- ↑ a b c d e f g h i Haley D. O'Brien, J. Tyler Faith, Kirsten E. Jenkins, Daniel J. Peppe, Thomas W. Plummer, Zenobia L. Jacobs, Bo Li, Renaud Joannes-Boyau, Gilbert Price, Yue-xing Feng, and Christian A. Tryon: Unexpected Convergent Evolution of Nasal Domes between Pleistocene Bovids and Cretaceous Hadrosaur Dinosaurs. Current Biology 2016, doi : 10.1016 / j.cub.2015.12.050
- ↑ a b c d e Martin Pickford and Herbert Thomas: An aberrant new bovid (Mammalia) in subrecent deposits from Rusinga Island, Kenya. Proceedings of the Koninklijke Nederlandsche Akademie van Wetenschappen B 87, 1984, pp. 441-452
- ↑ a b c d e f g J. Tyler Faith, Jonah N. Choiniere, Christian A. Tryon, Daniel J. Peppe and David L. Fox: Taxonomic status and paleoecology of Rusingoryx atopocranion (Mammalia, Artiodactyla), an extinct Pleistocene bovid from Rusinga Island, Kenya. Quaternary Research 75, 2011, pp. 697-707
- ↑ a b c Christian A. Tryon, J. Tyler Faith, Daniel J. Peppe, David L. Fox, Kieran P. McNulty, Kirsten Jenkins, Holly Dunsworth and Will Harcourt-Smith: The Pleistocene archeology and environments of the Wasiriya Beds, Rusinga Island, Kenya. Journal of Human Evolution 59, 2010, pp. 657-671
- ↑ a b Christian A. Tryon, Daniel J. Peppe, J. Tyler Faith, Alex Van Plantinga, Sheila Nightingale, Julian Ogondo and David L. Fox: Late Pleistocene artefacts and fauna from Rusinga and Mfangano islands, Lake Victoria, Kenya. Azania: Archaeological Research in Africa 47 (1), 2012; Pp. 14-38
- ↑ Kirsten Jenkins, J. Tyler Faith, Christian Tryon, Daniel Peppe, Sheila Nightingale, Julian Ogondo, Cara Roure Johnson and Steve Driese: New Excavations of a Late Pleistocene Bonebed and Associated MSA Artifacts Rusinga Island, Kenya. PaleoAnthropology 2012, p. A17
- ↑ David B. Weishampel: Acoustic analyzes of potential vocalization in lambeosaurine dinosaurs (Reptilia: Ornithischia). Paleobiology 7 (2), 1981, pp. 252-261
- ↑ Roland Frey, Ilya Volodin and Elena Volodina: A nose that roars: anatomical specializations and behavioral features of rutting male saiga. Journal of Anatomy 211, 2007, pp. 717-736
- ↑ Kseniya O. Efremova, Ilya A. Volodin, Elena V. Volodina, Roland Frey, Ekaterina N. Lapshina and Natalia V. Soldatova: Developmental changes of nasal and oral calls in the goitred gazelle Gazella subgutturosa, a nonhuman mammal with a sexually dimorphic and descended larynx. Natural Sciences 98, 2011, pp. 919–931
- ↑ Michael Garstang, David Larom, Richard Raspet and Malan Lindeque: Atmospheric controls on elephant communication. Journal of Experimental Biology 198, 1995, pp. 939-951
- ^ Lillian M. Spencer: Morphological Correlates of Dietary Resource Partitioning in the African Bovidae. Journal of Mammalogy 76 (2), 1995, pp. 448-471
- ^ Nicole Garret, David Fox, Kieran McNulty, Christian Tryon and Daniel Peppe: Isotope paleoecology of the Pleistocene Wasiriya Beds of Rusinga Island, Kenya. Journal of Vertebrate Paleontology, SVP Program and Abstracts Book 2010, p. 94A
- ↑ a b c Elisabeth S. Vrba: New fossils of Alcelaphini and Caprinae (Bovidae, Mammalia) from Awash, Ethiopia, and phylogenetic analysis of Alcelaphini. Paleontologia Africana 34, 1997, pp. 127-198
- ↑ Allen W. Gentry: Bovidae. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London, 2010, pp. 741-796
- ↑ J. Tyler Faith: Late Pleistocene and Holocene mammal extinctions on continental Africa. Earth-Science Review 128, 2014, pp. 105-121