Eteketoni
| Eteketoni | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Lower Miocene | ||||||||||||
| 20 to 18.5 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Eteketoni | ||||||||||||
| Pickford , 2019 | ||||||||||||
Eteketoni is an extinct genus from the family of Orycteropodidae and the order of Tubulidentata, to which the aardvark is the only current member. The genus is known only from a partial skeleton thatcomesfrom eastern Uganda . Dating to the Lower Miocene around 20 to 18.5 million years ago, Eteketoni is currently the oldest clear representative of the entire group of aardvark relatives. The animals matched today's aardvark in many features, including their typical tubular structure the molars, but were significantly smaller. In addition, the skull was noticeably flatter and there are individual differences in detail. Like their recent relative, they probably lived digging and specialized on ants and termites . The genus was scientifically introduced in 2019. It's kind of recognized.
features
Eteketoni is known from a skeleton that has only survived in fragments. This refers to a significantly smaller animal of around 8.5 kg body weight compared to today's aardvark. The anterior section with the rostrum is missing from the skull and it is severely crushed. However, it was originally designed to be clearly flat. At the skull, its width was around 4.6 cm, while its height was only 2.6 cm. This corresponds to a ratio of 1.75. In today's aardvark, the skull is noticeably higher, the width-height ratio is 1.44 to 1.52. The line of the forehead bulged in Eteketoni on the frontal bone above the orbit . When viewed from above, the frontal bone began wide and narrowed towards the orbit, but the cranial constriction behind the eye sockets was only weakly developed. This is also a clear difference to the aardvark, as well as to the extinct forms Leptorycteropus and Amphiorycteropus , in which the postorbital constriction is more pronounced. The infraorbital foramen opened above the posterior part of the first molar and was relatively small. The front section of the zygomatic arch was attached to the third molar. On the parietal bone , the temporal lines united in the posterior section to form a short and flat crest . This is not the case with the aardvark, because the temporal lines remain separated over the entire course. The occipital bulge on the occiput protruded beyond the back of the skull, but turned inside in the middle when viewed from above. In contrast to the aardvark, the occipital joints did not stand out so clearly.
The lower jaw is only fragmented. The horizontal bony body ran gently downwards at the lower edge. The greatest depth was reached on the second molar . Here the lower jaw was 1.25 cm high. The lower jaw widened slightly in the area of the molars. One mental foramen was located below the second and third premolars , and another below the last premolar and first molar. The leading edge of the ascending branch was at an angle of 55 ° to the alveolar plane . In comparison, this was steeper in Orycteropus , Myorycteropus and Amphiorycteropus . The crown process rose around 1.7 to 1.8 cm above the chewing surface of the teeth. It was separated from the articular process by a deep U-shaped indentation. The latter had a bulging joint surface. The angular process was very deep compared to the dental occlusal plane and was slightly sloping at the lower edge and thus much more gently than in the aardvark. For the rear dentition, four premolars and three molars per row of teeth are occupied in the upper jaw; in the lower jaw, the row of teeth has been handed down from the second premolar to the third molar. The front dentition is unknown. Typically for the tubulidentata, the teeth consisted of columnar structures made of dentin and embedded in a matrix of dental cement . They joined together to form the actual teeth. The premolars showed a simple lobed ( unilobaten ), the front molars a two-lobed ( bilobaten ) outline. The upper posterior molar was unilobed, the lower posterior slightly bilobed. The teeth of the posterior set of teeth were in a closed row, but separated short gaps 1 mm from each other. The length of the molar row was 2.1 cm in the upper jaw and 2.7 cm in the lower jaw. The largest tooth in each case was the second molar, which was up to 0.87 cm long in the upper row of teeth and up to 1.0 cm in the lower row. In the upper jaw, the two rows of teeth converged slightly to one another.
Individual vertebrae, the front legs and a few fragments of the rear legs have been preserved from the body skeleton. On the humerus , which was 8.6 cm long, a rounded joint head was formed, which was positioned slightly backwards. The bone shaft was straight, a strong deltopectoral ridge ran along it and formed a conspicuous bulge approximately at the level of the middle of the shaft. The lower end of the joint was massive. The ulnar is missing the upper end of the joint, the olecranon , which must have been very large in relation to the fracture surface. Individual distinctive bone ribs appeared on the shaft. The diaphysis itself, like that of the spoke, was lightly compressed. The latter bone reached a length of 5.7 cm and had a strong wrist end. In Eteketoni the hand consisted of at least four rays (II to V), whereby the outer ray (V) is only covered by joint surfaces on ray IV. Of these, the metacarpal bones of the second and third rays were significantly longer than those of the fourth, the first two measuring 3.3 to 3.2 cm in length, the latter around 2.6 cm. Basically, the bones resembled the corresponding elements in today's aardvark and in the extinct forms. To Myorycteropus but there was a proportion difference, since this larger compared to the arm length hands had. On the fully preserved finger of the third ray, the middle phalanx was shorter than the anterior and posterior. Its back side was characterized by a sharp rib along the central axis in accordance with Myorycteropus , while this section is more rounded in today's aardvark. The terminal phalanges usually tapered off to a point, indicating the claws that were once formed. The hind leg has only survived through a lower fibula fragment. Here, however, a widely spreading outer ankle was formed, which in relation exceeded the corresponding formations in the aardvark as well as in Leptorycteropus and Amphiorycteropus .
Fossil finds
Fossil remains of Eteketoni have so far only been found near Karamoja on the northwest slope of the Akisim Mountains in eastern Uganda in East Africa . The find area has long been known for its wealth of fossils. It is the Napak volcano , in the vicinity of which there are numerous important sites. Stratigraphically , gneisses of the Precambrian form the basis. The fossil-bearing layers on top of it are divided into individual sub-units, which from bottom to top comprise the Iriri Member , the Napak Member and the Akisim Member . They are separated from each other by volcanic deposits. This concerns the Lomorutoit Nephelinite Lava between the Iriri and the Napak member and the Akisim agglomerate between the Napak and the Akisim member . Radiometric dating of biotites gives the Napak member an absolute age of 20 to 18.5 million years, which corresponds to the Lower Miocene .
The Napak region gained importance primarily through the numerous finds of early representatives of Old World monkeys . This includes, among other things , vervet monkey relatives , for example from the extinct group of the Victoriapithecidae. Representatives of the Hyaenodonta , for example the genus Hyainailouros , and various ungulates and small mammals were also presented here. The Eteketoni finds come from site XIII, which belongs to the Napak member . In addition to the partial skeleton of the early aardvark, some individual finds such as isolated teeth and phalanges came to light. The finds were associated with the remains of several representatives of the deer piglets and the pig relative Nguruwe .
Paleobiology
The general design of the front legs is similar to that of today's aardvark and shows that Eteketoni was able to create underground passages and tunnels like this one. This is also indicated by the fibula fragment with the strong ankle. The deviation from the existing aardvarks Gelenkung of the fibula to the heel bone at Eteketoni enabled a stable base, supporting the view of a grave end of life. The relatively flat skull can be viewed as an adaptation to environments with limited vertical space. Possibly used Eteketoni thereby also flat natural crevices or caves under tree roots. The similar dentition and skull structure of Eteketoni suggest a diet based on ants and termites comparable to that of the aardvark. Due to its significantly smaller body size and the resulting narrower snout, Eteketoni could possibly also take prey directly from small holes in the ground or nest openings. This is only possible to a limited extent with the aardvark with its significantly larger stature. It must therefore tear up ants and termite nests with the claws of the front feet. Individual trace fossils from Napak can be interpreted as an indirect reference to the diet of Eteketoni . These include tunnel tubes with a diameter of 4 to 5 mm, which are connected to circular fungal structures and are probably caused by termites. The orbita at Eteketoni is similar to that of today's aardvark. This includes the formation of a postorbital process at the rear edge of the eye window and the position of the lacrimal foramen outside the eye socket. It can therefore be assumed that the fossil form led a nocturnal life in accordance with the recent representatives. Individual differences can be found in the position of the orbit, which in Eteketoni is slightly shifted laterally backwards than in the aardvark. It is unclear whether this had any effect on general vision.
Systematics
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Internal systematics of the Tubulidentata according to Pickford 2019
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Eteketoni is an extinct genus of the family of Orycteropodidae and the order of Tubulidentata. Both order and family belong recently with the aardvark ( Orycteropus afer ) only one member. The Tubulidentata in turn form part of the parentage of the Afrotheria , which represents one of the four main lines of the higher mammals . The order was never very rich in forms in the course of its tribal history . It first appeared in the Lower Miocene and was initially limited to Africa . In the Middle Miocene, however, their representatives also reached Eurasia , where they spread from southern Europe to southern Asia . Outside of Africa, however, the aardvark relatives disappeared again in the Pliocene at the latest . In general, they can be regarded as a rather rare element of fauna. Within the family of the Orycteropodidae, in addition to the aardvark, several other genera can be distinguished that have only been handed down in fossil form. These include Myorycteropus , Leptorycteropus and Amphiorycteropus . A special feature of all these forms is the structure of the molars from columnar dentin tubes, which gives the order of the tubulidentata . The genus Eteketoni is the oldest unequivocal member of the aardvark family to date. Possible closer relationships exist with Myorycteropus . Both forms are characterized by an ascending branch leaning more backwards on the lower jaw, which, however, recedes even more clearly in Eteketoni than is the case in Myorycteropus . As a separating feature, the former has larger teeth than the latter.
The first scientific description of Eteketoni comes from Martin Pickford in 2019. The basis was the partial skeleton of Napak in eastern Uganda as the only known fossil record to date (copy number Nap XIII 17'18). The generic name is borrowed from the Iriri dialect of the Karamojong and means something like "aardvark". Eteketoni is derived from the verb akiketeke , which can be translated as "scratch". It refers to the ability of the aardvark to dig underground with its limbs (so-called scratch-digging ). E. platycephalus was the only recognized species to be named. The specific epithet is again of Greek origin and consists of the words πλατόω ( plato ) for "flat" or "wide" and κεφαλή ( cephalé ) for "head" or "head". It refers to the flat skull, which is almost twice as wide as it is high.
literature
- Martin Pickford: Orycteropodidae (Tubulidentata, Mammalia) from the Early Miocene of Napak, Uganda. Munich Geoscientific Treatises Series A: Geology and Paläontologie 47, 2019, pp. 1–101
Individual evidence
- ↑ a b c d e f g h i Martin Pickford: Orycteropodidae (Tubulidentata, Mammalia) from the Early Miocene of Napak, Uganda. Munich Geoscientific Treatises Series A: Geology and Paläontologie 47, 2019, pp. 1–101
- ↑ a b Martin Pickford, Brigitte Senut, Sarah Musalizi, Dominique Gommery and Christopher Ssebuyungo: Early Miocene Victoriapithecid Monkey from Napak, Uganda. Geo-Pal Uganda 12, 2019, pp. 1–17
- ↑ David Pilbeam and Alan Walker: Fossil Monkeys from the Miocene of Napak, North-East Uganda. Nature 220, 1968, pp. 657-660
- Jump up ↑ Jorge Morales and Martin Pickford: New hyaenodonts (Ferae, Mammalia) from the Early Miocene of Napak (Uganda), Koru (Kenya) and Grillental (Namibia). Fossil Imprint 73 (3–4), 2017, pp. 332–359
- ^ Martin Pickford: Ruminants from the Early Miocene of Napak, Uganda. Annales de Paléontologie 88, 2002, pp. 85-113
- ↑ Laura Bento Da Costa, Brigitte Senut, Dominique Gommery and Martin Pickford: Dental remains of Lower Miocene small rodents from Napak (Ugandas): Afrocricetodontidae, Myophiomyidae, Kenyamyidae and Sciuridae. Annales de Paléontologie 105 (2), 2019, pp. 155–167
- ↑ Thomas Lehmann: Phylogeny and systematics of the Orycteropodidae (Mammalia, Tubulidentata). Zoological Journal of the Linnean Society 155, 2009, pp. 649-702
- ↑ Patricia A. Holroyd: Tubulidentata. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London, 2010, pp. 107-111