Antilohyrax
| Antilohyrax | ||||||||||||
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| Temporal occurrence | ||||||||||||
| Upper Eocene to Lower Oligocene | ||||||||||||
| 34 to 30 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Antilohyrax | ||||||||||||
| Rasmussen & Simons , 2000 | ||||||||||||
Antilohyrax is an extinct genus from the order of the hyrax . Within this, it belongs to an original branch of the group that no longer exists today. The representatives of Antilohyrax lived in the period from the Upper Eocene to the Lower Oligocene about 34 to 30 million years ago. Fossil finds are so far only documented from northern Africa , the most extensive material comes from the fossil deposit of Fayyum in northern Egypt . Remains of skulls and parts of the musculoskeletal system have survived. They refer to a medium-sized animal that lived mainly on soft, plant-based foods such as leaves and, as a fast runner, could also jump. Antilohyrax thus extendsthe morphological diversity of the early hyrax. The genus was introduced in 2000.
features
Antilohyrax is a medium-sized representative of the hyrax. Its body weight is reconstructed to about 30 to 35 kg, which is about ten times greater than today's species. Several skulls and parts of the postcranial skeleton have survived. The skull of Antilohyrax shows some peculiarities in relation to the modern hyrax. As with the recent species, the forehead line was very flat, according to other members of the Titanohyracidae , the rostrum was shortened. The nasal bone protruded further forward than in today's species and ended sharply above the anterior section of the median jawbone . This created a relatively large interior nasal space, which was framed in the lower and rear parts by the median jawbone. The upper jaw had a long contact zone with the frontal bone in front of the eye windows . This is no longer the case with today's sleepers due to the advanced orbit. The infraorbital foramen was formed above the third and fourth premolars . The frontal bone had a broad and flat shape, as in almost all sleepers. The postorbital bow appeared closed, which today only in the tree hyraxes ( Dendrohyrax occurs). The zygomatic arch was largely formed from the process of the zygomatic bone , only in the anterior third did it meet the process of the upper jaw. In the posterior part, the zygomatic bone was in connection with the temporal bone approximately at the level of the skull and jaw joint and formed the outer edge of the glenoid pit. It is possible that Antilohyrax, like some of today's hyrax, also had an interparietal bone formed between the temporal bones . The supraoccipital of the occiput was vertical and tall and narrow. It had a strong bone bulge on the upper edge. Striking at the base of the skull was a long, vertically directed paroccipital process , which comparatively surpassed the corresponding formations in today's snakes.
The lower jaw had no internal openings, such as those found in Saghatherium or Thyrohyrax . The symphysis was firmly fused and relatively long, it took up around 19% of the entire length of the jaw and reached behind the canine . The two halves of the lower jaw stood apart in a V-shape, the horizontal bone body was low. A mental foramen occurred under the third incisor or the canine as well as under the first and third premolars , sometimes two more were formed. The ascending branch was quite massive, but the crown process only protruded slightly and was slightly above the articular process. The angular process was not as prominent as in today's snakes and only slightly rounded back. Antilohyrax's dentition was hardly reduced. The inner upper incisor had a canine-like ( canine-shaped ) shape and was large, it sat slightly offset to the side and not exactly at the tip of the middle jawbone. This was followed by an only small, pen-like incisor. There were three incisors in each half of the lower jaw. The innermost had the most conspicuous shape, it was asymmetrically wide and thin and divided into eight to ten small, around 3 mm high pins, giving the impression of a tooth comb . All pens were similar except for the innermost one, which was wider and also divided again. Similar shaped incisors can be found today on giant gliders . The second incisor was also broad in shape, but had a long shear edge and was slightly sloping in the lower jaw. The third incisor was the same as the first, but only had five pins in total. A short diastema opened between the incisors and the canine . The premolars and molars stood together with the canine in both the upper and lower jaw in a closed row. All molars were built similarly. Their chewing surface was characterized by an extraordinarily selenodontic pattern, each with two successive crescent-shaped shear ridges. The size of the teeth increased continuously from front to back. The first premolar was only about 6 to 9 mm long, the last molar was 16 to 21 mm long.
Only parts of the hind legs of the rest of the body skeleton are known. The tibia and fibula were almost completely fused, only at the upper end of the joint were both bones separated at a short distance. In today's snakes, both bones are not fused, only the lower ends are in contact with one another through ligaments . The length of a whole bone was 21.6 cm. At the ankle of the shin there was a very large ankle characteristic of the hyrax . The ankle bone typically had no lateral articular surfaces, which is indicated by the serial or taxeopodal arrangement of the tarsal bones in the snails , unlike, for example, the reciprocal or diplarthral arrangement in the pair and unpaired ungulates . The articular surface for the connection with the navicular bone , the facies articularis navicularis, was striking . This dented clearly in the center, the deep notch was flanked by a slightly convex surface on each side. This is different from other sleepers with a flat or slightly arched joint surface.
Fossil finds
Antilohyrax finds are so far only known from North Africa . The most extensive fossil material was found at L-41 in the Fayyum region in northern Egypt . The site L-41 belongs to the lower section of the Gebel-Qatrani Formation and dates to the Upper Eocene ; the absolute age is around 34 million years. It is the oldest site within the formation. The deposits are embedded in a sequence of banded sands, but they differ strikingly from them. They consist of a fine-grained clay and siltstone of greenish to greenish-gray color, which probably goes back to a former lake. A high proportion of evaporites and a high concentration of sodium chloride are remarkable . As a result, the geological location clearly stands out from the rather coarser fluvial deposits of the Gebel-Qatrani Formation. L-41 was discovered in 1983; a special feature is the high number of skulls, some of which are associated with parts of the body skeleton. There are remains of fish, amphibians, reptiles, birds and mammals. In addition to a high diversity of snakes, the mammals also include primates , rodents and bats . Due to the good preservation of fossils of smaller vertebrates, the site L-41 is of great importance for the Fayyum region. From Antilohyrax been several skull and upper and lower jaw fragments have been recovered from the reference. A nearly complete skull lay together with the associated lower jaw. In addition, there are the rather rare elements of the rear legs. The individual found objects represent individuals of different ages.
Apart from the findings from the Fayyum, an ankle bone with the typical properties of antilohyrax from the Minqar Tibaghbagh site in the southwest of the Qattara Depression is also known in northern Egypt. The find was stored together with the remains of proboscis , manatees as well as various reptiles and fish also in banded sandstones, which represent a temporal equivalent to the Gebel Qatrani formation in the Fayyum. The find layer belongs to the Lower Oligocene.
Paleobiology
The special form of the dentition, especially the low-crowned teeth and the selenodontic chewing surface pattern of the molars with the prominent shear ridges on the cheek-side, but also the low and tapering lower jaw body, find their counterparts in ungulates with a specialization in soft vegetable foods such as leaves . The intense traces of wear on the molars indicate mainly vertical chewing movements when grinding the food, while lateral or forward and backward-looking movements play only a subordinate role. A dominance of the vertical chewing movements can also be assumed due to the enlarged mandibular fossa of the lower jaw, the more structured surface of the lower jaw joint and possibly also the more lateral position of the canine-like upper incisors indicate this. The food intake was probably supported by mobile lips. Signs of this can be found in the numerous bony ribs on the upper jaw and the middle jawbone, which acted as muscle attachment points, as well as in the high number of foramina on the lower jaw. Strong neck muscles were attached to the skull, which ensured a high mobility of the head, especially when moving up and down. This is indicated by the narrow, high occiput with a strong bulge in the neck, the structure of which is somewhat reminiscent of that of pigs . A clearly erect head made it possible for Antilohyrax to open up, for example, higher hanging branches or upper areas of larger bushes for ingestion.
The comb-like inner lower incisors have a special function. Today's hyraxes use their mandibular incisors to brush, but studies of the traces of abrasion in antilohyrax do not give any indications. Their correspondence with the incisors of the giant gliders can possibly assume a comparable function in feeding. In Antilohyrax , the inner lower incisors closed against a thick skin pad, which is indicated by a rough surface on the front edge of the median jawbone. As a result, the anterior chewing apparatus was very similar to that of today's horn-bearers and deer . The comb-like incisors of Antilohyrax could exert pressure on the leaves and possibly separate softer plant material from more fibrous. The second, rather spatula-shaped incisor of the lower jaw, on the other hand, closed with the canine-shaped incisor of the upper jaw and thus formed an effective cutting tool.
It is noteworthy that the crown process is rather short in today's snakes, which is usually associated with a reduction of the temporalis muscle and leads to a reduction in biting force. This adaptation is known in numerous herbivores today. However, the hyrax have an enlarged temporal pit as an attachment point for the muscle. The temporalis muscle, which is still large as a result, plays an important role in the defense behavior of today's sleepers by opening their mouths wide and presenting their canine-like incisors. Since this combination of features also occurs in Antilohyrax , a similar behavior can be assumed here.
The found elements of the hind limbs are in stark contrast to those of today's hyrax. With these, the legs and feet can be moved upwards and rotated and thus enable climbing in trees or on rocks. The fused tibia and fibula of Antilohyrax, on the other hand, restricted extensive rotational movements of the leg. The indented scaphoidal facet of the ankle bone had a similar function, preventing lateral outward movements of the ankle, but allowing wide longitudinal movements. The entire configuration is reminiscent of the hind leg of some highly mobile horn-carriers such as springboks or goats , which are also capable of jumping. Antilohyrax thus seems to have been adapted to rapid locomotion, which obviously also allowed powerful jumps.
Overall, Antilohyrax suggests a representative of the hyrax, which is an ecological equivalent to today's gazelles or goats. The Antilohyrax finds expand the previously known morphological diversity of the paleogenic hyrax. These are composed of pig-like forms such as Bunohyrax or Geniohyus and semi-aquatic animals such as Pachyhyrax . Furthermore, there were also fast-moving representatives such as Saghatherium , which were adapted to a hard plant-based diet , huge herbivores such as Titanohyrax or small members similar to today's species such as Thyrohyrax or even smaller members such as Microhyrax . This diversity was then lost in the course of the Neogene with the creation of the land bridge to Eurasia through the closure of the Tethys and the associated immigration of new groups of land mammals. Today's hyraxes therefore only provide a small glimpse into the once varied order.
Systematics
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Internal classification of the early hyrax according to Pickford 2015
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Antilohyrax is a genus from the extinct family of the Titanohyracidae within the order of the hyrax (Hyracoidea). The hyrax are generally considered to be closely related to the elephants and manatees , all three groups together make up the Paenungulata within the parentage of the Afrotheria . The Titanohyracidae belong to the early forms of hyrax and were first detectable in northern Africa in the Eocene . They emerged together with the Namahyracidae , the Geniohyidae and the Saghatheriidae during the hyrax's first radiation phase . This lasted largely until the Oligocene and took place entirely in Africa. During this time the hyrax represented a very diverse group with numerous representatives who were adapted to different biotopes . The Titanohyracidae include medium-sized to very large hyrax, some forms reached the size of small rhinos and are among the largest known hives. Characteristic features of the Titanohyracidae can be found in the muzzle part of the skull that is shortened compared to other early sleepers, the typical selenodontic chewing surface pattern of the molars and in the highly specialized lower incisors. In the postcranial skeleton, the Titanohyracidae were adapted to rapid locomotion. Sometimes the Titanohyracidae, together with the Geniohyidae and Namahyracidae, are subordinated to the Pseudhippomorpha , which unites the primitive hyrax. It contrasts with the more modern Procaviamorpha with the Saghatheriidae, the Pliohyracidae and the Procaviidae , the latter containing today's hyrax.
The genus Antilohyrax was first scientifically described in 2000 by D. Tab Rasmussen and Elwyn L. Simons , but the name was used four years earlier in a graduate thesis. The two authors had access to several fossil finds from the L-41 site of the Fayyum in northern Egypt. As a holotype , they chose a lower jaw that has the foremost incisor in both the right and left branches and the complete series of teeth from the canine to the third molar (copy number CGM 42205). The name Antilohyrax derives from the generic antelope from which the Blackbuck from the group of horn carriers include and Peter Simon Pallas was introduced in 1766 (from Greek ἀνθάλωψ ( anthalops ) for a deer-like animal with saw-like horns). Hyrax is, in turn, an addition to the name often used in Schliefern and refers to the synonym of the same name for Procavia , the genus of the Klippschliefers . It was established by Johann Hermann in 1783 (from Greek ὕραξ ( hýrax ) for "shrew"). The only known species is Antilohyrax pectidens . The specific epithet is of Latin origin, it is based on the words pecten for "comb" and dens for "tooth". It refers to the inner incisor of the lower jaw with its comb-like shape.
literature
- D. Tab Rasmussen and Mercedes Gutiérrez: Hyracoidea. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London, 2010, pp. 123-145
Individual evidence
- ↑ a b c d e f g h i D. Tab Rasmussen and Elwyn L. Simons: Ecomorphological diversity among Paleogene hyracoids (Mammalia): a new cursorial browser from the Fayum, Egypt. Journal of Vertebrate Paleontology 20 (1), 2000, pp. 167-176 ( [1] )
- ↑ a b c d e f Donald D. de Blieux and Elwyn L. Simons: Cranial and dental anatomy of Antilohyrax pectidens: a Late Eocene hyracoid (Mammalia) from the Fayum, Egypt. Journal of Vertebrate Paleontology 22 (1), 2002, pp. 122-136 ( [2] )
- ^ Elwyn L. Simons: Description of two genera and species of Late Eocene Anthropoidea from Egypt. PNAS 86, 1989, pp. 9956-9960 ( [3] )
- ↑ D. Tab Rasmussen and EL Simons: The oldest hyracoids (Mammalia: Pliohyracidae): new species of Saghatherium and Thyrohyrax from the Fayum. New Yearbook for Geology and Paleontology Abhandlungen 182, 1991, pp. 187-209
- ↑ Hesham M. Sallam, Afifi H. Sileem, Ellen R.Miller and Gregg F. Gunnell: Deciduous dentition and dental eruption sequence of Bothriogenys fraasi (Anthracotheriidae, Artiodactyla) from the Fayum Depression, Egypt. Palaeontologia Electronica 19 (3), 2016, p. 38A ( [4] )
- ↑ a b D. Tab Rasmussen and Mercedes Gutiérrez: Hyracoidea. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London, 2010, pp. 123-145
- ↑ Hendrik Jan Van Vliet, Anne S. Schulp, Gebely AMM Abu El-Kheir, Theo M. Paijmans, Mark Bosselaers and Charles J. Underwood: A new Oligocene site with terrestrial mammals and a selachian fauna from Minqar Tibaghbagh, the Western Desert of Egypt. Acta Palaeontologica Polonica 62 (3), 2017, pp. 509-525 ( [5] )
- ↑ D. Tab Rasmussen: The evolution of the Hyracoidea: A review of the fossil evidence. In: Donald R. Prothero and R. Schoch (Eds.): The evolution of Perissodactyls. New York, Oxford University Press, 1989, pp. 57-78
- ↑ Martin Pickford: New Titanohyracidae (Hyracoidea: Afrotheria) from the Late Eocene of Namibia. Communications of the Geological Survey of Namibia 16, 2015, pp. 200–214
- ^ Martin Pickford, Salvador Moyà Solà and Pierre Mein: A revised phylogeny of the Hyracoidea (Mammalia) based on new specimens of Pliohyracidae from Africa and Europe. New Yearbook for Geology and Paleontology, Treatises 205 (2), 1997, pp. 265–288
- ↑ Martin Pickford: Revision of the Early Miocene Hyracoidea (Mammalia) of East Africa. Comptes Rendus Palevol 3, 2004, pp. 675-690