Akhnatenavus
| Akhnatenavus | ||||||||||||
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Skull of Akhnatenavus , holotype of the species A. nefertiticyon |
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| Temporal occurrence | ||||||||||||
| Upper Eocene ( Priabonian ) to Lower Oligocene ( Rupelian ) | ||||||||||||
| 34 to 30 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Akhnatenavus | ||||||||||||
| Holroyd , 1999 | ||||||||||||
Akhnatenavus is a genus in the order Hyaenodonta , extinct carnivorous mammals that may be close to predators. The genus lived in the transition from the Eocene to the Oligocene about 34 to 30 million years ago in northern Africa . So far it is only known there from the Fayyum fossilsite. The found material consists of several teeth and skull parts. It is a medium-sized representative of the hyaenodonts with relatively delicate dentition, but which shows individual tendencies towards the formation of hypercarnivorous teeth. The genus received its first scientific description in 1999. The first known find material was recovered more than 90 years earlier.
description
Akhnatenavus was a medium-sized representative of the Hyaenodonta. For smaller shapes, an average body weight of 19.2 kg is determined based on the size of the teeth, which varies on average between 18.9 and 21.2 kg, taking into account the determination method used. Reaching Akhnatenavus about the size of today's lynx or wolverine . The shape has been handed down through some remains of the skull and bits of teeth, remains of the musculoskeletal system are missing so far. A relatively completely preserved skull is severely crushed. The nasal bone was elongated, initially narrowed laterally and then widened behind the infraorbital foramen . This sat above the third premolar . The suture of the nasal bone with the frontal bone was at a 45 ° angle to the suture of the nasal bone with the upper jaw . The orbit was framed below by the zygomatic bone , in front by the lacrimal bone and above by the frontal bone, the anterior border was above the second molar . The tearbone reached from the edge of the orbit far forward into the skull. At the contact of the two parietal bones a crest was formed, which pulled back to the crest of the occiput . The joint surfaces of the occiput for connection with the cervical spine were increased in height. The zygomatic arch part of the temporal bone was robust, but thinned forward. The glenoid pit connecting the mandibular joint was wide and low, the ratio of width to depth was 3: 1.
In the upper dentition, the canine tooth and the molar teeth consisting of the series from the second premolar to the third molar are preserved, the first premolar is indicated by an alveolus . The rear premolar and molar teeth of the lower dentition are present, the front molars up to the canine can only be determined by the tooth sockets, the incisors are unknown. In general, the dentition was less robust than related forms. The upper canine was large, the root exceeded the crown by one and a half times in length. The middle premolars were characterized by a high, pointed cusp (paraconus in the upper and protoconid in the lower jaw), the paraconus was slightly curved back on the teeth of the upper jaw, but not as clearly as in pterodon . The rear pre-molar tooth was more complex and larger, and a sharp shear edge appeared on the rear edge of the respective main tubercle. The premolars were not closed, but were separated from each other by short diastemas . Above all, the tooth gaps in the lower jaw are not documented in numerous other Hyainailourids. The molars had a sectorial structure typical of predators, with prominent pointed cusps (para-, proto- and metaconus or para-, proto- and metaconid). Typical of the Hyainailouridae were the para- and metaconus fused to each other on the two anterior maxillary molars (they together form the so-called amphiconus), the former towering over the latter. In contrast to later forms such as Metapterodon , both humps could be distinguished by a narrow furrow. In addition, the Protoconus was rather simply built. On the lower molars, the lower para and the somewhat higher protoconid framed a deep crevice, the metaconid had largely receded. The talonid, a deeper-lying area of the tooth surface, took up about a quarter of the length of the tooth on the two anterior mandibular molars and thus did not reach the dimensions of Pterodon . In contrast to Pterodon or Kerberos, the rearmost molar in the upper row of teeth was greatly reduced. Again in contrast to some later Hyainailouids, there was still a talonid on the rear lower molar. In the upper jaw, the tooth size increased continuously from the second premolar with 9.4 mm length to the second molar with around 15.2 mm length, the rearmost tooth was only 2.5 mm long. In contrast, the teeth in the lower jaw increased in size from the second premolar with a length of 7.5 mm to the third molar with a length of 15.9 mm.
Fossil finds
Akhnatenavus has only been documented by finds from the Fayyum region in northern Egypt in North Africa . The currently most extensive fossil material comes from the site L-41 . This is located in the lower section of the Gebel-Qatrani Formation , which in turn dates to the Upper Eocene with an absolute age of around 34 million years. L-41 represents the oldest site within the formation. The deposits consist of fine-grained, greenish to greenish-gray colored clay and silt stones . They are embedded in a sequence of banded sands. Most likely the deposits go back to a former lake. A high proportion of evaporites and a high concentration of sodium chloride are noticeable . The structure of the site clearly stands out from the rather coarser fluvial deposits of the Gebel-Qatrani Formation. Another peculiarity is the high number of skulls with partly associated parts of the body skeleton. So far remains of fish, amphibians, reptiles, birds and mammals have been detected. The great variety of snakes , primates , rodents and bats should be emphasized . But also the Hyaenodonta occur in quite extensive numbers. Besides Akhnatenavus , Brychotherium and Masrasector were also documented here. Due to the good preservation of fossils of smaller vertebrates, the site L-41 is of great importance for the Fayyum region. It was discovered in 1983 by a research team led by Elwyn L. Simons and subsequently presented in more detail by D. Tab Rasmussen, among others . From Akhnatenavus an almost complete skull, an upper jaw remnant and a lower jaw fragment have so far been discovered. The first cervical vertebra and a fragment of the rib were still attached to the entire skull . The skull is the oldest of a Hyainai tourid from the Afro-Arab region.
Another lower jaw was discovered at site A , which is stratigraphically 12 m above L-41 and is therefore somewhat younger, but still belongs to the lower Gebel-Qatrani formation. Site A can be viewed as one of the classic outcrops of the Fayyum region. It has been known since the beginning of the 20th century and was first opened by Hugh John Llewellyn Beadnell between 1898 and 1904. Extensive research took place here during the important American Museum of Natural History expedition in 1907. The deposits consist of a coarser layer of sand and gravel than the remains of a river. For this reason, the finds here are mostly made up of larger bone parts from skulls, pelvis or long bones, which give a more compact impression. Henry Fairfield Osborn published the discovery of the lower jaw two years after the expedition. In addition, other hyaenodonts are documented from site A , such as pterodons .
Paleobiology
The Akhnatenavus dentition has a generally graceful character, but it has individual hypercarnivore properties. The general characteristic of hypercarnivorous dentition is a decrease in complexity based on the original morphology of the posterior molars. This goes hand in hand with the loss of the perforating or breaking function, which leads to the predominance of the cutting properties. In Akhnatenavus this can be seen in the molar teeth of the lower jaw, for example in the reduction of the metaconid (perforating in connection with the parastyle of the maxillary molars) or the talonid (breaking in connection with the protoconus of the maxillary molars). In the upper jaw, this affects, among other things, the merging of the meta- and paraconus to form the amphiconus, which in turn is parallel to the loss of some small cusps in the lower jaw. In recent predators and predatory poults , hypercarnivore teeth correlate with a mainly carnal diet. Today's hypercarnivorous predators get more than 70% of their food from other vertebrates (excluding specialized fish-eaters).
Systematics
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Internal systematics of the Hyainailouridae according to Borths and Stevens 2019
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Akhnatenavus is a genus from the extinct family of the Hyainailouridae , which in turn forms part of the also extinct order of the Hyaenodonta . The Hyaenodonta originally belonged to the Creodonta group , sometimes somewhat misleadingly also referred to as "primal carnivores ", which were regarded as the sister group of today's carnivores within the superordinate group of the Ferae . However, the Creodonta turned out to be a non-self-contained group and were therefore split into the Hyaenodonta and the Oxyaenodonta . Both groups have in common the opposite predators further rearward shifted in the dentition refractive scissors , on the second Hyaenodonten maxillary and mandibular third are usually involved. The hyaenodonts existed for a long period from the Middle Paleocene around 60 million years ago to the Middle Miocene around 9 to 10 million years ago. A typical feature of the Hyainailouridae is the Para- and Metaconus united to the Amphiconus, whereby the former towers over the latter (vice versa with the Hyaenodontidae). Within the Hyainailouridae, Akhnatenavus belongs to the subfamily of the Hyainailourinae . In these, the degree of fusion of the para and metaconus is very advanced, but since both humps are still separated by a slight furrow, Akhnatenavus can be counted to a rather early form.
So far, two species of the genus have been described:
A. nefertiticyon is the older and smaller representative of both species . It also differs from A. leptognathus in the shorter rostrum, the shorter diastemata between the premolars and in individual tooth features. His finds all come from site L-41 . The younger A. leptognathus , however, is only from the reference A busy. The only known lower jaw was recovered from the American Museum of Natural History's Fayyum Expedition in 1907 and described as Pterodon leptognathus by Henry Fairfield Osborn in 1909 .
The first scientific description of the genus Akhnatenavus comes from Patricia A. Holroyd in 1999. She used the lower jaw presented by Osborn in 1909 for this. This is a right branch with the preserved teeth from the third premolar to the third molar as well as the alveoli of the canine and the two anterior premolars. The piece serves as a holotype (copy number AMNH 13263). The name Akhnatenavus refers to the ancient Egyptian king Akhnaten , pharaoh of the 18th dynasty. The species name leptognathus is made up of the Greek words λεπτός ( leptos ) for "small" or "tender" and γνάθος ( gnathos ) for "jaw", thus referring to the delicate and rather elongated structure of the lower jaw. In contrast, nefertiticyon is a reference to Nefertiti , Akhenaten's wife, while cyon in turn means "dog" (from Greek κύων ), freely translated the name is "Nefertiti dog". In their first description, Holroyd classified the genus in the Pterodntinae, according to the opinion of the time, a group of hyaenodonts with developed teeth. Most modern phylogenetic studies see Akhnatenavus today within the Hyainailourinae, under certain circumstances a classification into the tribe of the Hyainailourini takes place.
literature
- Matthew R. Borths, Patricia A. Holroyd and Erik R. Seiffert: Hyainailourine and teratodontine cranial material from the late Eocene of Egypt and the application of parsimony and Bayesian methods to the phylogeny and biogeography of Hyaenodonta (Placentalia, Mammalia). PeerJ 4, 2016, p. E2639, doi: 10.7717 / peerj.2639
- Patricia A. Holroyd: New Pterodontinae (Creodonta: Hyaenodontidae) from the late Eocene-early Oligocene Jebel Qatrani Formation, Fayum Province, Egypt. PaleoBios 19 (2), 1999, pp. 1-18
Individual evidence
- ↑ a b c d e f g h Matthew R. Borths, Patricia A. Holroyd and Erik R. Seiffert: Hyainailourine and teratodontine cranial material from the late Eocene of Egypt and the application of parsimony and Bayesian methods to the phylogeny and biogeography of Hyaenodonta (Placentalia, Mammalia). PeerJ 4, 2016, p. E2639, doi: 10.7717 / peerj.2639
- ↑ a b c d e Patricia A. Holroyd: New Pterodontinae (Creodonta: Hyaenodontidae) from the late Eocene-early Oligocene Jebel Qatrani Formation, Fayum Province, Egypt. PaleoBios 19 (2), 1999, pp. 1-18
- ^ A b Elwyn L. Simons: Description of two genera and species of Late Eocene Anthropoidea from Egypt. PNAS 86, 1989, pp. 9956-9960
- ^ A b D. Tab Rasmussen and Elwyn L. 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 ( [1] )
- ^ A b c Henry Fairfield Osborn: New carnivorous mammals from the Fayum Oligocene, Egypt. Bulletin of the American Museum of Natural History 26, 1909, pp. 415-424.
- ↑ Floréal Solé and Sandrine Ladevèze: Evolution of the hypercarnivorous dentition in mammals (Metatheria, Eutheria) and its bearing on the development of tribosphenic molars. Evolution & Development 19 (2), 2017, pp. 56-68
- ↑ Matthew R. Borths and Nancy J. Stevens . Simbakubwa kutokaafrika, gen et sp. nov. (Hyainailourinae, Hyaenodonta, 'Creodonta,' Mammalia), a gigantic carnivore from the earliest Miocene of Kenya. Journal of Vertebrate Paleontology, 2019, p. E1570222, doi: 10.1080 / 02724634.2019.1570222
- ↑ Kenneth D. Rose: The beginning of the age of mammals. Johns Hopkins University Press, Baltimore, 2006, pp. 1–431 (pp. 122–126)
- ↑ Michael Morlo, Gregg Gunnell, and P. David Polly: What, if not nothing, is a creodont? Phylogeny and classification of Hyaenodontida and other former creodonts. Journal of Vertebrate Paleontology 29 (3 suppl), 2009, p. 152A
- ↑ Floréal Solé: New proviverrine genus from the Early Eocene of Europe and the first phylogeny of Late Paleocene-Middle Eocene hyaenodontidans (Mammalia). Journal of Systematic Paleontology 11, 2013, pp. 375-398
- ↑ a b Floréal Solé, Eli Amson, Matthew Borths, Dominique Vidalenc, Michael Morlo and Katharina Bastl: A New Large Hyainailourine from the Bartonian of Europe and Its Bearings on the Evolution and Ecology of Massive Hyaenodonts (Mammalia). PLoS ONE 10 (9), 2015, p. E0135698, doi: 10.1371 / journal.pone.0135698
- ^ Margaret E. Lewis and Michael Morlo: Creodonta. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London, 2010, pp. 543-560
- ↑ Floréal Solé, Julie Lhuillier, Mohammed Adaci, Mustapha Bensalah, Mohammed Mahboubi and Rodolphe Tabuce: The hyaenodontidans from the Gour Lazib area (? Early Eocene, Algeria): implications concerning the systematics and the origin of the Hyainailourinae and Teratodontinae. Journal of Vertebrate Paleontology 12 (3), 2014, pp. 303-322
