Brychotherium
| Brychotherium | ||||||||||||
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Lower jaw of Brychotherium , holotype |
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| Temporal occurrence | ||||||||||||
| Upper Eocene ( Priabonium ) | ||||||||||||
| 34 million years | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Brychotherium | ||||||||||||
| Borths , Holroyd & Seiffert , 2016 | ||||||||||||
Brychotherium is a genus in the order Hyaenodonta , extinct carnivorous mammals that may be close to predators. The only remains of the genus found so far come from the Fayyum fossil deposit in northern Egypt and date to the Upper Eocene around 34 million years ago. There are several mandibular and skull fragments. They represent relatively small animals with more generalized teeth. The genus was scientifically introduced in 2016. The name Brychotherium was used in some cases before that.
description
Brychotherium was a rather small representative of the Hyaenodonta with an assumed body weight of 5.2 to 6.2 kg. The size is comparable to a red fox or silver badger . The genus is based on several lower jaw finds plus two fragmented skulls. Only the front part of the latter has survived. The middle jaw bone rose steeply backwards, the joint bone seam with the upper jaw ended approximately at the level of the canine . Due to the alignment of the middle jaw bone, the interior of the nose was probably set back, but the nasal bones are only incompletely preserved. However, the rear section widened significantly. The facial area of the upper jaw was wide, and the infraorbital foramen opened above the second premolar . The upper jaw had no part of the anterior margin of the orbit . Instead, this was done by a broad process of the tear bone . The lower edge of the eye window was formed by the zygomatic bone . This also showed a wide contact with the lacrimal bone, so both bones excluded the upper jaw from the orbit. The frontal bone formed the upper edge of the orbit . Overall, the front edge of the eye window was above the first molar . At the back of the frontal bone, the crown of the head started . The palatine bone was narrow in front and widened backwards. The choans started behind the third molar. The symphysis of the lower jaw reached up to the third premolar; in no previously known find was it fused. The lower edge of the lower jaw arched slightly convex, about in the middle below the crown process it broke over a slight kink and then ran out to the angled process. The front edge of the crown process was at an angle of around 125 ° to the alveolar surface . A very large mental foramen lay below between the third and fourth premolars; in front of it there were two other smaller ones below the second and first premolar teeth.
Only the canines , a large part of the premolars and molars have survived from the dentition , the position of the incisors can only be determined for the upper half of the dentition using the alveoli. Here at least the second and third incisors were formed, which increased in size from the inside out. The canine was large and twice the width of the last incisor. It had a pressed conical shape. The root of the upper canine reached far back into the bone, where it lay over the first and second premolars. As a rule, there were no diastemas between the individual molars, only in two lower jaws the second and third premolars were not closed. In the upper jaw only the crown of the last premolar is preserved. The mandibular premolars were characterized by a high, pointed cusp (protoconid) and thus appeared to be highly triangular. The two central premolar teeth were roughly asymmetrical. The last lower premolar had sharp shear edges on the long sides. The molars, which had a typical sectorial structure, had three high, pointed cusps on the chewing surface, which were formed in the upper jaw by the para-, meta- and protoconus, in the lower jaw by the para-, meta- and protoconid. As with all representatives of the Teratodontinae , the para- and metaconus of the first two molars in the upper jaw were fused together at the base, but in contrast to the Hyainailourinae , the tips were free and clearly separated. Also different from the Hyainailourinae, the Metaconus usually protruded beyond the Paraconus. In Brychotherium , however, the paraconus was not as significantly reduced as in the closely related Dissopsalis and Anasinopa . In this trait, Brychotherium agreed more closely with Glibzegdouia . An exception here is Furodon , which had a higher paraconus. In Brychotherium, both humps had a more elliptical cross-section and thus a more compressed shape than in Anasinopa . The protoconus was broad and significantly lower than the other two cusps. The posterior shear edge of the metaconus (postmetacrista) led via a deep indentation to the shear edge of the metastyle, a smaller hump at the end of the tooth. The last maxillary molar showed noticeable reductions and consisted mainly of the para- and protoconus. The molars of the lower jaw were characterized by a relatively large talonid, a deeper lying area of the chewing surface. It was between 25 and 33% of the length of the entire tooth and therefore did not reach the dimensions of Glibzegdouia . The well-developed metaconid was smaller than the proto- and paraconid, in Glibzegdouia it was significantly higher. The edge between the latter two formed a deep indentation. While the protoconid was even higher than the paraconid on the anterior molar, both humps on the last molar were the same height. Overall, however, they were more massive there than on the two preceding molars. In the upper jaw, the teeth enlarged from the last premolar with a length of 7.1 mm to the second molar with a length of 9.7 mm, the last molar was then only 3.7 mm long. In contrast, the anterior premolar in the lower jaw was 5.3 mm long, the posterior molar 9.6 mm long, and the teeth between them gradually increased in size.
Fossil finds
The previously known finds of Brychotherium have all been found in the Fayyum area in northern Egypt in North Africa . They come from the site L-41 in the lower section of the Gebel Qatrani Formation . According to paleomagnetic investigations, this dates back to the Upper Eocene with absolute ages around 34 million years. It is the oldest site within the formation. The deposits consist of greenish to greenish-gray colored clay and silt stones , which are embedded in a sequence of banded sands. The fine-grained deposits are relics of a former lake. They are characterized by a high proportion of evaporites and a high concentration of sodium chloride . In its entire structure, the site differs so strikingly from the other, more coarse clastic, fluvial deposits of the Gebel-Qatrani Formation. As a further specialty, a high number of skulls with partly associated parts of the body skeleton can be highlighted. The L-41 fossil record includes remains of fish, amphibians, reptiles, birds and mammals. Among other things, the high variety of snakes , primates , rodents and bats is remarkable. Among the Hyaenodonta are far Akhnatenavus , Masrasector and Brychotherium documented. Due to the good preservation of the remains of smaller vertebrates, the site L-41 is of great importance for the Fayyum region. Their discovery goes back to 1983 conducted field investigations by a research team led by Elwyn L. Simons , subsequently it was presented in more detail by D. Tab Rasmussen among others . Brychotherium is so far occupied with several lower jaw parts and two incomplete skulls. One of the skulls lay together with a right branch of the lower jaw, here it is assumed that it is a single individual. The two skulls are among the oldest of a representative of the Teratodontinae in Afro-Arabic countries.
Systematics
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Internal systematics of the Teratodontinae according to Solé & Mennecart 2019
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Brychotherium is a genus from the extinct subfamily of the Teratodontinae , which in turn forms part of the also extinct order of the Hyaenodonta . The Hyaenodonta originally formed part of the Creodonta , some of which are sometimes misleadingly referred to as "primitive carnivores". It was assumed that the Creodonta formed the sister group of today's carnivores (Carnivora) within the parent group of the Ferae . However, the Creodonta turned out to be a non-self-contained group, they 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 first appeared in the Middle Paleocene around 60 million years ago and died out in the Middle Miocene around 9 to 10 million years ago. Within the Hyaenodonta, the Teratodontinae represent the sister group of the Hyainailouridae family, both are placed together in the parent group of the Hyainailouroidea . In the Teratodontinae, the para- and metaconus of the maxillary molars are characteristically fused only at the base, with the latter protruding above the former. This distinguishes them, among other things, from the Hyainailouridae with their para- and metaconus fused to the amphiconus, in which the paraconus is also higher. In terms of the height of the two cusps, the Teratodontinae are similar to the Hyaenodontidae , but these also have fused cusps. Brychotherium is the sister group of a clade from phylogenetically younger representatives of the Teratodontinae such as Dissopsalis , Teratodon and Anasinopa . Masrasector , a very small member of the Teratodontinae, who was also found in the Fayyum , also belongs to this close relationship .
The generic name Brychotherium was coined by Patricia A. Holroyd in 1994 in her doctoral thesis. In the period that followed, some scientists used it for informational purposes on several occasions; in some cases , the shape was rated as an African representative of a Sinopa group. The fossil material known at the time was limited to individual lower jaws. Only additional material prompted Matthew R. Borths to carry out the first scientific description together with Holroyd and Erik R. Seiffert in 2016 , which gave the genus its official recognition. The holotype (copy number CGM 83750) is a right branch of the lower jaw from the Fayyum, which still has the row of teeth from the canine to the last molar. The name Brychotherium is composed of the Greek words bρύχω ( brycho for " grinding teeth") and θηρίον ( thēríon for "animal"). Together with the genus, a species was introduced and named Brychotherium ephalmos . The epithet also comes from the Greek ( έφαλμος ephalmos ) and means "marinated". It refers to the high salty properties of the reference L-41 .
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
Individual evidence
- ↑ a b c d e 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
- ^ Elwyn L. Simons: Description of two genera and species of Late Eocene Anthropoidea from Egypt. PNAS 86, 1989, pp. 9956-9960
- ↑ 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] )
- ↑ Floréal Solé and Bastien Mennecart: A large hyaenodont from the Lutetian of Switzerland expands the body mass range of the European mammalian predators during the Eocene. Acta Palaeontologica Polonica 64, 2019, doi: 10.4202 / app.00581.2018
- ↑ 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
- ↑ 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
- ↑ Matthew R. Borths and Nancy J. Stevens: The first hyaenodont from the late Oligocene Nsungwe Formation of Tanzania: Paleoecological insights into the Paleogene-Neogene carnivore transition. PLoS ONE 12 (10), 2017, p. E0185301, doi: 10.1371 / journal.pone.0185301
- ↑ 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
- ↑ Naoko Egi, Patricia A. Holroyd, Takehisa Tsubamoto, Aung Naing Soe, Masanaru Takai and Russell L. Ciochon: Proviverrine hyaenodontids (Creodonta: Mammalia) from the Eocene of Myanmar and a phylogenetic analysis of the proviverrines from the para-Tethys area. Journal of Systematic Palaeontology 3 (4), 2005, pp. 337-358
- ↑ Rajendra S. Rana, Kishor Kumar, Shawn P. Zack, Floreal Solé, Kenneth D. Rose, Pieter Missiaen, Lachham Singh, Ashok Sahni and Thierry Smith: Craniodental and Postcranial Morphology of Indohyaenodon raoi from the Early Eocene of India, and Its Implications for Ecology, Phylogeny, and Biogeography of Hyaenodontid Mammals. Journal of Vertebrate Paleontology 35 (5), 2015, p. E965308, doi: 10.1080 / 02724634.2015.965308
