Mubhammys
| Mubhammys | ||||||||||||
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The upper jaw and upper dentition of Mubhammys , A and B depict the holotype |
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| Temporal occurrence | ||||||||||||
| Upper Eocene to Lower Oligocene | ||||||||||||
| 34 to 28 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Mubhammys | ||||||||||||
| Sallam & Seiffert , 2016 | ||||||||||||
Mubhammys is an extinct genus from the group of porcupine relatives . Within this it forms a very original form of the Phiomorpha , which means that there is a closer relationship to today's cane rats and rock rats . Remnants of Mubhammys were found at the important fossil deposit of the Fayyum area in northern Egypt , and also in Western Sahara . The finds are generally very fragmented and consist of skull and dentition remains. They refer to comparatively large animals, which are characterized by a generally porcupine-like structure of the skull and the lower jaw. A large opening on the palate is also noticeable. Correspondingly, with some of today's Phiomorpha, Mubhammys did not switch between the deciduous and the permanent premolar teeth. The genus was introduced in 2016.
features
Mubhammys is a relatively large representative of the early Phiomorpha. So far, however, the material available only comprises highly fragmented remains of the skull and lower jaw as well as isolated teeth. This means that only a few characteristic features can be determined on the skull. The most striking feature was the large opening on the palate , which developed from the foramen incisivum and is sometimes referred to as the "anterior palatal window". It reached back to the last premolar . The zygomatic arch started in front of the third premolar. The lower jaw was slender and had a typical hystricognathic structure due to the laterally protruding angular process. On the lip side, the masseteric fossa extended to the first molar . At the top and bottom it was framed by two prominent bone ridges as the attachment point for the masseter muscle . The lower edge of the horizontal bone body was conspicuously curved downwards, its course was determined by the curvature of the alveolus of the incisor . The mental foramen was oval in shape. It was small and positioned in front of the anterior premolar and the beginning of the masseteric fossa.
The upper row of teeth consisted of the incisor, the last two premolars and the three molars, the lower one lacked the front premolar, otherwise it corresponded to the upper one. The upper incisor was short but extremely strong. In contrast, the lower one was long in shape. Both had an oval cross-section, the cutting surface was more extensive in the upper than in the lower. The enamel only covered the front of the tooth and pulled a little on the side surfaces. In principle, the incisors corresponded to the incisor teeth . The posterior dentition separated an extensive diastema from the anterior. However, it can only be fully grasped in the lower row of teeth, where it reached the length of the first two rear teeth together and had a slightly dented shape. The premolars consisted only of the milk teeth, permanent premolars were not formed in Mubhammys , which was confirmed by computer tomographic examinations. In this characteristic Mubhammys agrees with some modern Phiomorpha, but differs from ancestral original representatives like Turkanmys and Acritophiomys . The anterior upper premolar (dp3) was small and nail-like, the posterior (dp4) trapezoidal and four-humped. In the lower jaw, the premolar was oval in shape with five cusps. For the molars of rodents, a complex structure consisting of several cusps is typical, which are connected by transverse ridges or yokes ( called Lophen ), the individual shapes can be distinguished by the respective number of cusps and ridges. In general, the rear molars in Mubhammys were rectangular to trapezoidal. There were four cusps on the upper molars (para-, meta-, proto-, and hypoconus), all of which were roughly the same size. They stood together in pairs, with the individual pairs of cusps being connected by strips running at right angles to the longitudinal axis of the teeth. The Protoloph ran between the Para- and Protoconus, the Metaloph between the Meta- and Hypoconus. Two other bars sat in front of or behind these two, namely the anteroloph in front of the protoloph and the posteroloph behind the metaloph. This gave the molars a tetralophodontic structure (consisting of four ridges). The lower molars each had five cusps, of which two each formed a pair (meta- and protoconid or ento- and hypoconid), the fifth cusp (hypoconulid) sat on the rear edge of the tooth. The front pair of cusps (meta- and protoconid) were connected by the metalophulid, the rear pair (ento- and hypoconid) by the hypolophid. A third bar, the posterolophid, included the hypoconulid. The metalophulid was less developed in Mubhammys than in the related Birkamys . An additional second metalophulid between the first and the hypolophid as in Birkamys or Acritophiomys did not occur, and the mesolophid, which occurred on the first molar in Acritophiomys , was missing . The second molar formed the largest tooth in both the upper and lower teeth. It had a length of 1.95 mm and a width of 2.1 mm at the top, the lower one was about the same length, but only 1.8 mm wide. The rearmost molars were each only small in size.
Fossil finds
The most extensive finds of Mubhammys come from the Fayyum area in northern Egypt in North Africa . There they were found at the site L-41 , which is about 46 m above the base in the lower section of the Gebel Qatrani Formation . According to paleomagnetic studies, L-41 is dated to the Upper Eocene and has an absolute age of around 34 million years. This makes it the oldest site in the formation. It was discovered in 1983 during field investigations by a team of researchers led by Elwyn L. Simons , and D. Tab Rasmussen , among others, provided a more detailed idea . The deposits consist of greenish to greenish-gray colored clay and silt stones , which in turn are embedded in a sequence of banded sands. The fine-grained deposits go back to a former lake; a high proportion of evaporites and a high concentration of sodium chloride are remarkable . In the entire structure, L-41 differs noticeably from the other, more coarsely 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. So far, fossil remains of fish, amphibians, reptiles, birds and mammals have been found in L-41 . The great variety of snails , primates , rodents and bats can be emphasized . Above all, the good preservation of the remains of smaller vertebrates gives L-41 great importance for the Fayyum region. The rodents can show hundreds of skeletal elements, including remains of Mubhammys as well as those of Acritophiomys , Birkamys and Gaudeamus . So far, all proven forms belong to the hystricognathi without exception. Remnants of thorntail squirrels have only been documented from the older Qasr-el-Sagha formation in Fayyum , but there is no evidence from Phiomorpha representatives. To Mubhammys majority remains include the skull, lower jaw and teeth.
In addition, a fragment of the upper jaw and several isolated teeth from the Samlat formation in the far west of the Sahara on the mainland opposite the headland of Ad-Dakhla in Western Sahara were brought to light . The fossils were embedded in sandy deposits that were created by the action of an estuary . The age of the finds is about 33 million years, which falls in the immediate beginning of the Lower Oligocene .
Systematics
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Internal systematics of the hystricognathi according to Sallam and Seiffert 2016
To clarify the phylogenetic position, the Caviomorpha and Hystricidae according to Sallam et al. 2011 added |
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Internal systematics of the hystricognathi according to Marivaux and Boivin 2019
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Mubhammys is an extinct genus from the group of Hystricognathi within the suborder of the porcupine relatives (Hystricomorpha). As a very diverse group, the Hystricognathi include Eurasian , African, and American representatives of rodents (Rodentia). They include the porcupines (Hystricidae), as well as the guinea pig relatives (Caviomorpha) and the Phiomorpha . The structure of the skull and the lower jaw can be highlighted as a characteristic feature, the latter indicating, for example, a prominent position of the angular process. The origin of the entire group is most likely to be found in Asia , the oldest evidence going back here to the Middle Eocene almost 50 million years ago. The current African and American distribution areas were reached at the transition to the Upper Eocene around 40 million years ago.
The design of the molars with three or four ridges refers Mubhammys to the developed representatives of the hystricognathi, original shapes had more ridges. In the Phiomorpha, for example, the middle bar, the mesoloph or the mesolophid, was reduced. Another common feature of Mubhammys with some recent Phiomorpha is the permanently pronounced milk premolars. Possibly there is a closer relationship to today's cane rats (Thryonomyidae), rock rats (Petromuridae) or the sand graves (Bathyergidae). The view does not contradict the molecular genetic analyzes, since the Phiomorpha separated from the Caviomorpha in the Upper Eocene around 36 million years ago, the Hystricidae had split off a few million years earlier. According to phylogenetic studies, Mubhammys can be regarded as the closest relative of Birkamys , which is also found in the Fayyum area . An exact assignment to a specific family within the Phiomorpha has not yet been made. Both genera are sister groups to the later Phiomorpha including the recent forms.
In this view, is Mubhammys next Acritophiomys and Birkamys one of the oldest known representatives of Phiomorpha. The discovery of Mubhammys and Birkamys points out that the whereabouts of the Milchprämolaren in the dentition of Phiomorpha began phylogenetically early and as a feature already in the turn of Eocene to Oligocene was pronounced. In addition, the large palatal window can be understood as an inclusive characteristic of various early pliomorpha, since it can also be detected very early in the development of the hystricognathi. Within the group, there were significant changes in size in the course of the Paleogene , which, in addition to large forms such as Mubhammys, also produced dwarfed representatives such as Birkamys . A phylogenetic study from 2019, however , sees Mubhammys as the basal form of the hystricognathi and, together with Birkamys , assigns the form to the family circle of Phiocricetomys , which they identify as "phiocricetomyins". These rodents, originally counted among the Myophiomyidae, are characterized by extremely low-crowned molars with low transverse ridges. The examination positions the group outside the phiomorpha and gives it a more basal position within the hystricognathi, which means that the suppression of the permanent premolars would have arisen several times within the porcupine relatives.
Two types of mubhammys are currently recognized:
- M. atlanticus Marivaux , Adnet , Benammi , Yans & Benammi , 2017
- M. vadumensis Sallam & Seiffert , 2016
M. vadumensis from the Fayyum was established as the type form , whereas M. atlanticus is documented from Western Sahara. Both types differ in the tooth features, the shape from the western Sahara has, among other things, an additional short ridge between the proto- and metalophul, the mesolophul, on the upper jaw molars.
The first scientific description of Mubhammys was carried out by Hesham M. Sallam and Erik R. Seiffert in 2016. The material from the Fayyum in Egypt served as the basis. The holotype (copy number CGM 66001) is represented by a left upper jaw fragment with the row of teeth from the third premolar to the third molar. The name Mubhammys is made up of the Arabic word mubham for "mysterious" or "enigmatic" and the Greek word μῦς ( mŷs ) for "mouse". The authors identified M. vadumensis as the species . The word vadum is of Latin origin and means something like "flat". It refers to the deposition conditions at that time in a shallow lake during the formation period of the site L-41 . The second species was introduced the following year. Their name, M. atlanticus , refers to their occurrence in the westernmost area of North Africa on the Atlantic Ocean .
literature
- Hesham M. Sallam and Erik R. Seiffert: New phiomorph rodents from the latest Eocene of Egypt, and the impact of Bayesian "clock" -based phylogenetic methods on estimates of basal hystricognath relationships and biochronology. PeerJ 4, 2016, p. E1717 doi: 10.7717 / peerj.1717
Individual evidence
- ^ Albert E. Wood: The African Oligocene Rodentia. In: Elwyn L. Simons and Albert E. Wood (Eds.): Early Cenozoic Mammalian Faunas Fayum Province, Egypt. Bulletin of the Peabody Museum of Natural History 28, 1968, pp. 23-105
- ↑ a b c d e f g h i Hesham M. Sallam and Erik R. Seiffert: New phiomorph rodents from the latest Eocene of Egypt, and the impact of Bayesian "clock" -based phylogenetic methods on estimates of basal hystricognath relationships and biochronology . PeerJ 4, 2016, p. E1717 doi: 10.7717 / peerj.1717
- ^ Albert E. Wood and RW Wilson: A Suggested Nomenclature for the Cusps of the Cheek Teeth of Rodents. Journal of Paleontology 10 (5), 1936, pp. 388-391
- ^ A b Hesham M. Sallam, Erik R. Seiffert and Elwyn L. Simons: A basal phiomorph (Rodentia, Hystricognathi) from the late Eocene of the Fayum Depression, Egypt. Swiss Journal of Palaeontology 131, 2012, pp. 283-301
- ↑ a b Laurent Marivaux, El Mabrouk Essid, Wissem Marzougui, Hayet Khayati Ammar, Sylvain Adnet, Bernard Marandat, Gilles Marzeraud, Rodolphe Tabuce and Monique Vianey Liaud: A new and primitive species of Protophiomys (Rodentia, Hystricognathi) from the late middle Eocene of Djebel el Kébar, Central Tunisia. Palaeovertebrata 38 (1), 2014, p. E2
- ^ 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
- ↑ a b c d Laurent Marivaux, Sylvain Adnet, Mohamed Benammi, Johan Yans and Mouloud Benammi: Earliest Oligocene hystricognathous rodents from the Atlantic margin of Northwestern Saharan Africa (Dakhla, Marocco): systematics, paleobiogeographical, and paleoenvironmental implications. Journal of Vertebrate Paleontology 37 (5), 2017, p. E1357567 doi: 1080 / 02724634.2017
- ↑ a b Hesham M. Sallam, Erik R. Seiffert and Elwyn L. Simons: Craniodental Morphology and Systematics of a New Family of Hystricognathous Rodents (Gaudeamuridae) from the Late Eocene and Early Oligocene of Egypt. PLoS ONE 6 (2), 2011, p. E16525 doi: 10.1371 / journal.pone.0016525
- ^ A b Laurent Marivaux and Myriam Boivini: Emergence of hystricognathous rodents: Palaeogene fossil record, phylogeny, dental evolution and historical biogeography. Zoological Journal of the Linnean Society, 2019, pp. 1-36
- ^ A b Laurent Marivaux, Monique Vianey-Liaud, Jean-Loup Welcomme and Jean-Jacques Jaeger: The role of Asia in the origin and diversification of hystricognathous rodents. Zoologica Scripta 31, 2002, pp. 225-239
- ↑ René Lavocat: Rodentia and Lagomorpha. In: Vincent J. Maglio and HBS Cooke (Eds.): Evolution of African Mammals. Harvard University Press, 1978, pp. 69-89
- Jump up ↑ Pauline Coster, Mouloud Benammi, Vincent Lazzari, Guillaume Billet, Thomas Martin, Mustafa Salem, Awad Abolhassan Bilal, Yaowalak Chaimanee, Mathieu Schuster, Xavier Valentin, Michel Brunet and Jean-Jacques Jaeger: Gaudeamus lavocati sp. nov. (Rodentia, Hystricognathi) from the early Oligocene of Zallah, Libya: first African caviomorph? Natural Sciences 97 (8), 2010, pp. 697–706
- ^ A b Hesham M. Sallam, Erik R. Seiffert, Michael E. Steiper, and Elwyn L. Simons: Fossil and molecular evidence constrain scenarios for the early evolutionary and biogeographic history of hystricognathous rodents. PNAS 106 (39), 2009, pp. 16722-16727 doi: 10.1073 / pnas.0908702106
