Gaudeamus
| Gaudeamus | ||||||||||||
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Skull of Gaudeamus , holotype of the species Gaudeamus aslius |
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| Temporal occurrence | ||||||||||||
| Upper Eocene to Lower Oligocene | ||||||||||||
| 34 to 28 million years | ||||||||||||
| Locations | ||||||||||||
| Systematics | ||||||||||||
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| Scientific name of the family | ||||||||||||
| Gaudeamuridae | ||||||||||||
| Sallam , Seiffert & Simons , 2011 | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Gaudeamus | ||||||||||||
| Wood , 1968 | ||||||||||||
Gaudeamus is an extinct genus from the group of porcupine relatives . Within this it belongs to the Hystricognathi and to the family of Gaudeamuridae , whose exact relationships are still unclear. The representatives of the genusoccurredin the period from the Upper Eocene to the Lower Oligocene 34 to 28 million years ago in what is now North Africa . Fossil finds were discovered in the Fayyum in Egypt and occasionally at other sites in the region. They largely comprise skull and dentition material that can be assigned to several types. The animals from the further relatives of the porcupines were relatively large. In addition to the cranial and lower jaw structure, which is generally reminiscent of the porcupine, special features are found in the design of the teeth with transverse ridges, as well as in the change of the premolars from the deciduous to the permanent dentition and in a large opening on the palate . The genus was introduced in 1968. It received its own family status in 2011, which is explained by the characteristic morphology of the animals.
features
Gaudeamus was a relatively large representative of the hystricognathi. The skulls that have been handed down are largely complete, but flattened and partially broken by the pressure of positioning. The rostrum was moderately long. The median jaw bone contained the two incisors , the alveoli of which filled most of the roof. The lateral processes of the middle jawbone connected with the nasal bone and the upper jaw. The nasal bone reached back to the last premolar or first molar . The upper jaw was high and contained a typically hystricognathic, large infraorbital foramen , to which the masseter muscle was attached at the same time . It opened in front of the row of teeth and was at the same time limited by the front attachment of the zygomatic arch . Possibly it was originally oriented vertically on the skull, which is equivalent to today's cane rats , but differs from the guinea pigs and the tassel spines. The frontal bone took up the middle third of the skull. Here the postorbital process led away laterally. It was triangular in shape and larger than most hystricognathi today. Two temporal lines ran on the frontal bone. They united about the middle of the parietal bone to form a weak crest . The crest of the crown increased in strength towards the rear, comparable to the tassel spikes. The parietal bone itself formed the back third of the skull. The occiput has so far only been passed down severely damaged, but it had large joint surfaces stretched backwards for the connection with the cervical spine. The temporal bone formed the posterior border of the orbit . A large tympanic bubble was formed at the base of the skull , which took up about a quarter of the length of the skull and consisted entirely of the temporal bone. The palate was characterized by a large opening that reached to the first molar and is known as the “large palatal window”.
The lower jaw was robust and formed by the hystricognathic angular process that protruded to the side compared to the row of teeth. This resulted in a clear indentation between the angular process and the horizontal bone body in the side view. The masseter muscle was anchored to this indentation. In contrast, the horizontal bony body swung out clearly downwards; its shape was dictated by the alveoli of the incisors. The symphysis ended on the fourth premolar. The mental foramen was below the last premolar or just before it at the end of the diastema . The anterior edge of the ascending branch rose laterally behind the last molar and was directed obliquely backwards with a curved course. There was a noticeable indentation between the last molar and the branch attachment, as also occurs in the tassel spines. The crown process exceeded the articular process, the latter in turn was far above the occlusal plane. The articular surface was oval in shape with the greater length in the longitudinal direction of the lower jaw. The masseteric fossa was visible on the side of the ascending branch ; it was broad at the back and narrowed towards the front, where it ended roughly at the transition from the last premolar to the first molar. Above and below it was flanked by a strong bone bulge. The angular process ended sharply.
The dentition consisted of an incisor, a premolar (the last) and three molars, both above and below. The incisors represented incisors . They were strongly curved and oval in cross-section with the long axis perpendicular to the skull. The upper one measured 3.57 mm in width and 1.82 mm in length. Tooth enamel only appeared on the respective front side, it also covered half of the side surfaces. The cutting surface was triangular in shape. The posterior teeth separated a long, indented diastema. It reached half the length of the row of teeth in the lower jaw, but was shorter than in the upper dentition. Here, two thirds of it was formed by the middle jaw bone. The molars were largely rectangular in shape, with the exception of the triangular last molar. In general, the rear teeth were designed with a high crown ( hypsodontal ). The chewing surface of the molars of Gaudeamus had the characteristic structure that is known from rodents, with several cusps and ridges or yokes (known as Lophen ) in between. The respective number of humps and ridges has taxonomic value. In the upper dentition, the molars each had four cusps on the chewing surface (para-, meta-, proto- and hypoconus). These stood together in pairs and were each connected by melting strips. In contrast to many other relatives of the porcupines, these bars did not run at right angles to the tooth axis, but were oriented diagonally, so that the teeth were basically similar to those of the cane rats. The paraconus on the lip side was not connected to the protoconus on the tongue side via the protoloph. Rather, it hit a branch of the neighboring hypoconus. On the front of the tooth the anteroloph ran directly to the protoconus, on the back of the tooth the posteroloph sat between the metaconus and the hypoconus. For other hystricognathi this was usually done by the metaloph, which was extremely short for Gaudeamus . For most species of Gaudeamus there was an additional mesoloph that ran to the side of the metaloph. Overall, the upper molars appeared tetralophodontic (with four ridges). Something similar can be said about the mandibular molars. These also had four main cusps (meta-, ento-, proto- and hypoconid), a fifth cusp, the hypoconulid at the end of the tooth, which is often formed in the hystricognathi, was missing here. The hypolophid was oriented from the tongue-side entoconid diagonally in the direction of the lip-side protoconid, which it met via an extension. The actual connection to the hypoconid did not exist. The metalophulid ran along the front edge of the tooth, the posterolophid on the back, which extended from the hypoconid to the entoconid. These three ridges gave Gaudeamus' lower molars their distinctive appearance. They also divided the chewing surface into two almost equally large depressions. In some individuals, the anterior pelvis was halved again by an additional metalophulid. In contrast to the cane rats with their similar tooth design, Gaudeamus exchanged the premolars from the deciduous to the permanent dentition. So far, only the lower milk premolars have survived. Typically for rodents and due to their grinding function in the first set of teeth, these had a higher number of ridges than the permanent premolars, with Gaudeamus there were up to five. The second molar formed the largest tooth in both the upper and lower teeth. The size varied from 1.88 to 2.38 mm in length and from 2.00 to 2.88 mm in width.
Fossil finds
Finds by Gaudeamus have so far only come from North Africa . The most important find here is the Fayyum region in northern Egypt . The genus could be observed at several sites within the Gebel Qatrani Formation , which are distributed over different stratigraphic sections. The oldest and most extensive material to date came to light in L-41 . The site, which was discovered in 1983 by a team of researchers led by Elwyn L. Simons and later presented in more detail by D. Tab Rasmussen and others , is located about 46 m above the base, in the lower section of the rock unit. According to paleomagnetic studies, it belongs to the Upper Eocene with an absolute age of around 34 million years. Due to the rather fine-grained deposits, which can probably be traced back to a former lake, and the high proportion of smaller vertebrates , L-41 differs significantly from the other sites of the Gebel Qatrani Formation. The rodents alone include hundreds of fossil finds, including Gaudeamus , Birkamys , Mubhammys and Acritophiomys . In Gaudeamus several crushed skull plus skull parts, further jaw in addition to fragments and isolated teeth omitted. Additional fossil remains were discovered at sites A and B , which stratigraphically lie around 12 m above L-41 and consist of rather coarser sediments collected by rivers . They date to the Lower Oligocene . The finds made here by Gaudeamus , several lower jaws, were already recovered in the 1960s, they formed the basis for the scientific naming of the genus. An inexactly localized lower jaw, which was presented by Max Schlosser in 1911 when processing finds from German expeditions to the Fayyum, is older in terms of research history . Schlosser referred him to Phiomys at the time , his actual nature was only recognized in the 1960s. All the rodents of the Gebel Qatrani Formation found currently represent representatives of the Hystricognathi. Other lines of rodents such as the thorntail squirrels only came to light in the Fayyum at the present time in the older Qasr-el-Sagha formation , but there is no evidence of the Phiomorpha here.
Outside the Fayyum, remains of Gaudeamus have been reported from the Zallah site near the oasis of the same name in the Sirte Basin in central Libya . The site complex represents the relic of a former river delta and dates to the Lower Oligocene around 32 million years ago. Individual teeth were found here. Isolated teeth from the Samlat Formation in Western Sahara on the mainland opposite the Dakhla peninsula may also belong to the genus . The abundant small vertebrate finds were embedded in a sandy matrix, which suggests a former estuary . It existed at the 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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Gaudeamus is an extinct genus from the group of Hystricognathi within the suborder of porcupine relatives (Hystricomorpha). The very diverse group of hystricognathi occurs in Eurasia as well as in Africa and America and forms part of the order of rodents (Rodentia). It includes the porcupines (Hystricidae), the guinea pig relatives (Caviomorpha) and the Phiomorpha . A characteristic feature is the special structure of the skull and the lower jaw; in the latter, the position of the angular process is important. The origin of the group is possibly in Asia , the oldest finds there date to the Middle Eocene almost 50 million years ago. The Hystricognathi reached Africa and America in the transition to the Upper Eocene around 40 million years ago.
Within the Hystricognathi, Gaudeamus is placed in the own family of the Gaudeamuridae and is currently their only member there. The exact relationship is currently unclear, in the past three different options were discussed. Due to the characteristic tooth structure with the sloping ridges, which are reduced in number, Gaudeamus shows clear similarities to the pipe rats (Thryonomyidae), which are assigned to the Phiomorpha. Some researchers therefore saw both as more closely related. However, there are significant differences to the cane rats. The tooth structure at Gaudeamus , for example, is more complex, and the premolars were replaced in the individual development, so that there are two generations with the deciduous and permanent teeth. In principle, the Phiomorpha have a rich fossil record in North Africa that goes back to the Upper Eocene. Other authors again suspected Gaudeamus to have a closer relationship with the guinea pig relatives , since the very early Caviomorpha such as Eoincamys also have a comparable tooth design. The generally younger age data of the Caviomorpha compared to Gaudeamus turn out to be problematic , as well as multiple migration between Africa and South America would be necessary. A third possible family group are the porcupines. Their first fossil record, however, falls in the Upper Miocene around 11 million years ago, which would leave a large temporal gap. It is possible that the matching tooth morphology of both Gaudeamus and Eoincamys, as well as the cane rats, is a convergent formation. Molecular genetic analyzes make a close relationship to the latter rather unlikely. According to these, the Phiomorpha separated from the Caviomorpha in the Upper Eocene around 36 million years ago. A greater diversification of today's Phiomorpha only took place in the period from the Upper Oligocene to the Lower Miocene . Accordingly, the tube rats and the rock rats (Petromuridae) emerged as sister groups around 18 million years ago. The porcupines, on the other hand, broke away from the common line about 39 million years ago. Much better skull remains than are currently available are needed to substantiate or check possible family relationships. Another phylogenetic study from 2019 sees the Gaudeamuridae also in close relationship to the Caviomorpha.
There are four known species from the genus Gaudeamus :
- G. aegyptius Wood , 1968
- G. aslius Sallam , Seiffert & Simons , 2011
- G. hylaeus Sallam , Seiffert & Simons , 2011
- G. lavocati Coster , Benammi , Lazzari , Billet , Martin , Salem , Bilal , Chaimanee , Schuster , Valentin , Brunet & Jaeger , 2010
The four species differ largely in the characteristics of the teeth, so the molars of G. aegyptius are equipped with fewer ridges than those of the other species, in which the mesoloph also occurs. There are hardly any differences in size between the species. G. aegyptius , the nominate form , is documented at sites A and B in the Fayyum and thus appeared in the Lower Oligocene . G. aslius and G. hylaeus are known from the site L-41 in the same room, which dates to the Upper Eocene . Evidence of both representatives may also be available from the somewhat more recent deposits of Dakhla in Western Sahara. Another species was G. lavocati outside the Fayyum at the Lower Oligocene site of Zallah in Libya. Other species are likely to occur, as some Fayyum fossil remains show different characteristics. For the time being, however, these have been assigned to the known species. From the current point of view, Gaudeamus and the Gaudeamuridae had only a short phylogenetic development phase. There are no finds of the genus or family from the site BQ-2 in the Fayyum, which is around 3 million years older than L-41 , and there are no references to sites at the same time such as Dor el-Talha in Libya . On the other hand, no evidence of the Gaudeamuridae is known from more recent sources, although the fossil record from the African Oligocene is rather sparse.
The genus Gaudeamus was first scientifically described in 1968 by Albert E. Wood . Several years of research in the Fayyum under the direction of Elwyn L. Simons preceded the installation . The find material that Wood used for his new species comes from sites A and B of the Gebel Qatrani Formation . It consisted of several lower jaws and isolated teeth. Wood identified a left branch of the lower jaw with the row of teeth from the fourth milk premolar to the second molar plus a not yet erupted last premolar as a holotype (copy number CGM 26920). The local workers who dug during the on-site research had only limited command of the English language . So they called the lower jaw discovered during the excavations (English jaw ) with joy (English for "joy"). As a result, they generally called the rodent mandibles found joy mouse , which translates as “ joy mouse ”. The word connection was later Latinized by Mary R. Dawson with Gaudeamus (the Latin saying gaudeamus (in German "we are happy") is mainly known from a student song ; Dawson reinterpreted the final syllable after Latin mūs for "mouse"). Wood adopted this for his initial description.
In his first description, Wood Gaudeamus assigned to the Phiomyidae family within the Phiomorpha. He defined G. aegyptium as the only species at that time . Later, in 1978, René Lavocat referred the genus to the Thryonomyidae and saw them as a direct relative of the cane rats. The view was later adopted several times. In her dissertation from 1994 Patricia A. Holroyd classified the family status for Gaudeamus as incertae sedis . With reference to new fossil material from the site L-41 in the Fayyum, she created another species with G. hylaeus . Since her work was never published publicly, the species remained unofficial, but some studies have given the name back. It was not until 2011 that Hesham M. Sallam and research colleagues published a valid species description for G. hylaeus . In their analyzes, however, Holroyd's species proved to be highly variable, which is why they outsourced an additional G. aslius . At the same time they created a new family called Gaudeamuridae, derived from Gaudeamus, which they classified outside of the Phiomorpha due to the clearly different characteristics.
literature
- 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
- 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
Individual evidence
- ↑ a b c d e f g h i 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 j k l 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
- ^ 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
- ^ 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 e 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
- ^ Max Schlosser: Contributions to the knowledge of the Oligocene land mammals from the Fayum, Egypt. Contributions to the paleontology and geology of Austria-Hungary and the Orient 24, 1911, pp. 51–167 (pp. 90–94 and Table 5 (13): 7 and 7a) ( [1] )
- ↑ a b c d e 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 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 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
- ↑ 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
- ^ Albert E. Wood: The juvenile tooth pattern of certain African rodents. Journal of Mammalogy 43 (3), 1952, pp. 310-322
- ^ 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
- ↑ Frank Barbière and Laurent Marivuax: Phylogeny and evolutionary history of hystricognathous rodents from the Old World during the Tertiary: new insights into the modern "phiomorph" families. In: PG Cox and L. Hautier (eds.): Evolution of the rodents: Advances in phylogeny, functional morphology and development. Cambridge University Press, 2015, pp. 87-119
- ↑ René Lavocat: Rodentia and Lagomorpha. In: Vincent J. Maglio and HBS Cooke (Eds.): Evolution of African Mammals. Harvard University Press, 1978, pp. 69-89
- ^ A b Alisa J. Winkler, Christiane Denys and D. Margaret Avery. Rodentia. In: Lars Werdelin and William Joseph Sanders (eds.): Cenozoic Mammals of Africa. University of California Press, Berkeley, Los Angeles, London, 2010, pp. 263-304
- ↑ Patrick J. Lewis and Elwyn L. Simons: Morphological trends in the molars of fossil rodents from the Fayum Depression, Egypt. Palaeontologica Africana 42, 2007, pp. 37-42
