Simomylodon

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Simomylodon
Temporal occurrence
Upper Miocene to Upper Pliocene
5.3 to 2.8 million years
Locations
Systematics
Sub-articulated animals (Xenarthra)
Tooth arms (pilosa)
Sloths (folivora)
Mylodontoidea
Mylodontidae
Simomylodon
Scientific name
Simomylodon
Saint-André , Pujos , Cartelle , De Iuliis , Gaudin , McDonald & Quispe , 2010

Simomylodon is an extinct genus of sloths from the family of the Mylodontidae . It occurred in the period fromthe end ofthe Upper Miocene to the end of the Pliocene 5.3 to 2.8 million years ago in South America . The most important finds come from the central Altiplano in Bolivia and include several skulls and remains of teeth as well as individual parts of the musculoskeletal system. Based on this, a rather small representative of the Mylodontidae can be inferred. Within the fossil material, a robust and graceful shape can be distinguished, which is probably associated with male and female animals. The partially different skull characteristics allow conclusions to be drawn about deviating behavior. The genus was scientifically introduced in 2010. It is currently assigned a species.

features

Simomylodon was a rather small member of the Mylodontidae, whose body weight was estimated at around 228 kg. Finds of the genus include several skulls and additional postcranial skeletal elements. The skull was elongated, the top of the skull and the base of the skull ran almost parallel to one another in a side view, but the front section was slightly lower than the rear. When viewed from above, the posterior section of the skull was strikingly wide compared to its total length. This is reminiscent of Pleurolestodon , but differs from other Mylodonts such as Glossotherium and Paramylodon . The rostrum was short. The nasal bone showed a sharp constriction shortly before the eye windows and widened increasingly both forwards and backwards. The front edge was largely convex. The snout that widens forward when viewed from above is a typical feature of the Mylodonts. In a lateral view, the muzzle was dominated by the upper jaw, which fused with the nasal bone over almost its entire length. The middle jaw bone had a V-shaped to more curved shape. The frontal and parietal bones were flat. Slight temporal ridges rose on the parietal bones, which ran parallel but did not unite to form a crest . The zygomatic arch was not closed. As usual in sloths , the front section of the arch, attached to the cheekbone , consisted of three appendages, one ascending, one horizontal and one descending. The largest was the ascending process, which began broadly at the base and ended in a rounded tip. The horizontal process was triangular in shape and met the long, narrow posterior arch section of the temporal bone . The extremely long shape of the posterior zygomatic arch section can be regarded as an atypical feature of the Mylodonts. The descending extension partly ended in a hook shape. The tearbone was wide and formed part of the orbital margin, with the section involved in the eye window exceeding that of the face. The occiput was vertical to sloping backwards. The occiput was strongly developed throughout. The joints for articulation with the cervical spine protruded prominently and were clearly separated from each other. At the base of the skull, the wing legs showed clear distension. The roof of the palate widened forward analogously to the rostrum and was thus V-shaped.

The lower jaw was about 24 cm long and was about 5.5 cm high below the molar-like teeth. That made him look short and stocky. At the lower edge, the horizontal bone was almost straight, a characteristic of the Mylodonts. The symphysis extended to the front, typical of the sloth, to form an appendage that was short and wide in Simomylodon and ended in a straight edge, comparable to Glossotherium and Lestodon , but different from Paramylodon . In the lateral profile, the lower edge of the symphysis ran irregularly through various bulges and indentations. The variable formation of the foramina mentalia with one to six openings is remarkable, the size and number of which fluctuated greatly, even with individual individuals. The mandible foramen opened on the inside of the lower jaw, well behind the last tooth and below the crown process. On the ascending branch, all three processes (crown, articular and angular process) were clearly separated from each other. The front edge of the ascending branch did not cover the last molar-like tooth. This agrees with Paramylodon , but differs from Pleurolestodon and Mylodon . The crown process rose steeply and had a hook-shaped end. The articular process was roughly level with the occlusal plane of the teeth, and the joint itself was wider than it was long. The angular process at the rearmost end of the lower jaw stood out clearly from the horizontal bone body due to its bulging course of the lower edge.

The Simomylodon set of teeth was typical for sloths. The upper row of teeth consisted of five, the lower row of four teeth, so a total of 18 teeth were formed. All teeth were in a row with the exception of the foremost tooth of the lower jaw, which was slightly shifted to the side. In the upper dentition the rows diverged from one another, in the lower they were more parallel. Both in the upper as well as lower set of teeth of the respective foremost tooth had a eckzahnartige ( caniniforme on) form, all other teeth were molarenartig ( molariform ). This unites Simomylodon with most Mylodonts except about Mylodon , whose front tooth in the upper row of teeth was reduced. There was no diastema between the canine- shaped and molar-shaped teeth, which differs from Lestodon with its extraordinarily large tooth gap. The front, canine-like tooth had a semicircular to triangular cross-section. It was relatively small, which roughly corresponds to Glossotherium and Pleurolestodon , but differs significantly from Lestodon with its greatly enlarged front teeth. The molar-like teeth had the flat chewing surface, which is characteristic of mylodonts, made up of two lobed ( bilobatic ) structures that appeared diamond-shaped or T-shaped in outline. Only the anterior upper molar-like tooth was oval in cross-section. The upper row of teeth was between 9.0 and 10.4 cm long, of which the molar teeth were between 7.5 and 8.6 cm. The largest tooth was always the rearmost.

From the body skeleton of simomylodon mainly the elements of the front and rear legs have been handed down. The humerus was 26 cm in length. A pronounced deltopectoral ridge sat on its shaft, which acted as a muscle attachment point. It was more pronounced than with Glossotherium or Lestodon . The lower end of the joint protruded characteristically, but the outer epicondyle was less noticeably developed than in Glossotherium . The spoke reached a length of 19 cm and was comparatively shorter and more compact than that of Paramylodon . The femur was 32 cm long. Like most ground sloths, it was flat like a board. Its shaft curved slightly to one side. On the outer longitudinal edge there was a roughened point, which indicated the third rolling mound and was more developed than in Glossotherium . At just 17 cm in length, the shin was only half as long as the thighbone. This is typical of Mylodonts and a clear contrast to the Megatheriidae, for example, with their noticeably longer lower leg sections. The joint ends were robust and broad in Simomylodon . Hands and feet have only been handed down with individual root bones and metapodia . The occasional adhesion of the third metacarpal bone to the head bone should be emphasized here . The second and third metacarpal bones were 5.5 and 6.7 cm long, respectively.

Fossil finds

Most of the Simomylodon fossil finds were recovered in the central part of the Altiplano in southwestern Bolivia . The remains are spread over several sites. The currently oldest is a skull from Choquecota in the Oruro department about 3.5 km southwest of the eponymous town. It was stored in the upper area of ​​the Rosa Pata formation, which largely belonged to the Miocene , in a sequence of deposits of reddish sandstones around 15 m under a prominent tuff band . This in turn is called Toba 76 and is common as a marker horizon in the central Altiplano. Radiometric dating gives the tuff an age of around 5.3 million years, which refers it to the transition from the Upper Miocene to the Lower Pliocene . All other finds are more recent and stratigraphically come from the area above the Toba 76 Tuff. They were mostly uncovered in the Umala formation . The rock unit consists of sandy to clayey deposits. The find area of ​​Ayo Ayo and Viscachani around 70 km south of La Paz in the department of the same name is of importance here . Here again another tuff, the Ayo Ayo Tuff , completes the sediment sequence . With an age of around 2.8 million years, it corresponds to the Upper Pliocene. Ayo Ayo and Viscachani are currently the northernmost sites in the Altiplano, they also represent the locus typicus of Simomylodon . In addition to a partial skull, various skull and lower jaw fragments as well as parts of the body skeleton were found here. In total, there are more than 80 found objects. Further fossil material in the form of several, sometimes complete, skulls came to light in Pomata-Ayte, also in the Oruro department, and in Inchasi and Casira in the Potosí department . The latter location is the southernmost of the Altiplano. The fossil remains here, including a palatine bone and a lower jaw fragment, were stored in the Tafna formation . Their exact stratigraphic position has so far been little researched, but it probably also originated in the transition from the Miocene to the Pliocene.

Away from the find province in the Altiplano, a lower jaw fragment from Arenas Blancas on the lower reaches of the Arroyo Chasicó around 10 km north of the Laguna Chasicó in the south of the Argentine province of Buenos Aires could also be counted as Simomylodon . The approximately 11 cm long find was found in the Arroyo Chasicó formation , which generally dates to the Upper Miocene.

Paleobiology

Simomylodon can be divided into two types with regard to cranial and mandibular morphology : a robust and a graceful form. The robust skulls are characterized by a wider rostrum compared to the total length. In detail, they also have a rather curved central jawbone and a short and wide palate. The graceful skulls, on the other hand, have more distinctly V-shaped central jaw bones and long, narrow palates. Further deviations can be found in the posterior skull with a largely vertical occiput in the strong and an oblique backward in the slender types. In the latter, the occipital joints stand out more clearly than in the former, the condyles of which are closer to the skull. On the lower jaw, robust forms have a significantly deeper horizontal bone body than the delicate ones in comparison. Similar differences can also be found in the postcranial skeleton. As a rule, such striking morphological differences can be regarded as an expression of a sexual dimorphism , whereby in mammals the stronger types are related to males, the slimmer types to females.

The two morphotypes may also lead to different behaviors. For extinct sloths, the width of the snout is an important indicator of food intake. For example, shapes with broad snouts can be classified as rather grass-eating, while those with pointed snouts were probably specialized in soft leafy or mixed vegetable foods. Male animals often have a more energetic life and need high amounts of food, female animals prefer higher-quality food to care for their offspring. In Simomylodon , the more robust, broad-nosed skull of the male and the more delicate, narrow-nosed of the female could reflect such differences. Evidence of this can also be found in the posterior section of the skull. Due to the vertical position of the occiput, the male individuals kept the skull rather low, which indicates a grass-based diet. The sloping back of the head of the female animal advocates a higher head position and thus a more leafy diet. Different food preferences can also indicate a different use of space. Grass specialists tend to have larger action spaces with more rambling migratory movements than animals with a preference for a soft vegetable diet. This is also perfectly acceptable for simomylodon .

Systematics

Internal systematics of the Mylodontidae according to Boscaini et al. 2019
 Mylodontidae  


 Urumacotherium


   

 Pseudoprepotherium



   


 Paroctodontotherium


   

 Octodontotherium



   

 Brievabradys


   



 Lestodon


   

 Bolivartherium



   

 Thinobadistes


   

 Sphenotherus


   

 Lestobradys





   

 Pleurolestodon


   


 "Glossotherium" chapadmalense


   

 Simomylodon



   



 Kiyumylodon


   

 Mylodon



   

 Paramylodon



   

 Glossotherium









Template: Klade / Maintenance / Style

Simomylodon is an extinct genus from the also extinct family of the Mylodontidae . The Mylodontidae form a branch within the suborder of the sloths (Folivora). They are often referred to the Mylodontoidea superfamily together with the Orophodontidae and the Scelidotheriidae (however, the Scelidotheriidae and the Orophodontidae are sometimes only considered a subfamily of the Mylodontidae). In a classic system based on skeletal-anatomical features , the Mylodontoidea represent one of the two great lines of development of the sloths alongside the Megatherioidea . After molecular genetic analyzes and protein examinations , a third major line can be distinguished with the megalocnoidea . According to the latter two analytical methods, the Mylodontoidea with the two-toed sloth ( Choloepus ) also include one of the two species of sloth that still exist today. The Mylodontidae are one of the most diverse groups within the sloth. The high-crowned teeth with their, unlike those of the Megatherioidea and Megalocnoidea, rather flat ( lobate ) chewing surfaces can be emphasized as characteristic features. This particular tooth structure is often associated with greater adaptation to grass-rich food. The rear teeth have a round, oval or more complex cross-section and correspond to molar-like teeth, the frontmost teeth are designed in the shape of a canine. The rear foot is also clearly rotated so that the sole points inwards. The Mylodonts can be detected for the first time in the Oligocene , one of the earliest forms is Paroctodontotherium from Salla-Luribay in Bolivia.

The internal structure of the Mylodontidae is complex and currently under discussion. The largely recognized groups include the late lines of development of the Mylodontinae with Mylodon as a type form and the Lestodontinae , whose character form is Lestodon ( also called Mylodontini and Lestodontini on the tribal level). The latter group also includes Paramylodon and Glossotherium . The subdivision of the terminal forms of the Mylodonts into the Lestodontinae and Mylodontinae was confirmed in one of the most extensive studies on the tribal history of the sloths from 2004, which is based on skull features, and was subsequently substantiated several times. However, a later analysis from 2019 questions the integrity of the two lines again. On the other hand, a higher-resolution work on the phylogenesis of the Mylodonts presented in the same year supports the branching of the terminal representatives. An important difference between the Mylodontinae and Lestodontinae is the form of the canine-like front teeth, as these are large in the latter and separated from the rear teeth by a long diastema, but in the former they are only small in size or are partially reduced and closer together stand up to the molar-like teeth. In the past, numerous other subfamilies were set up, for example the Nematheriinae for representatives from the Lower Miocene or the Octomylodontinae for all basal forms. However, their respective recognition varies depending on the processor. Another group can be found with the Urumacotheriinae, whose introduction dates back to 2004. The late Miocene representatives of northern South America form their basic stock. In principle, most researchers urge a revision for the entire family, as many of the higher taxonomic units have no formal diagnosis. Simomylodon is generally considered to be closely related to Pleurolestodon , which in turn has , according to numerous phylogenetic studies, closer ties to Glossotherium and Paramylodon . Simomylodon is sometimes referred to a more basal area within the Mylodontinae.

The first scientific description of simomylodon was in 2010 by Pierre-Antoine Saint-André and fellow researchers. The foundations from the Ayo Ayo and Viscachani sites in the Bolivian department of La Paz served as the basis , as well as that from Pomata-Ayte in the department of Oruro , where Viscachani is considered a type locality . The holotype (copy number GB 078) consists of a front part of the skull that is missing teeth. The genus name Simomylodon derives on the one hand from the Greek word σίμός for " snub- nosed" and refers to the partly blunt expression of the middle jawbone, on the other hand it refers to the genus Mylodon , which, according to the first authors of the time, could be derived from Simomylodon . The only species named by Saint-André and colleagues was Simomylodon uccasamamensis . The specific epithet has its origin in Sanskrit ( ucca for "high" and samam for "plain" or "wide") and is a reference to the find region in the Altiplano ( Spanish for "plateau"). Saint-André had already mentioned the species name uccasamamensis in 1994 in a modified form ( uccasamamense ) in his unpublished graduate thesis in connection with " Simotherium ".

In the same essay, the first description to Simomylodon contained, Saint-André and his team of researchers established the new genus Pleurolestodon Asked Art P. dalenzae basis of a complete skull of Choquecota in the Bolivian department of Oruro. Like uccasamamense , Saint-André had already used the species name dalenzae in his doctoral thesis in 1994, but linked it with “ Glossotheriscum ”. Due to numerous discoveries that no differences Simomylodon revealed, synonymisierte in 2019, a research team led by Alberto Boscaini Pleurolestodon dalenzae with Simomylodon uccasamamensis . The latter species is therefore the only recognized species within the genus Simomylodon . Other fossil material, such as individual lower jaws from Inchasi in the Oruro department, was previously referred to other genera of the Mylodonts, such as Glossotheridium .

literature

  • Pierre-Antoine Saint-André, François Pujos, Cástor Cartelle, Gerardo De Iuliis, Timothy J. Gaudin, H. Gregory McDonald and Bernardino Mamani Quispe: Nouveaux paresseux terrestres (Mammalia, Xenarthra, Mylodontidae) du Néogène de l'Altiplano Bolivia. Geodiversitas 32 (2), 2010, pp. 255-306
  • Alberto Boscaini, Timothy Gaudin, Bernardino Mamani Quispe, Philippe Münch, Pierre-Olivier Antoine and François Pujos: New well-preserved craniodental remains of Simomylodon uccasamamensis (Xenarthra, Mylodontidae) from the Pliocene of the Bolivian Altiplano: phicationsyloobiogice, and implicationsyloigraphaleographic, implostratale . Zoological Journal of the Linnean Society 185 (2), 2019, pp. 459-486
  • Alberto Boscaini, Timothy J. Gaudin, Néstor Toledo, Bernardino Mamani Quispe, Pierre-Olivier Antoine and François Pujos: The earliest well-documented occurrence of sexual dimorphism in extinct sloths: evolutionary and palaeoecological insights. Zoological Journal of the Linnean Society 20, 2019, pp. 1-11

Individual evidence

  1. ↑ a b c Ascanio D. Rincón, Andrés Solórzano, H. Gregory McDonald and Mónica Núñez Flores: Baraguatherium takumara, Gen. et Sp. Nov., the Earliest Mylodontoid Sloth (Early Miocene) from Northern South America. Journal of Mammalian Evolution 24 (2), 2017, pp. 179-191
  2. ↑ a b c d e f g h Pierre-Antoine Saint-André, François Pujos, Cástor Cartelle, Gerardo De Iuliis, Timothy J. Gaudin, H. Gregory McDonald and Bernardino Mamani Quispe: Nouveaux paresseux terrestres (Mammalia, Xenarthra, Mylodontidae) du Néogène de l'Altiplano bolivia. Geodiversitas 32 (2), 2010, pp. 255-306
  3. ↑ a b c d e Alberto Boscaini, Timothy Gaudin, Bernardino Mamani Quispe, Philippe Münch, Pierre-Olivier Antoine and François Pujos: New well-preserved craniodental remains of Simomylodon uccasamamensis (Xenarthra, Mylodontidae) from the Pliocene of the Bolivianlogeniplano: phy , chronostratigraphic, and paleobiogeographic implications. Zoological Journal of the Linnean Society 185 (2), 2019, pp. 459-486
  4. ^ A b Federico Anaya and Bruce J. MacFadden: Pliocene mammals from Inchasi, Bolivia: the endemic fauna just before the Great American Interchange. Bulletin of the Florida Museum of Natural History 39 (3), 1995, pp. 87-140
  5. ↑ Sofía I. Quiñones, Ángel R. Miño-Boilini, Alfredo E. Zurita, Silvina A. Contreras, Carlos A. Luna, Adriana M. Candela, María Camacho, Marcos D. Ercoli, Natalia Solís and Diego Brandoni: New records of Neogene Xenarthra (Mammalia) from eastern Puna (Argentina): diversity and biochronology. Journal of Paleontology 93 (6), 2019, pp. 1258–127, doi: 0.1017 / jpa.2019.64
  6. ↑ Cristian Oliva and Diego Brandoni: Primer registro de Mylodontinae (Tardigrada, Mylodontidae) en el Huayqueriense (Mioceno tardío) de la provincia de Buenos Aires, Argentina. Revista del Museo Argentino de Ciencias Naturales, ns 14 (2), 2012, pp. 325-332
  7. ↑ a b c Alberto Boscaini, Timothy J. Gaudin, Néstor Toledo, Bernardino Mamani Quispe, Pierre-Olivier Antoine and François Pujos: The earliest well-documented occurrence of sexual dimorphism in extinct sloths: evolutionary and palaeoecological insights. Zoological Journal of the Linnean Society, 2019, pp. 1-11
  8. ^ M. Susana Bargo, Néstor Toledo and Sergio F. Vizcaíno: Muzzle of South American Pleistocene Ground sloths (Xenarthra, Tardigrada). Journal of Morphology 267, 2006, pp. 248-263
  9. ↑ M. Susana Bargo and Sergio F. Vizcaíno: Paleobiology of Pleistocene Ground sloths (Xenarthra, Tardigrada): biomechanics, morphogeometry and ecomorphology applid to the masticatory apparatus. Ameghiniana 45 (1), 2008, pp. 175-196
  10. ↑ a b c Luciano Varela, P. Sebastián Tambusso, H. Gregory McDonald and Richard A. Fariña: Phylogeny, Macroevolutionary Trends and Historical Biogeography of Sloths: Insights From a Bayesian Morphological Clock Analysis. Systematic Biology 68 (2), 2019, pp. 204-218
  11. ↑ Frédéric Delsuc, Melanie Kuch, Gillian C. Gibb, Emil Karpinski, Dirk Hackenberger, Paul Szpak, Jorge G. Martínez, Jim I. Mead, H. Gregory McDonald, Ross DE MacPhee, Guillaume Billet, Lionel Hautier and Hendrik N. Poinar : Ancient mitogenomes reveal the evolutionary history and biogeography of sloths. Current Biology 29 (12), 2019, pp. 2031-2042, doi: 10.1016 / j.cub.2019.05.043
  12. ↑ Samantha Presslee, Graham J. Slater, François Pujos, Analía M. Forasiepi, Roman Fischer, Kelly Molloy, Meaghan Mackie, Jesper V. Olsen, Alejandro Kramarz, Matías Taglioretti, Fernando Scaglia, Maximiliano Lezcano, José Luis Lanata, John Southon, Robert Feranec, Jonathan Bloch, Adam Hajduk, Fabiana M. Martin, Rodolfo Salas Gismondi, Marcelo Reguero, Christian de Muizon, Alex Greenwood, Brian T. Chait, Kirsty Penkman, Matthew Collins and Ross DE MacPhee: Palaeoproteomics resolves sloth relationships. Nature Ecology & Evolution 3, 2019, pp. 1121-1130, doi: 10.1038 / s41559-019-0909-z
  13. ^ H. Gregory McDonald and Gerardo de Iuliis: Fossil history of sloths. In: Sergio F. Vizcaíno and WJ Loughry (eds.): The Biology of the Xenarthra. University Press of Florida, 2008, pp. 39-55.
  14. ^ H. Gregory McDonald: Evolution of the Pedolateral Foot in Ground Sloths: Patterns of Change in the Astragalus. Journal of Mammalian Evolution 19, 2012, pp. 209-215
  15. ↑ Bruce J. Shockey and Federico Anaya: Grazing in a New Late Oligocene Mylodontid Sloth and a Mylodontid Radiation as a Component of the Eocene-Oligocene Faunal Turnover and the Early Spread of Grasslands / Savannas in South America. Journal of Mammal Evolution 18, 2011, pp. 101-115
  16. ↑ Malcolm C. McKenna and Susan K. Bell: Classification of mammals above the species level. Columbia University Press, New York, 1997, pp. 1-631 (pp. 94-96)
  17. ↑ Timothy J. Gaudin: Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 2004, pp. 255-305
  18. ↑ a b Luciano Brambilla and Damián Alberto Ibarra: Archaeomylodon sampedrinensis, gen. Et sp. nov., a new mylodontine from the middle Pleistocene of Pampean Region, Argentina. Journal of Vertebrate Paleontology 38 (6), 2018, p. E1542308, doi: 10.1080 / 02724634.2018.1542308
  19. ↑ a b Alberto Boscaini, François Pujos and Timothy J. Gaudin: A reappraisal of the phylogeny of Mylodontidae (Mammalia, Xenarthra) and the divergence of mylodontine and lestodontine sloths. Zoologica Scripta 48 (6), 2019, pp. 691-710, doi: 10.1111 / zsc.12376
  20. ^ Andrés Rinderknecht, Enrique Bostelmann T., Daniel Perea and Gustavo Lecuona: A New Genus and Species of Mylodontidae (Mammalia: Xenarthra) from the Late Miocene of Southern Uruguay, with Comments on the Systematics of the Mylodontinae. Journal of Vertebrate Paleontology 30 (3), 2010, pp. 899-910
  21. ^ Francisco Ricardo Negri and Jorge Ferigolo: Urumacotheriinae, nova subfamília de Mylodontidae (Mammalia, Tardigrada) do Mioceno Superior-Plioceno, América do Sul. Revista Brasileira de Paleontologia 7 (2), 2004, pp. 281-288
  22. ↑ Ascanio D. Rincón, H. Gregory McDonald, Andrés Solórzano, Mónica Núñez Flores and Damián Ruiz-Ramoni: A new enigmatic Late Miocene mylodontoid sloth from northern South America. Royal Society Open Science 2, 2015, p. 140256, doi: 10.1098 / rsos.140256
  23. ^ Cástor Cartelle, Gerardo De Iuliis, Alberto Boscaini and François Pujos: Anatomy, possible sexual dimorphism, and phylogenetic affinities of a new mylodontine sloth from the late Pleistocene of intertropical Brazil. Journal of Systematic Palaeontology 17 (23), 2019, pp. 1957–1988, doi: 10.1080 / 14772019.2019.1574406