Archaeomylodon

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Archaeomylodon
Temporal occurrence
Lower to Middle Pleistocene
700,000 years
Locations
Systematics
Sub-articulated animals (Xenarthra)
Tooth arms (pilosa)
Sloths (folivora)
Mylodontoidea
Mylodontidae
Archaeomylodon
Scientific name
Archaeomylodon
Brambilla & Ibarra , 2018

Archaeomylodon is an extinct genus of sloths from the group of Mylodontidae . So far, it is known only from a single skull, the dimensions of whichcorrespond tothose of the giant Lestodon . The skull differs from this but by its narrower and higher snout. In addition, the front, canine-like teeth, which are usually large in many Mylodonts, are greatly reduced. The find comes from the pamphlet region of South America and was stored in deposits around 700,000 years old. It belongs to the beginning of the Middle Pleistocene . The genus was scientifically introduced in 2019.

features

Archaeomylodon has so far only been documented on the skull of an adult animal, which lacks the median jawbone and the zygomatic arches . It has a preserved length of 59.7 cm, the width at the skull is 23.8 cm and the height 21 cm. This makes him one of the largest known mylodonts. The animals are likely to have reached the size of the giant Lestodon , for which a weight of up to 4 tons has been reconstructed. The skull had an elongated, tubular shape, typical of large ground sloths, and was almost rectangular in plan. Only in the area of ​​the eyes was there a small constriction and a small enlargement in the nasal bone- maxilla section. The front section was narrower than that of Lestodon , but wider than that of Mylodon . In side view, the forehead line was flat, there was no dome-like bulge, such as that found in Glossotherium or Thinobadistes . The nasal bone was oriented slightly upwards. When viewed from the front, a high nostril was created that was reminiscent of Mylodon and differed from the clearly flat one in Glossotherium . The anterior zygomatic arch origin emerged from the upper jaw above the third molar-like tooth. The parasagittal ridges on the parietal bone were wide apart, comparable to Mylodon , but in contrast to the close position to each other in Lestodon . The occiput had a high and more round shape when viewed from the rear , corresponding to Mylodon . With Lestodon and Glossotherium this was rather flattened and therefore wider. On the underside of the skull, the edges of the palate were largely parallel to each other and were not oriented divergently forward as in Glossotherium and Lestodon .

The teeth are only incomplete. But it consisted of five teeth per half of the jaw. The foremost tooth was like many Mylodonten eckzahnartig ( caniniform ) designed the back four, however molarenartig ( molariform ). This is reminiscent of Lestodon and Glossotherium , but differed from Mylodon , in which the upper canine-shaped teeth were regressed. In contrast to the first two, the rows of teeth were not clearly spaced to the front, but rather were arranged parallel to one another. Only in the foremost area did they diverge slightly from one another. As a result, the two canine-like front teeth were not shifted laterally outwards, but were much closer together. In addition, the clear diastema to the following first molar-like tooth was missing . Overall, the canine-shaped tooth was very small and therefore already greatly reduced in size, which was reminiscent of Mylodonopsis and was a clear difference to the large teeth of Lestodon and Glossotherium . In cross-section it had a rather circular shape. Only the rearmost molar of the following teeth is preserved, the others are indicated by the position of the respective alveoli . It had a flat chewing surface design, typical for Mylodonts, consisting of two flap- like ( lobate ) sections, the rear being smaller than the front. The entire alveolar row of molars was approximately 14.4 cm in length.

Fossil finds

The only known find of Archaeomylodon , an almost complete skull, was discovered in Cantera Iglesias near Partido San Pedro in the north of the Argentine province of Buenos Aires . The site is located south of the Río Paraná in the pampas region of South America. The skull was stored there in calcareous deposits in the upper section of the Ensenada Formation . According to radiometric measurement methods, they could be determined to be around 700,000 years old, which corresponds to the beginning of the Middle Pleistocene .

Paleobiology

As a rule, the mylodonts are considered to be specialized grazers. An attempt was made to reconstruct food preferences based on the shape of the snouts of various extinct sloths. Here, wide snouts indicate grass-eaters and narrow snouts indicate leaf-eaters, comparable to the difference between the white rhinoceros and the black rhinoceros . Archaeomylodon differs significantly from Lestodon and Glossotherium with its narrower snout . It is therefore assumed that the animals may have a generalist diet on plant foods.

Systematics

Internal systematics of the Mylodontoidea according to Brambilla et al. 2018
 Mylodontoidea  

 Baraguatherium


   

 Octomylodon


   

 Nematherium


   


 Scelidotherium


   

 Catonyx



   

 Pseudoprepotherium


   

 Octodontotherium


   


 Archaeomylodon


   

 Mylodon



   

 Paramylodon


   

 Pleurolestodon


   

 Glossotherium


   

 Lestodon


   

 Thinobadistes











Template: Klade / Maintenance / 3

Template: Klade / Maintenance / Style

Archaeomylodon is an extinct genus from the also extinct family of the Mylodontidae . The Mylodontidae represent a branch of the suborder of the sloths (Folivora). Within this they are often grouped together with the Orophodontidae and the Scelidotheriidae in the superfamily of the Mylodontoidea (sometimes the Scelidotheriidae and the Orophodontidae are only considered to be a subfamily of the Mylodontidae). In a classic view, based on skeletal anatomical studies, the Mylodontoidea represent one of the two great lines of development of the sloths alongside the Megatherioidea . Molecular genetic studies and protein analyzes assign a third group to these two groups, the megalocnoidea . Within the Mylodontoidea are the two-toed sloths ( Choloepus ), one of the two species of sloth that still exist today. The Mylodontidae form one of the most diverse groups within the sloth. Outstanding features can be found in their high-crowned teeth, which, unlike those of the Megatherioidea, have a rather flat ( lobate ) chewing surface. This is often associated with increased adaptation to grass-rich foods. The rear teeth have a round or oval cross-section, the front ones are shaped like a canine. The rear foot is also clearly rotated so that the sole points inwards. The Mylodonts already appeared in the Oligocene , one of their earliest records is Paroctodontotherium from Salla-Luribay in Bolivia.

The internal structure of the Mylodontidae is complex and widely discussed. The late groups of the Mylodontinae with Mylodon as the type form and the Lestodontinae , whose character form is Lestodon , but sometimes also includes Paramylodon and Glossotherium (sometimes also listed as Mylodontini and Lestodontini on the tribal level) are widely recognized . The subdivision of the terminal group of the Mylodonts into the Lestodontinae and Mylodontinae was confirmed in one of the most extensive studies on the tribal history of the sloths based on skull features in 2004, which was subsequently substantiated several times. However, a later analysis from 2019 doubts them again. A higher-resolution phylogenetic study of the Mylodonts published in the same year underpins the two-part structure of the terminal forms. Accordingly, the Mylodontinae and Lestodontinae can be distinguished on the basis of the canine-like front teeth. In the latter, these are large and separated from the rear teeth by a long diastema, while the former have only small or partially reduced canine-shaped teeth that are usually closer to the molar-like teeth. In the past, numerous other subfamilies were established, including, for example, the Nematheriinae for representatives from the Lower Miocene or the Octomylodontinae for all basal forms. Their recognition mostly varies depending on the editor. Another group can be found with the Urumacotheriinae, which were only established in 2004. The late Miocene representatives of northern South America form their basic stock. In principle, a revision is requested for the entire family, since many of the higher taxonomic units have no formal diagnosis.

The combination of features of Archaeomylodon such as the tubular skull, the heterodontic dentition with posterior molar-shaped and an anterior canine- shaped tooth and the design of the molar-like teeth in general clearly refer the genus to the Mylodonts. The anterior caniniform tooth is very small in Archaeomylodon , which distinguishes the shape from other large Mylodonts such as Lestodon and Glossotherium . According to phylogenetic analyzes, it is most similar to Mylodon , which occurred mainly in the southern part of South America. In contrast to Archaeomylodon , Mylodon has a more reduced set of teeth, in which the front canine-like teeth have receded completely. Both genera are possibly in a sister group relationship to each other.

The genus Archaeomylodon was first scientifically described in 2018 by Luciano Brambilla and Damián Alberto Ibarra . The basis was the skull from San Pedro in the Argentine province of Buenos Aires , which represents the holotype and belongs to a fully grown animal (specimen number MPS 119). The generic name is made up of the Greek word ἀρχαῖος ( archaios for "old") and the scientific name Mylodon as a type of the Mylodontidae. The prefix archaeo- refers to the higher age of the new genus in relation to the mostly Upper Pleistocene finds of other Mylodonts. A. sampedrinensis was the only species named, the specific epithet being a reference to the locality near San Pedro.

meaning

The majority of the fossil sloth finds from the Pleistocene in South America fall in the uppermost section of this geological unit. These include some giant forms such as Megatherium and Eremotherium from the group of Megatheriidae or Lestodon from the group of Mylodontidae . Fossil remains from the Middle Pleistocene are far less common. With Archaeomylodon is one of the few giant forms in front of this period. It shows the increasing body size development in some lines of the sloths, which gradually manifested itself in the transition from the Pliocene to the Pleistocene. The process coincides with the Great American Fauna Exchange . This began around 2.5 million years ago with the closure of the Isthmus of Panama and the creation of the land bridge between North and South America. As a result, numerous endemic species of South America reached the northern continent, while native animals there penetrated south. The increasing body size of the South American sloth could represent a reaction to increased competition from new herbivores or the appearance of new types of predators such as predators . A similar development in many species in North America is striking with regard to body size increase.

literature

  • 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

Individual evidence

  1. ↑ M. Susana Bargo, Sergio F. Vizcaíno, Fernando M. Archuby and R. Ernesto Blanco: Limb bone proportions, strength and digging in some Lujanian (Late Pleistocene-Early Holocene) mylodontid ground sloths (Mammalia, Xenarthra). Journal of Vertebrate Paleontology 20 (3), 2000, pp. 601-610
  2. ↑ a b c d e f g h i 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
  3. ^ 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
  4. ↑ M. Susana Bargo and Sergio F. Vizcaíno: Paleobiology of Pleistocene ground sloths (Xenarthra, Tardigrada): biomechanics, morphogeometry and ecomorphology applied to the masticatory apparatus. Ameghiniana 45 (1), 2008, pp. 175-196
  5. ↑ a b 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
  6. ↑ 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
  7. ↑ 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
  8. ^ 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.
  9. ^ 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
  10. ↑ 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
  11. ↑ 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)
  12. ↑ Timothy J. Gaudin: Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 2004, pp. 255-305
  13. ↑ 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
  14. ↑ 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
  15. ^ 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
  16. ^ 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
  17. ↑ 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
  18. ^ H. Gregory McDonald: Paleoecology of extinct xenarthrans and the Great American Biotic Interchange. Bulletin of the Florida Museum of Natural History 45, 2005, pp. 313-333