Megathericulus

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Megathericulus
Temporal occurrence
Middle Miocene
15.8 to 11.2 million years
Locations
Systematics
Sub-articulated animals (Xenarthra)
Tooth arms (pilosa)
Sloths (folivora)
Megatherioidea
Megatheriidae
Megathericulus
Scientific name
Megathericulus
Ameghino , 1904

Megathericulus is an extinct genus of sloths from the family group of Megatheriidae . It occurred in the Middle Miocene around 16 to 11 million years ago in the southern and central parts of South America . Finds have comedown to usfrom Argentina , Bolivia and Peru , among others. It is a smaller representative of the Megatheria, which due to its dentition structure with homodontic teeth belongs to the more modern line of development within the family. Due to his age, he is one of the earliest members of this line. The genus was scientifically introduced in 1904. Only one species is currently recognized.

features

Megathericulus is a small representative of the Megatheriidae. The known find material of the genus consists of individual skulls, remains of teeth and parts of the musculoskeletal system. The skull measured up to 33 cm in length, it was elongated and narrow with the greatest width in the area of ​​the anterior zygomatic arch attachment and the mastoid process as well as slight constrictions near the orbit . In its general form it was largely similar to the skulls of Planops or Pyramiodontherium , while that of Megatherium was much more robust. In side view it was low in height. The forehead line was arched and sloping in the direction of the rostrum . The latter was extremely elongated, with the front, toothless area corresponding to the extent of the tooth-bearing area. In later megatheria the anterior, toothless section was mostly shorter in proportion. The temporal pits were prominent and approached each other towards the center line of the skull, but did not form a conspicuous crest . The infraorbital foramen opened about 2 cm above the alveolar plane . The anterior arch of the zygomatic arch started between the second and third molar-like tooth, which is slightly further back than in the case of anisodontherium and pyramiodontherium . The occiput was vertical, the joints for articulation with the cervical spine were slightly above the chewing plane of the maxillary teeth, roughly in the middle of the height of the skull. They were thus higher than with Anisodontherium and Pyramiodontherium but lower than with Megatherium . The palate pulled out like a spatula through the elongated snout. It was very narrow and with a width of 2.5 cm did not exceed the dimensions of the tooth alveoli.

In side view, the lower jaw had a lower edge that was clearly bulged downwards, which is a typical feature of megatheria. The lowest point and thus the greatest height of the horizontal bone body was reached under the third to fourth molar-like tooth. The position was significantly further behind than in the genealogically younger Megatheria. The Alveolarfläche was slightly dented, which is roughly the ratio at Anisodontherium or Eomegatherium corresponded, but the straight course at Pyramiodontherium differed. The symphysis ended shortly before the foremost molarenartigen tooth as Anisodontherium while at Pyramiodontherium and Pliomegatherium reached further back. The anterior edge of the ascending branch started at an obtuse angle to the alveolar plane of the horizontal body of the bone. Below the anterior end of the ascending branch was the posterior opening of the mandibular canal .

The teeth of Megathericulus corresponded to the typical ones of the sloths with five teeth per upper jaw and four teeth per lower jaw half. So there were a total of 18 teeth. The teeth of the upper jaw stood closed in parallel rows, but the outer edge each formed a slight curve. In the lower jaw, too, the teeth formed a closed row, a lateral displacement of the first tooth, as is often observed in the representatives of the Mylodontidae and Megalonychidae , did not occur. The teeth had the structure typical of the Megatheriidae. They were all molar-like in shape ( molar-shaped ) and thus different from most other sloths homodont . The chewing surfaces had two sharp, transverse ridges, which were separated by a V-shaped recess. As a special feature of Megathericulus , the extreme anterior and posterior narrowing of the teeth can be emphasized, so that they appear strongly rectangular in cross-section. This made the last upper tooth 0.7 cm long and 1.6 cm wide. This feature shows similarities to Anisodontherium , while the phylogenetically younger forms in particular had more square to trapezoidal tooth cross-sections. According to most megatheria, the teeth were very high crowned ( hypsodon ), which explains the special shape of the lower jaw with the bulge of the lower edge. The hypsodontic index (ratio of the height of the horizontal bone of the lower jaw to the length of the row of teeth) for Megathericulus was 0.92 and thus indicates an average value for Megatheria ( Megatheriops and Pyramiodontherium below 0.9, Megatherium and Anisodontherium above 1.0) . The length of the upper row of teeth was about 8 cm.

Parts of the front and rear legs of the body skeleton are documented. The humerus was 36 to 38 cm long and generally slim. The large and small bony protrusions on the head (greater and lesser tuberosities) reached large dimensions. A strong and extensive deltopectoral ridge ran along the shaft, which is no longer clearly evident in later megatheria. The humerus widened considerably downwards and measured between 13.6 and 16.2 cm at the joint end ( elbow joint ). The ratio of the lower width to the total length of the bone corresponded roughly to that of Megatherium and was significantly larger than that of Pyramiodontherium and Megatheriops . With a few exceptions, most of the other long bones are only fragmented. The ulna was characterized by a very short and narrow upper articular process ( olecranon ). In the first aspect, this agrees with other Megatheria, the latter is different from the mostly broad olecranon of the other family representatives. As with almost all Megatheria but in contrast to other sloths, the lower end of the tibia and fibula were fused together. The shin itself measured around 28 cm in length and was also slim. It largely corresponded to that of Pyramiodontherium . Based on the joint facets on the traditional second metacarpal bone, it can be concluded that a metacarpal-carpal complex (MCC) was also formed in Megathericulus . This consisted of the fused first metacarpal bone and the large polygonal bone and is a typical characteristic of the Megatheria and some other large ground sloths.

Fossil sites

Megathericulus is documented by numerous finds from the central and southern part of South America . The fossil remains that determine the genus come from the vicinity of the Laguna Blanca in the Argentine province of Chubut . They consist of an anterior skull fragment, the teeth of which are missing, and a complete right talus bone . The finds are generally assigned to the Middle Miocene . Further finds are documented from the west of the same province, including a left lower jaw branch and also a right ankle bone from the Collón-Curá formation . The rock unit is made up of limestone and sandstone into which volcanic deposits are incorporated. The deposits were created under different formation conditions such as flood plains and still water areas. Their absolute age has been determined from 15.8 to 11.2 million years using radiometric dating . From the southwestern part of the province of Chubut and the neighboring province of Santa Cruz to the south, numerous fragmented remains were recovered in the Río Mayo formation , including parts of the lower jaw and various elements of the musculoskeletal system. The fossils come from two different points of discovery and each represent a single individual per location, which can be deduced from the corresponding sizes and conservation statuses. Compared to the finds from the Collón-Curá formation, they are somewhat younger, based on the dating of a striking horizon below the fossil-bearing strata to around 11.8 million.

Outside Argentina, Megathericulus has been reported from Bolivia , among others . The extremely rich fossil deposit of Quebrada Honda in the southern Bolivian department of Tarija should be emphasized here . The site was discovered in the 1970s and has been researched continuously ever since. The absolute ages of the extensive discovery region range from 13 to 12 million years. Due to the large extent of the find area and the possibly not always uniform age, different local faunas are distinguished. A partial skeleton of Megathericulus consisting of a complete skull without a lower jaw and remains of the front leg was found in an outcrop on the north bank of the Río Rosario. A layer of tuff carved into the fossil-bearing layers resulted in an age of 12.4 million years. The finds here are assigned to the Papachacra local fauna . Another remnant, a humerus, came to light in an outcrop further south and belongs to the Huayllajara local fauna . Particularly noteworthy is a toothless lower jaw from the Río Sepa , a tributary of the Río Urubamba in the Peruvian part of the Amazon region . The find fits into a very rich fauna community known as Fitzcarrald local fauna, which is between 17 and 10 million years old. The deposits in which the fossils are embedded can be traced back to what was once a large area of ​​wetland made up of swamps, lakes and rivers that drained north into the Caribbean . As Pebas megawetland, they represent the forerunner of today's Amazon rainforest . The lower jaw find itself is said to be 13.5 to 11.8 million years old.

Systematics

Internal systematics of the Megatheriidae according to Varela et al. 2019
 Megatheriidae  
  Megatheriinae  





 Eremotherium


   

 Megatherium



   

 Proeremotherium



   

 Pyramiodontherium



   

 Anisodontherium



   

 Diabolotherium


   

 Megathericulus




  Planopinae  


 Planops


   

 Prepotherium



   

 Prepoplanops




Template: Klade / Maintenance / Style

Megathericulus is a genus from the extinct family of Megatheriidae within the suborder of the sloths (Folivora). The species-poor group of sloths today showed a high diversity of forms in their phylogenetic past. Different lines of development can be distinguished within the sloth. In a classical system based on skeletal anatomical features , the Megatheriidae together with the Megalonychidae and Nothrotheriidae form a more closely related group, the superfamily of the Megatherioidea . After molecular genetic investigations and protein analyzes , the Bradypodidae with the three-toed sloths ( Bradypus ) should also be included here. The Megatheriidae produced the largest known representatives of the sloth, including the eponymous Megatherium and Eremotherium . Both are mainly proven from the Pleistocene , the former was limited to the Pampas and Andean regions of South America, the latter reached the southern part of North America in the course of the Great American Faun Exchange . Megathericulus is considered to be the basal form of the genealogically more modern branch of the Megatheria, which are summarized in the subfamily of Megatheriinae and also contain the two giant forms mentioned. Evidence of this can be found primarily in the tooth morphology with the consistently homodontic , molar-like teeth. In the more original megatheria from the Planopinae group , the foremost tooth is still shaped like a canine.

The genus Megathericulus was first scientifically described by Florentino Ameghino in 1904 . He used for a toothless front part of a skull and a right ankle bone (copy number MACN A 11151). As the type locality , Ameghino Tehuelche indicated antiguo del Chubut (Laguna Blanca) , which is in what is now the Argentine province of Chubut . He named M. patagonicus as the only species , with the specific epithet referring to the larger Patagonia landscape . In 1939, Ángel Cabrera introduced the species M. primaevus on the basis of individual postcranial skeletal parts (ribs, ulna , shin as well as ankle and heel bones ) from the Cañadon Ftamichi near Paso Flores in the Argentine province of Río Negro . These come from the Collón-Curá formation, but were dated by Cabrera to a somewhat older age (beginning of the Middle Miocene). Some later authors saw the assignment of the material to Megathericulus and thus to the Megatheriinae not as clearly given. However, further new finds from the Collón-Curá formation did not reveal any differences to corresponding finds of M. patagonicus and in 2019 led to the equation of Cabrera's species with Ameghino's nominate form .

Another species had already been established in 1930 by Lucas Kraglievich with M. friasensis , citing a partial skull from the Río Frias in Chile , but according to most authors it is a representative of the Scelidotheriidae , which in turn belong to the family group of the Mylodontidae . In 2013, a research team led by pointing François Pujos with M. cabrerai and M. andinum two ways to Megathericulus , originally in the genus Eomegatherium stood. Both also go back to Kraglievich 1930. For the description he used individual, heavily dismembered skull parts and some long bone fragments from Patagonia. Due to the clearly fragmented state of the finds, other scientists consider an allocation to Megathericulus to be implausible and keep the two species within Eomegatherium for the time being , since better find material would be required for a more precise and clear allocation. Accordingly, M. patagonicus remains the only species of the genus Megathericulus for the time being .

meaning

Megathericulus is currently the oldest representative of the modern line of Megatheria (Megatheriinae) and the only one that is definitely dated from the Middle Miocene . The genus occurs fossil in both the southern and central areas of the continent. The origin of the megatheriinen and thus the extremely large forms of the sloth was generally associated with the southern part of South America. The closest known members of the Megatheriines come from the Upper Miocene. These include anisodontherium and pyramiodontherium , both of which have been handed down from the pampa region . From the same or a more recent period, modern representatives of the Megatheria from northern South America have also been reported with Urumaquia and Proeremotherium . The evidence of megathericulus in the Amazon region of Peru and thus far north of the presumed region of origin at least shows that the genetically more modern megatheria already spread northwards at a very early point in time. Megatherine leg bones from the fossil deposit of La Venta on the middle reaches of the Río Magdalena in Colombia are probably about the same age as the find from the Peruvian Amazon region .

literature

  • Diego Brandoni, Alfredo A. Carlini, Federico Anaya, Phil Gans and Darin A. Croft: New remains of Megathericulus patagonicus Ameghino, 1904 (Xenarthra, Tardigrada) from the Serravallian (Middle Miocene) of Bolivia; chronological and biogeographical implications. Journal of Mammalian Evolution 25 (3), 2018, pp. 327-337, doi: 10.1007 / s10914-017-9348-y
  • Diego Brandoni, Laureano González Ruiz and Joaquín Bucher: Evolutive implications of Megathericulus patagonicus (Xenarthra, Megatheriinae) from the Miocene of Patagonia, Argentina. Journal of Mammalian Evolution, 2019, doi: 10.1007 / s10914-019-09469-9
  • Gerardo de Iuliis, Diego Brandoni and Gustavo J. Scillato-Yané: New remains of Megathericulus patagonicus Ameghino, 1904 (Xenarthra, Megatheriidae): Information on primitive features of megatheriines. Journal of Vertebrate Paleontology 28 (1), 2008, pp. 181-196

Individual evidence

  1. ↑ a b c d e f Diego Brandoni, Laureano González Ruiz and Joaquín Bucher: Evolutive implications of Megathericulus patagonicus (Xenarthra, Megatheriinae) from the Miocene of Patagonia, Argentina. Journal of Mammalian Evolution, 2019, doi: 10.1007 / s10914-019-09469-9
  2. ↑ a b c d François Pujos, Rodolfo Salas-Gismondi, Guillaume Baby, Patrice Baby, Cyrille Goillot, Julia Tejada and Pierre-Olivier Antoine: Implication of the Presence of Megathericulus (Xenarthra: Tardigrada: Megatheriidae) in the Laventan of Peruvian Amazonia. Journal of Systematic Palaeontology 11 (8), 2013, pp. 973-991
  3. ↑ a b c d e f Gerardo de Iuliis, Diego Brandoni and Gustavo J. Scillato-Yané: New remains of Megathericulus patagonicus Ameghino, 1904 (Xenarthra, Megatheriidae): Information on primitive features of megatheriines. Journal of Vertebrate Paleontology 28 (1), 2008, pp. 181-196
  4. ↑ a b c d Diego Brandoni, Alfredo A. Carlini, Federico Anaya, Phil Gans and Darin A. Croft: New remains of Megathericulus patagonicus Ameghino, 1904 (Xenarthra, Tardigrada) from the Serravallian (Middle Miocene) of Bolivia; chronological and biogeographical implications. Journal of Mammalian Evolution 25 (3), 2018, pp. 327-337, doi: 10.1007 / s10914-017-9348-y
  5. ↑ Julia V. Tejada-Lara, Rodolfo Salas-Gismondi, François Pujos, Patrice Baby, Mouloud Benammi, Stéphane Brusset, Dario de Franceschi, Nicolas Espurt, Mario Urbina and Pierre-Olivier Antoine: Life in Proto-Amazonia: Middle Miocene mammals from the Fitzcarrald arch (Peruvian Amazonia). Palaeontology 58 (2), 2015, pp. 341-378
  6. ↑ 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
  7. ↑ Timothy J. Gaudin: Phylogenetic relationships among sloths (Mammalia, Xenarthra, Tardigrada): the craniodental evidence. Zoological Journal of the Linnean Society 140, 2004, pp. 255-305
  8. ↑ 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
  9. ↑ 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
  10. ^ 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.
  11. ↑ Florentino Ameghino: Nuevas especies de mammíferos cretáceos y terciarios de la República Argen Tina. Anales de la Sociedad Científica Argentina 58, 1904, pp. 225–291 (pp. 281–282) ( [1] )
  12. ↑ Gerardo De Iuliis, Guillermo H. Ré and Sergio F. Vizcaíno: The Toro Negro megatheriine (Mammalia, Xenarthra): A new species of Pyramiodontherium and a review of Plesiomegatherium. Journal of Vertebrate Paleontology 24 (1), 2004, pp. 214-227
  13. ↑ Diego Brandoni and Gerardo De Iuliis: A new genus for the Megatheriinae (Xenarthra, Phyllophaga, Megatheriidae) from the Arroyo Chasicó Formation (Upper Miocene) of Buenos Aires Province, Argentina. New Yearbook for Geology and Paleontology Abhandlungen 244 (1), 2007, pp. 53–64
  14. Jump up ↑ Diego Brandoni and Alfredo A. Carlini: On the presence of Pyramiodontherium (Mammalia, Xenarthra, Megatheriidae) in the Late Miocene of Northeastern Argentina and its biogeographical implications. Revista Italiana di Paleontologia e Stratigrafia 115 (1), 2009, pp. 111-123
  15. ^ Diego Brandoni, Jaime E. Powell, and Osvaldo E. González: Anisodontherium from the Late Miocene of North-Western Argentina. Acta Palaeontologica Polonica 57 (2), 2012, pp. 241-249
  16. ^ Alfredo A. Carlini, Diego Brandoni and Rodolfo Sánchez: First Megatheriines (Xenarthra, Phyllophaga, Megatheriidae) from the Urumaco (Late Miocene) and Codore (Pliocene) Formations, Estado Falcón, Venezuela. Journal of Systematic Palaeontology 4 (3), 2006, pp. 269-278
  17. ^ Alfredo A. Carlini, Diego Brandoni and Rodolfo Sánchez: Additions to the knowledge of Urumaquia robusta (Xenarthra, Phyllophaga, Megatheriidae) from the Urumaco Formation (Late Miocene), Estado Falcón, Venezuela. Paläontologische Zeitschrift 82 (2), 2008, pp. 153–162
  18. ^ Alfredo A. Carlini, Diego Brandoni, Rodolfo Sánchez and Marcelo R. Sánchez-Villagra: A new Megatheriinae skull (Xenarthra, Tardigrada) from the Pliocene of Northern Venezuela - implications for a giant sloth dispersal to Central and North America. Palaeontologia Electronica 2018, S. 21.2.16A, doi: 10.26879 / 771
  19. ↑ H. Gregory McDonald: Xenarthrans: Pilosans. In: Richard F. Kay, Richard H. Madden, Richard L. Cifelli, and John J. Flynn (Eds.): Vertebrate Paleontology in the Neotropics. The Miocene Fauna of La Venta, Colombia. Smithsonian Institution Press, Washington, 1997, pp. 233-245