Mixotoxodon

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Mixotoxodon
Live reconstruction of mixotoxodon

Live reconstruction of mixotoxodon

Temporal occurrence
Old Pleistocene to New Pleistocene
1.806 to 0.012 million years
Locations
Systematics
South American ungulates (Meridiungulata)
Notoungulata
Toxodontia
Toxodontidae
Toxodontinae
Mixotoxodon
Scientific name
Mixotoxodon
Van Frank , 1957
Art
  • Mixotoxodon larensis Van Frank , 1957

Mixotoxodon was a genus of the extinct Notoungulata that was foundin Central America , the northern half of South America, and southern North America during the Pleistocene . The only known species of the so far monotypical genus is Mixotoxodon larensis .

Research history and etymology

The first description of the genus and type species was carried out in 1957 by Richard Van Frank based on evidence already in 1938/39 by the US paleontologist George Gaylord Simpson near San Miguel in the eastern part of the district of Jiménez in the Venezuelan state of Lara had been recovered to whose name the additional species larensis is formed. The genus name Mixotoxodon is derived from the ancient Greek μῖξις mixis 'mixture' and the already existing genus name Toxodon for the type genus Toxodontidae. Van Frank chose the name to indicate a peculiarity in the dentition of the lower jaw, which in his opinion had features of two subfamilies, both the Toxodontinae and the Haplodontheriinae.

The Pleistocene mammal remains in the vicinity of San Miguel were discovered by the Salesian monk , teacher and historian Hermano Nectario María. In September 1938 Simpson traveled to Lara at the invitation of the Venezuelan government and accompanied by his second wife Anne Roe to dig for fossils with Nectario María near San Miguel. The excavations were supported by locals from the vicinity of the sites and produced fossil evidence for at least two species from the Toxodontidae family , a giant sloth of the genus Eremotherium , teeth of horses and osteoderms of glyptodons . The evidence associated with Mixotoxodon from these excavations is now at the American Museum of Natural History (AMNH). A mandibular fragment with the inventory number AMNH 48854 was identified as the holotype .

The skull of a representative of the Toxodontidae was found in the province of Alajuela in Costa Rica as early as 1934 and initially described as belonging to the genus Toxodon . It was not until 1993 that the fossil was recognized as Mixotoxodon larensis . At this point in time, of the originally almost complete skull, which was kept under inventory number CFM 846 at the Museo Nacional de Costa Rica (MNCR), only a meager remnant of the dentate upper jaw and a few individual teeth remained. However, a sketch and photos of the original fossil published in 1939 still allowed conclusions to be drawn about the anatomy of the skull.

features

Skull reconstruction based on the known fossil finds

Mixotoxodon resembled a modern rhinoceros in its outer shape . Van Frank describes the size as comparable to that of Toxodon platensis , which would correspond to a head-trunk length of 2.9 m with a body mass of more than a ton . Other authors give body masses of up to 3.8 tons for mixotoxodon .

Although of a similar size, Mixotoxodon differs from Toxodon in particular in its straight, approximately cylindrical snout . While the lower jaw of Toxodon widens significantly at its distal end, similar to today's hippos , in Mixotoxodon it is almost straight.

Further, generic features relate to special features in the form of the teeth. The premolars do not have any enamel on the tongue side . The first lower molar m1 shows a clear enamel fold ("meta-entoconid fold") between the metaconid and entoconid (two cusps of the chewing surface of the lower molars), which in the second lower molar (m2) is only very weak or completely absent.

Only very few postcranial skeletal elements are known that can be assigned to Mixotoxodon . Van Frank mentions in his first description a Axiswirbel , a radius bone , five Elle bone , a kneecap and a heel bone that may be mixotoxodon larensis be assigned.

Geographical and temporal distribution

Geographical distribution of the known fossil finds

In addition to the type locality in Venezuela, Van Frank mentioned in his first description the Department of Copán in Honduras and the Department of San Miguel in El Salvador as further areas where Mixotoxodon larensis was found .

By 2008, numerous sites were known that stretched from southern Mexico via Guatemala , Honduras, El Salvador, Nicaragua , Costa Rica and Panama to northern South America. In South America itself, finds from Venezuela, Colombia , Brazil and Bolivia were known.

In 2011 and 2013, finds of Mixotoxodon from the province of Santiago del Estero in Argentina and the south of Texas were known, which significantly expanded the range to the south and north.

The oldest fossil records of Mixotoxodon come from sites in El Salvador and possibly also Costa Rica, which are placed in the Old Pleistocene (Early Irvingtonian (about 1.8–1.0 Ma ) of the North American land mammal zoning  NALMA ). Most of the finds come from the Middle to Young Pleistocene ( Rancholabrean (about 0.5-0.012 Ma) of the North American land mammal zoning NALMA). The finds from Argentina and Texas can also be assigned to the latter period.

Systematics

 Toxodontidae  

 Proadinotherium


   
 Nesodontinae  

 Adinotherium


   

 Nesodon



 Toxodontinae  

 Palyeidodon


   

 Hyperoxotodon


   




 Xotodon


   

 Calchaquitherium



   

 Pisanodon


   

 Pericotoxodon


   

 Paratrigodon


   

 Trigodon






   


 Nonotherium


   

 Posnanskytherium



   

 Andinotoxodon


   

 Hoffstetterius


   

 Ocnerotherium


   

 Toxodon


   

 Dinotoxodone



Template: Klade / Maintenance / 3




   

 Piauhytherium


   

 Gyrinodon


   

 Falcontoxodon


   

 Mixotoxodon


Template: Klade / Maintenance / 3







Template: Klade / Maintenance / Style
Systematic position of Mixotoxodon within the Toxodontidae; after Carrillo et al., 2018

The internal systematics of the Toxodontidae, and thus also the systematic position of Mixotoxodon , has by no means been conclusively clarified.

At the time of the first description of Mixotoxodon , the Toxodontidae were divided into three subfamilies, the Nesodontinae , the Toxodontinae and the Haplodontinae, the latter two being distinguished among other things by the fact that the Toxodontinae had a meta-entoconide fold on the lower molars m1–2 was present, while this feature was absent on the lower molars m1–3 of the Haplodontheriinae. Van Frank now had a taxon that seemed to combine features of both subfamilies and referred to it in the choice of the generic name. He decided to put Mixotoxodon in the subfamily of the Toxodontinae and at the same time raised the question of whether a distinction between Toxodontinae and Haplodontinae actually made sense.

Regardless of Van Frank's doubts, the Toxodontidae family was expanded by two additional subfamilies, the Xotodontinae and the Dinotoxodontinae, by 1990. The validity of the Dinotoxodontinae was questioned again in 1993 by the French paleontologist Pierre-Antoine Saint-André . At the same time he placed Mixotoxodon in the subfamily of the Haplodontheriinae.

In a comprehensive phylogenetic analysis, Norma L. Nasif et al. , 2000 explain that, apart from the Nesodontinae, none of the propagated subfamilies formed a monophyletic group . They therefore united all taxa that were not assigned to the Nesodontinae in a common subfamily Toxodontinae. The division of the Toxodontidae into only two subfamilies was confirmed by later editors, but there is still no general consensus on the internal systematics of the Toxodontinae .

Nasif et al., 2000 found Mixotoxodon in a common clade with Calchaquitherium , Xotodon and Nonotherium . Analía M. Forasiepi et al., 2014 identified Mixotoxodon as the sister taxon of Calchaquitherium , but found both genera in a common clade with Trigodon and Paratrigodon , as well as Pericotoxodon , Pisanodon and Posnanskytherium , while Xotodon and Nonotherium formed a separate subclade after their analysis . In an analysis published by Ricardo A. Bonini et al., 2017, Mixotoxodon was also shown to be a sister taxon of Calchaquitherium . The two genera together with Pisanodon , Trigodon and Paratrigodon , as well as Pericotoxodon, formed their own partial clade, which was accompanied by Xotodon and Nonotherium as each independent sister taxa. The genus Posnanskytherium is found in this analysis in a different subclade, apart from it.

The cladogram presented here follows an analysis published by Juan D. Carrillo et al., 2018. Mixotoxodon is found in this analysis together with Piauhytherium , Gyrinodon and Falcontoxodon in a common partial clade within the Toxodontinae. The genera Xotodon , Calchaquitherium , Trigodon , Paratrigodon , Pericotoxodon and Pisanodon form a separate partial clade and the genera Nonotherium and Posnanskytherium appear as members of a third partial clade within the Toxodontinae.

Paleecology

Mixotoxodon was, like all representatives of the Toxodontidae, probably a pure herbivore. The high-crowned and constantly growing, rootless teeth ( hypselodontia ) were interpreted as an indication of grasses ( C 4 plants ) as preferred food and, accordingly, a largely open savannah landscape as a habitat. The δ 13 C - isotope signatures in the enamel of mixotoxodon but -Funden from Panama and Honduras demonstrate a substantial amount of C 3 plants in the food spectrum and the corresponding habitats are called C 3 plants dominated forests with largely closed canopy, seasonal droughts and interpreted only subordinate grassland areas dominated by C 4 plants .

Mixotoxodon is the only known representative of the Notoungulata that reached North America as part of the Great American Fauna Exchange . Mixotoxodon fossils occur regularly together with fossil remains of Eremotherium and the genus Equus, especially in sites of the younger Pleistocene (Rancholabrean) . The conspicuous common occurrence of these taxa was also called "EME-accumulation" (after the participating genera Eremotherium , Mixotoxodon and Equus ) and seems to represent a typical association of fauna of the younger Pleistocene in this area.

literature

  • E. Anderson: Who's who in the Pleistocene: a mammalian bestiary. In: Paul S. Martin , Richard G. Klein (Eds.): Quaternary Extinctions. A Prehistoric Revolution. The University of Arizona Press, Tucson AZ 1984, ISBN 0-8165-1100-4 , pp. 40-89.
  • Alberto L. Cione, Eduardo P. Tonni, Leopoldo Soibelzon: The Broken Zig-Zag: Late Cenozoic large mammal and tortoise extinction in South America. In: Revista del Museo Argentino de Ciencias Naturales. 5, 1, 2003, ISSN  1514-5158 , pp. 1-19, (PDF) .

Individual evidence

  1. ↑ a b c d e f g h i R. Van Frank: A Fossil Collection from Northern Venezuela: 1. Toxodontidae (Mammalia, Notoungulata). In: American Museum Novitates , number 1850, 1957, 38 p., ( Digitized version ).
  2. ^ A b GG Simpson: Research in Venezuela. In: Science , Volume 90, Number 2331, 1939, pp. 210-211, doi : 10.1126 / science.90.2331.210 .
  3. ^ MR Sánchez-Villagra: A short history of the study of Venezuelan vertebrate fossils. In: MR Sánchez-Villagra, OA Aguilera & AA Carlini (Eds.): Urumaco and Venezuelan Paleontology: The Fossil Record of the Northern Neotropics. Indiana University Press, Bloomington, Indiana, 2010, ISBN 978-0-253-35476-1 , pp. 9-18 ( digitized version )
  4. ↑ a b CA Laurito: Análisis topológico y sistemático del Toxodonte de Bajo de los Barrantes, provincia de Alajuela, Costa Rica. In: Revista Geológica de América Central , Volume 16, 1993, pp. 61-68, ( digitized ).
  5. ^ A b c SG Lucas, GE Alvarado & E. Vega: The Pleistocene mammals of Costa Rica. In: Journal of Vertebrate Paleontology , Volume 17, Number 2, 1997, pp. 413-427, ( digitized ).
  6. ↑ a b c AD Rincón: New remains of Mixotoxodon larensis Van Frank 1957 (Mammalia: Notoungulata) from Mene de Inciarte tar pit, north-western Venezuela. In: Interciencia , Volume 36, Number 12, 2011, pp. 894-899, ( digitized ).
  7. ^ RA Fariña, SF Vizcaíno & MS Bargo: Body mass estimation in Lujanian (Late Pleistocene-Early Holocene of South America) mammal megafauna. In: Mastozoologia Neotropical , Volume 5, Number 2, 1998, pp. 87-108, ( digitized version ).
  8. ^ M. Buckley: Ancient collagen reveals evolutionary history of the endemic South American 'ungulates'. In: Proceedings of the Royal Society B , Volume 282, 2015, 20142671, doi : 10.1098 / rspb.2014.2671 .
  9. ↑ A. Elissamburu: Estimación de la masa corporal en géneros del Orden Notoungulata. In: Estudios Geológicos , Volume 68, Number 1, 2012, pp. 91–111, ( digitized version ).
  10. ^ A b c GS Morgan: Vertebrate Fauna and Geochronology of the Great American Biotic Interchange in North America. In: SG Lucas, GS Morgan, JA Spielmann & DR Prothero (eds.): Neogene Mammals , New Mexico Museum of Natural History and Science Bulletin 44, Albuquerque, 2008, pp. 93-140, ( digitized ).
  11. ↑ a b NR Chimento & FL Agnolin: Mamíferos del pleistoceno superior de santiago del estero (Argentina) y sus afinidades paleobiogeográficas. In: Papéis Avulsos de Zoologia , Volume 51, Number 6, 2011, pp. 83-100, ( digitized version ).
  12. ^ A b EL Lundelius Jr., VM Bryant, R. Mandel, KJ Thies & A. Thoms: The First Occurrence of a Toxodont (Mammalia, Notoungulata) in the United States. In: Journal of Vertebrate Paleontology , Volume 33, Number 1, 2013, pp. 229-232, ( digitized ).
  13. ^ A b JD Carrillo, E. Amson, C. Jaramillo, R. Sánchez, L. Quiroz, C. Cuartas, AF Rincón & MR Sánchez-Villagra: The Neogene Record of Northern South American Native Ungulates. In: Smithsonian Contributions to Paleobiology , number 101, 2018, pp. 1–67, ( digitized ).
  14. ↑ P.-A. Saint-André: Hoffstetterius imperator ng, n. Sp. du Miocène supérieur de l'Altiplano bolivien et le statut des Dinotoxodontinés (Mammalia, Notoungulata). In: Comptes rendus de l'Académie des sciences Series 2 , Volume 316, Number 4, 1993, pp. 539-545.
  15. ↑ a b c NL Nasif, S. Musalem & E. Cerdeño: A new toxodont from the Late Miocene of Catamarca, Argentina, and a phylogenetic analysis of the Toxodontidae. In: Journal of Vertebrate Paleontology , Volume 20, Number 3, 2000, pp. 591-600, ( digitized ).
  16. ↑ AM Forasiepi, E. Cerdeño, M. Bond, GI Schmidt, M. Naipauer, FR Straehl, AG Martinelli, AC Garrido, MD Schmitz & JL Crowley: New toxodontid (Notoungulata) from the Early Miocene of Mendoza, Argentina. In: Paläontologische Zeitschrift , Volume 89, Number 3, 2014, pp. 611–634, ( digitized version ).
  17. ^ RA Bonini, GI Schmidt, MA Reguero, E. Cerdeño, AM Candela & N. Solís: First record of Toxodontidae (Mammalia, Notoungulata) from the late Miocene – early Pliocene of the southern central Andes, NW Argentina. In: Journal of Paleontology , Volume 91, Number 3, 2017, pp. 566-576, ( digitized version ).
  18. ^ A. Rancy: Fossil Mammals of the Amazon as a Portrait of a Pleistocene Environment. In: JF Eisenberg & KH Redford (eds.): Mammals of the Neotropics, Volume 3: Ecuador, Bolivia, Brazil , University of Chicago Press, 1999, ISBN 0-226-19542-2 , pp. 20-26, ( reading sample ).
  19. ↑ SG Lucas: Late Pleistocene Mammals from El Hatillo, Panama. In: Revista Geológica de América Central , Volume 50, 2014, pp. 139–151, ( digitized ).

Web links

Commons : Mixotoxodon  - collection of images, videos and audio files