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Theosodon Temporal range: Early-Mid Miocene (Colhuehuapian-Laventan) 21.0–11.8 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Theosodon patagonicum skull cast of a specimen from Patagonia, Argentina.
T. garretorum, 1901 skeleton illustration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	†Litopterna
Family:	†Macraucheniidae
Subfamily:	†Cramaucheniinae
Genus:	†Theosodon Ameghino, 1887
Type species
†Theosodon lydekkeri Ameghino, 1887
Species
T. arozquetai McGrath et al., 2018 T. fontanae Ameghino, 1891 T. garretorum Scott, 1910 T. gracilis Ameghino, 1891 T. karaikensis Ameghino, 1904 T. lallemanti Mercerat, 1891 T. lydekkeri Ameghino, 1887 T. patagonicum (Ameghino, 1891)
Synonyms
Pseudocoelosoma Ameghino, 1891

Theosodon is an extinct genus of litoptern mammal from the Early to Middle Miocene of South America.

Description

Theosodon was long-legged with a long neck resembling modern llamas or guanacos. It was large for a litoptern, reaching up to 2 metres (6.6 ft) in length and weighing up to 125–170 kilograms (276–375 lb).

It had a long neck and tapir-like, three-toed feet, and like other litopterns and modern horses, tapirs and rhinos, it bore its weight on its middle toes.

Extraordinarily, rather than having nostrils at the front of its head, Theosodon had its nostrils on the top of its snout, halfway between the forehead and the tip of the snout, and its nostrils pointed upwards rather than forwards, possibly as an adaptation for browsing on prickly vegetation.

History and species

Theosodon has been known since the 19th century, and by 1910 seven species had been described within the genus, all from the early Miocene Santa Cruz Formation in Argentina. The name Theosodon means "god tooth". The first fossils were only dental remains, but it is unknown why this name was given. Though seven species had originally been described, the exact number of discovered species remains uncertain as it varies between different authors. There are either ten or seven species, and in 2014 Schmidt and Ferrero put forward that the genus needed a full taxonomic revision due to this issue.

"Theosodon" hystatus

In 1931, fossils found in the late Miocene Arroyo Chasicó Formation were assigned to the genus under the name Theosodon hystatus. This was questioned in 1995, and in 2014 it was moved to the genus Paranauchenia due to similarities to the species Paranauchenia denticulata. This move was supported by phylogenetic analysis that showed the two species formed monophyletic clade.

"Theosodon" arozquetai

In 2018 a new species of macraucheniid litoptern was described based on the partial remains of a skull and two metapodials. A phylogenetic analysis tentatively linked the species to Theosodon as a sister clade and it was named Theosodon arozquetai pending revision. Its body mass was estimated to be somewhere from 80.8 to 116.2 kilograms (178 to 256 lb). It dated to the middle Miocene, about 13 million years ago, somewhat later than most other Theosodon species.

Classification

Theosodon is in the subfamily Cramaucheniinae within the family Macraucheniidae. A phylogenetic analysis of the family in 2014 found that Cramaucheniinae is a paraphyletic group, and that Theosodon is a sister clade to the subfamily Macraucheniinae, the least primitive of the members of Cramaucheniinae.

Paleobiology

Theosodon was a terrestrial and cursorial animal that may have lived in both forests and more open environments. Due to its size and its long neck, Theosodon was likely a high browser, stripping leaves off of trees and shrubs high off the ground. Theosodon had a slender jaw compared to many other litopterns, indicating its food was softer, such as dicotyledons. As its nostrils are upward-facing and at the centre of its head rather than the front, Theosodon may have used this adaptation to feed on thorny plants. Some modern animals such as giraffes feed on thorny plants, and their nostrils are also further back and face more upwards than forwards.

Other fossils were found in the Sarmiento Formation of Argentina, the Yecua Formation of Bolivia, the Honda Group of Colombia, the Chucal and Río Frías Formations of Chile and the Ipururo Formation of Peru.

References

1. Scott, William B. (1910). The Litopterna of the Santa Cruz Beds. Reports of the Princeton University Expeditions to Patagonia, 1896–1899. Princeton: Princeton University Press.
2. ^ Croft, Darin A. (18 August 2016). "Chucal, Chile". Horned Armadillos and Rafting Monkeys: The Fascinating Fossil Mammals of South America. Indiana University Press. pp. 104–117. ISBN 978-0-253-02084-0.
3. Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. p. 247. ISBN 1-84028-152-9.
4. ^ Schmidt, Gabriela I.; Ferrero, Brenda S. (September 2014). "Taxonomic Reinterpretation of Theosodon hystatus Cabrera and Kraglievich, 1931 (Litopterna, Macraucheniidae) and Phylogenetic Relationships of the Family". Journal of Vertebrate Paleontology. 34 (5): 1231–1238. Bibcode:2014JVPal..34.1231S. doi:10.1080/02724634.2014.837393. hdl:11336/18953.
5. Fonseca, Lurdes (31 May 2018). "Just out | Two new macraucheniids (Mammalia: Litopterna) from the late middle Miocene (Laventan South American Land Mammal Age) of Quebrada Honda, Bolivia @ Journal of Vertebrate Paleontology | Paleowire". Retrieved 6 June 2018.
6. Cassini, Guillermo; Vizcaíno, Sergio (9 December 2011). "An Approach to the Biomechanics of the Masticatory Apparatus of Early Miocene (Santacrucian Age) South American Ungulates (Astrapotheria, Litopterna, and Notounguluata): Moment Arm Estimation Based on 3D Landmarks". Journal of Mammalian Evolution. 19 (1): 9–25. doi:10.1007/s10914-011-9179-5. hdl:11336/17970.
7. Cassini, Guillermo (April 2013). "Skull Geometric Morphometrics and Paleoecology of Santacrucian (Late Early Miocene; Patagonia) Native Ungulates (Astrapotheria, Litopterna, and Notoungulata)". Ameghiniana. 50 (2): 193–216. doi:10.5710/AMGH.7.04.2013.606. hdl:11336/26393. S2CID 128999112.
8. Soria, Miguel Fernando (1981). "Los Litopterna del Colhuehuapense (Oligoceno tardío) de la Argentina". Revista del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia." (3): 1–54.
9. Kramarz, Alejandro G.; Bond, Mariano (2005). "Los Litopterna (Mammalia) de la Formación Pinturas, Mioceno Temprano-Medio de Patagonia". Ameghiniana (in Spanish). 42 (3): 611–625. ISSN 1851-8044.
10. Theosodon at Fossilworks.org

v t e Genera of South American native ungulates
Kingdom: Animalia Phylum: Chordata Class: Mammalia Superorder: Laurasiatheria
Xenungulata, Pyrotheria, Astrapotheria, and other minor groups †Kollpaniidae? Andinodus Molinodus Pascualodus? Pucanodus Simoclaenus Tiuclaenus †Didolodontidae Didolodus Enneoconus Ernestokokenia Escribania? Lamegoia Paulogervaisia Raulvaccia Ricardocifellia Saltaodus Umayodus Xesmodon †Protolipternidae Asmithwoodwardia Miguelsoria Protolipterna †Xenungulata †Carodniidae Carodnia Etayoa Notoetayoa Rodcania †Pyrotheria †Colombitheriidae Colombitherium Proticia †Pyrotheriidae Baguatherium Berracotherium Carolozittelia Griphodon Propyrotherium Pyrotherium †Astrapotheria Eoastrapostylops †Trigonostylopidae Shecenia Tetragonostylops Trigonostylops †Astrapotheriidae Antarctodon Astrapodon Comahuetherium Liarthrus Maddenia Parastrapotherium †Albertogaudryinae Albertogaudrya Astraponotus †Astrapotheriinae Astrapothericulus Astrapotherium Scaglia †Uruguaytheriinae Granastrapotherium Hilarcotherium Uruguaytherium Xenastrapotherium
Litopterna †Eulitopterna †Adianthidae Adianthus Proadiantus Proectocion? Proheptaconus Thadanius Tricoelodus †Macraucheniidae Polymorphis †Cramaucheniinae Caliphrium Coniopternium Cramauchenia Llullataruca Phoenixauchenia Pternoconius Theosodon †Macraucheniinae Cullinia Huayqueriana Macrauchenia Macraucheniopsis Micrauchenia Oxyodontherium Paranauchenia Promacrauchenia Scalabrinitherium Windhausenia Xenorhinotherium †Proterotherioidea †Anisolambdidae †Anisolambdinae Anisolambda Eolicaphrium Guilielmofloweria Lambdaconops Paranisolambda Polyacrodon Protheosodon Wainka †Sparnotheriodontinae Heteroglyphis Notiolofos Phoradiadius Sparnotheriodon Victorlemoinea †Proterotheriidae Mesolicaphrium Neodolodus Olisanophus Promylophis Prothoatherium Pseudobrachytherium Salladolodus †Megadolodinae Bounodus Megadolodus †Proterotheriinae Anisolophus Brachytherium Diadiaphorus Diplasiotherium Eoauchenia Epecuenia Epitherium Lambdaconus Neobrachytherium Neolicaphrium Paramacrauchenia Picturotherium Prolicaphrium Proterotherium Tetramerorhinus Thoatheriopsis Thoatherium Uruguayodon Villarroelia †Notopterna †Amilnedwardsiidae Amilnedwardsia Ernestohaeckelia Rutimeyeria †Indaleciidae Adiantoides Indalecia †Notonychopidae Notonychops Requisia Incertae sedis Kyraodus Proacrodon
Notoungulata incertae sedis Acoelodus Archaeogaia Carolodarwinia Perutherium †Notioprogonia Satshatemnus Seudenius †Henricosborniidae Henricosbornia Nanolophodon Othnielmarshia Peripantostylops Simpsonotus †Notostylopidae Boreastylops Chilestylops Edvardotrouessartia Homalostylops Notostylops Otrhonia Parastylops †Toxodontia †Homalodotheriidae Asmodeus Chasicotherium Homalodotherium Trigonolophodon †Isotemnidae Anisotemnus Coelostylodon Distylophorus Hedralophus Isotemnus Lophocoelus Pampatemnus Periphragnis Pleurocoelodon Pleurostylodon Rhyphodon Thomashuxleya †Eutoxodontia †Leontiniidae Anayatherium Ancylocoelus Colpodon Coquenia Elmerriggsia Gualta Henricofilholia Huilatherium Leontinia Martinmiguelia Purperia? Scarrittia Taubatherium Termastherium †Notohippidae Acoelohyrax Argyrohippus Deuterotherium? Edvardocopeia Eomorphippus Eurygenium Mendozahippus Moqueguahippus Morphippus Nesohippus Notohippus Pampahippus Pascualihippus Patagonhippus Perhippidion Plexotemnus Puelia Purperia? Rhynchippus Rosendo Stilhippus Teushentherium Trimerostephanos †Toxodontidae †Nesodontinae Adinotherium Nesodon Proadinotherium †Toxodontinae Abothrodon Andinotoxodon Calchaquitherium Ceratoxodon Charruatoxodon Dinotoxodon Eutomodus Falcontoxodon Gyrinodon Haplodontherium Hemixotodon Hoffstetterius Hyperoxotodon Mesenodon Mesotoxodon Minitoxodon Mixotoxodon Neoadinotherium Neotoxodon Nesodonopsis Nonotherium Ocnerotherium Palyeidodon Paratrigodon Pericotoxodon Piauhytherium Pisanodon Plesiotoxodon Posnanskytherium Prototrigodon Stenotephanos Stereotoxodon Toxodon Toxodontherium Trigodon Trigodonops Xotodon †Typotheria Campanorco Griphotherion †Archaeopithecidae Archaeopithecus Teratopithecus †Oldfieldthomasiidae Allalmeia Brachystephanus Camargomendesia Colbertia Dolichostylodon Itaboraitherium Kibenikhoria Maxschlosseria Oldfieldthomasia Paginula Suniodon Tsamnichoria Ultrapithecus Xenostephanus †Interatheriidae Antofagastia Ignigena Johnbell Munizia Punapithecus †Interatheriinae Archaeophylus Argyrohyrax Boleatherium Brucemacfaddenia Caenophilus Choichephilum Cochilius Eopachyrucos Federicoanaya Interatherium Juchuysillu Miocochilius Neoicochilus Patriarchus Proargyrohyrax Progaleopithecus Protypotherium Santiagorothia †Notopithecinae Antepithecus Guilielmoscottia Notopithecus Transpithecus †Mesotheriidae Fiandraia? Trachytherus †Mesotheriinae Altitypotherium Caraguatypotherium Eotypotherium Eutypotherium Hypsitherium Mesotherium Microtypotherium Plesiotypotherium Pseudotypotherium Rusconitherium Typotheriopsis †Archaeohyracidae Archaeohyrax Archaeotypotherium Bryanpattersonia Eohyrax Pascualhyrax Protarchaeohyrax Pseudhyrax Punahyrax †Hegetotheriidae †Hegetotheriinae Ethegotherium Hegetotheriopsis Hegetotherium Hemihegetotherium Prohegetotherium Pseudohegetotherium Sallatherium †Pachyrukhinae Medistylus Propachyrucos Prosotherium Tremacyllus †Pachyrukhini Pachyrukhos Paedotherium Tremacyllus

• Macraucheniids
• Miocene mammals of South America
• Laventan
• Colloncuran
• Friasian
• Santacrucian
• Colhuehuapian
• Neogene Argentina
• Fossils of Argentina
• Neogene Bolivia
• Fossils of Bolivia
• Neogene Chile
• Fossils of Chile
• Neogene Colombia
• Fossils of Colombia
• Honda Group, Colombia
• Neogene Peru
• Fossils of Peru
• Fossil taxa described in 1887
• Taxa named by Florentino Ameghino
• Prehistoric placental genera
• Golfo San Jorge Basin
• Sarmiento Formation
• Austral or Magallanes Basin
• Santa Cruz Formation