''Rhyphodon'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

notoungulate Notoungulata is an extinct order of ungulates that inhabited South America from the early Paleocene to the end of the Pleistocene, living from approximately 61 million to 11,000 years ago. Notoungulates were morphologically diverse, with forms re ...

, who lived from the Middle to the Late

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

in what is today

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

Description

This genus is only known from cranial remains, but by comparing it with some of its better known relatives, it is possible to reconstruct its appearance. ''Rhyphodon'' probably was a medium-sized herbivore, the size of a large

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the gray wolf. Also called the domestic dog, it was selectively bred from a population of wolves during the Late Pleistocene by hunter-gatherers. ...

. The skull, more than 20 centimeters long, had a relatively short muzzle and a primitive and complete set of teeth. The teeth shared similarities with those of its relative '' Periphragnis'', from which they were distinguished by a lack of cingulum and a greater coverage of wrinkled enamel on the molars. A fossil attributed to ''Rhyphodon'' preserves an endocranial cast, allowing researchers to reconstruct the shape of various structures of the animal brain; the endocranium was similar to other archaic

ungulate Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with Hoof, hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined ...

s such as '' Phenacodus'' and ''

Notostylops ''Notostylops'' ("south pillar face") is a genus of extinct South American ungulates from Eocene Argentina. Fossils of the genus have been found in the Sarmiento, Casamayor, Andesitas Huancache and Koluel Kaike Formations.

'', but with some observable differences. ''Rhyphodon'' had slightly smaller olfactory bulbs than the basal notoungulate ''Notostylops'', and those were folded downward. The cerebellum was larger and as broad as it was long, while the piriform lobes were laterally expanded. Compared to ''Notostylops'', the cerebral hemispheres were less convoluted. There was no separate optic canal and no posterolateral cerebral venous canal.

Classification

The genus ''Rhyphodon'' was first described in 1899 by

Santiago Roth Santiago Roth (14 June 1850 – 4 August 1924) was a Swiss Argentine paleontologist and academic known for his fossil collections and Patagonian expeditions. Life Kaspar Jakob (Spanish: Santiago) was born and raised in Herisau, Canton Appenzell ...

, based on fossil remains initially thought to be dating from the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

and only later recognized as dating back to the Eocene. The type species, ''Rhyphodon lankesteri'' was discovered near Lago Musters in

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

in Late Eocene terrains. An earlier species, ''Rhyphodon angusticephalus'', is known from the Cañadón Colorado, in the

Chubut Province Chubut ( from Tehuelche language, Tehuelche 'transparent'; ) is a provinces of Argentina, province in southern Argentina, situated between the 42nd parallel south (the border with Río Negro Province), the 46th parallel south (bordering Santa ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. ''Rhyphodon'' has been historically placed within the family Isotemnidae, the earliest and least specialized known family of toxodonts. However, this group may have been paraphyletic, and constituted of various forms more or less specialized within Toxodonta; according to a 2011 study, ''Rhyphodon'' is related to the genus '' Pampahippus''.Billet, Guillaume (2011). "Phylogeny of the Notoungulata (Mammalia) based on cranial and dental characters". Journal of Systematic Palaeontology. 9 (4): 481–97. doi:10.1080/14772019.2010.528456. OCLC 740994816.

References and bibliography

*G. G. Simpson. 1948. The beginning of the age of mammals in South America. Part I. Bulletin of the American Museum of Natural History 91:1-232 *G. G. Simpson. 1967. The beginning of the age of mammals in South America. Part II. Bulletin of the American Museum of Natural History 137:1-260 {{Taxonbar, from=Q60977375 Toxodonts Eocene mammals of South America Paleogene Argentina Fossils of Argentina Fossil taxa described in 1899 Prehistoric placental genera