''Hemihegetotherium'' 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 ...

of hegetotheriid notoungulate that lived from the Middle to the Late

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

of what is now

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 ...

Description

It was a medium-sized animal and had long legs. Although not as those of modern

lagomorph The lagomorphs () are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (rabbits and hares) and the Ochotonidae ( pikas). There are 110 recent species of lagomorph, of which 109 species in t ...

s, to which it was, in other regards, superficially similar. Like some of its relatives, the first pair of incisors of ''Hemihegetotherium'' was large, and it had simplified but high-crowned (hypsodont) molars and

premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...

s. The structure of those teeth were so simplified in ''Hemihegetotherium'' that they consisted of simply a curved cylinder of enamel filled with dentin ; compared to ''Hegetotherium'', the molars were more convex, with a semi-elliptical section. However, those teeth had pointed cusps along their outer margin. ''Hemihegetotherium'' had a tibia and fibula solidly fused together in their extremities, both distal and proximal.

Classification

The genus ''Hemihegetotherium'' was first described in 1914 by

Gaetano Rovereto Gaetano Rovereto (15 November 1870 – 23 November 1952) was an Italian geologist and paleontologist who, though critical of applying theories to geology, favoured cyclical processes to explain geological formations. He published on geomorphology, a ...

, based on fossil remains discovered in the Las Floras Formation (

San Juan Province, Argentina San Juan Province () is a Provinces of Argentina, province of Argentina, located in the western part of the country. Neighbouring provinces are, moving clockwise from the north, La Rioja Province (Argentina), La Rioja, San Luis Province, San Lui ...

) ; the type species is ''Hemihegetotherium achataleptum''. The other species are ''H. torresi'', from the Late Miocene of Argentina, and ''H. trilobus'', from the Middle Miocene of Quebrada Honda in

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

, this last species distinguished from the other species of the genus by the presence of a trilobed third lower molar, hence its species name. ''H. tantillum'', described in 2019, shared similarities with ''H. trilobus'', and was found 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 ...

. ''Hemihegetotherium'' was a member of

Hegetotheriidae Hegetotheriidae is an extinct family of notoungulate mammals known from the Oligocene through the Pliocene of South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a c ...

(hence its generic name, meaning "half '' Hegetotherium''"), a group of usually small notoungulates with the superficial appearance of

rodent Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...

s or

hare Hares and jackrabbits are mammals belonging to the genus ''Lepus''. They are herbivores and live Solitary animal, solitarily or in pairs. They nest in slight depressions called forms, and their young are precociality, able to fend for themselves ...

s. ''Hemihegetotherium'' was similar but less specialized than the eponymous genus ''Hegetotherium''.

Paleoecology

''Hemihegetotherium'' was a terrestrial herbivore, probably consumming low and particularly fibrous plants, both in open and forested areas. The limbs of ''Hemihegetotherium'' may have been suitable both for running and digging.

Bibliography

*Croft DA, Anaya F (2006) A new middle Miocene hegetotheriid (Notoungulata: Typotheria) and a phylogeny of the Hegetotheriidae. Journal of Vertebrate Paleontology 26:387–399. *F. D. Seoane, S. R. Juñent, and E. Cerdeño. 2017. Phylogeny and paleobiogeography of Hegetotheriidae (Mammalia, Notoungulata). Journal of Vertebrate Paleontology 37(1):e1278547:1-13 *B. Vera (2019). "A new species and the record of Hemihegetotherium (Notoungulata, Hegetotheriidae) in the middle to Late Miocene of Patagonia, Argentina". Journal of South American Earth Sciences. 93: 23–35. doi:10.1016/j.jsames.2019.04.017. {{Taxonbar, from=Q60978539 Typotheres Miocene mammals of South America Neogene Argentina Fossils of Argentina Fossils of Bolivia Neogene Bolivia Fossil taxa described in 1914 Prehistoric placental genera