''Hemihegetotherium'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of hegetotheriid notoungulate that lived from the Middle to the Late

Miocene The Miocene ( ) is the first 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 means "less recen ...

of what is now

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...

Description

It was a medium-sized animal, approximately the size of large

lowland paca The lowland paca (''Cuniculus paca''), also known as the spotted paca, is a large rodent found in tropical and sub-tropical America, from east-central Mexico to northern Argentina, and has been introduced to Cuba and Algeria. The animal is cal ...

; it may have reached a length of approximately one meter, and the larger species, such as ''Hemihegetotherium achataleptum'', could reach a weight of 20 kilograms. ''Hemihegetotherium'' 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 (hares and rabbits) and the Ochotonidae (pikas). The name of the order is derived from the Ancient Greek ''lagos'' (λαγ� ...

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 teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mouth ...

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 the application of theories to geology, was in favour of cyclical processes to explain geological formations. He published o ...

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

San Juan Province, Argentina San Juan Province () is a province of Argentina, located in the western part of the country. Neighbouring provinces are, moving clockwise from the north, La Rioja, San Luis and Mendoza. It borders with Chile to the west. The province has an a ...

) ; 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 , image_flag = Bandera de Bolivia (Estado).svg , flag_alt = Horizontal tricolor (red, yellow, and green from top to bottom) with the coat of arms of Bolivia in the center , flag_alt2 = 7 × 7 square p ...

, 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 () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...

. ''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 r ...

(hence its generic name, meaning "half ''

Hegetotherium ''Hegetotherium'' is an extinct genus of mammals from the Early to Middle Miocene (Colhuehuapian-Colloncuran in the SALMA classification) of South America. Fossils of this genus have been found in the Cerro Bandera, Cerro Boleadoras, Chichina ...

''"), a group of usually small notoungulates with the superficial appearance of

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

s or

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

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