Sparnotheriodontidae is an enigmatic extinct family of litopterns known primarily from teeth. Sparnotheriodontids are one of two South American native ungulate clades known to have reached Antarctica, the other being

astrapotheres Astrapotheria is an extinct order of South American and Antarctic hoofed mammals that existed from the late Paleocene to the Middle Miocene, ."The uruguaytheriine Astrapotheriidae from the rich middle Miocene Honda Group of the upper Magdalen ...

Description

Sparnotheriodontids ranged in size from the mid-sized ''Phoradiadus'' to the large ''Sparnotheriodon''. ''Sparnotheriodon'' and one species of ''Notiolofos'', ''N. arquinotiensis'', have been estimated to have had masses of roughly . Another species of ''Notiolofos'', ''N. regueroi'', was smaller, with a body mass estimated to have been between 25 and 58 kg.

Classification

The phylogenetic position of Sparnotheriodontidae is uncertain. Most researchers consider them to belong to

Litopterna Litopterna (from grc, λῑτή πτέρνα "smooth heel") is an extinct order of fossil hoofed mammals from the Cenozoic era. The order is one of the five great orders of South American ungulates that were endemic to the continent, until the G ...

. In contrast, Cifelli and Bergqvist have argued that sparnotheriodontids are

condylarths Condylarthra is an informal group – previously considered an order – of extinct placental mammals, known primarily from the Paleocene and Eocene epochs. They are considered early, primitive ungulates. It is now largely considered to be a wast ...

. Their methodology, based on attempting to associate isolated teeth and isolated postcranial bones based on size and relative abundance, has been criticized. Phylogenetic analyses conducted by Chimento and Agnolin in 2020 and Kramarz et al. 2021 both included one sparnotheriodontid, ''Victorlemoinea'', and found it to be a basal litoptern. Unlike most authors, who treat sparnotheriodontids as a

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

, in 1997 McKenna and Bell classified them as a subfamily of

Macraucheniidae Macraucheniidae is a family in the extinct South American ungulate order Litopterna, that resembled various camelids. The reduced nasal bones of their skulls was originally suggested to have housed a small proboscis, similar to that of the sai ...

Genera

Sparnotheriodontidae contains the genera ''

Victorlemoinea ''Victorlemoinea'' is an extinct litoptern genus of the family Sparnotheriodontidae, that lived from the Early to Middle Eocene. Fossils of ''Victorlemoinea'' have been found in the Las Flores, Sarmiento and Koluel Kaike Formations of Argent ...

'', ''

Sparnotheriodon ''Sparnotheriodon'' is an extinct genus of sparnotheriodontid litoptern that lived during the Middle Eocene of what is now Argentina, leaving fossils in the Sarmiento Formation The Sarmiento Formation ( Spanish: ''Formación Sarmiento''), in o ...

'', '' Phoradiadus'', and '' Notiolofos''. ''Victorlemoinea'' and ''Sparnotheriodon'' may be synonymous. Soria regarded '' Heteroglyphis'' as a probable sparnotheriodontid, but McKenna and Bell and Bond et al. included it in Anisolambdinae, with the former considering it a synonym of '' Protheosodon''.

History of study

The first described sparnotheriodontid, ''Victorlemoinea'', was named by

Florentino Ameghino Florentino Ameghino (born Giovanni Battista Fiorino Giuseppe Ameghino September 19, 1853 – August 6, 1911) was an Argentine naturalist, paleontologist, anthropologist and zoologist, whose fossil discoveries on the Argentine Pampas, especially ...

in 1901. In 1980, Miguel Soria named ''Sparnotheriodon'' and established the family Sparnotheriodontidae for it. He initially classified the family as belonging to Notoungulata. Sparnotheriodontids were first identified in Antarctica in 1990.

Paleobiology, paleoecology, and paleobiogeography

Sparnotheriodontids lived in South America and Antarctica. Sparnotheriodontids and

are the only clades of terrestrial placental mammals confirmed to have lived in Antarctica. Sparnotheriodontids were browsing herbivores adapted to forest environments. Their rarity in the fossil record suggests they were specialists. Sparnotheriodontids may have been ecological equivalents to ''

Meniscotherium ''Meniscotherium'' is an extinct genus of dog-sized mammal which lived 54–38 million years ago. It was a herbivore and had hooves. Fossils have been found in Utah, New Mexico. and Colorado. Many individuals have been found together, indicating ...

'', which is not closely related but had similar teeth. ''Victorolemoinea'' lived during the Riochican and Itaboraian South American land mammal ages, which date to the

Ypresian In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

age of the

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

. ''Notiolofos'' ranged from the early Eocene to the Rupelian age of the Oligocene.

References

Works cited

* * * * * * * * * * * * * {{Taxonbar, from=Q33135273 Condylarths Litopterns Prehistoric mammal families Paleogene mammals of South America Ypresian first appearances Rupelian extinctions