Notohippidae is a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

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 ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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 ...

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s from

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 ...

. Notohippids are known from the

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 ...

and

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...

s.McKenna, Malcolm C., and Bell, Susan K. 1997. ''Classification of Mammals Above the Species Level.'' Columbia University Press, New York, 631 pp.

Description

Although the name notohippids means "southern horses," these animals did not resemble

horses The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 milli ...

. The name refers to their

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

, which were very similar to those of horses, featuring sharp

incisors Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...

and high-crowned

molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...

suitable for shredding grass. The shape of the skull and, particularly, the dentition is the result of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last comm ...

with the equids,

perissodactyl Perissodactyla (, ), or odd-toed ungulates, is an order of Ungulate, ungulates. The order includes about 17 living species divided into three Family (biology), families: Equidae (wild horse, horses, Asinus, asses, and zebras), Rhinocerotidae ( ...

mammals that developed on the northern continents. The body of notohippids was rather stocky, supported by relatively elongated legs equipped with claws (and not hooves). The earliest forms of notohippids possessed low-crowned molars, but over the course of evolution, the teeth gradually became more prismatic, and covered with a thick layer of cement. The skull also became longer, and as a result of this elongation, spaces formed between the incisors, canines and molars.

Classification

The notohippid family was first described 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, especial ...

1894 Events January * January 4 – A military alliance is established between the French Third Republic and the Russian Empire. * January 7 – William Kennedy Dickson receives a patent for motion picture film in the United States. * Ja ...

. The first notohippids developed during the Lower Eocene, '' Pampahippus'' arising from ancestors likely found in the archaic families Isotemnidae or Oldfieldtomasiidae. Later, over the course of the

, more specialized forms emerged, including ''

Notohippus ''Notohippus'' is an extinct genus of notoungulate mammal from the Early Miocene (Santacrucian in the SALMA classification) Santa Cruz Formation, Río Bote, Argentina.Rhynchippus'' ''

Eurygenium ''Eurygenium'' is an extinct genus of Notoungulata, notoungulate belonging to the family Notohippidae. It lived during the Late Oligocene in what is today South America. Description It was a medium-sized mammal ; the best known species, ''Euryg ...

'', '' Eomorphippus'', '' Morphippus'', '' Mendozahippus'', '' Pascualihippus'', '' Argyrohippus''. One of the last forms attributed to this family, the large '' Colpodon'' from the Lower Miocene, is likely a probable aberrant representative of the family Leontiniidae. The notohippids are part of the notoungulates, a large group of South American mammals that developed various forms of different appearances andsizes over the course of the

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

. The notohippids, in particular, belong to the

toxodont Toxodontia. Retrieved April 2013. is a suborder of the Meridiungulata, meridiungulate order Notoungulata. Most of the members of the five included families, including the largest notoungulates, share several dental, auditory and tarsal specializ ...

group, of which they are considered among the most basal members. Recent studies, however, indicate that the notohippid family is not a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

group, but rather

and therefore invalid in a cladistic sense, as it consists of increasingly evolved forms that are closer to the origins of other notoungulate groups.

References

Toxodonts Eocene mammals Oligocene mammals Eocene first appearances Burdigalian extinctions Prehistoric mammal families Paraphyletic groups {{notoungulate-stub