Equus neogeus is an extinct species of equine native to South America during the Pleistocene. It was formerly thought to be several distinct species within the subgenus Amerhippus, but was later shown to be a single morphologically variable species. It is thought to be closely related to true horses.

Quick Facts Scientific classification, Binomial name ...

Equus neogeus Temporal range: Pleistocene (Ensenadan-Lujanian) ~1–0.012 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Skull
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Perissodactyla
Family:	Equidae
Genus:	Equus
Species:	†E. neogeus
Binomial name
†Equus neogeus Lund, 1840
Synonyms
†Equus (Amerhippus) andium †Equus (Amerhippus) insulatus †Equus (Amerhippus) lasallei †Equus (Amerhippus) santaeelenae

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While they have formerly been referred to as belonging to 5 separate species, this has been revised down into three,^[1] and more recently a single, morphologically variable species Equus neogeus.^[2][3] Some authors continue to recognise three species, restricting Equus neogeus to large-sized individuals spanning from the Pampas to Northeast Brazil, while separating the smaller Equus andium for populations in the northern-central Andes, and Equus insulatus for medium-sized animals spanning from Bolivia to Venezuela. These authors suggest that E. insulatus was the ancestor of the other species.^[4] Historically, South American Equus species were placed in the subgenus Amerhippus, but this has subsequently been questioned.^[4] A 2008 study of mitochondrial DNA fragments of a specimen of E. neogeus found it to be nested within mitochondrial lineages of E. caballus,^[5] however, later studies suggested that this result required more specimens to be analysed for confirmation.^[6] A close relationship to caballine horses was also supported by a 2019 morphological analysis study.^[7]

Equus neogeus measured roughly 1.5 m (4.9 ft) tall and weighed approximately 400 kg (880 lb).^[8]

They were one of two groups of equines in South America, alongside Hippidion.^[9] Fossils have been recovered from the Tarija Formation of Bolivia, the Serranía del Perijá in Venezuela, the Chiu-Chiu Formation of Chile, the Sabana Formation of the Bogotá savanna in Colombia,^[10] and from various locations in Ecuador.^[8] Equus first appeared in South America during the late Early Pleistocene-earliest Middle Pleistocene, around 1 to 0.8 million years ago, based on remains found near Tarija, Bolivia.^[11]

A 2019 study suggested that Equus neogeus specimens from Uruguay were primarily grazers that fed on both C4 and C3 grasses in prairies and open woodlands.^[12]

Equus neogeus became extinct at the end of the Late Pleistocene as part of the Quaternary extinction event, along with the vast majority of other large mammals in South America.^[13] The youngest remains date to approximately 11,700 years Before Present (BP), in Río Quequén Salado, in the southwest of Buenos Aires province, Argentina.^[11] At the Arroyo Seco 2 site in the Argentinian Pampas, remains of Equus neogeus are associated with human artifacts, indicating that they were butchered by humans at the site, which dates to 14,782–11,142 cal yr BP, suggesting that hunting by recently arrived humans may have played a role in its extinction.^[14]