Question: are there any predecessors or extinct species horses

Context: During the Beagle survey expedition, the young naturalist Charles Darwin had remarkable success with fossil hunting in Patagonia. On 10 October 1833, at Santa Fe, Argentina, he was ``filled with astonishment'' when he found a horse's tooth in the same stratum as fossil giant armadillos, and wondered if it might have been washed down from a later layer, but concluded this was ``not very probable''. After the expedition returned in 1836, the anatomist Richard Owen confirmed the tooth was from an extinct species, which he subsequently named Equus curvidens, and remarked, ``This evidence of the former existence of a genus, which, as regards South America, had become extinct, and has a second time been introduced into that Continent, is not one of the least interesting fruits of Mr. Darwin's palæontological discoveries.''
