Dereivka was originally thought to be a Eneolithic (or Copper Age) village in the Dneiper Valley of the Ukraine, dated 3380-4570 BC, excavated by Dmitriy Yakolevich Telegin of the Russian Academy of Sciences in the 1980s.
The site contained what Telegin interpreted as the earliest evidence yet for the domestication of the horse, based on evidence of bit wear on the horse teeth. In recent years, other researchers such as Marsha Levine have argued that the evidence at Dereivka only indicates hunting of wild horses; but most of the animal bones from the earlier excavations has been discarded.
Update: Recent redating of Dereivka has placed this site as much later, the Scythian period of the 6th and 7th centuries BC.
Sources
See the article on horse domestication for more information
Levine, Marsha A. 1999 Botai and the origins of horse domestication. Journal of Anthropological Archaeology 18(1):29-78.
