Before revision: Analysis of genetic material recovered from their remains showed that half of the genetic material known from Columbian mammoths came from the Krestovka lineage and the other half from woolly mammoths, with the hybridization happening more than 420,000 years ago, during the Middle Pleistocene.
After revision: Analysis of genetic material recovered from their remains showed that half of the ancestry of the Columbian mammoths originated from the Krestovka lineage and the other half from woolly mammoths, with the hybridization happening more than 420,000 years ago, during the Middle Pleistocene.