In 2013, a study sequenced the complete and partial mitochondrial genomes of 18 fossil canids from the Old and New Worlds whose dates range from 1,000 to 36,000 YBP, and compared these with the complete mitochondrial genome sequences from modern wolves and dogs. Clade A included 64% of the modern dogs sampled, and these are a sister group to a clade containing three fossil pre-Columbian New World dogs dated between 1,000 and 8,500 YBP. This finding supports the hypothesis that pre-Columbian New World dogs share ancestry with modern dogs and that they likely arrived with the first humans to the New World. Together, clade A and the pre-Columbian fossil dogs were the sister group to a 14,500 YBP wolf found in the Kessleroch cave near Thayngen in the canton of Schaffhausen, Switzerland, with a most recent common ancestor estimated to 32,100 YBP.