The Golden vizcacha rat (Pipanacoctomys aureus), is a new species of octodontid in the Octodontidae family. It is the only member of the Pipanacoctomys genus. This animal is tetraploid and has 4x = 2n = 92 chromosomes. This species and its sister-species the Plains viscacha rat (Tympanoctomys barrerae) (4x = 102) appear to have arisen from the diploid Viscacha rat (Octomys mimax) (2x = 2n = 56) as a result of doubling and then loss of some chromosomes. It is threatened by conversion of its very restricted habitat to agricultural use.