 "B. namadicus" and "B. primigenius" are thought to have split 0.61 and 0.85 million years ago based on a study of the accumulation of differences in mitochondrial DNA by MacHugh "et al".in 1997, with Badam and Sankhyan in 2009 dating the existence of "B. namadicus" to the middle to late Pleistocene.Colbert's theory was expanded by Pilgrim in 1947 and followed by subsequent authors, until 2007 when Bienvenido Martínez-Navarro "et al".