 The genera Escherichia and Salmonella diverged around 102 million years ago ( credibility interval : 57 – 176 mya ) which coincides with the divergence of their hosts : the former being found in mammals and the latter in birds and reptiles . This was followed by a split of the <unk> ancestor into five species ( E. <unk> , E. coli , E. <unk> , E. <unk> , and E. <unk> ) . The last E. coli ancestor split between 20 and 30 million years ago . 
