The cheetah was formerly considered to be particularly primitive among the cats and to have evolved approximately 18 million years ago. However, new research suggests the last common ancestor of all 40 existing species of felines lived more recently than about 11 million years ago. The same research indicates that the cheetah, while highly derived morphologically, is not of particularly ancient lineage, having separated from its closest living relatives (Puma concolor, the cougar, and Puma yaguarondi, the jaguarundi) around five million years ago. These felids have not changed appreciably since they first appeared in the fossil record.