 Indohyus was a small chevrotain @-@ like animal that lived about 48 million years ago in what is now the Kashmir . It belongs to the artiodactyl family Raoellidae , and is believed to be the closest sister group of Cetacea . Indohyus is identified as an artiodactyl because it has two trochlea hinges , a trait unique to artiodactyls . About the size of a raccoon or domestic cat , this herbivorous creature shared some traits of modern whales , most notably the involucrum , a bone growth pattern which is the diagnostic characteristic of any cetacean ; this is not found in any other species . It also showed signs of adaptations to aquatic life , including dense limb bones that reduce buoyancy so that they could stay underwater , which are similar to the adaptations found in modern aquatic mammals such as the hippopotamus . This suggests a similar survival strategy to the African mousedeer or water chevrotain which , when threatened by a bird of prey , dives into water and hides beneath the surface for up to four minutes . 
