 Modern cetaceans have internal , rudimentary hind limbs , such as reduced femurs , fibulas , and tibias , and a pelvic girdle . Indohyus has a thickened ectotympanic internal lip of the ear bone . This feature compares directly to that of modern cetaceans . Another similar feature was the composition of the teeth , which contained mostly calcium phosphate which is needed for eating and drinking by aquatic animals , though , unlike modern day toothed whales , they had a heterodont ( more than one tooth morphology ) dentition as opposed to a homodont ( one tooth morphology present ) dentition . Although they somewhat resembled a wolf , the fossils of pakicetids showed the eye sockets were much closer to the top of their head than that of other terrestrial mammals , but similar to the structure of the eyes in cetaceans . Their transition from land to water led to reshaping of the skull and food processing equipment because the eating habits were changing . Ultimately , the change in position of the eyes and limb bones is what led the pakicetids to become waders . The ambulocetids also began to develop long snouts , which is seen in current cetaceans . Their limbs ( and hypothesized movement ) were very similar to otters . 
