 Unlike remingtonocetids and ambulocetids , protocetids have large orbits which are oriented laterally . Increasingly lateral @-@ facing eyes might be used to observe underwater prey , and are similar to the eyes of modern cetaceans . Furthermore , the nasal openings were large and were halfway up the snout . The great variety of teeth suggests diverse feeding modes in protocetids . In both remingtonocetids and protocetids , the size of the mandibular foramen had increased . The large mandibular foramen indicates that the mandibular fat pad was present . However the air @-@ filled sinuses that are present in modern cetaceans , which function to isolate the ear acoustically to enable better underwater hearing , were still not present . The external auditory meatus ( ear canal ) , which is absent in modern cetaceans , was also present . Hence , the method of sound transmission that were present in them combines aspects of pakicetids and modern odontocetes ( toothed whales ) . At this intermediate stage of hearing development , the transmission of airborne sound was poor due to the modifications of the ear for underwater hearing while directional underwater hearing was also poor compared to modern cetaceans . 
