of this creature, the ears of pakicetids are specialized for hearing on land. However, pakicetids were able to listen underwater by using enhanced bone conduction, rather than depending on the tympanic membrane like other land mammals. This method of hearing did not give directional hearing underwater. Pakicetids have long thin legs, with relatively short hands and feet which suggest that they were poor swimmers. To compensate for that, their bones are unusually thick (osteosclerotic), which is probably an adaptation to make the animal heavier to counteract the buoyancy of the water. According to a 2001 morphological analysis by Thewissen et al., pakicetids display no aquatic skeletal adaptation; instead they display adaptations for running and jumping. Hence pakicetids were most likely aquatic waders. Ambulocetidae Ambulocetus, which lived about 49 million years ago, was discovered in Pakistan in 1994. They were vaguely crocodile-like mammals, possessing large brevirostrine jaws. In the Eocene, ambulocetids inhabited the bays and estuaries of the Tethys Sea in northern Pakistan. The fossils of ambulocetids are always found in near-shore shallow marine deposits associated with abundant marine plant fossils and littoral mollusks. Although they are found only in marine deposits, their oxygen isotope values indicate that they consumed a range of water with different degrees of salinity, with some specimens having no evidence of sea water consumption and others that did not ingest fresh water at the time when their teeth were fossilized. It is clear that ambulocetids tolerated a wide range of salt concentrations. Hence, ambulocetids represent a transition phase of cetacean ancestors between fresh water and marine habitat. The mandibular foramen in ambulocetids had increased in size, which indicates that a fat pad was likely to be housed in the lower jaw. In modern toothed whales, this fat pad in the mandibular foramen extends posteriorly to the middle ear. This allows sounds to be received in the lower jaw, and then transmitted through the fat pad to the middle ear. Similar to pakicetids, the orbits of ambulocetids are on the top of the skull, but they face more laterally than in pakicetids. Ambulocetids had relatively long limbs with particularly strong hind legs, and they retained a tail with no sign of a fluke. The hindlimb structure of Ambulocetids shows that their ability to engage in terrestrial locomotion was significantly limited compared to that of contemporary terrestrial mammals, and likely did not come to land at all. The