Pakicetus was terrestrial as expected in the first in the transition from land to sea.
"1. Our lengthy debate can be found starting at (latest):
WIYC summary of Pakicetus
"Unlike any other cetacean, the pakicetid outer ear was unspecialized and similar to that of land mammals... "
"It is most likely that the specializations of the pakicetid middle ear are analogous to those of some subterranean mammals and are related to the reception of substrate-borne vibrations or sound when the ear is in contact with the ground..."
"Taken together, the features of the skull indicate that pakicetids were terrestrial, and the locomotor skeleton displays running adaptations ..."
"Pakecetids were terrestrial mammals, no more amphilbious than a tapir."
'Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyles'
J.G.M. Thewissen, E.M. Williams, L.J. Roe, S.T. Hussain
Nature/Vol 413 / 20 September 2001 / www.nature.com"
The characteristics that are terrestrial start to change in the whales that followed. Note that Pakicetus is a whale by the nature of the sigmoid process on the ear.
"The pakicetid middle ear was highly specialize and included the pachy-osteoscleotic ossicles, an inbolucrum and a plate-like sigmoid process."
IBID p. 278
Also, it is clear that even though pakicetid hearing was terrestrial, their ear structures are intermediate between modern cetaceans and modern artiodactyls.
"Thewissen and Hussain examined a small ear bone or ossicle called the incus of Pakicetus. They say that in shape and proportions it is intermediate between the equivalent bone in modern cetaceans and that in modern artiodactyls. They also claim that its orientation relative to the malleus - the second of the chain of three ossicles in the middle-ear cavity - is at a similar halfway stage."