glenn
"We analysed four of the oldest-known cetaceans, Pakicetus,
Nalacetus and Ambulocetus are found in the early to middle Eocene
Kuldana Formation of Pakistan. Pakicetus and Nalacetus are
found only in shallow freshwater deposits and probably spent
considerable time on land. Ambulocetus occurs only in littoral
beds. Indocetus is known from the Middle Eocene Harudi Formation
of western India and occurs only in neritic beds.
"The difference in [del]18 O values between Pakicetus and
Nalacetus on the one hand and Indocetus on the other is similar
in magnitude and direction to that between modern freshwater and
marine cetaceans, suggesting that Pakicetus and Nalacetus
ingested fresh water. This difference is consistent with habitat
inferences from sedimentological data. Pakicetids, the
geologically oldest whales, were clearly not marine. The [del]18
O values of Indocetus are much higher than those of the lower
Kuldana cetaceans and match those of modern marine cetaceans,
suggesting that Indocetus ingested sea water only. Indocetus
was thus totally independent of freshwater and the taxon was
fully marine.
"The[del]18 O values of Ambulocetus are most similar to
those of the other Kuldana cetaceans, implying that Ambulocetus
ingested fresh water. This is surprising as the taxon is found
in unambigouosly marine beds high in the Kuldana formation.
Also, Ambulocetus has never been found in the freshwater deposits
that abound in this part of the Kuldana Formation."
"There are two possible explanations. Ambulocetus, although
it lived in the litorral realm, may have sought out fresh water
sources to drink because its osmoregulatory system was unable to
handle the excess salt load of its environment. Alternatively,
it may have lived in fresh water during the (early) part of its
life when its teeth were mineralized, then migrated to the sea
later on. This explanation lends credence to the idea that the
life history of early cetaceans resembled that of modern
pinnipeds." ~J.G.M. Thewissen, et al, "Evolution of Cetacean
Osmoregulation", Nature, May 30, 1996, p. 380
Foundation,Fall and Flood
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