EVOLUTION Ancient Cetaceans
|Although there are missing pieces to the cetacean evolution
puzzle, a recent find in Pakistan by paleontologist J.G.M. Thewissen, unearthed
a 50 million year old whale fossil with legs and feet. Called Ambulocetus
natans, this is the earliest known Archaeoceti with functional
back legs for locomotion on both land and water. Hindlimbs are not present
in modern cetaceans but vestigial bones are found embedded within flank
muscles; an example of divergent evolution.
He has also discovered the skull of the oldest known cetacean, Pakicetus, which is also assumed to have been largely terrestrial.
By the time of Basilosaurus, a completely aquatic cetacean living around 40 million years ago, the hindlegs were so small that they were no longer functional for swimming . (Monastersky, 1994)