Did whales with fully developed hind legs like Georgiacetus exist at the same time as more marine whales like Basilosaurus and Dorudon late into the Eocene? I'm having trouble locating the exact point where the walking whales became fully aquatic whales and I was wondering when the two lineages branched off and both lived until the end of the Eocene. Did flukes and flipper-feet exist at the same time? (Not in the same individual, obviously)
Some basilosaur remains are known from the late middle Eocene, and we know Georgiacetus and similar whales were around during the middle Eocene, but I’m not sure if they survived quite far enough into the epoch to coexist with more modern-looking whales. (Sorry I can’t give you a more satisfying answer :/)
One of the earliest members of Pelagiceti (“Basilosauridae” + other stuff + modern whales) is Basilotritus wardii* from the early Bartonian and the last “protocetid” appears to be Carolinacetus from the early-mid Bartonian, so yeah, there was some overlap.
* This species seems to have hindlimbs intermediate between “protocetids” and basilosaurids.
Gol’din, P. & Zvonok, E. (2013) Basilotritus uheni, a New Cetacean (Cetacea, Basilosauridae) from the Late Middle Eocene of Eastern Europe. Journal of Paleontology 87(2) 254-268.