Fossil evidence for the origin of aquatic locomotion in archaeocete whales. Thewissen et al. Perhaps Ambulocetus should be classified with the archaeocetes, perhaps not. And Basilosaurus , younger by 10 My. Specimen with complete hindlegs now shows the increased adaptation to a seemingly fully aquatic lifestyle.
Legs are too small to support body weight on land.
Shimamura et al. Artiodactyls are paraphyletic, the even-toed ungulates give rise to whales. BUT the most primitive artiodactyls appear in the early Eocene. The most diverse ungulate order. See PJH Fig.