Which specimen had tiny hind legs with a mobile knee and several toes and lived 35-40 mya? basilosaurus pakicetus sinonyx ambulocetus

This answer to this question is Basilosaurus. This was a genus of prehistoric cetacean. It lived during the Late Eocene 40 to 35 million years ago. This species had tiny hind limbs and only three toes. To illustrate, a 16 m  individual had 35 cm long hind limbs with fused tarsals and only three digits.