The most current that shows terrestrial whale and completes the sequence.
Post-cranial bones were found and it was a boon to understanding whale evolution. We had a terrestrial animal that fit nicely into the sequence by having ears that were cetacean, ankles that were artiodactyl, and teeth that were similar to the mesonychids. All of these characteristics established it as part of the series.
What is most important is that it establishes the long predicted walking whale - the animal that was to be the last obligate terrestrial in the sequence. Both Darwing and Flower predicted this and Thewissen and Hussain provided the key fossil evidence.