Pakicetus, shown above right, is a Middle Eocene archaeocete from the Kuldana Formation of Pakistan; it is currently the earliest known well-preserved cetacean, and the archaeocete features are clearly visible in this replica skull from UCMP's collections.
Pakicetus is so far known only from its skull, but recent finds in Pakistan have produced other whale species that show very primitive characters in both the skull and the rest of the skeleton. These animals had relatively well developed limbs, but were aquatic. Below right is a drawing of the known skeleton of Rodhocetus, a recently discovered archaeocete from Pakistan, a few million years younger than Packicetus. Rodhocetus had well-developed hind limbs (although only the thighbone, or femur, has been preserved), but unlike land mammals, Rodhocetus did not have its vertebrae in the pelvic region fused together into a sacrum. Early whales such as Rodhocetus show many similarities with an early group of land mammals known as mesonychids, which are also close to the root of the hoofed mammals. In fact, some fossil teeth that were once identified as mesonychids are now known to have come from archaeocetes.
http://www.ucmp.berkeley.edu/mammal/cet ... acean.html