Basilosaurids and dorudontids lived in the late Eocene, approximately 35 and 41 million years ago. They are mainly known from the eastern United States and from Egypt, but were probably worldwide in their distribution. Basilosaurids were enormous (possibly up to 60 feet long) and had snake-like bodies. They had a tailfluke, but it is not clear whether that was the main propulsive organ. Dorudontids were proportionally more like dolphins. Both basilosaurids and dorudontids had complete hindlimbs that included a mobile knee and several toes. However these extremities were tiny, so small that they were certainly not important in aquatic propulsion.
Protocetids
The Protocetids were better-adapted for the water and lived around 45 million years ago. The best-known is Rhodocetus. The major Protocetid adaptation was the appearance of flukes (horizontal bars) on their tails, which enabled faster swimming. However, the skeletons of Rhodocetus indicate that they retained substantial hind......

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Title: Evidence Of Evolution
Approximate Word Count: 1940
Approximate Pages: 8 (250 words per double-spaced page)

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