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 legs. They lived in shallow seas, and may have had a similar lifestyle to seals, or even dolphins; it is not clear whether they ever came onto the land.
Basilosaurus and Dorudon
Characteristics of Ambulocetidae:
Pterygoid process same height as braincase
Medially places, laterally facing orbits
Medium sized mandibular foramen
Remingtonocetids are known from 49-43 million year old deposits in India and Pakistan. Their skeletons are similar to ambulocetids in retaining large hind limbs. They differ from ambulocetids in having smaller orbits (and eyes), long slender snouts, and a wide basicranium which places the ear regions far from the midline. The widely separated ears, combined with the small eyes, may have been an adaptation for enhanced emphasis on hearing to locate prey.
Characteristics of Remingtonocetides:
Convex posterior palate extending beyond the tooth row
Ear region placed laterally with oblong... [continues]
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