The readaptation of Eocene sirenians to life in water

Abstract

Eocene sirenians and cetaceans simultaneously and independently evolved similar morphological adaptations to aquatic life. These included increased flexibility in the sacral region, reduction and loss of hind limbs, shortening of the neck, increased skeletal mass, and other modifications. Loss of hind limbs was probably driven by selection for the maintenance of horizontal trim. The advantage of a shorter neck lay in the more anterior position and consequently the greater turning moments of forelimb control surfaces that it made possible.