Sirenia

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Sirenians have major aquatic adaptations: forelimbs have modified into arms used for steering, the tail has modified into a paddle used for propulsion, and the hind limbs are but two small remnant bones floating deep in the muscle. They appear fat, but are fusiform, hydrodynamic, and highly muscular. Their skulls are highly modified for taking breaths of air at the water''s surface and dentition is greatly reduced. The skeletal bones of both the manatee and dugong are very dense which helps to neutralize the buoyancy of their blubber. The manatee appears to have an almost unlimited ability to produce new teeth as the anterior teeth wear down. They have only two teats, located under their forelimbs, similar to elephants. The elephants are thought as the closest living relative of the sirenians. The lungs of sirenians are unlobed. In sirenians, the lungs and diaphragm extend the entire length of the vertebral column. These adaptations help sirenians control their buoyancy and maintain their horizontal position in the water... Mehr