The manatee swims with up and down (dorsoventral) motions of its body and fluke. This is similar to the swimming motions of the cetaceans (dolphins and whales) but is unlike the side to side swimming motions of fish and seals. The muscles of the manatee have little of the myoglobin (muscle hemoglobin) that is typical of the muscles of other diving mammals—this means manatees cannot store as much oxygen as seals and dolphins, which is reflected in their relatively short (8-15 minute) and shallow (10-20 feet) dives.

A manatee’s teeth are similar to the molars of some other mammals and are located in the back half of the lower and upper jaws. Manatee teeth are unique in that they are replaced horizontally, as opposed to vertically as in most other mammals. Tooth replacement is continuous (polyphyodont) throughout their lives, as opposed
to that of other mammals which replace a single set of teeth once in a lifetime (diphyodont).

The ribs of the manatee arch up to allow the lungs to be positioned much higher along the vertebral column than is found in most other mammals. The elongated lung distributes the buoyant forces along more of the body than would be possible in a more typically shaped lung (thus helping the manatee to float horizontally). This orientation also minimizes the pressure differences between different parts of the lung.

Their ribs and other long bones lack marrow cavities, which produces a dense and relatively heavy skeleton. Marrow, which produces red blood cells, is mostly restricted to the centra (bodies) of the vertebrae and possibly the sternum. Manatees do not have hind limbs. Their pelvic bones are vestiges of the more complex structures of their ancestors. The pelvic vestiges are attachment sites for muscles.

(text and photos from Florida Fish and Wildlife Conservation Commission, FWC)