Order Sirenia

The order Sirenia includes all manatees and sea cows that are characterized by body fusiform; entirely aquatic; without neck, no visible separation of head from body; small eyes, eyelids imperfectly developed; small external auditory meatus, ear absent; pectoral appendages paddle shaped, digits not externally visible; carpal elements vary between families; pelvic appendages are absent; flattened tail and laterally expanded, rounded or forked posteriorly; skin tough and rugose, naked or sparsely haired; bones of skull and postcranial skeleton massive and dense; nasal bones absent or vestigial; six to eight cervical vertebrae; clavicles absent; absent sacrum; anterior caudal vertebrae having chevron bones; toothless or having incisors and molariforms that are separated by wide diastema; small, fixed and rugose tongue; single pair of pectoral mammae; stomach with several chambers. Distribution is tropical in America and Asia. Two families occur in North America: Dugongidae and Trichechidae.