| Noun | 1. | sirenian mammal - any of two families of large herbivorous aquatic mammals with paddle-shaped tails and flipper-like forelimbs and no hind limbsaquatic mammal - whales and dolphins; manatees and dugongs; walruses; seals order Sirenia, Sirenia - an animal order including: manatees; dugongs; Steller's sea cow manatee, Trichechus manatus - sirenian mammal of tropical coastal waters of America; the flat tail is rounded dugong, Dugong dugon - sirenian tusked mammal found from eastern Africa to Australia; the flat tail is bilobate Hydrodamalis gigas, Steller's sea cow - extinct large sirenian mammal formerly found near the Asiatic coast of the Bering Sea |