ステラーカイギュウ
With a length of , "Rytiodus" was about twice the size as modern sirenians, surpassed only by Steller's sea cow, which was up to long. Like its closest modern relatives, the dugongs, "Rytiodus" had a pair of flippers, a streamlined body and a tail fin. Its flattened snout allowed it to feed in shallow coastal waters. Unlike modern sirenians, "Rytiodus" had short tusks which it may have used to extract food from the sand.