Hydrodamalis is a genus of extinct herbivorous sirenian marine mammals, and included the Steller's sea cow (Hydrodamalis gigas), the Cuesta sea cow (Hydrodamalis cuestae), and Hydrodamalis spissa. They were the largest member of the order Sirenia, which includes its closest living relative, the dugong (Dugong dugon), and the manatees (Trichechus spp.). They reached up to 9 metres (30 ft) in length, making the Steller's sea cow among the largest mammals other than whales to have existed in the holocene epoch. Steller's sea cow was first described by Georg Wilhelm Steller, Cuesta by Daryl Domning, and H. spissa by Hitoshi Furusawa. The Steller's sea cow was the only member of the genus to survive into modern times, and, although had formerly been abundant throughout the North Pacific, by the