What is "protosiren"

Protosiren ( taxonomic family Protosirenidae) is an extinct early genus of the order Sirenia. Protosiren existed throughout the Lutetian and Bartonian stages of the Middle Eocene. Its geographic distribution was intercontinental: fossils have been found in the United States ( North Carolina), Egypt, France, Hungary, India, and Pakistan. Like the extant sirenians ( manatee and dugong), Protosiren is thought to have fed on sea grasses as well as freshwater plants. Unlike extant sirenians, Protosiren had hind limbs. Although the limbs were well-developed, they were small and the sacroiliac joint was weak. Consequently, Protosiren is thought to have been mainly aquatic. It rarely ventured on land.