The Sirenia are thought to have evolved from four-legged land mammals over 60 million years ago , with the closest living relatives being the Proboscidea ( elephants ) and Hyracoidea ( hyraxes ) .
The Sirenia are thought to have evolved from four-legged land mammals over 60 million years ago . Their closest living relatives are the Proboscidea ( elephants ) and Hyracoidea ( hyraxes ) .