However , one South Dakotan individual was 6 -- 7 meters ( 20 -- 23 ft ) long .
Most short - necked plesiosaurs were relatively small , with body lengths of less than ten feet .
One South Dakotan individual was 6 -- 7 meters ( 20 -- 23 ft ) long .
Most short - necked plesiosaurs were relatively small , with body lengths of less than ten feet .