The next sauropod find to be described and misidentified as something other than a dinosaur were a set of hip vertebrae described by Harry Seeley in 1870. Seeley found that the vertebrae were very lightly constructed for their size and contained openings for air sacs ("pneumatization"). Such air sacs were at the time known only in birds and pterosaurs, and Seeley considered the vertebrae to come from a pterosaur. He named the new genus "Ornithopsis", or "bird face" because of this.