According to weight estimates by Ryosuke Motani , a Stenopterygius weighed around 163 - whilst a Ophthalmosaurus icenicus weighed 930 â `` 950kg ( 1.03 â `` 1.04 short tons ) . According to weight estimates by Ryosuke Motani a Stenopterygius weighed around 163 - whilst a Ophthalmosaurus icenicus weighed 930 - .