8 5 0 , ▁G ide on ▁Mant ell ▁recognized ▁the ▁din osa ur ian ▁nature ▁of ▁several ▁b ones ▁assigned ▁to ▁Cet ios aur us ▁by ▁O wen . ▁Mant ell ▁noticed ▁that ▁the ▁leg ▁b ones ▁contained ▁a ▁med ull ary ▁cav ity , ▁a ▁characteristic ▁of ▁land ▁animals . ▁He ▁assigned ▁these ▁spec im ens ▁to ▁the ▁new ▁genus ▁P elor osa urus , ▁and ▁grouped ▁it ▁together ▁with ▁the ▁din osa urs . ▁However , ▁Mant ell ▁still ▁did ▁not ▁recognize ▁the ▁relationship ▁to ▁Cet ios aur us . ▁ ▁The ▁next ▁sau rop od ▁find ▁to ▁be ▁described ▁and ▁mis ident ified ▁as ▁something ▁other ▁than ▁a ▁din osa ur ▁were ▁a ▁set ▁of ▁hip ▁verte bra e ▁described ▁by ▁Harry ▁See ley ▁in ▁ 1 8 7 0 . ▁See ley ▁found ▁that ▁the ▁verte bra e ▁were ▁very ▁light ly ▁constructed ▁for ▁their ▁size ▁and ▁contained ▁open ings ▁for ▁air ▁sac s ▁( p neum at ization ). ▁Such ▁air ▁sac s ▁were ▁at ▁the ▁time ▁known ▁only ▁in ▁birds ▁and ▁p ter osa urs , ▁and ▁See ley ▁considered ▁the ▁verte bra e ▁to ▁come ▁from ▁a ▁p ter osa ur . ▁He ▁named ▁the ▁new ▁genus ▁Or n ith opsis , ▁or ▁" bird ▁face " ▁because ▁of ▁this . ▁ ▁When ▁more ▁complete ▁spec im ens ▁of ▁Cet ios aur us ▁were ▁described ▁by ▁Phill ips ▁in ▁ 1 8 7 1 , ▁he ▁finally ▁recognized ▁the ▁animal ▁as ▁a ▁din osa ur