ested ▁by ▁amateur ▁scient ist ▁Jim ▁Schmidt ) ▁in ▁which ▁the ▁long ▁legs ▁of ▁adult ▁sau rop ods ▁allowed ▁them ▁to ▁easily ▁cover ▁great ▁distances ▁without ▁changing ▁their ▁overall ▁mechan ics . ▁ ▁Air ▁sac s ▁Al ong ▁with ▁other ▁sa ur isch ian ▁din osa urs ▁( such ▁as ▁ther op ods , ▁including ▁birds ), ▁sau rop ods ▁had ▁a ▁system ▁of ▁air ▁sac s , ▁ev iden ced ▁by ▁indent ations ▁and ▁h ollow ▁cav ities ▁in ▁most ▁of ▁their ▁verte bra e ▁that ▁had ▁been ▁inv aded ▁by ▁them . ▁P neum atic , ▁h ollow ▁b ones ▁are ▁a ▁characteristic ▁feature ▁of ▁all ▁sau rop ods . ▁These ▁air ▁spaces ▁reduced ▁the ▁overall ▁weight ▁of ▁the ▁massive ▁ne cks ▁that ▁the ▁sau rop ods ▁had , ▁and ▁the ▁air - s ac ▁system ▁in ▁general , ▁allowing ▁for ▁a ▁single - direction ▁air flow ▁through ▁st iff ▁l ungs , ▁made ▁it ▁possible ▁for ▁the ▁sau rop ods ▁to ▁get ▁enough ▁o xygen . ▁ ▁The ▁bird - like ▁h ollow ing ▁of ▁sau rop od ▁b ones ▁was ▁recognized ▁early ▁in ▁the ▁study ▁of ▁these ▁animals , ▁and , ▁in ▁fact , ▁at ▁least ▁one ▁sau rop od ▁spec imen ▁found ▁in ▁the ▁ 1 9 th ▁century ▁( Or n ith opsis ) ▁was ▁originally ▁mis ident ified ▁as ▁a ▁p ter osa ur ▁( a ▁flying ▁re pt ile ) ▁because ▁of ▁this . ▁ ▁Arm or ▁ ▁Some ▁sau rop ods ▁had ▁arm or