oph ysis , ▁are ▁position ed ▁at ▁the ▁same ▁level . ▁The ▁five ▁sac ral ▁verte bra e ▁have ▁not ▁yet ▁f used ▁into ▁a ▁real ▁sac rum . ▁The ▁tail ▁verte bra e ▁are ▁pl aty co el ous ▁with ▁low ▁sp ines ▁and ▁back ward ▁sl ant ing ▁che v rons . ▁ ▁There ▁are ▁at ▁least ▁twelve ▁pairs ▁of ▁d ors al ▁rib s ; ▁some ▁disp la ced ▁elements ▁might ▁represent ▁a ▁th ir teenth ▁pair . ▁The ▁third ▁and ▁fourth ▁rib ▁have ▁expanded ▁lower ▁ends ▁that ▁in ▁life ▁probably ▁were ▁attached ▁to ▁cart il agin ous ▁s ternal ▁rib s , ▁themselves ▁connected ▁to ▁stern a ▁that ▁in ▁the ▁hol ot ype ▁spec imen ▁have ▁not ▁( y et ) ▁o ss ified . ▁The ▁lower ▁r ump ▁is ▁covered ▁by ▁a ▁basket ▁of ▁eigh teen ▁pairs ▁of ▁g astr alia ▁or ▁bel ly ▁rib s . ▁Myst er ious ▁sh aft ▁parts ▁present ▁near ▁the ▁for el im bs ▁are ▁by ▁Dal ▁S asso ▁& ▁Mag anu co ▁interpreted ▁as ▁the ▁remains ▁of ▁a ▁nin ete enth ▁front most ▁element ▁consisting ▁of ▁two ▁completely ▁f used ▁sh aft s ▁hom olog ous ▁to ▁the ▁normal ▁med ial ▁elements ▁of ▁a ▁pair ▁of ▁g astr alia ; ▁such ▁a ▁che v ron - like ▁b one ▁has ▁also ▁been ▁reported ▁with ▁Jur aven ator . ▁The ▁g astr alia ▁form ▁a ▁her ring bone ▁pattern , ▁the ▁left ▁and ▁right ▁med ial ▁elements ▁over la pping ▁each ▁other