▁dist ally , ▁whereas ▁in ▁Our an osa urus ▁the ▁sp ines ▁actually ▁become ▁th icker ▁dist ally ▁and ▁fl atten . ▁The ▁posterior ▁sp ines ▁were ▁also ▁bound ▁together ▁by ▁o ss ified ▁tend ons , ▁which ▁st iff ened ▁the ▁back . ▁Finally , ▁the ▁sp ine ▁length ▁pe aks ▁over ▁the ▁for el im bs . ▁ ▁The ▁first ▁four ▁d ors al ▁verte bra e ▁are ▁unknown ; ▁the ▁fifth ▁already ▁be ars ▁a ▁ ▁that ▁is ▁pointed ▁and ▁slightly ▁hook ed ; ▁Ta quet ▁pres umed ▁it ▁might ▁have ▁anch ored ▁a ▁tend on ▁to ▁support ▁the ▁neck ▁or ▁sk ull . ▁The ▁t enth , ▁ele vent h ▁and ▁tw elf th ▁sp ines ▁are ▁the ▁longest , ▁at ▁about ▁. ▁The ▁last ▁d ors al ▁sp ine , ▁the ▁sevent e enth , ▁has ▁a ▁gro oved ▁posterior ▁edge , ▁in ▁which ▁the ▁anterior ▁corner ▁of ▁the ▁lower ▁sp ine ▁of ▁the ▁first ▁sac ral ▁verte bra ▁is ▁locked . ▁The ▁sp ines ▁over ▁the ▁six ▁sac ral ▁verte bra e ▁are ▁marked ly ▁lower , ▁but ▁those ▁of ▁the ▁tail ▁base ▁again ▁longer ; ▁towards ▁the ▁end ▁of ▁the ▁tail ▁the ▁sp ines ▁gradually ▁short en . ▁▁ ▁The ▁d ors al ▁" s ail " ▁is ▁usually ▁explained ▁as ▁either ▁function ing ▁as ▁a ▁system ▁for ▁therm or eg ulation ▁or ▁a ▁display ▁structure . ▁An ▁alternative ▁hypothesis ▁is ▁that ▁the ▁back ▁might ▁have ▁carried ▁a ▁hum p ▁consisting ▁of ▁mus cle ▁t issue