Question: dinosaur with fin on back walks on 4 legs
Answer: Dimetrodon ( / daɪˈmiːtrədɒn / ( listen ) or / daɪˈmɛtrədɒn / , meaning `` two measures of teeth '' ) is an extinct genus of synapsids that lived during the Cisuralian ( Early Permian ) , around 295 -- 272 million years ago ( Ma ) .