Mastodonsaurus and other similar animals were referred to as labyrinthodonts , named like Labyrinthodon for teeth that were highly folded in cross section . Owen 's " Labyrinthodon Jaegeri " was later found at Guy 's Cliffe , England by paleontologist William Buckland . Other specimens were found in the red sandstone of Warwickshire . As more fossils were uncovered in England , Owen depicted these labyrinthodonts as the " highest " form of batrachian and compared them to crocodiles , which he considered the highest form of reptiles . He also noted the large labyrinthodonts of the Keuper ( a unit of rocks that dates to the Late Triassic ) were younger than more advanced reptiles in the Magnesian and Zechstein , which are Late Permian in age . Owen used these fossils to counter the notion that reptiles evolved from a sequential progression from early amphibians ( what he called " metamorphosed fishes " ) .