In 1888 , von Zittel divided stegocephalians among three taxa : Lepospondyli , Temnospondyli , and Stereospondyli . He placed microsaurs in Lepospondyli , a group which he characterized as having simple , spool @-@ shaped vertebral centra . Temnospondyli included forms with the centra divided into pleurocentra and intercentra . All members of Stereospondyli had amphicoelous centra composed only of the intercentra . Cope objected to von Zittel 's classification , considering the vertebrae of lepospondyls and stereospondyls indistinguishable because each had a simple spool shape . He continued to use Ganocephala and Labyrinthodonta ( which he alternatively referred to as Rhachitomi ) to distinguish animals based on the absence or presence of occipital condyles .