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