 In 1888 , von <unk> divided <unk> among three taxa : <unk> , <unk> , and <unk> . He placed <unk> in <unk> , a group which he characterized as having simple , <unk> @-@ shaped <unk> <unk> . <unk> included forms with the <unk> divided into <unk> and <unk> . All members of <unk> had <unk> <unk> composed only of the <unk> . Cope objected to von <unk> 's classification , considering the vertebrae of <unk> and <unk> indistinguishable because each had a simple <unk> 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 <unk> <unk> . 
