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the name Agnatha ("jawless") for a group that included the cyclostomes and fossil groups in which jaws could not be observed. Vertebrates were subsequently divided into two major sister-groups: the Agnatha and the Gnathostomata (jawed vertebrates). In 1927, Erik Stensiö suggested that the two groups of living agnathans (i.e. the cyclostomes) arose independently from fossil agnathans. In 1977, Søren Løvtrup argued that

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