Article: The dawn of the vertebrates: characters versus common ascent in the rise of current vertebrate phylogenies [Palaeontological Association 1995 annual address]

Armoured fossil jawless fishes, or 'ostracoderms', have long been regarded as being ancestral to Recent hagfishes and lampreys. The latter were supposed to have lost the mineralised exoskeleton and undergone a 'degeneracy' linked with their burrowing or ecloparasitic modes of life. However, recent cladistic analyses suggest that most, if not all 'ostracoderms' are more closely related to jawed vertebrates than to either lampreys or hagfishes, although they are clearly jawless. These views are very similar to those expressed by the early British palaeontologists who made the first attempts at placing these extinct taxa in the classification of the vertebrates. The chaotic history of the phylogenctic position of the 'ostracoderms' seems to be due to varying approaches to the use of either characters or common ascent in phylogeny reconstruction.