ABSTRACT
The phylogenetic position of “ostracoderms” has been a matter of heated debate during most of the twentieth century, notably because of the question of their relationships to the major living vertebrate clades. The interpretation of euconodonts as vertebrates has raised heated debate during the last 20 years and this ended with the demonstration that conodont growth is at odds with that of vertebrate odontodes, because they grew in an opposite way. Cyclostomes display two different types of cartilage: the “soft cartilage” and “hard cartilage”, which depend on their respective composition in collagen. Euphaneropids have a somewhat lamprey-like vertebral column made of arcualia, large calcified fin supports, and large calcified radials in both median and paired fins. Currently, euphaneropids are considered either the sister group to cyclostomes or a highly derived form of anaspids with a secondarily regressed dermoskeleton.
