of shared features such as paired fins, the origins of the jawed vertebrates may lie close to the Cephalaspidomorphi. Many biologists no longer use the name Cephalaspidomorphi because relations among Osteostraci and Anaspida are unclear, and the affinities of the lampreys are also contested. Others have restricted the cephalaspidomorphs to include only groups more clearly related to the Osteostraci, such as Galeaspida and Pituriaspida, that were largely unknown in the 1920s. Lampreys Some reference works and databases have regarded Cephalaspidomorphi as a Linnean class whose sole living representatives are the lampreys. Evidence now suggests that lampreys acquired the characters they share with cephalaspids by convergent evolution. As such, many newer works about fishes classify lampreys in a separate group called Petromyzontida or Hyperoartia. References Janvier, Philippe. Early Vertebrates. Oxford, New York: Oxford University Press, 1998. External links The Tree of Life discusses relations among jawless fish Paleozoic jawless fish Silurian first appearances Devonian extinctions