A NEW-WORLD OCCURRENCE OF NOTIDANODON-LANCEOLATUS (CHONDRICHTHYES, HEXANCHIDAE) AND COMMENTS ON HEXANCHID SHARK EVOLUTION

Notidanodon lanceolatus Woodward is reported from Late Aptian strata o f northern California. This specimen, the oldest fossil cow shark (Hex anchidae) in the New World, greatly extends the geographic distributio n of this species and confirms the eurytopic distribution of this genu s. We suggest that cow shark teeth evolve in an orderly sequence in wh ich the mesial edge of the tooth is at first smooth (Notidanus muenste ri), then serrate (Notidanus serratus, Notorynchus aptiensis), and fin ally dentate (Notidanodon lanceolatus).