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Published online by Cambridge University Press: 20 May 2016
Notidanodon lanceolatus Woodward is reported from Late Aptian strata of northern California. This specimen, the oldest fossil cow shark (Hexanchidae) in the New World, greatly extends the geographic distribution of this species and confirms the eurytopic distribution of this genus. We suggest that cow shark teeth evolve in an orderly sequence in which the mesial edge of the tooth is at first smooth (Notidanus muensteri), then serrate (Notidanus serratus, Notorynchus aptiensis), and finally dentate (Notidanodon lanceolatus).