Re-evaluation of teeth referred to the Late Cretaceous shark Ptychodus polygyrus from North America are hereby determined to be synonymous with another species having similar tooth morphology, Ptychodus marginalis Agassiz. Ptychodus marginalis differs from P. polygyrus by having an elevated and rounded tooth crown with transverse ridges restricted centrally on the apex of the crown with a clearly defined marginal area. The type specimen of P. marginalis was described from Middle Cenomanian to Middle Turonian deposits in the English Chalk, and teeth possessing identical tooth morphologies are found within contemporary units in North America, whereas teeth having the typical P. polygyrus morphology are restricted to Late Santonian-Early Campanian deposits.
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