Iowa Code § 701.7: Felony defined and classified.

A public offense is a felony of a particular class when the statute defining the crime declares it to be a felony. Felonies are class “A” felonies, class “B” felonies, class “C” felonies, and class “D” felonies. Where the statute defining the offense declares it to be a felony but does not state what class of felony it is or provide for a specific penalty, that felony shall be a class “D” felony.