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This study reevaluates the tooth morphology used to define species within the genus  Edestus  (Chondrichthyes, Euchondrocephali). Known as the scissor tooth shark,  Edestus  produced a unique dentition of spiraled tooth families positioned in the symphysis (midline) of the upper and lower jaws. Morphometric analysis of more than 200 ejected teeth and intact spiral tooth whorls demonstrates that teeth from the upper and lower whorls differ in shape and ontogeny. Comparison of these data to the type specimens of 13 existing species reduces the number of morphologically distinct  Edestus  to just four species and refines the stratigraphic occurrence and expansion of the group.  E .  triserratus  has a narrow bullet-shaped crown that points anteriorly and has roots of intermediate length.  E .  minor  crowns have a wider triangular base, whereas the crowns of  E .  heinrichi  form nearly equilateral triangles and are supported by an elongated root.  E .  vorax , which also has roughly equilateral triangular crowns, has short and deep roots, and is only known from very large specimens that are distinct from the growth series of  E .  heinrichi . Tooth and whorl morphologies among the species are consistent with cranial anatomy observed in a juvenile  E .  heinrichi  and with transverse tooth-wear patterns to suggest  Edestus  used a forward to backward slicing motion to bite its prey. Extrapolating body size from tooth whorl length provides a conservative estimate that  E .  heinrichi  could exceed 6.7 m in length.  Edestus  fossils are recovered from coastal marine to estuarine deposits spanning roughly six million years (313–307 Ma).  Edestus  first appears in England during the latest Bashkirian (313 Ma, Carboniferous), a few million years after its most closely resembling genus  Lestrodus . Diversification and range expansion of  Edestus  coincides with the Moscovian transgression that flooded Laurentia and the Russian platform.

Redefining species concepts for the Pennsylvanian scissor tooth shark, Edestus