Ptychodus atcoensis

P. atcoensis was a rare species of durophagous shark that lived during the Late Cretaceous. Its contemporary P. whipplei was far more abundant and tended to have a higher, bullet-shaped crown; this disparity in morpholgy suggests they may have preyed on different things.

From Shawn Hamm's thesis:
"Diagnosis. Tooth Crown high and rounded, oriented 90° to the margin area in the medial files; crown crossed by six to eight thick, chevron-shaped parallel ridges; lateral files have moderately high crowns with four to five parallel ridges; posterior teeth are low crowned with two to three ridges; differs from other species as the ridges are thick, chevron shaped and terminate sharply at a coarsely granular and concentric margin."