place earlier during the Late Turonian. The youngest fossil of C. mantelli was found in the Bearpaw Formation of Alberta, dating as 73.2 million years old. A single tooth identified as Cretoxyrhina sp. was recovered from the nearby Horseshoe Canyon Formation and dated as 70.44 million years old, suggesting that Cretoxyrhina may have survived into the Maastrichtian. However, the Horseshoe Canyon Formation has only brackish water deposits despite Cretoxyrhina being a marine shark, making a likely possibility that the fossil was reworked from an older layer. Phylogenetic studies through morphological data conducted by Shimada in 2005 suggested that Cretoxyrhina may alternatively be congeneric with the genus of the modern thresher sharks; the study also stated that the results are premature and may be inaccurate and recommended that Cretoxyrhina is kept within the family Cretoxyrhinidae, mainly citing the lack of substantial data for it during the analysis. Another possible model for Cretoxyrhina evolution, proposed in 2014 by paleontologist Cajus Diedrich, suggests that C. mantelli was congeneric with the mako sharks of the genus Isurus and was part of an extended Isurus lineage beginning as far the Aptian stage in the Early Cretaceous. According to this model, the Isurus lineage was initiated by 'Isurus appendiculatus' (Cretolamna appendiculata), which evolved into Isurus denticulatus (Cretoxyrhina mantelli ) in the Mid-Cenomanian, then 'Isurus mantelli' (Cretoxyrhina mantelli ) at the beginning of the Coniacian, then Isurus schoutedenti during the Paleocene, then Isurus praecursor, where the rest of the Isurus lineage continues. The study claimed that the absence of corresponding fossils during the Maastrichtian (72–66 Ma) was not a result of a premature extinction of C. mantelli, but merely a gap in the fossil record. Shimada and fellow paleontologist Phillip Sternes published a poster in 2018 which voiced doubt over the credibility of this proposal, noting that the study's interpretation is largely based on data that had been arbitrarily selected and failed to cite either Shimada (1997) or Shimada (2005), which are key papers regarding the systematic position of C. mantelli. Biology Morphology Dentition Distinguishing characteristics of Cretoxyrhina teeth include a nearly symmetrical or slanted triangular shape, razor-like and non-serrated cutting edges, visible tooth necks (bourlette), and a thick enamel coating. The dentition of Cretoxyrhina possesses the basic dental characteristics of a mackerel shark, with tooth rows closely spaced without any overlap. Anterior teeth are straight and near-symmetrical, while lateroposterior teeth are slanted. The side of the