PRELIMINARY FINDINGS FROM THE GEOMETRIC MORPHOMETRIC COMPARISON OF SPECIES WITHIN THE GENERA ISURUS AND CARCHARODON

The evolutionary relationships within and between the genera Isurus and Carcharodon are unclear and often debated. While numerous hypotheses have been suggested for revision of this group few quantitative analyses have been applied. Geometric morphometrics methods were used to digitize and compare the shape of the upper left anterior tooth position from 11 species of taxa from the Isurus and Carcharodon (Cosmopolitodus) complexes. Procrustes method and relative warp analysis (RWA) was used to ordinate tooth shape by taxa. The first RWA axis differentiated teeth based primarily on crown shape and the height of each root lobe above the center of the root, with I. xiphodon (nomen dubium) representing the positive-most extreme and I. oxyrinchus representing the negative-most extreme. The second RWA axis differentiated teeth primarily based on root width and crown curvature (mesial/distal slant), with I. praecursor representing the positive-most extreme and I. planus representing the negative-most extreme. Subsequent linear modeling of the first axis identified no significant difference between teeth of C. carcharias, C. hubbelli, and I. xiphodon, or between C. hastalis and I. escheri. Concurrently, significant overlap was found between I. retroflexus and I. paucus. The second axis explained less variation, while modeling identified significant overlap in tooth morphology between I. desori, I. escheri, C. hastalis, C. hubbelli and I. oxyrinchus, as well as between I. paucus, I. retroflexus, I. xiphodon, and C. carcharias. Overlap was also seen, to a lesser extent, between C. carcharias and I. praecursor. The combined graph of these two axes successfully clustered similar morphological traits together, and provides a useful tool in parsing out evolutionary relationships.