Morphology and systematic implications of fossil and recent Lamnid shark vertebrae using computerized tomography (CT-scanning)

The use of CT-scanning to better understand shark anatomy is a relatively new technique. The amount of information gained from work on the internal morphology of the braincase has shown to significantly increase when CT-scanning is employed, and more importantly, having done so through non-invasive means. This project applies this technique to Lamnid shark vertebral columns with the intention of determining phylogenetically useful characters from vertebral centra without destroying the specimens, and more specifically, to shed additional light on the phylogenetic position of the fossil shark, Carcharodon megalodon. The use of fossil material in this project strengthens the need for non-invasive means. After scans were made, both external and internal measurements were used, as well as morphological features, to determine characters and character states. Phylogenetic analyses were mixed. The Carcharhiniform specimens (used as the outgroup) were grouped together, though they were not the most basal of the specimens: Alopias vulpinus, the Thresher shark, was. The Carcharodon megalodon specimens grouped together with other Lamnids, which in itself is promising, though not significant enough to further clarify their position. The CT-scanning was successful in identifying internal structures for study. This technique is highly influenced by the technology available for scanning, as well as by the preservation quality of the specimens.