Dental Morphology of Prickly and Bramble Sharks (Echinorhinidae).

Echinorhiniformes and Echinorhinidae are a distinct order and family of sharks comprising two species showing several outstanding morphological characteristics, such as their tooth morphologies. Their teeth display unique shapes among sharks with main and secondary cusps which also allow tracking the fossil record of Echinorhinidae. In this study, we review the dental morphological characters of Echinorhinus spp. and further analyse intraspecific morphological variation in a population tentatively identified as E. cf. brucus from the Indian Ocean. Previously suggested hypotheses of intra- and interspecific morphological variations are critically tested, i.e., we examine ontogenetic changes in dental morphologies in E. cf. brucus and test for species-specific differences of dental morphologies between E. brucus, E. cf. brucus, and E. cookei. Results show that within and between species dental variation is limited. Neither tooth size nor cusp angle are jaw position specific. An ontogenetic change in cusplet numbers is detected. Species-specific dental morphological differences within the examined specimens of Echinorhinus were not found; however, the overall tooth formula may be a useful character for species identification. Further, our tooth measurements are useful for estimating the average total length of specimens, which, in combination with the detected ontogenetic change in cusplet numbers, we suggest using for the characterization of the fossil record of Echinorhinus.