Meeting Abstract
Characters based on tooth microstructure and tooth development have been included in phylogenetic studies of sharks (Chondrichthyes: Elasmobranchii: Selachii), but many critical details have not been compared as closely as needed. We used histology and micro-CT scanning to study tooth morphology and development in the Sharpnose Sevengill Shark (Hexanchiformes: Hexanchidae: Heptranchias perlo) using the same methods we previously used to study the Blue Shark (Carcharhiniformes: Carcharhinidae: Prionace glauca) and the White Shark (Lamniformes: Lamnidae: Carcharodon carcharias). We found that the Sharpnose Sevengill Shark has relatively few rows of replacement teeth, which is similar to the Blue Shark, but that that the fully developed teeth are composed primarily of osteodentine and lack a well-developed pulp cavity. This condition, categorized as osteodont, also occurs in lamniform sharks such as the White Shark. A low number of rows of replacement teeth suggests that tooth replacement rates are relatively slow, which could be correlated with factors such as diet or metabolism. But it is striking that the Sharpnose Sevengill Shark and White Shark have similar tooth microstructure, for they are only distantly related. As yet, we do not have an explanation for this apparently convergent condition in tooth microstructure.
