Dental crown morphological variation and heterodonty in carcharhiniform sharks.

Elasmobranch teeth are highly mineralized structures that constitute the majority of the fossil record for this group. Despite their taxonomic and evolutionary significance, detailed descriptions of dental morphology remain scarce. The order Carcharhiniformes, the most diverse among sharks, comprises 304 valid species that display remarkable diversity and complexity in dentition. This study aims to describe and illustrate crown morphological variation within Carcharhiniformes, with a focus on family-level patterns and types of heterodonty. Tooth samples were obtained from specimens preserved in 70% ethanol and from dry jaws. A total of 66 samples, representing all families except Dichichthyidae, were examined and photographed using a scanning electron microscope (SEM). The types of heterodonty considered include dignathic, gynandric, monognathic, and ontogenetic. Dignathic and monognathic heterodonty were further classified as weak, moderate, and strong. Four sub-arrangements were recognized: imbricate, independent, mixed, and overlap, as well as the pavement and independent dentition arrangements. New data reveal previously unrecognized patterns of variation across the four types of heterodonty in Carcharhinidae, Scyliorhinidae, Proscylliidae, Triakidae, and Pentanchidae. High-resolution SEM images allowed detailed characterization of crown morphology, highlighting subtle diagnostic features and family-level differences across heterodonty types. Dental complexity in Carcharhiniformes is largely driven by the distribution and combination of heterodonty types. These detailed dental descriptions provide a valuable framework for understanding the diversity and evolutionary significance of dentition within the most diverse order of sharks.