Extinction threatens to cause morphological and ecological homogenization in sharks

Global shark biodiversity is in decline, with numerous species facing extinction because of anthropogenic influence. Loss of species richness is expected to diminish trait diversity, encompassing ecological roles and physiological adaptations. We investigate whether the extinction of threatened species, as classified by the International Union for Conservation of Nature, drives morphological and ecological homogenization within Carcharhinus, a speciose genus of requiem sharks. We assembled a dataset of tooth morphology from 30 species and combined it with functional data such as diet, habitat, and body size. Simulated extinction scenarios, where species were sequentially removed from the highest to lowest threat level, revealed that the loss of threatened species would result in marked homogenization of morphology and ecology. Along this extinction trajectory, trait structures become increasingly depauperate, marked by contracting depth ranges and declining body-size diversity. Our results indicate that the diverse dental morphologies, shaped over millions of years, are at risk of disappearing-eroding the genus's capacity to support varied ecological roles.