# Extinction threatens to cause morphological and ecological homogenization in sharks

## TL;DR

Extinction of threatened shark species is causing a loss of diversity in their physical traits and ecological roles.

## Contribution

The study shows that extinction of threatened shark species leads to homogenization of morphology and ecology in the genus Carcharhinus.

## Key findings

- Simulated extinction scenarios show significant homogenization of shark morphology and ecology.
- Loss of threatened species reduces trait diversity, including body size and habitat range.
- Dental morphologies shaped over millions of years are at risk of disappearing.

## Abstract

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.

The selective extinction of threatened shark species is poised to drive substantial morphological and ecological homogenization.