The study found that sharks have depleted functional diversity compared to the last 66 million years

New research from Swansea University and the University of Zurich has found that sharks maintained a high level of functional diversity for most of the past 66 million years, before steadily declining to its current low during the last 10 million years.

The study is published in Global ecology and biogeography.

Modern sharks are among the ocean’s most endangered species, yet they have remarkably survived numerous environmental changes in their 250-million-year history. Today, more than 500 species play many different ecological roles, from apex predators to nutrient transporters.

Ecological roles are determined by species characteristics such as body size and what and how they eat. As such, measuring the diversity of these traits allows scientists to quantify the range of ecological roles in a community, also known as functional diversity.

Because sharks have soft cartilaginous skeletons that are unlikely to fossilize, it is difficult to directly measure these characteristics in extinct species. However, measurements from their teeth, which are hard and therefore well-preserved in the fossil record, can act as proxies that can in turn be used to quantify functional diversity in the geological past.

Lead author Jack Cooper, Ph.D. student at Swansea University, said: “Measurements such as tooth size, shape and edge types broadly reflect shark functional characteristics such as body size and diet, allowing us to assess their functional diversity over time.”

The researchers measured more than 9,000 fossil and living shark teeth from approximately 500 species, collected from museum collections and the literature, and quantified functional diversity throughout the Cenozoic Era, 66 million years ago to the present.

They found that sharks maintained a high level of functional diversity – meaning a wide range of ecological roles – throughout most of the Cenozoic era. This diversity peaked about 20 million years ago in the Miocene Epoch. However, they also found that after this peak, the range of shark ecological functions has steadily declined over the past 10 million years, with current shark functional diversity lower than at any time in the past 66 million years.

By quantifying the ecological contributions of individual species, the scientists found that the observed decline was caused by the decline of ecologically unique and specialized species. Among such losses was the extinction of the megalodon, the largest shark that ever lived, which was an apex superpredator, an ecological role that no shark living today plays.

He added: “Not only did we see a clear decline in functional diversity, but we also found that extinct sharks as a whole contribute to a wider range of ecological roles than living sharks.”

Ultimately, the results warn that human threats, such as overfishing, which is driving today’s sharks to extinction, are likely to further erode sharks’ already diminished ecological contributions to ecosystem functioning.

Lead author Dr. Catalina Pimiento, Professor at the University of Zurich and Associate Professor at Swansea University, said: “By identifying modern species retaining part of the Cenozoic functional space, our study could potentially complement conservation priorities for preserving the functional diversity of sharks.” in our changing world.”