Argentine study reveals 50 million years of cetacean evolution

A team of Argentine scientists has achieved a significant milestone in national science by reconstructing 50 million years of evolutionary and ecological history for cetaceans. Their findings, published in the journal Nature Communications, offer a new quantitative framework for understanding how whales and dolphins transitioned from terrestrial to aquatic life.

The research, led by experts from the National Patagonic Center (Cenpat-Conicet) and the National University of La Plata, analyzed a dataset of 127 species, both extinct and extant. They evaluated variables such as body size, diet, auditory capabilities, and locomotion.

One of the most striking discoveries is the decoupling between taxonomic diversity and ecological disparity. During periods like the Miocene, there were many species, but they often filled similar ecological roles. Conversely, mass extinction events in the Pliocene-Pleistocene era eliminated numerous lineages without significantly altering the overall ecological structure. This suggests that the success of cetaceans was not solely dependent on the number of species, but on the maintenance of crucial roles, such as large filter feeders or apex predators.

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The objective was to better understand how the evolution of cetaceans occurred over 50 million years. This is a group of mammals that returned to the water and, in that process, underwent enormous modifications. They have a rather particular evolutionary history, with many changes in the number of species, and were affected by different factors.

"The objective was to better understand how the evolution of cetaceans occurred over 50 million years. This is a group of mammals that returned to the water and, in that process, underwent enormous modifications," said Mónica Buono, a paleomammalogy specialist and one of the lead researchers. "Although some aspects had been reported before, this is the first time we were able to quantify them. We observed that, while species diversity fluctuated greatly, certain ecological specializations and adaptations were acquired and maintained over time, even though the group was heavily affected by extinctions at various points."

The study identifies three key moments in cetacean evolution: the definitive transition from land to water between the Eocene and Oligocene; the appearance of baleen in whales and echolocation in dolphins from the late Oligocene to early Miocene; and the emergence of modern diversity after major extinctions during the Pliocene-Pleistocene transition.

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Although some aspects had been reported before, this is the first time we were able to quantify them. We observed that, while species diversity fluctuated greatly, certain ecological specializations and adaptations were acquired and maintained over time, even though the group was heavily affected by extinctions at various points. Among these specializations are filter feeding with baleen in mysticetes and echolocation in odontocetes.