A team of Argentinian scientists has published a study in Nature Communications that sheds light on the evolution of whales, dolphins, and porpoises over the last 50 million years. The research, led by specialists from CONICET and the National University of La Plata, analyzes how these marine mammals transitioned from living on land to dominating the oceans, and what factors determined their evolutionary success.
The study, which required years of collecting fossil and current data, focuses on three key moments that shaped the history of cetaceans. The researchers not only counted species but also assessed their ecological roles, arriving at a surprising conclusion: the number of species does not always correlate with the variety of roles they play in the ecosystem.
The three key moments in the evolution of cetaceans
The first major milestone occurred about 33 million years ago, during the transition from the Eocene to the Oligocene. At that time, the ancestors of whales and dolphins abandoned terrestrial life and fully adapted to the aquatic environment. It was the transition from archaeocetes, primitive limbed whales, to neocetes, the group that includes all modern cetaceans.
The second period occurred between the late Oligocene and the early Miocene, approximately 23 million years ago. Two key innovations emerged during this time: baleen in whales for filtering food and echolocation in dolphins and porpoises, which allows them to navigate and hunt using sound. These adaptations proved so successful that they have remained virtually unchanged to this day.
The third episode took place during the Plio-Pleistocene, about 2,6 million years ago. This period saw a mass extinction of ancient lineages , but also the emergence of the species diversity we know today. Scientists observed that, despite the disappearance of many life forms, fundamental ecological roles were preserved.
The decoupling between species and ecological functions
One of the most striking findings of the study is the decoupling between taxonomic diversity and ecological disparity . During the Miocene, for example, there was a large number of species, but little variety in their roles: many occupied similar niches. In contrast, during the Plio-Pleistocene, although the number of species decreased drastically, ecological roles remained stable.
“We evaluated how these different ecological factors influenced the evolutionary success of species,” explained Mónica Buono, one of the authors. The team analyzed variables such as body size, diet, locomotion, and hearing abilities. They discovered that critical ecological roles , such as those of large filter feeders or apex predators, persisted over time, even as the species that filled them changed.
This finding contradicts the idea that cetacean diversity depended primarily on climatic or environmental factors. The researchers found that key adaptations, such as baleen and echolocation, remained stable for millions of years, and that environmental changes did not always directly impact species diversity.
Implications for marine conservation
The study's authors emphasize that protecting a large number of species is not enough to preserve the balance of the oceans . It is more important to ensure the maintenance of essential ecological functions, such as the filtration of large volumes of water and predation at the top of the food chain. "Our work provides a quantitative framework for understanding why some adaptations have been so successful," noted co-author Mariana Viglino.
The study also reveals that some groups, such as sperm whales, radically changed their ecological niche. Twenty million years ago, they were apex predators, similar to the behavior of modern orcas , while today they specialize in catching squid in the deep sea using suction. This type of variation demonstrates that evolutionary paths were conditioned by key acquisitions, but with internal flexibility in certain lineages.
The research, which included 127 fossil and extant species, is based on one of the most comprehensive databases on cetaceans, compiled from collections in Argentina, Chile, Belgium, and the United States. Scientists hope this work will become a benchmark for future paleontological studies and for designing conservation strategies based on ecological function, rather than traditional taxonomy.
Thus, the evolution of whales and dolphins not only tells us about the past, but also offers lessons for the present: the key to their success lies not in the number of species, but in the persistence of the roles that keep the marine ecosystem alive. This approach, according to researchers, can be applied to other vertebrate groups and help us rethink how we protect biodiversity.
