A giant discovery: the ancient river dolphin of the Amazon

Scientists from the University of Zurich have found a new type of freshwater dolphin in Peru, called Pebanista yacuruna: this discovery mysteriously links Amazonian dolphins with Asian ones and changes what we know about their evolution

Paleontology experts from the University of Zurich have shed light on a previously unknown species of freshwater dolphin that lived 16 million years ago, discovered in the Amazon region of Peru. This finding is particularly intriguing due to the close relationship between the new species and the river dolphins of South Asia, despite the vast geographical distance.

River dolphins are among the most unique and endangered cetaceans in the world, representing the last traces of various cetacean families that once populated the Earth. While they share similar characteristics, these mammals are not directly related but are the last sign of diverse evolutionary lines.

The University of Zurich led an international collaboration that uncovered the largest river dolphin fossil ever recorded, measuring between 3 and 3.5 meters in length, naming the creature Pebanista yacuruna in honor of a legendary Amazonian aquatic civilization. The research, published in Science Advances, offers a unique perspective on extinction dynamics and adaptation throughout Earth’s history.

A giant among dolphins

The Pebanista belongs to the Platanistoidea, cetaceans that were once widespread in the world’s oceans between 24 and 16 million years ago. Researchers suggest that these ancient oceanic dolphins adapted to the prey-rich river ecosystems of proto-Amazonia. Aldo Benites-Palomino, from the Paleontology Department at UZH, explained that 16 million years ago, the appearance of the Peruvian Amazon was radically different, dominated by an extensive system of lakes and swamps known as Pebas. This unique environment stretched across what are now Colombia, Ecuador, Bolivia, Peru, and Brazil, encompassing a variety of aquatic and terrestrial ecosystems.

The transformation of the Pebas system into the modern Amazon, about 10 million years ago, eliminated the prey of the Pebanista, leading to its extinction. This event made room for the current Amazon river dolphins (genus Inia), which were also at risk of extinction in the oceans due to the emergence of new cetacean species.

The research reveals significant details about the evolutionary history of freshwater dolphins, demonstrating that size is not the only distinctive trait of the Pebanista. Contrary to expectations, the fossils revealed a close relationship with the river dolphins of South Asia (genus Platanista), sharing unique features such as facial crests, essential for echolocation. This ability is vital for river dolphins living in murky waters, where visibility is limited, as explained by Gabriel Aguirre-Fernández, a researcher at UZH who participated in the study, and Marcelo R. Sánchez-Villagra, director of the Department of Paleontology at UZH:

After two decades of work in South America, we had found several giant forms from the region, but this is the first dolphin of this type. We were particularly intrigued by its unique biogeographic history over deep time.

Collecting fossils in the Amazon presents significant challenges. Fossils are only accessible during the dry season and must be collected quickly before the rains render them unrecoverable. The holotype of Pebanista was discovered in 2018 by an expedition led by Peruvian paleontologist Rodolfo Salas-Gismondi, culminating in the surprising discovery of a large dolphin skull, now preserved at the Museo de Historia Natural in Lima. This discovery not only enriches our understanding of cetacean evolution but also highlights the importance of conserving river ecosystems, threatened by the loss of biodiversity.

Source: Science Advances

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