Scientists have discovered the fossilized skull of a giant river dolphin, of a species believed to have fled the sea and taken refuge in Peru’s Amazon rivers 16 million years ago. The extinct species would have measured up to 3.5 meters in length, making it the largest river dolphin ever found.
The discovery of this new species, Pebanista yacurunahighlights the looming risks to the world’s remaining river dolphins, all of which face similar extinction threats in the next 20 to 40 years, according to the lead author of new research published in Science advances today. Aldo Benites-Palomino said it belonged to the Platanistoidea family of dolphins commonly found in oceans between 24m and 16m years ago.
Surviving river dolphins were “the remnants of what were once very diverse marine dolphin groups”, he said, which presumably left the oceans to find new food sources in freshwater rivers.
“Rivers are the escape valve … for the ancient fossil we found, and it’s the same for all river dolphins alive today.”
Benites-Palomino discovered the fossil in Peru in 2018 when he was still an undergraduate student. He is now working on a doctorate at the University of Zurich’s Department of Paleontology, and says the research paper has been delayed by the pandemic.
He first noticed part of the fossil, a fragment of the jawbone, while walking with a colleague. “As soon as I recognized it, I saw the sockets of the teeth. I shouted, ‘this is a dolphin.’ We could not believe it.
“Then we realized it was not related to the Amazon river pink dolphin,” he said. “We [had] an animal, a giant, found whose nearest living relative is 10,000 km away in Southeast Asia.”
Marcelo R Sánchez-Villagra, director of the University of Zurich’s paleontology department, said the find was interesting. “After two decades of work in South America, we have found several giant forms from the region, but this is the first dolphin of its kind,” he said.
The fossil, Benites-Palomino said, was remarkable both for its size and because it had no links to the river dolphins that now swim in the waters it once inhabited.
A shared problem facing river dolphins – including the fossil’s closest living relatives that swim in the Ganges and Indus rivers – is the looming risk of extinction. Urban development, pollution and mining were the key causes, he said, and had already driven the Yangtze River dolphin to extinction.
