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(CNN) — Imagine a dolphin. Now imagine something twice the size of a human.
About 16 million years ago, a giant dolphin roamed the depths of the water space. But unlike most modern dolphins, its home wasn’t the ocean; It lived in a freshwater lake in the Peruvian Amazon. And although there are species of Amazonian freshwater dolphins alive today, they are not close relatives of those ancient marine mammals. Its closest living relatives are river dolphins, which live more than 10,000 kilometers away in South Asia, according to researchers who recently identified the previously unknown extinct mammal.
Analysis of the newly identified ancient dolphin’s skull told paleontologists that its body may have been at least 3.5 meters long; This makes it about 20% to 25% larger than modern river dolphins and the largest known freshwater dolphin.
But the skull, which measured about 27 inches (70 centimeters) long, was missing, so the ancient dolphin may have been even larger than that, scientists reported March 20 in the journal Science Advances, published by the American Association for the Advancement of Science. Science.
What makes the find even more exceptional are the insights it offers into the evolutionary history of freshwater dolphins, the study authors wrote, because these creatures are extremely rare in the fossil record. This is because there are fewer individual dolphins in freshwater ecosystems and strong water currents often prevent fossils from being well preserved.
They named the newly discovered species Pebanista yacuruna; The genus refers to Peru’s Pebas Formation, where the fossil was found, and “yacuruna” is the Native Kichua language term for legendary water people in local legend.
“I think this is a remarkable discovery, especially considering that a species of river dolphin belonging to a completely different group of odontocetes (toothed whales) has been found in South America,” said Jorge Velez-Juarbe, curator of marine mammals at Natural magazine. Los Angeles County Historical Museum in an email.
“I wonder how many more records of extinct river dolphins are waiting to be discovered,” Velez-Juarbe, who was not involved in the research, told CNN.
‘Everyone went crazy’: Fossil features reveal rare findings
Modern freshwater dolphins are known for their extremely long snouts compared to the thicker snouts of marine dolphins. There are the South Asian river dolphin (genus Platanista) and the Amazon river dolphin (genus Inia), also known as the pink river dolphin, and several species and subspecies exist in the two groups.
The Yangtze river dolphin (Lipotes vexillifer) in China represents a third genus, but the species has not been seen in the wild for 40 years and may be extinct, according to the International Union for Conservation of Nature (IUCN). In fact, the IUCN says that all existing river dolphin species are threatened with extinction or critically endangered.
Researchers discovered the Amazon dolphin fossil near the Napo River in Loreto, Peru, in 2018. The study’s lead author, Aldo Benites-Palomino, a doctoral candidate in the Department of Paleontology at the University of Zurich, told CNN that he stopped to examine some strange-looking pieces of rock on the ground. Study co-author John J. Flynn, who is also curator of mammal fossils at the American Museum of Natural History in New York City, pointed out what appeared to be a skull emerging from an embankment.
“I said, ‘Hey John, does this relate to this piece I have,'” Benites-Palomino recalled. What he was holding turned out to be a rostrum (the rounded end of a snout) taken from the buried skull. When they cleaned the tooth sockets enough to see their shape, Benites-Palomino realized they were looking at something unusual.
“We started shouting: ‘It’s a dolphin! It’s a dolphin!’” Benites-Palomino said.
At first they thought it would be an ancient relative of modern Amazon river dolphins. But further examination revealed that the size and shape of the eye socket was similar to that of South Asian river dolphins, which have much smaller eyes than their South American cousins.
“That was a moment where everyone went crazy because it wasn’t an Amazon river dolphin,” Benites-Palomino said. This showed scientists that the two species of dolphins were moving deeper into the area independently and at different times.
Researching dolphin diversity
Platanistoids (the group that includes P. yacuruna and the modern river dolphins of South Asia) were widespread about 20 million years ago. The ancestors of modern Amazon river dolphins were widespread in the oceans about 10 to 6 million years ago, Benites-Palomino said.
Because both groups of cetaceans are so diverse, some species likely migrated into river and lake ecosystems in search of less competition for food. This freshwater environment of the Amazon was rich in nutrients and teeming with life; It was home to crocodiles, turtles, and fish, as well as mammals such as sloths, rodents, ungulates, and primates.
“In general, ‘river dolphins’ can be considered apex predators in these ecosystems,” Velez-Juarbe said.
P. yacuruna was among the first wave of dolphins to test the waters in Amazon rivers and lakes; According to the study, the absence of predators in its new home may explain how the species grew so large. However, environmental changes such as drought may have subsequently doomed P. yacuruna and driven it to extinction, opening its freshwater habitat to the ancestors of extant pink river dolphins.
“We now know that this species lived there in the past, but Amazonia is also important for our current Inia geoffrensis,” Benites-Palomino said. “[The discovery] “It highlights that this is an extremely important environment for the evolution of freshwater cetaceans.”
The disappearance of P. yacuruna is a grim reminder that this important environment can be disrupted very easily. Today, modern Amazon river dolphins face an uncertain future as mercury pollution, mostly from gold mining, invades the food chain, according to the World Wildlife Fund. Velez-Juarbe added that the newly found fossil points to the fragility of freshwater ecosystems and the vulnerability of those living in these ecosystems (past and present) to environmental changes, whether such changes are natural or man-made.
“Pebanista adds another layer to the complex evolutionary history of cetaceans, and particularly ‘river dolphins’; the few surviving species are the last remnants of once more diverse groups.”
Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works magazines.
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