Researchers dispute the claim that the ancient whale was the heaviest animal ever known
Last August, a team of paleontologists announced they had discovered the fossilized bones of a gigantic ancient whale. Perucetus, as they called it, may have weighed more than 200 tons, which would make it the heaviest animal that ever lived.
But in a study published Thursday, a pair of scientists did just that challenged that bold statement. “The numbers don’t make sense,” said Nicholas Pyenson, a paleontologist at the Smithsonian National Museum of Natural History and one of the authors of the new study.
In their new analysis, Dr. Pyenson and Ryosuke Motani, a paleontologist at the University of California, Davis, that Perucetus probably weighed 60 to 70 tons, which would have made it about the size of a sperm whale.
They also analyzed fossils of blue whales and provided a new estimate of that species’ weight. They concluded that blue whales weigh up to 270 tons – much more than previous estimates 150 tons – which would make them by far the heaviest known species in the history of the animal kingdom.
Perucetus first came to light in 2010, when Mario Urbina, a paleontologist at the Natural History Museum of the National University of San Marcos in Lima, Peru, spotted a bone in a desert in southern Peru. He and his colleagues unearthed thirteen vertebrae, four ribs and part of a pelvis.
The bones showed many characteristics of whale bones. But they were also astonishingly large and heavy. Dr. Urbina and his colleagues reconstructed the entire skeleton of Perucetus by studying the much smaller whales that lived at the same time. They were also inspired by living manatees, which have a dense skeleton that allows them to stay underwater to graze on seagrass.
Dr. Urbina and his colleagues eventually arrived at a reconstruction of a bizarre animal. It had a huge eclair-shaped trunk, a small head, flippers and rudimentary hind legs.
But Dr. Motani, an expert in the field reconstruct the bodies of extinct marine animals, was amazed at their conclusions. “I thought: how is that possible? How can you fit that mass into that volume?” he said.
Dr. Motani contacted Dr. Pyenson, an expert on whale fossils. They both believed that modeling Perucetus after manatees was a mistake, as only whales have evolved to truly gigantic sizes.
“It’s very important to compare apples to apples,” said Dr. Pyenson.
For their own research, Dr. Pyenson and Dr. Motani took a fresh look at living whales. Since no one can drag a live blue whale onto a scale, no one has ever measured its weight accurately. Dr. Pyenson and Dr. Motani collected data collected by Japanese whalers in the 1940s and used it as the basis for a new estimate.
They also created a three-dimensional model of the blue whale and used it to make a model of Perucetus. Using this approach, they estimated that Perucetus weighed 60 to 70 tons, much less than the other research team had concluded.
Eli Amson, an expert on bone tissue at the State Museum of Natural History in Stuttgart, Germany and author of the original study, disagreed with the new approach. “This extinct whale had a very different biology than that of recent whales,” he said.
Dr. Amson said he and his colleagues are now creating their own three-dimensional model of the ancient species. They found that Perucetus looked even more like manatees than they initially thought, reinforcing their conclusion that it matched or even exceeded the blue whale in weight, he said.
Dr. Pyenson said Perucetus remains an important discovery despite the smaller size he and Dr. Motani suggest. Paleontologists have long believed that whales evolved to enormous sizes only in the past few million years. Even at 60 tons, Perucetus would have been a giant among early whales.
“Whales were clearly exploring large sizes,” said Dr. Pyenson.