Colossal Ancient Whale May Be Heaviest Animal Ever 

Move over blue whales: A newly described ancient whale may have been the largest and heaviest animal ever.

Over a dozen bones collected in southern Peru suggest that the new species, dubbed Perucetus colossus, had a skeletal mass two or three times greater than a blue whale, researchers report Wednesday in Nature.

At its greatest size, the giant marine mammal may have weighed as much as 340 tons, or the equivalent of 34 school busses strapped together,

But this was no megalodon: The super-dense bones suggest this giant was gentle, likely munching on plants in shallow waters similar to modern-day sea cows, the researchers say.

“It’s completely unlike anything I had ever seen before,” said Alberto Collareta, a paleontologist at the University of Pisa and study co-author. The bones' overall shape resembles those of similar species, he said, “but it’s like someone inflated them as a joke. The full skeleton would have been way heavier than any other marine animal.”

The bones — 13 vertebrae, four ribs and one hip bone —- were excavated from the Peruvian desert 13 years ago. The bones themselves are huge, but they are also dense, about twice that of the largest blue whale vertebra.

By comparing P. colossus bones to those of similar species, the researchers estimated the full size and shape of the whale, which proved larger than any other known animal.

The mass of the skeleton alone was likely 5 to 7 metric tons, the researchers estimate, much heavier than a blue whale. Extending as much as 65 feet long, the full body mass of the P. colossus could have reached 340 tons — nearly twice that of an adult blue whale and three times larger than Argentinosaurus, one of the biggest dinosaurs ever found.

“Estimating body size from bones is tricky at the best of times and even trickier here as the fossil is rather incomplete. Even so, the estimates in the paper seem plausible,” said Felix Marx, a paleontologist at Museum of New Zealand Te Papa Tongarewa who wasn’t involved in the study.

In turn, it's difficult to know what kind of life P. colossus led. Still, the researchers suspect the whale stayed in shallow waters, perhaps feeding on seagrass. Being so incredibly massive could have helped P. colossus calmly munch away amid waves that would toss around smaller creatures, the researchers suspect, though having a complete skull would provide more information. Its comparatively tiny head is based on skulls from closely related whales. “I would be so happy to find a skull, it would surely help understand its diet and feeding habits.”

The ancestors of modern whales began their evolutionary journey from land to sea approximately 50 million years ago. Scientists had thought that size gradually increased over this timeframe, culminating in the massive blue whales that traverse the oceans today. But this discovery upends that theory, suggesting some whales evolved to be gigantic within a dozen million years of arriving on the scene.

“Perucetus is very different from anything else we’ve ever found,” said Marx. “It really does change our perception of these ancient whales."