Perucetus colossus was only two-thirds the size of a blue whale, but its dense bones may have made it much heavier.
Until now, the blue whale was widely considered to be the heaviest animal of all time, weighing up to 200 tons and sometimes measuring more than 100 feet in length. But a new discovery from University of Pisa paleontologists may dethrone the blue whale in favor of a prehistoric cetacean from 37 million years ago.
Per a National Geographic report, University of Pisa paleontologist Giovanii Bianucci and colleagues recently uncovered an immense cetacean that was likely a bit shorter than the blue whale, but possibly much heavier. Named Perucetus colossus, this prehistoric whale was roughly 60 feet long, but could have weighed more than 300 tons.
Mario Urbina, study co-author and paleontologist at the National University of San Marcos, found the prehistoric whale’s skeleton 13 years ago among rocks in southern Peru’s Ica Valley. But paleontologists weren’t immediately impressed — largely because some of the bones were themselves as large as boulders.
“At first, he had to convince the other members of the team that what he found was actually some fossil, because of the weird shape of it,” recalled study co-author Eli Amson of the State Museum of Natural History Stuttgart in Germany.
However, researchers soon realized that these boulder-like bumps were actually massive pieces of vertebrae. Field teams spent the next decade excavating the site and freeing Perucetus from its rocky resting place.
In all, paleontologists excavated 13 vertebrae, four ribs, and part of Perucetus’ hip from the Ica Valley. According to the New York Times, the whale bones were unusually dense, which made it difficult for researchers to identify what sort of animal they belonged to.
It wasn’t until they discovered the pelvis bone that they truly began to understand what they were looking at. While the other bones were strangely thick, the pelvis was small and delicate. It also had crests and other features distinctive of whales.
The anatomy, location, and time period all indicated that this whale was a relative of Basilosaurus, a prehistoric whale with a long snout and sharp, cutting teeth. These whales evolved from an even more ancient species of dog-sized land animals around 50 million years ago, and although they were fully aquatic, they still retained vestiges of their land-locked counterparts — particularly, small hind legs with toes.
Around 35 million years ago, however, Basilosaurus began to die out, and as they went extinct, a new group of whales emerged to take their place. These whales became the ancestors of today’s whales.
Perucetus’ pelvis may have been reminiscent of Basilosaurus’, but it was unlike any Basilosaurus pelvis ever found before. Upon examining the bone, Amson found that its ribs and spine actually contained extra layers of outer bone, resulting in their bloated, odd shapes.
While a typical bone contains a multitude of pores that reduce its weight without sacrificing strength, Perucetus’ bones were solid throughout. In fact, the fossil is so hard and dense that attempting to drive a nail into it with a hammer “would make nothing but sparks,” Amson said.
Amson and colleagues created 3-D scans of the fossil bones to make a digital reconstruction of the whale’s full skeleton, which they then compared to other basilosaurids that have been fully preserved.
Operating under the assumption that the rest of Perucetus would be equally dense, they estimated that its complete skeleton, if roughly the same size as other basilosaurids, would weigh between 5.8 and 8.3 tons. In this case, Perucetus would have had the heaviest skeleton of any mammal — nearly twice as heavy as a blue whale’s.
So, despite only being two-thirds the size of a blue whale, it would have likely weighed roughly the same.
“It’s definitely in the blue whale ballpark,” Amson said. And that’s the low estimate. According to INSIDER, researchers determined that Perucetus could have weighed up to 340 tons, which would make it the heaviest animal on record.
Other experts weren’t quite as convinced. Nicholas Pyenson, a paleontologist at the Smithsonian National Museum of Natural History who was not involved in the study, said, “Until we find the rest of the skeleton, I think we should shelve the heavyweight-contender issue.”
However, Hans Thewissen, a paleontologist at Northeast Ohio Medical University, who was also not involved in the study, weighed in, saying, “I agree with the excitement around the weight.”
Researchers also suggested that Perucetus would likely have lived its life in a similar fashion to manatees, which also have fairly dense bones. Manatees, unlike whales, graze on the ocean floor and move about slowly by raising and lowering their tails.
Based on where researchers found Perucetus’ bones, they estimated that it moved slowly through coastal waters no deeper than 150 feet, though they have no clue at present how these prehistoric leviathans fueled their massive bodies.
“My personal favorite idea, though it is only speculation, is that Perucetus was a scavenger,” Amson said, “feeding on the carcasses of other large animals.”
Without a complete skeleton, however, much of Perucetus’ life will remain a mystery. The team’s findings were published on Aug. 2, 2023 in the journal Nature.
After reading about this massive prehistoric whale, read about the discovery of a four-legged whale in Egypt that was once called the “God of Death.” Or, read the story of a whale who washed up on a beach in Oregon — and was then blown up with dynamite.