Tremble blue whales! One of your distant, now extinct ancestors could surpass your record as the heaviest animal to ever live on Earth, according to a study released Wednesday.
The marine juggernaut called Perucetus colossus, whose first fossils were discovered in Peru in 2010, lived 39 million years ago. Its average weight was estimated at 180 tons by a team of scientists whose work is published in Nature.
A figure insufficient to win the title of heaviest animal of all time, since the largest modern blue whale ever listed weighed 190 tons according to Guinness World Records. A record, therefore, surpassing even the giant dinosaurs that disappeared millions of years ago.
But extrapolating from the massive bones of Perucetus colossus (the “colossal whale of Peru”), the researchers suggest that the weight of the ancient cetacean could vary from 85 to… 340 tons.
They remain cautious in their conclusions, but “there is no reason to believe that the specimen discovered in Peru was the largest of its kind,” says Eli Amson, co-author of the study.
“There is a good chance that some individuals have broken the record” of the blue whale, adds this paleontologist from the National Museum of Natural History in Stuttgart in Germany. What is certain is “that we are in the same range”.
The first fossil of Perucetus colossus was discovered in 2010 in the desert off the southern coast of Peru by paleontologist Mario Urbina. But it “looked more like a rock than a fossil,” according to Eli Amson.
A very small head
A total of 13 gigantic vertebrae — one of which weighed almost 200 kg — were found at the site, along with four ribs and a hip bone.
It took years and many trips to collect and prepare the fossils, and even longer for the team of Peruvian and European researchers to figure out exactly what they were dealing with: a new species of basilosauridae, an extinct family of cetaceans.
The current cetacean family includes dolphins, whales and porpoises. Their earliest ancestors lived on the land — some looked like little deer.
Over time, they migrated to water, and basilosauridae were the first cetaceans to adopt a fully aquatic lifestyle. To adapt to this change (and to be able to store more energy in particular), these marine mammals began to grow in size, an evolutionary process called gigantism.
They reached their maximum body mass 30 million years earlier than estimated, according to the study.
Like other basilosauridae, Perucetus colossus had a “ridiculously small” head compared to its body, although no bones were found to prove it, says the Dr Amson.
In 10 meters of water
Without teeth, it is impossible to know for sure what these aquatic giants ate. But the scientist hypothesizes that they raked the seabed, in particular because they could not swim quickly.
The animal certainly moved in shallow waters given the heaviness of its bones: the entire skeleton of the specimen found in Peru weighed between five and seven tons, more than twice the weight of the skeleton of a blue whale.
“It is undoubtedly the heaviest skeleton of all mammals known to date, as well as of all aquatic animals”, underlines the author of the study.
The hulking mammal needed a heavy skeleton to compensate for the enormous amount of floating fat — and air in its lungs — that might have brought it to the surface.
This fine balance between bone density and fat allowed him to stay in the middle of about 10 meters of water “without moving a muscle”, explains Eli Amson.
Perucetus colossus “is very different from anything we’ve found so far,” said Felix Marx, a marine mammal expert at New Zealand’s Te Papa Tongarewa museum, who was not involved in the study.
The fossils are on display at the Natural History Museum in Lima.