Peruvian fossil challenges blue whales for size

Scientists have identified a new candidate for the heaviest animal ever on planet Earth.

It’s an ancient, long-extinct whale that would have tipped the scale at close to 200 tons.

Only some of the very largest blue whale specimens could have rivaled its strength, researchers say.

The fossilized bones of the creature were unearthed in the desert of southern Peru, hence its name Perucetus colossus.

Dating of the sediments surrounding the remains suggests that it lived about 39 million years ago.

“The fossils were actually discovered 13 years ago, but their size and shape meant it took three years just to get them to Lima (the capital of Peru), where they have been studied ever since,” said Dr. Eli Amson, a co. -employee on the discovery team led by paleontologist Dr. Mario Urbina.

Eighteen bones were recovered from the marine mammal – an early type of whale known as a basilosaurid. These included 13 vertebrae, four ribs and part of a hip bone.

But even considering these fragmentary elements and their age, scientists were still able to decipher an enormous amount about the creature.

In particular, it is clear that the bones were extremely dense, caused by a process known as osteosclerosis, in which internal cavities are filled. The bones were also oversized, in the sense that they had extra growth on their outer surfaces – something called pachyostosis.

These were not disease traits, the team said, but rather adaptations that would have given this large whale the necessary buoyancy control when foraging in shallow water. Similar bony features are seen, for example, in modern manatees or manatees, which also live in coastal zones in certain parts of the world.

When confronted with the skeleton of a long-extinct species, scientists use models to try to reconstruct the animal’s body shape and mass. They do this based on what they know about the biology of comparable living things.

It is predicted Perucetus would have been around 17-20m in length, which is not unusual. But its bone mass alone would have been somewhere between 5.3 and 7.6 tons. And when you add organs, muscle and blubber, it could have weighed – depending on the assumptions – anywhere between 85 tonnes and 320 tonnes.

Dr. Amson, curator at the German Natural History Museum in Stuttgart, uses a median number of 180.

The largest blue whales recorded during the era of commercial exploitation were at this scale.

“What we would like to say is that Perucetus is in the same ballpark as the blue whale,” he told BBC News.

“But there’s no reason to think our individual was particularly large or small; it was probably just part of the general population. So it’s worth remembering that when we use the median estimate, it’s already in the upper ranges of what blue whales can measure.”

One of the comparators used by the research team in their studies is a blue whale, which will be very familiar to anyone who has visited the Natural History Museum in London.

Nicknamed Hope, this animal’s skeleton took pride of place in the institution when it was hung from the ceiling of the main hall in 2017.

But before it was installed, the skeleton was scanned and described in great detail and is now an important data resource for scientists around the world.

In life, Perucetus’ the skeletal mass would have been two to three times that of Hope, although the London mammal was a good five meters longer.

Richard Sabin, curator of marine mammals at the NHM, is excited about the new find and would love to bring some aspects of it to London for display.

“We took the time to digitize Hope – to measure not only the weight of the bones but also their shape, and our whale has now become something of a touchstone for humans,” he said.

“We don’t get hung up on labels – like ‘which was the biggest specimen?’ – because we know that at some point science will always come together with new data.

“What’s great about Perucetus is that it demonstrated so much mass about 30 million years ago, when we thought gigantism occurred in cetaceans only 4.5 million years ago.”