Paleontologists on Wednesday exposed the fossilized bones of one of the strangest whales in history. The 39-million-year-old leviathan, called Perucetus, may have weighed around 200 tonnes, as much as a blue whale – by far the heaviest animal known, so far.
While blue whales are sleek, fast swimmers, Perucetus is a different animal. Researchers suspect it lazily drifted in shallow coastal waters like a mammoth manatee, propelling its sausage-like body with its oar-shaped tail.
Some experts caution that more bones need to be discovered before a firm estimate of Perucetus’ weight can be made. But they all agreed that the strange find will change the way paleontologists look at the evolution of whales from land mammals.
“It’s a unique and fascinating fossil, for sure,” said Nicholas Pyenson, a paleontologist at the Smithsonian National Museum of Natural History, who was not involved in the study. “It’s clear from this discovery that there are so many other ways of being a whale that we haven’t discovered yet.”
Mario Urbina, a paleontologist at the Museum of Natural History at the National University of San Marcos in Lima, Peru, first laid eyes on Perucetus in 2010. He was hiking in the Atacama Desert in southern Peru when he noticed a rocky outcrop jutting out from the sand When he and his colleagues finished excavating it, the lump proved to be a massive vertebra.
Upon further excavation, the researchers found 13 vertebrae in total, along with four ribs and part of a pelvis. Except for the pelvis, all the fossils are remarkably dense and unusually thick, making it hard to tell what kind of animal they are.
Only the pelvis revealed exactly what the scientists found. Unlike other bones, the pelvis is small and finely developed. It had crests and other distinctive features that revealed it was a whale – specifically, from an early branch of the whale evolutionary tree.
Whales evolved from dog-sized land mammals about 50 million years ago. Some of the earliest species evolved short legs and probably led a seal-like existence, hunting fish and then hauling themselves ashore to breed.
The first whales disappeared after a few million years. They were replaced by a group of fully aquatic whales called basilosaurids. These spiky animals can grow as large as a school bus but retain traces of their life on land — including tiny hind legs, complete with toes.
Basilosaurids dominated the oceans until about 35 million years ago. When they disappeared, another group of whales appeared, giving rise to the ancestors of living whales.
Today’s largest whales, such as blue whales and fin whales, only reached their enormous size in the last few million years. Changes in ocean currents supported extensive populations of krill and other invertebrates near the poles. Whales can grow very large by scooping up prey in lunging dives.
The pelvis of Perucetus revealed that it was a basilosaurid, but the whale turned out to be a basilosaurid unlike anything found before. Eli Amson, a bone tissue expert at the State Museum of Natural History in Stuttgart, Germany, found that its ribs and spine had extra layers of outer bone, giving them a bloated shape. .
A typical bone is full of pores, making it lighter without sacrificing strength. Dr. noticed Amson that the seeds of Perucetus are solid throughout. The fossil is so hard in parts that it is impossible to drive a nail into it with a hammer.
“It will do nothing but sparks,” he said.
Dr. Amson and his colleagues made three-dimensional scans of the fossil bones to reconstruct the whale’s entire skeleton. They compared Perucetus with other basilosaurids that were preserved from head to tail.
If the rest of Perucetus was a denser, thicker version of these whales, its complete skeleton would have weighed between 5.8 and 8.3 tons. That means Perucetus had the heaviest skeleton of any mammal – bones twice as heavy as a blue whale.
That massive skeleton also suggests that Perucetus had a thick, barrel-like body. Although Perucetus was only about two-thirds the length of a blue whale, Dr. Amson and his colleagues that it weighs almost the same.
“It’s definitely in the blue whale ballpark,” said Dr. Amson.
Dr. thought Pyenson, of the Smithsonian National Museum of Natural History, that it is premature to make such an estimate. “Until we find the rest of the plot, I think we should shelve the heavyweight-contender issue,” he said.
But Hans Thewissen, a paleontologist at Northeast Ohio Medical University, who was not involved in the study, said the estimate is reasonable. “I agree with the fuss around weight,” he said.
The fossil suggests that Perucetus reached such a large size without feeding as blue whales do. Analysis of its bones suggests it lived like a gigantic manatee.
Manatees feed on sea grass on the ocean floor. Their lungs are full of air, and their intestines produce gas as they digest their food. To stay underwater, manatees have evolved dense bones as ballast.
The spine structure of Perucetus is similar to that of a manatee. Dr. thought Amson the whale swims manatee-style, slowly raising and lowering its tail.
Based on the rocks where the fossils were found, Dr. suspects. Amson and his colleagues found that Perucetus moved slowly in coastal waters not exceeding 150 feet. But how they powered their giant bodies is still a mystery.
said Dr. Amson that Perucetus may have also eaten sea grass, but that would make it the first herbivorous whale known to science. “We think it’s unlikely, but who knows?” he said.
Dr. still thinks Amson that Perucetus possibly lived as a scavenger, picking up corpses.
On the contrary, Dr. favored. Thewissen theorized that these whales scooped up mud from the sea floor to eat the worms and shellfish it contained – something gray whales do today.
The head of Perucetus will have adaptations for either way of life. “I want to see this man’s skull,” said Dr. Thewissen.
However it lived, Perucetus was proof that whales didn’t have to wait until recently to get big. “The most important message is not that we can enter the Guinness Book of World Records,” said Dr. Amson. “It has another path to gigantism.”
