Paleontologists on Wednesday unveiled the fossilized bones of one of many strangest whales in historical past. The 39-million-year-old leviathan, referred to as Perucetus, might have weighed about 200 tons, as a lot as a blue whale — by far the heaviest animal identified, till now.
Whereas blue whales are modern, fast-swimming divers, Perucetus was a really completely different beast. The researchers suspect that it drifted lazily by way of shallow coastal waters like a mammoth manatee, propelling its sausage-like physique with a paddle-shaped tail.
Some consultants cautioned that extra bones must be found earlier than a agency estimate of Perucetus’s weight might be made. However all of them agreed that the weird discover would change the way in which paleontologists noticed the evolution of whales from land mammals.
“This can be a bizarre and stupendous fossil, for certain,” mentioned Nicholas Pyenson, a paleontologist on the Smithsonian Nationwide Museum of Pure Historical past, who was not concerned within the examine. “It’s clear from this discovery that there are such a lot of different methods of being a whale that now we have not but found.”
Mario Urbina, a paleontologist on the Museum of Pure Historical past on the Nationwide College of San Marcos in Lima, Peru, first set eyes on Perucetus in 2010. He was strolling throughout the Atacama Desert in southern Peru when he observed a rocky bump bulging out of the sand. When he and his colleagues completed digging it out, the lump proved to be a big vertebra.
Digging additional, the researchers discovered 13 vertebrae in complete, together with 4 ribs and a part of a pelvis. Aside from the pelvis, all of the fossils had been remarkably dense and surprisingly thickened, making it exhausting to determine what sort of animal they belonged to.
Solely the pelvis revealed precisely what the scientists had discovered. Not like the opposite bones, the pelvis was small and delicately shaped. It had crests and different distinctive options that exposed it to be a whale’s — particularly, from an early department of the evolutionary tree of whales.
Whales advanced from dog-sized land mammals about 50 million years in the past. A number of the earliest species advanced quick limbs and most probably led a seal-like existence, trying to find fish after which hauling themselves onto the shore to breed.
These early whales disappeared after just a few million years. They had been changed by a bunch of totally aquatic whales referred to as basilosaurids. These slinky beasts may develop so long as a faculty bus however retained vestiges of their life on land — together with tiny hind legs, full with toes.
Basilosaurids dominated the oceans till about 35 million years in the past. As they turned extinct, one other group of whales emerged, giving rise to the ancestors of residing whales.
At this time’s largest whales, like blue whales and fin whales, solely reached their gargantuan sizes up to now few million years. Shifts in ocean currents supported huge populations of krill and different invertebrates close to the poles. The whales may develop immense by scooping up these prey on lunging dives.
The pelvis of Perucetus revealed it to be a basilosaurid, however the whale had advanced right into a basilosaurid not like any discovered earlier than. Eli Amson, an professional on bone tissue on the State Museum of Pure Historical past in Stuttgart, Germany, discovered that its ribs and backbone had additional layers of outer bone, giving them bloated shapes.
A typical bone is filled with pores, which make it lighter with out sacrificing energy. Dr. Amson noticed that the bones of Perucetus had been strong all through. The fossil is so exhausting in elements that it will be inconceivable to drive a nail into it with a hammer.
“It will make nothing however sparks,” he mentioned.
Dr. Amson and his colleagues made three-dimensional scans of the fossil bones with a view to reconstruct the whale’s full skeleton. They in contrast Perucetus to different basilosaurids which were preserved from head to tail.
If the remainder of Perucetus had been a denser, thickened model of those whales, its full skeleton would weigh between 5.8 and eight.3 tons. That may imply Perucetus had the heaviest skeleton of any mammal — bones that had been twice as heavy as a blue whale’s.
That cumbersome skeleton additionally means that Perucetus had a thick, barrel-like physique. Though Perucetus was solely about two-thirds the size of a blue whale, Dr. Amson and his colleagues suspect that it weighed about the identical.
“It’s undoubtedly within the blue whale ballpark,” Dr. Amson mentioned.
Dr. Pyenson, of the Smithsonian Nationwide Museum of Pure Historical past, thought it was untimely to make such an estimate. “Till we discover the remainder of the skeleton, I feel we should always shelve the heavyweight-contender problem,” he mentioned.
However Hans Thewissen, a paleontologist at Northeast Ohio Medical College, who was not concerned within the examine, mentioned the estimate was affordable. “I agree with the thrill across the weight,” he mentioned.
The fossil means that Perucetus reached such a giant dimension with out feeding as blue whales do. The evaluation of its bones suggests it lived extra like a gargantuan manatee.
Manatees graze on sea grass on the ocean ground. Their lungs are filled with air, and their guts produce fuel as they ferment their meals. To remain underwater, manatees have advanced dense bones as ballast.
The construction of Perucetus’s backbone is just like that of a manatee. Dr. Amson envisioned the whale swimming in a manatee type, slowly elevating and decreasing its tail.
Primarily based on the rocks the place the fossils had been discovered, Dr. Amson and his colleagues suspect that Perucetus moved slowly by way of coastal waters no deeper than 150 ft. However how they fueled their big our bodies continues to be a thriller.
Dr. Amson mentioned it was potential that Perucetus additionally ate up sea grass, however that might make it the primary herbivorous whale identified to science. “We deem it unlikely, however who is aware of?” he mentioned.
Dr. Amson even imagines Perucetus probably residing as a scavenger, selecting over carcasses.
Against this, Dr. Thewissen favored the concept these whales scooped up mud from the ocean ground to eat the worms and shellfish it contained — one thing that grey whales do at the moment.
The top of Perucetus would have variations for whichever lifestyle it pursued. “I might like to see the cranium of this man,” Dr. Thewissen mentioned.
Nonetheless it made a residing, Perucetus is proof that whales didn’t have to attend till not too long ago to get big. “Crucial message will not be that we will enter the Guinness Ebook of World Information,” mentioned Dr. Amson. “It’s that there’s one other path to gigantism.”
