Blue whale reclaims title of largest animal on the planet

New research shows that the ancient whale species Perucetus was very large but still smaller than today's blue whale.

Size comparison of the blue whale, the extinct Perucetus whale and humans. Photo: Cullen Townsend — Size comparison of the blue whale, the extinct Perucetus whale and humans. Photo: *Cullen Townsend*

Last August, a team of paleontologists announced the discovery of fossilized bones of a giant ancient whale. According to them, the Perucetus whale could have weighed more than 200 tons, making it the heaviest animal that ever lived on Earth. But in a study published in the journal PeerJ, two scientists dismissed that speculation. According to Nicholas Pyenson, a paleontologist at the Smithsonian Museum of Natural History and one of the two authors of the new study, the figure is nonsense, Interesting Engineering reported on March 1.

Analysis by Pyenson and Ryosuke Motani, a paleontologist at the University of California, Davis, concluded that Perucetus could have weighed 60 to 70 tons, about the size of a sperm whale. They also analyzed blue whale fossils and came up with a new estimate of the species' weight. They concluded that blue whales weighed up to 270 tons, much larger than previous estimates of 150 tons. This makes them the heaviest known species in the history of the animal kingdom.

Perucetus first attracted attention in 2010 when Mario Urbina, a paleontologist at the Natural History Museum at the National University of San Marcos in Lima, Peru, came across a bone in the desert of southern Peru. He and his colleagues unearthed 13 vertebrae, four ribs, and part of a pelvis. The bones had many of the hallmarks of whale bones, but were unusually large and heavy. Urbina’s team reconstructed the entire skeleton of Perucetus by studying much smaller whales that lived at the same time. They also took inspiration from manatees living today, whose compact skeletons allow them to submerge themselves in the water to graze on seagrass.

Urbina and his colleagues came up with a strange reconstruction. It had a huge trunk, a small head, flippers, and hind legs. Motani, an expert in reconstructing extinct marine animals, was puzzled by the conclusion. He contacted Pyenson, an expert on fossil whales. Both felt that modeling Perucetus after manatees was a mistake, since only whales evolved to such extreme sizes.

In the new study, Pyenson and Motani looked at living whales. Because it’s impossible to weigh a living blue whale, no one has ever accurately measured its weight. The team looked at data collected by Japanese whaling vessels in the 1940s and used that information as the basis for their new estimate. They also created a 3D model of a blue whale, which they used as a model of Perucetus. Using this approach, they estimated that Perucetus weighed 60 to 70 tons, much less than previously thought.

Eli Amson, a bone histologist at the Natural History Museum in Stuttgart, Germany, and co-author of the previous study, disagrees with Pyenson and Motani’s approach. According to him, the extinct blue whale had very different biology from recent whales. He and his colleagues are now creating their own 3D model of the ancient animal. They have found that Perucetus was much more manatee-like than originally thought, supporting the conclusion that it was as large as or larger than the blue whale in weight.

Pyenson says Perucetus is still a big find, despite the small size he and Motani conclude. Paleontologists have long thought whales evolved to enormous sizes only in the past few million years. Even at 60 tons, Perucetus is still a giant among early whales.

An Khang (According to Interesting Engineering )

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