Final yr, paleontologists found the fossil of a 39-million-year-old extinct whale in Peru that appeared to defy the bounds of vertebrate measurement.The group behind the fortunate discover estimated Perucetus colossus’ physique mass to be someplace between 85 and 340 tonnes. However at 17 to twenty meters in size (round 56 to 65 toes), this could have made the animal impossibly dense, argue paleontologists Ryosuke Motani and Nicholas Pyenson, who weren’t concerned within the preliminary discovery.”It will have been a job for the whale to remain on the floor, and even to depart the ocean backside – it could have required steady swimming in opposition to gravity to do something within the water,” says Motani from the College of California Davis.As a substitute, Motani and his colleague Pyenson,​ from the Smithsonian Nationwide Museum of Pure Historical past, counsel Perucetus’ unusually dense bones threw off the physique mass calculations College of Pisa earth scientist Giovanni Bianucci and colleagues revealed in 2023.”Perucetus didn’t exceed the physique mass of right this moment’s blue whales, and extra intently matched the physique measurement and weight of sperm whales,” Motani and Pyenson​ discover of their new evaluation.The bones of P. colossus. (Giovanni Bianucci)The P. colossus skeleton Bianucci and colleagues first described was incomplete, with no cranium to assist decide the animal’s eating regimen.But the fossilized bones that had been uncovered – an assortment of vertebrae, ribs, and an incomplete pelvis – have uncommon options, extra like these present in manatees (Trichechus) than right this moment’s whales.Manatees’ bones are thickened with further layers, which reduces the bone’s inside cavities and will increase their outer measurement. This bone state, often known as pachyostosis, just isn’t solely seen in trendy sea cows however within the extinct marine reptiles, plesiosaurs, too. It helped them regulate buoyancy of their aquatic habitats.It appears Perucetus might have shared this tactic, with extra bone mass offsetting their fats’s floating potential to maintain them neutrally buoyant.An artist’s impression of P. colossus. (Alberto Gennari)The unique calculations assumed that physique and skeletal mass scaled collectively constantly. However not like in trendy whales, a manatee’s bodily flesh is comparatively mild in comparison with its skeleton.Taking this into consideration, Motani and Pyenson suggest a 17-meter-long Perucetus ought to weigh between 60 to 70 tonnes.”The brand new weight permits the whale to come back to the floor and keep there whereas respiration and recovering from a dive, like most whales do,” says Motani.Even when the studied specimen was not but absolutely grown, and an grownup grew as much as 20 meters, their 110 tonnes continues to be no match for a blue whale’s 270 tonnes.Measurement comparability of a contemporary blue whale (Balaenoptera musculus) and the extinct Perucetus colossus based mostly on Motani and Pyenson’s calculations. (Cullen Townsend)So blue whales (Balaenoptera musculus) nonetheless reign supreme relating to the title of most huge animal of all time.Whereas not the most important, Perucetus was nonetheless significantly hefty so doubtless a high shopper on physique measurement alone, the researchers conclude. “However it stays unclear what its function might have been in Center Eocene nearshore ocean meals webs.”This analysis was revealed in PeerJ.