Scientists Are Having a Whale of a Time With This Massive Cetacean

According to a recent study, a whale that lived 39 million years ago may be the largest animal to have ever lived.

In 2010, a paleontologist named Mario Urbina discovered the first fossil of an ancient cetacean. It was later dubbed Perucetus colossus, the suffix due to its remarkable size (body mass) that, according to a recent study, may have climbed past that of a blue whale – which is considered to be the largest animal to have ever existed on Earth.

Since the initial find over a decade ago, 13 vertebrae, four ribs and part of a hip have been excavated; on August 2, 2023, a new study was published in the journal Nature that examined the lifestyle, diet, and size of P. colossus. The study estimated that its body mass might have been anywhere between 85 to 340 metric tons, with an average of 180 metric tons. The largest blue whale ever recorded was about 190 tons, though most only reach around 150 tons. 

In order to estimate P. colossus’s body mass, the researchers used “skeletal fraction” or “SF” (the ratio of skeletal mass to total body mass). However, its body mass is difficult to estimate due to its high bone density, which is very different from other cetaceans. The researchers who examined the bones of P. colossus detected strong osteosclerosis – a process that increases the density of bones by filling in their internal cavities that are normally filled with air – as well as the highest degree of bone mass increase (BMI) known to date. Because of these differences between it and other cetaceans, it’s difficult to base P. colossus’s body mass on skeletal measurements alone. 

A skeletal drawing of Perucetus colossus with preserved bones marked in white (Photograph: Ivan Iofrida)

Researchers have stated that its bone mass may have been compensated for by large amounts of blubber (which is less dense than other soft tissues). This would therefore strongly lower the overall density of its soft tissues, bringing its total body mass down. 

To arrive at the estimates of 85 and 340 metric tons, extreme values from existing marine mammals were used. Manatees have a high degree of BMI (though still not to the same level as P. Colossus). Using the average SF of a manatee, the 85 ton estimate was reached. However, most whales have a much lower SF than that of a manatee. Using the lowest SF of currently living cetaceans, the estimate of 340 tons was reached. 

P. Colossus’s bone density is important to understanding not only just how heavy it may have been, but also what its lifestyle may have looked like. The adaptation of osteosclerosis indicates that it likely lived in shallow waters, where its high bone density and high body mass served to allow it to remain at the seafloor for long periods of time. These same adaptations would have also helped it to be more resistant to strong coastal waves. The bones themselves also indicate that it was likely slow-swimming, based on the shape of its vertebrae that is quite similar to that of a manatee’s. 

However, P. Colossus’s diet still remains much of a mystery.

“Unless we find more material, hopefully a skull with teeth, we really don’t know,” says Eli Amson, paleontologist and curator of mammal fossils at Stuttgart State Museum of Natural History. Amson also contributed to the recent study regarding P. Colossus, which cites multiple possible scenarios for what its diet might have looked like (though, without a skull or teeth, is currently speculation). It may have been herbivorous and have fed on seagrass or seaweed. Alternatively, it may have fed on crustaceans, mollusks, or other sedentary creatures that live on the seafloor. It also might have scavenged on carcasses of vertebrates or could have been a suction or filter-feeder. 

However, of the possibilities for P. Colossus’s diet, it is unlikely that it was herbivorous. No other cetaceans share this diet.

“We can rule out a ‘sperm whale type’ of lifestyle,” Amson said. Sperm whales actively hunt for food during deep dives that routinely reach depths of over 2,000 feet. This kind of feeding style would not have been possible for P. Colossus, given its bone density and adaptations that would have made it a slow swimmer.

Paleontologist Eli Amson explains that the details of P. Colossus’s lifestyle and diet are still unclear (Photograph: Stuttgart State Museum of Natural History)

“Everything is still on the table, I would say,” Amson said, though he states that they can be sure that P. Colossus’s diet and lifestyle involved shallow diving, based on its aforementioned adaptations. 

Excavation of the site and further research is still ongoing, and the research team hopes to uncover more fossils that will be able to reveal more about P. Colossus’s lifestyle and diet. The team returns every year to the site to work on understanding more about it. 

“This is certainly not going to happen tomorrow,” Amson concluded. “It takes a crazy amount of time and energy to get [the fossils] out of the desert and prepare them.” Still, as research continues, it is likely that we’ll learn more about P. Colossus and the details surrounding its adaptations and ecological niche. 

—-Support is needed to continue research on P. Colossus. For Peruvian paleontologists working on P. Colossus and other specimens (including over 60 specimens which serve as the basis for describing new species), space is a valuable but also limited resource. With an active research lab, their collection’s growth has been exponential, leading to the relocation of their preparation lab to a temporary location that lacks most of the necessary infrastructure. In order to continue work, the researchers are in need of a new preparation lab. If you’d like to donate to assist in their cause, please contribute through this link. Any and all contributions are greatly appreciated.