The heaviest animal that ever lived

The paleontologist Mario Urbina made an extraordinary discovery 13 years ago. After decades of analyzing fossils in the coastal desert of southern Peru, he found sediments so large and oddly shaped that photos could stand out left the other researchers perplexed. It’s about Perucetus Colossusan ancient species of whale, according to a study published today in the journal Nature. It is believed to be one of the largest and heaviest animals out there.

The animal was modeled in 3D by a partial skeleton, which includes 13 vertebrae, four ribs and one hip bone. It is estimated that he lived in the middle Eocene. does about 39 million years.

“This discovery documents the existence of a basilosaur (a now-extinct family of whales) characterized by: huge and heavy bonesmore than any other vertebrate that has ever existed,” he tells SINC Giovanni Bianuccifrom the University of Pisa (Italy) and first author of the work.

The blue whale has a competitor

The international team scanned the surface of the preserved bones to measure their volume, drilled holes to assess their internal distribution and used them complete skeletons of close relatives to estimate how much the bone structure of the new species weighed in life.

Estimates of its size and weight compete with those of the blue whale that have been considered so far the heaviest animal in history. The authors appreciate that P. Colossus had a skeleton two to three times larger than that of a living whale and body mass from 85 to 340 tons.

3D model of the colossus Perucetus, along with that of a smaller close relative (Cynthiacetus peruvianus) and the Wexford blue whale. / Florent Goussard/Natural History Museum, London

“We have been extremely conservative in our approach,” said Eli Amson of the Natural History Museum in Stuttgart, Germany, who led the study. “The lower estimate reflects, and is, a very conservative view larger than those of some adult blue whales“, he adds.

When asked if it could be the heaviest animal ever recorded, he explains: “We can say that with a high degree of certainty.” Its weight was similar to that of the blue whale and even greater“.

All of the bones of this archaic whale are extremely dense and compact, the scientists said. “This type of thickening and heaviness of the skeleton, called pachyosteosclerosis, does not occur in any living whalealthough it’s been observed in sirens (like manatees),” says Bianucci.

There are two types of bone changes in pachyosteosclerosis. On the one hand the Addition of extra bone on the outer surface of skeletal elements (giving them a swollen appearance called paquitosis). On the other hand, the Filling of internal cavities with compact bones (osteosclerosis), which means even more weight.

These changes are not pathological, but are well known in many aquatic mammals and reptiles that live mainly in shallow coastal waters. The extra weight helps these animals regulate their buoyancy and adapt underwater. In modern whales, which can dive much deeper and live far from shore, the bone structure is much lighter.

Several field campaigns were required to collect samples of the newly found animal. Each vertebra weighs more than 100 kilos and the ribs reach 1.4 meters in length. Conserved in the Natural History Museum of the Universidad Nacional Mayor San Marcos (Lima, Peru), this specimen represents one of the first whales to adopt a fully aquatic lifestyle.

Tendency to gigantism

The whale fossil record is of great importance in documenting the evolutionary history of mammalian life Some land animals returned to the sea. The results suggest that the trend towards gigantism in marine mammals may have started earlier than previously thought.

Being tall is believed to give a certain competitive advantage

Giovanni Bianucci, first author of the study

“Whales have evolved phenomena of gigantism at least twice: in a relatively short time, about five million years ago, with the evolution of modern baleen whales (Balaenptera musculus) and about 40 million years ago with the basilosaursof which Perucetus it is the most extraordinary representative,” states the researcher.

One of the researchers poses with the fossils for display at the Natural History Museum in Lima, Peru. / Rodolfo Salas Gismondi and Niels Valencia

Previous records have identified adaptations to an aquatic lifestyle, including a tendency towards gigantism and an increase in body mass. “Gigantism is a phenomenon that has appeared independently and at different times in many lineages of vertebrates,” explains Bianucci. “One assumes that the large body size confers a species Competitive advantagebut how and why exactly it evolved is still up for debate.”

The results indicate that the whales had reached their maximum body mass about 30 million years earlier than previously thoughtand in the coastal context. This work changes the understanding of the evolution of whales. “The complete adaptation to the marine environment, where Problems related to severity decreasemay have favored the increase in size in archaic whales,” comments the paleontologist.

A hyper-specialized whale

The buoyancy associated with increased bone mass is consistent with a shallow water lifestyle. gigantism in the P. Colossus can also be associated with it natural selection, because it “allows you to dive near the bottom longer in shallow water,” the study’s author points out. “Indeed, large air-breathing marine vertebrates do longer immersion time than the smaller ones,” he adds.

The results support the theory that basilosaurids existed hyper-specialized for this type of coastal environment. According to Bianucci, this could also favor their extinction: “Hyperspecialization makes species more vulnerable and.” less able to adapt to rapid environmental changes“.

Specifically, this whale lived in areas with high food availability. “The sudden decline in productivity in coastal waters towards the end of the Eocene probably worked in these animals’ favor in favor of their ancestors current whales and dolphinsthat invaded open marine environments,” the researcher concludes.

The team, which also includes Mario Urbina, will continue touring the Peruvian desert because they believe it will still has a lot to reveal. The preparation and conservation of all these important fossils is one of the great challenges of the Lima Museum’s Department of Paleontology.