2023-08-02 17:00:34
Paleontologist Mario Urbina made an exceptional 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 field photos left the other researchers stumped. Its about A colossal porcupinean 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 on record.
The animal has been modeled in 3D from a partial skeleton, which includes 13 vertebrae, four ribs and a hip bone. It is estimated that he lived during the middle Eocene, does about 39 million years.
The bones of this animal are the largest and heaviest of any vertebrate that has ever existed.
“This discovery documents the existence of a basilosaurid (a family of cetaceans now extinct) characterized by huge and heavy bonesmore than any other vertebrate that has ever existed”, he declares to SINC Giovanni Bianuccifrom the University of Pisa (Italy) and first author of the paper.
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 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 rival those of the blue whale, which until now was considered the heaviest animal in history. The authors estimate that P. colossus had a skeleton two to three times larger than that of the living cetacean, with a 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, from the Stuttgart Natural History Museum (Germany) and leader of the study. “The lower estimate reflects an extremely conservative assessment, and even so it is greater than that of some adult blue whales”, he adds.
On whether it could be the heaviest animal ever recorded, he explains: “We can say with a high degree of certainty that its weight was similar to that of the blue whale, and even greater”.
All the bones of this archaic whale are extremely dense and compact, according to the scientists. “This type of thickening and heaviness of the skeleton, called pachyosteosclerosis, not found in any living cetaceanalthough it is observed in sirenians (such as manatees)”, says Bianucci.
Pachiosteosclerosis is a set of bone modifications that is not observed in any current cetacean.
Pachyosteosclerosis consists of two types of bone modifications. On 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 bone (osteosclerosis), which adds even more weight.
These modifications are not pathological, but are well known in many aquatic mammals and reptiles that live primarily in shallow coastal waters. The extra weight helps these animals to regulate their buoyancy and adjust underwater. In modern cetaceans, which can dive much deeper and live far from shore, the bone structure is much lighter.
Multiple field campaigns were necessary to collect samples of the newly found animal. Each vertebra weighs more than 100 kilos and the ribs reach a length of 1.4 meters. This specimen, which is preserved in the Natural History Museum of the Universidad Nacional Mayor San Marcos (Lima, Peru), represents one of the first cetaceans to switch to a fully aquatic lifestyle.
Tendency to gigantism
The fossil record of cetaceans is of great importance when it comes to documenting the evolutionary history of mammalian life, when some land animals returned to the ocean. The findings suggest that the trend towards gigantism in marine mammals may have started earlier than previously thought.
Large body size is believed to confer some form of competitive advantage
Giovanni Bianucci, first author of the study
“Cetaceans developed phenomena of gigantism at least twice: in relatively recent times, 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”, indicates the researcher.
One of the researchers poses with the fossils for the exhibition organized at the Museum of Natural History in Lima (Peru). / Rodolfo Salas-Gismondi and Niels Valencia
Previous records have identified adaptations to an aquatic lifestyle, including a tendency to gigantism and an increase in body mass. “Gigantism is a phenomenon that has emerged, independently and at different times, in many lineages of vertebrates,” explains Bianucci. “It is believed that the large body size confers some kind of competitive advantagebut exactly how and why it evolved is still up for debate.”
The findings indicate that the cetaceans had reached their maximum body mass about 30 million years earlier than previously thought, and in a coastal context. This work changes the understanding of the evolution of whales. “The complete adaptation to the marine environment, where severity-related problems decreasemay have favored the increase in size in archaic cetaceans”, comments the paleontologist.
A hyperspecialized whale
Buoyancy associated with increased bone mass is consistent with a shallow water lifestyle. gigantism in the P. colossus can also be associated with natural selection, since this “allows you to dive longer near the bottom in shallow water,” highlights the author of the study. “In fact, large air-breathing marine vertebrates have a longer duration of immersion than the smaller ones”, he adds.
This family of cetaceans was hyperspecialized to live near the coast, in shallow waters.
The results support the theory that basilosaurids were hyper-specialized for this type of coastal environment. According to Bianucci, this could also facilitate their extinction: “hyperspecialization makes species more vulnerable and less able to adapt to rapid environmental changes”.
Specifically, this cetacean lived in areas with high food availability. “The sudden drop in productivity in coastal waters, towards the end of the Eocene, probably impacted these animals in favor of the ancestors of current whales and dolphinswhich invaded open sea environments”, concludes the researcher.
The team, which also includes Mario Urbina, will continue touring the Peruvian desert, because they are convinced that still has a lot to reveal. Preparing and conserving all these important fossils is one of the great challenges of the Department of Paleontology of the Museum of Lima.
Reference:
Bianucci, G. et al., “A heavyweight early whale pushes the boundaries of vertebrate morphology”. Nature (2023)
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