A primitive whale that lived 39 million years ago off the Peruvian coast could surpass the blue whale as the heaviest animal ever to inhabit the Earth. The new species described this Wednesday in an article in Nature challenges the known evolutionary history of cetaceans (the group of aquatic mammals that include whales and dolphins), advancing their gigantism by 30 million years.
The discovery of Perucetus colossus, whose name literally translates to Peruvian colossal whale, dates back 13 years, when local paleontologist Mario Urbina found some gigantic fossil remains off Peru’s southern desert coast. After several campaigns, an international team of scientists managed to recover 13 vertebrae weighing more than 100 kilograms each, 7 ribs up to one and a half meters in length, and a hip bone of the new species.
After analyzing the volume of each bone and its internal composition, and comparing the data with those of its closest relatives, the researchers have estimated that Perucetus colossus measured about 20 meters and weighed between 85 and 340 tons. The new species “challenges the blue whale [of up to 200 tons and 30 meters in length] for the title of the heaviest animal that has ever existed,” the authors of the research note in the paper.
Despite being much smaller, P. colossus weighed the same or more than the blue whale. The explanation for this apparent paradox is found in an extremely heavy skeleton. Mammalian bones “normally look like a baguette, in the sense that they have a solid crust (compact bone) that surrounds a spongy interior,” paleontologists from Northeastern Ohio Medical University (USA) explain in an analysis of the article. .) Johannes G. M. Thewissen and David A. Waugh, who have not participated in the research. On the other hand, those of the new discovered species “are mostly or exclusively made of compact bone,” they point out.
In addition to an almost entirely solid interior, the exterior of the extinct cetacean skeleton was also encased in extra layers of bone material. In short, the bones of Perucetus colossus were thicker and more dense than those of modern whales, with which their bone mass was much greater, between 2 and 3 times that of the blue whale.
These atypically heavy bones, which are shared by some other aquatic mammals such as manatees, have allowed researchers to infer that the new species probably lived in coastal areas. Animals with these characteristics move slowly, so they “tend to live in shallow water, to stay close to the surface to breathe […] and are better adapted for the consumption of slow or even immobile prey, which usually They are found on the sea floor”, Olivier Lambert, paleontologist at the Royal Belgian Institute of Natural Sciences and co-author of the study, explains to this newspaper.
In fact, the researchers hypothesize in their article that the extinct species could have been a scavenger, and have fed on the remains of “sunken vertebrates” on the seabed, as some sharks do. However, since no fossil remains of the skull or the dental area have been found, the idea is, for now, purely speculative.
Perucetus colossus will make experts reassess their knowledge about the evolution and lifestyle of large aquatic mammals. On the one hand, “gigantism has long been associated with filter feeding”, something that does not seem likely in the case of the new species, Lambert points out, referring to the strategy of some whales to eat by filtering large amounts of water to catch prey.
On the other, the time in which it lived, 39 million years ago, throws away the dominant idea in the scientific community that cetacean gigantism is a recent evolutionary trait, which had occurred in the last 5 million years. years. The ancestors of the whales had an extraordinary weight already at least 30 million years earlier than thought.
“Discoveries of such extreme body shapes are an opportunity to reassess our understanding of animal evolution. It seems that we only have a dim idea of ??how amazing the form and function of whales can be”, conclude Thewissen and Waugh in their analysis.
