Unusually-Shaped Colossus Whale Could Possibly Be the Heaviest Animal in History

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A reconstruction of the extinct whale Perucetus colossus in its coastal habitat. Its estimated body length is around 20 meters. Credit: Alberto Gennari

Fossil Discovery

Scientists excavating in a Peruvian desert have discovered the fossilized bones of a bizarre ancient whale, Perucetus colossus, which may have been the heaviest animal ever to live[1]. The partial skeleton of Perucetus was found more than a decade ago by Mario Urbina from the University of San Marcos’ Natural History Museum in Lima. The international research team spent years digging out 13 vertebrae, four ribs, and a hip bone from the side of a steep, rocky slope in the Ica desert, a region in Peru that was once underwater and is known for its rich marine fossils.

Whale Comparisons

Perucetus colossus had a skeleton that may have weighed two to three times that of a blue whale[1]. Blue whales, the heaviest animals alive today, weigh up to 330,000 pounds. The estimated body mass of Perucetus colossus ranged from 85 to 340 metric tons (187,393 to 749,572 pounds), which is equivalent to or exceeds that of the blue whale. Despite being only 20 meters (66 feet) long, the skeleton of P. colossus would have been two to three times heavier than that of a 25-meter blue whale due to its denser bones. Its body mass would have come in at 85 to 340 tonnes.

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Perucetus colossus had unusually voluminous, dense, and compact bones, a characteristic called pachyosteosclerosis. This characteristic is absent in living cetaceans but present in sirenians, another marine mammal group including manatees and dugongs. The weight and size of Perucetus could have been evolutionary adaptations to life in shallow and agitated coastal waters, where a particularly heavy skeleton acts as a ‘ballast’ for stability. The researchers suspect Perucetus lived like sirenians, not an active predator but an animal that fed near the bottom of shallow coastal waters.

This discovery challenges what we know about the evolution of cetaceans, as it means they reached their peak body mass 30 million years earlier than originally thought[3]. The described species, Perucetus colossus, was clearly a large animal with a heavy skeleton, making it a contender for the title of heaviest animal on record.

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Excavation and Analysis

The research team applied modern technology to study the Perucetus colossus bones further. They utilized 3D scanners to analyze the surface and even drilled into them to peek inside. Based on the massive but incomplete skeleton, the experts estimated the whale’s size and weight by comparing it to modern marine mammals.

Possible Diets and Lifestyle

Due to the absence of the skull, it is difficult to determine the exact diet and lifestyle of Perucetus colossus. However, researchers have hypothesized three possible diets for the ancient whale: it might have been a herbivorous plant eater like a sea cow, which would be unique among cetaceans; it could have fed on small mollusks and crustaceans in sandy bottoms, similar to the contemporary gray whale; or it could have scavenged vertebrate carcasses. The dense bones of P. colossus suggest that it spent its time in shallow coastal waters, possibly as a bottom feeder searching for clams, crustaceans, and other morsels among the sand[13].

Implications for Whale Evolution

The discovery of Perucetus colossus has far-reaching implications for our understanding of whale evolution. It suggests that cetaceans developed gigantism at least twice: in relatively recent times, with the evolution of the large baleen whales, and some 40 million years ago, with the radiation of the Basilosaurus relatives of which Perucetus is the most extraordinary representative. This new find indicates that peak body mass was reached 30 million years earlier than previously thought, challenging our understanding of whale evolution[3].

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[1] https://www.nbcnews.com/news/world/heaviest-animal-ever-whale-peru-desert-rcna97912
[2] https://www.cbsnews.com/pittsburgh/news/colossal-whale-might-be-heaviest-animal-ever-study/
[3] https://newatlas.com/biology/perucetus-colossus-largest-animal-ever-existed-blue-whale/