Its length can exceed 30 meters and its weight can reach up to 200 tons. If you stacked 2,700 average-weight humans it would match the mass of 30 elephants, or be roughly twice the size of the biggest dinosaurs. An adult species can carry a tongue heavier than an elephant’s. The heart itself is comparable in heft to a small car, and the blood vessels are so vast that a person could swim through them in a single breathless moment.
For centuries, the blue whale (Balaenoptera musculus) has been regarded as Earth’s largest animal. That claim is now under scrutiny. A recent archaeological discovery in Peru reveals fossil remains of a whale that existed millions of years ago and dwarfed the blue whale. Researchers have named this giant Perucetus colossus, or the Giant Peruvian whale, suggesting it may be the heaviest animal ever known.
Estimates of Perucetus giant’s body mass range from 85 to 340 tons, a figure that would equal roughly 50 large adult African elephants or around 5,000 humans. The fossil suggests the animal was still growing. This creature is placed within the basilosaurid lineage of whales, a group in the order Cetacea that encompasses modern whales, dolphins, and porpoises.
The discovery includes 13 vertebrae, four ribs and a hip bone. Based on the available data, the animal’s length would have ranged between 17 and 20 meters. Although the skeleton is shorter than a contemporary blue whale, its skeletal mass may have surpassed that of any known cetacean or other large vertebrates, including its colossal relative.
extreme adaptations
Scientists describe a remarkable feature known as pachyosteosclerosis, a pronounced thickening of the skeleton that is not seen in living cetaceans but is found in large aquatic herbivores like manatees and dugongs. This bone mass would have given the animal added stability and buoyancy control in coastal waters.
The study notes that cetacean evolution shows land-dwelling ancestors transitioning to fully aquatic life, with size increasing over time. In whales, this trend culminates in enormous bodies capable of sustained pelagic swimming.
The researchers explain: Perucetus giant, a basilosaurid whale from middle Eocene Peru, demonstrates the greatest known degree of bone mass increase in an open-water mammal so far, an adaptation once linked to shallower diving but here connected to an ancient coastal lifestyle.
“Estimated skeletal mass for Perucetus giant exceeds that of any known aquatic mammal or vertebrate,” scientists concluded from the skeletal fraction found to estimate total body mass, noting the creature as a serious contender for the title of heaviest animal on record.
Another result places the maximum body mass of cetaceans earlier than previously thought. Earlier ideas suggested gigantism appeared about 4.5 million years ago in coastal, highly productive environments; new calculations push the era of extreme whale size further back by tens of millions of years.
A ‘graveyard’ of fossil vertebrates
The size and weight of this species hint at evolutionary adaptations for life in shallow, choppy coastal waters. A heavy skeleton could act as ballast, stabilizing a fully aquatic animal in environments where waves and currents are frequent.
The creature never needed to return to land to reproduce, given its enormous mass would make terrestrial movement impractical due to gravity.
The Perucetus discovery is the culmination of years of fieldwork in Peru’s Ica Valley. It sits among a remarkable fossil record of vertebrates, including Peregocetus pacificus, the oldest known quadruped cetacean in the Pacific, and earlier relatives such as Mystacodon Selenensis and the gigantic Livyatan melvillei.
The first vertebra of this giant whale was uncovered in 2012. Scientists chose a name reflecting both its Peruvian origin and ancient lineage: Peru, Cetus for whale in Latin, and Kolossós meaning “large statue” in ancient Greek.
Although the skull is missing, researchers propose three possible diets. One possibility is a herbivorous diet, similar to modern sea cows, a curious departure among cetaceans. A second possibility is feeding on small mollusks and crustaceans on sandy bottoms like gray whales. A third is scavenging on vertebrate carcasses. Scientists do not rule out other possibilities, acknowledging that this diet could be entirely different from what was previously imagined.
Reference: Nature, 2023, study on Perucetus giant. The publication presents the fossil evidence and interpretations for the animal’s size, mass, and ecological niche.
In sum, the Perucetus discovery reshapes ideas about the diversity and scale of ancient whales and underscores how much remains to be learned about the early evolution of cetaceans in ancient coastal ecosystems.