If you're thinking dinosaurs, think again. Scientists have revealed the heaviest animal to ever have existed, and it's a whale.
The ancient species of whale, known as Perucetus colossus, is approximately 39 million years old, from the Eocene epoch (when rising temperatures saw a plethora of new animals including the first horses, bats and whales).
With an estimated body length of 20m (66ft), and a body mass of 85-340 tonnes, it may be the heaviest and one of the largest known animals ever, according to a new study published in journal Nature.
The ancient whale's skeletal mass was 2 to 3 times that of the blue whale we know today. The blue whale has, until now, been thought to be the heaviest animal to ever exist, with a skeletal mass of 3,500kg (7,700 pounds).
Perucetus colossus was discovered in Peru 13 years ago by palaeontologist and co-author on this study Mario Urbina. Since that time, scientists have been estimating the whale's size and weight based on its partial skeleton.
"We kept the project ultra-secret during all these years," another of the paper's authors Dr Eli Amson, mammal fossil curator at Stuttgart State University of Natural History, Germany, told BBC Science Focus.
But what did it look like, and how did it move? With a tiny head and a huge body, there is a lot of room for speculation.
"The head of Perucetus is a complete mystery," Amson said. "Perucetus was most likely not an agile swimmer (can you imagine the inertia of such a tremendous body?). Considering its enormous mass and swimming style, Perucetus moved very slowly."
In evolutionary history, scientists previously thought that cetaceans – a group of mammals including dolphins and whales – might have been part of the movement of terrestrial mammals back to the ocean.
Previous fossil records have helped to identify adaptations to a marine environment – including a trend towards gigantism. One of the benefits of being so big is better body temperature regulation.
The new addition of Perucetus colossus to the fossil record reveals much about marine evolution. The estimations of the ancient whale's size suggest, in fact, that cetaceans reached peak body mass 30 million years before we thought.
About our expert:
Dr Eli Amson is the curator of mammal fossils at Stuttgart State University of Natural History, Germany. His research has been published in Evolution Letters, the Journal of Mammalian Evolution, and Evolutionary Biology.
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