Media release

From: Springer Nature

Palaeontology: Colossal ancient whale may be the heaviest known animal

The newly discovered Perucetus colossus, an ancient species of whale, is thought to be one of the largest and heaviest animals on record, reports a study published in Nature. Estimates of its size and weight, based on a partial skeleton, rival those of the blue whale, which was previously thought to be the heaviest animal ever to exist. The findings suggest that the trend towards gigantism in marine mammals may have begun earlier than previously thought.

The fossil record of cetaceans (a suborder of mammals that includes dolphins, whales and porpoises) is of great importance when documenting the evolutionary history of mammalian life when some terrestrial animals were returning to the ocean. Previous records have identified adaptations to an aquatic lifestyle, which include a trend towards gigantism and an associated increase in body mass, although the peak body mass is thought to have been a relatively recent diversification.

Eli Amson and colleagues describe a new basilosaurid whale with an estimated skeletal mass that exceeds that of any known mammal or sea creature. Named P. colossus, the animal  is modelled from a partial skeleton, including 13 vertebrae, 4 ribs and 1 hip bone, discovered in Southern Peru and estimated to be approximately 39 million years old. It is predicted that the skeletal mass would be 2–3 times that of a 25-m-long blue whale; the authors estimated that P. colossus had a body mass between 85 and 340 tonnes. As the estimated body mass equals or exceeds the body mass of the blue whale, this new species would challenge the latter’s status as the heaviest animal ever to exist.

These findings indicate that cetaceans had reached peak body mass an estimated 30 million years before previously assumed, with the features of P. colossus being fully adapted to an aquatic environment. The buoyancy associated with the increase in bone mass is consistent with a shallow-water lifestyle, supporting the theory that basilosaurids were hyper-specialized for this type of coastal environment and shedding further light on this order of ancient animals.