This huge ancient whale may be the biggest animal ever discovered

Until now, a blue whale species (scientifically named Balaenoptera musculus) was considered the biggest mammal ever to exist. 

The newly found species weighed between 85 and 340 tonnes. It is thought to be 2-3 times larger than the size of a 25-meter-long blue whale.

“The findings suggest that the trend towards gigantism in marine mammals may have begun earlier than previously thought,” noted the release. 

These findings suggest that cetaceans attained peak body mass 30 million years earlier than previously thought. 

The giant creatures, like P. colossus, evolved to be completely suited to an aquatic habitat, regardless of body mass or size. 

“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,” said the official statement. 

Cetacean fossils are considered highly important as they provide insight into one of the most major evolutionary transitions in mammalian lifestyle — when certain terrestrial species started to return to the marine habitat. 

The findings have been reported in the journal Nature.

Study abstract:

The fossil record of cetaceans documents how terrestrial animals acquired extreme adaptations and transitioned to a fully aquatic lifestyle. In whales, this is associated with a substantial increase in maximum body size. Although an elongate body was acquired early in cetacean evolution3, the maximum body mass of baleen whales reflects a recent diversification that culminated in the blue whale4. More generally, hitherto known gigantism among aquatic tetrapods evolved within pelagic, active swimmers. Here we describe Perucetus colossus—a basilosaurid whale from the middle Eocene epoch of Peru. It displays, to our knowledge, the highest degree of bone mass increase known to date, an adaptation associated with shallow diving5. The estimated skeletal mass of P. colossus exceeds that of any known mammal or aquatic vertebrate. We show that the bone structure specializations of aquatic mammals are reflected in the scaling of skeletal fraction (skeletal mass versus whole-body mass) across the entire disparity of amniotes. We use the skeletal fraction to estimate the body mass of P. colossus, which proves to be a contender for the title of heaviest animal on record. Cetacean peak body mass had already been reached around 30 million years before previously assumed, in a coastal context in which primary productivity was particularly high.