When Alberto Collareta first saw the extinct animal’s stone-sized vertebrae, he couldn’t believe what he saw. He wondered how such a large creature could even move around.
“I was standing in front of something that was unlike anything I had ever seen,” said Collareta, a researcher at the University of Pisa and co-author of a study published Wednesday in the journal Nature, describing the newly excavated species of giant prehistoric whale.
Named for its discoveries Perucetus colossusor simply P. colossusperhaps the titanic animal is not just a record-setter. P. colossus also forcing scientists to rethink their ideas about how animals are able to grow to gigantic sizes.
“This is another way you can get big,” said Hans Thewissen, a paleontologist and whale evolution expert at Northeast Ohio Medical University. With a body that vaguely resembled a manatee rather than a blue whale, it clearly did something different than other whales to maintain its enormous mass.
But not everyone is convinced that this colossus, while undoubtedly large, is really more massive than a blue whale. The research team acknowledges their estimates for the animal’s body mass range widely, from 85 tonnes all the way up to 340 tonnes. The team unearthed only a partial skeleton without a skull, prompting some scientists to say more fossils are needed before anyone crowns a new heavyweight champion of the animal kingdom.
“I don’t think we know enough about this group of whales to really weigh in on which interpretation of its body weight is the right one,” said Nick Pyenson, a paleontologist at the Smithsonian Institution. “I’m really skeptical of these advanced estimates.”
But he added: “Obviously, it’s really big.”
In the animal kingdom, it’s usually good to be big. It is easier to deter predators, care for young and move when an animal is large and in charge.
But there are many factors that weigh against an animal’s growth. On land, one of the biggest is gravity itself. Legs can only be so strong to support a heavy frame.
In water, buoyancy helps aquatic animals balloon over eons to gigantic sizes. Blue whales and their relatives only evolved to their current size over the past few million years, after a sudden increase in ocean upwelling provided them with an abundance of krill, their favorite meal, which helped fuel their growth.
With ribs over a yard long and vertebrae weighing over 200 pounds each, the 39-million-year-old fossilized remains of P. colossus required several field campaigns to excavate from the foot of a mountain in southern Peru’s Ica Valley after its discovery 13 years ago. The animal’s scientific name means “colossal whale from Peru.” The specimen is today housed at the Natural History Museum in Lima.
Its bones were thick and compact, more like a humpback whale than a blue whale, suggesting it wasn’t chasing fast-moving prey such as krill. It must have done something else to maintain its weight.
The research team said instead P. colossus may have fed from the sea floor, munched on sea grass, feasted on benthic animals or scavenged carrion.
There are a few problems with some of these hypotheses. First, no whales are known to feed on plants. And it would take a lot of dead animals to maintain a scavenger hunt that big P. colossus. “I have a hard time thinking how many bodies would be needed to sustain this animal,” Thewissen said.
Important questions about an extinct whale
However it broke, the discovery reveals that there are several ways in which whales can evolve into giants. “That is clear Perucetus shows that there are many, many other ways to be a whale,” Pyenson said. “And we haven’t really discovered all those ways yet. So it’s really exciting.”
The research team admits that their ideas about the diet of their discovery are speculative. And they acknowledge that there is a wide range in their estimates of the whale’s size, because of the skeleton’s many missing pieces and because of uncertainty about how best to add flesh to the bone in 3D models.
“We have been extremely conservative in our approach and do not give a single estimate but a range of values,” said Eli Amson, a researcher at the Stuttgart State Museum of Natural History in Germany, who also co-authored the paper.
Noting that the lower estimate of 85 tons is still “larger than some adult blue whales,” he said his team cannot be definitive about whether P. colossus or the blue whale is heavier.
“But we can say with a high degree of certainty that its weight was in the ballpark of the blue whale’s,” he added.
The only way to get a better idea of what P. colossus‘s life – and girth – was like finding more fossils. The research team plans to continue roaming the Peruvian desert for bones.
Near the top of the wish list is a skull, which would help solve the riddle of exactly what P. colossus ate to get so big.
“We really need a skull,” Collareta said.