That’s just one example. Size estimates of many of the planet’s extinct giants have been challenged in the past decade as new data and analytical techniques have emerged, researchers report in the September issue of Ecology and evolution.

To some extent, that is how science works, say evolutionary biologist Joel Gayford and his colleagues. But the scale of the dispute over size in some cases requires much more caution in making those initial estimates, the researchers say.

“There is an ongoing trend of publishing… articles of great importance the largest in the world, the heaviest in the world something,” says Gayford, now at James Cook University in Brisbane, Australia. “Soon there’s another article in a less popular journal that says, ‘Wait, that wasn’t that long at all.'”

When it comes to estimating body size, there isn’t always much to go on. Extinct Otodus megalodonthe largest shark that ever lived left behind only its teeth; an ancient whale PerucetusInitially estimated to be heavier than the modern blue whale, it left behind only a few vertebrae, ribs and the pelvis of one individual (SN: 8/2/23). To draw conclusions from these fragments about the entire animal, scientists can compare the fossils with living or extinct relatives — if any are known — or feed the data into computer analyses of evolutionary trees.

However, these extrapolations are based on assumptions that may mislead researchers.

Megalodon is one of several examples that Gayford and colleagues focus on. Scientists thought it was closely related to white sharks, so they assumed its body was proportionally wide to match its length, which is about 11 meters. However, a recent study has disproved that assumption, suggesting instead that Megalodon could have been a few meters longer, but also slimmer, built more like a bus than a van (SN: 21.01.24).

Similarly, the methodology underlying the initial estimates of the whale’s size Perucetus were called into question earlier this year. Using a variety of calculation methods, researchers lowered its estimated weight from a maximum of 340 metric tons to about 100 — still a large whale, they argued, but not in the weight class of a blue whale, which can weigh as much as 245 metric tons.

Paleontologists have previously pointed to “false size estimates” as creating lasting biases when it comes to perceptions of how big you can be, Gayford says. These size estimates matter, the team notes, because species larger than most can have a disproportionately large impact on ecology, such as food resources and predator-prey relationships. And changes in the environment—such as the loss of those food sources—can in turn have a disproportionately large impact on the giants.

Paleontologists praised the study for highlighting a major challenge in the field. “It rightly points out that we need to be careful and acknowledge the wide margins of error when reconstructing any extinct taxon,” says vertebrate paleontologist Jack Cooper of Swansea University. But not every case study in the paper has been analyzed as rigorously, he says. For example, there is still much reasonable debate about how best to estimate MegalodonSize.

Cooper adds that the report wrongly claimed that his own work on the giant shark, based on a rare vertebra fossil, was “impossible to replicate.” That, he says, makes him “concerned about what else was wrongly reported in their broader review.”

Gayford says in response that he and his coauthors were referring to the rarity of the fossils, not criticizing Cooper’s work—and adds that this underscores the inherent challenges of estimating size from a sparse fossil record. And, he says, scientific journals bear some of the burden of claims of disproportionate size. “They’re less likely to publish detailed, methodologically sound, but not particularly surprising conclusions. And that has a side effect on what people can focus their research on.”

One way to address this, he says, is to recognize that size itself doesn’t matter all that much when it comes to whether a creature is worth studying. “The idea is to get people to understand that it’s not the size or weight of an animal that makes it interesting,” Gayford says. “It’s still a huge, amazing animal that we can learn a lot about.”