Nanuqsaurus, which is in the background, and Pachyrhinosaurus, whose skull is in the foreground, were among the dinosaur species included in a new study led by scientists at the University of Alaska Fairbanks and the University of Reading that challenges Bergmann’s rule . Photo credit: James Havens
When you throw dinosaurs into the mix, sometimes you find that a rule just isn’t right.
A new study led by scientists at the University of Alaska Fairbanks and the University of Reading challenges Bergmann’s rule, an 18th-century scientific principle that holds that animals in cooler, high-latitude climates tend to be larger than close relatives who live in warmer climates.
The fossil record shows otherwise.
“Our study shows that the evolution of different body sizes in dinosaurs and mammals cannot be simply reduced to a function of latitude or temperature,” said Lauren Wilson, a graduate student at UAF and lead author of a paper published in the journal Nature communication. “We found that Bergmann’s rule applies only to a subset of homeothermic animals (those that maintain a stable body temperature) and only when one takes temperature into account and ignores all other climatic variables. This suggests that Bergmann’s ‘rule’ is actually the exception rather than the rule.”
Examining Bergmann’s rule in dinosaurs and modern species
The study began with a simple question that Wilson discussed with her study advisor: Does Bergmann’s rule apply to dinosaurs?
After analyzing hundreds of data points from the fossil record, the answer seemed to be a resounding “no.”
The data set included the northernmost dinosaurs known to scientists, those in Alaska’s Prince Creek Formation. They experienced freezing temperatures and snowfall. Nevertheless, the researchers did not find any significant increase in body size in any of the Arctic dinosaurs.
Next, the researchers tried the same evaluation with modern mammals and birds, the descendants of prehistoric mammals and dinosaurs. The results were largely the same: latitude was not a predictor of body size in modern birds and mammals species. There was little relationship between body size of modern birds and temperature, but this was not the case for prehistoric birds.
The researchers say the study is a good example of how scientists can and should use the fossil record to test current scientific rules and hypotheses.
“The fossil record provides insight into completely different ecosystems and climate conditions, allowing us to assess the applicability of these ecological rules in a whole new way,” said Jacob Gardner, a postdoctoral researcher at the University of Reading and other lead author of the paper.
Scientific rules should apply to fossil organisms just as they do to modern organisms, said Pat Druckenmiller, director of the University of Alaska Museum of the North and one of the paper’s co-authors.
“You can’t understand modern ecosystems if you ignore their evolutionary roots,” he said. “You have to look into the past to understand how things became what they are today.”
Reference: “Global latitudinal gradients and the evolution of body size in dinosaurs and mammals” by Lauren N. Wilson, Jacob D. Gardner, John P. Wilson, Alex Farnsworth, Zackary R. Perry, Patrick S. Druckenmiller, Gregory M. Erickson, and Chris L. Organ, April 5, 2024, Nature communication.
DOI: 10.1038/s41467-024-46843-2