Bergmann’s rule is a scientific principle stating that animals in high-latitude, cooler climates tend to be larger than close relatives living in warmer climates.
A pair of adult Nanuqsaurus tyrannosaurs, standing in the background, and pachyrhinosaurus, skull in the foreground, were among the dinosaur species included in the study that calls into question Bergmann’s rule. Image credit: James Havens.
“Our study shows that the evolution of diverse body sizes in dinosaurs and mammals cannot be reduced to simply being a function of latitude or temperature,” said Lauren Wilson, a graduate student at the University of Alaska.
“We found that Bergmann’s rule is only applicable to a subset of homeothermic animals (those that maintain stable body temperatures), and only when you consider temperature, ignoring all other climatic variables.”
“This suggests that Bergmann’s ‘rule’ is really the exception rather than the rule.”
In the study, Wilson and colleagues tested for Bergmann’s rule in Mesozoic dinosaurs and mammaliaforms that radiated within relatively temperate global climate regimes.
Their analysis also included new fossil data from the extreme high-latitude Late Cretaceous Arctic Prince Creek Formation.
The Arctic dinosaurs experienced freezing temperatures and snowfall. Despite this, the authors found no notable increase in body size for any of them.
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 bird and mammal species.
There was a small relationship between the body size of modern birds and temperature, but the same was not the case for prehistoric birds.
“The fossil record provides a window into completely different ecosystems and climate conditions, allowing us to assess the applicability of these ecological rules in a whole new way,” said Dr. Jacob Gardner, a postdoctoral researcher at the University of Reading.
“Scientific rules should apply to fossil organisms in the same way they do modern organisms,” added Dr. Pat Druckenmiller, director of the University of Alaska Museum of the North.
“You can’t understand modern ecosystems if you ignore their evolutionary roots.”
“You have to look to the past to understand how things became what they are today.”
The study was published in the journal Nature Communications.
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L.N. Wilson et al. 2024. Global latitudinal gradients and the evolution of body size in dinosaurs and mammals. Nat Commun 15, 2864; doi: 10.1038/s41467-024-46843-2