Dinosaurs debunk a classic climate theory called 'Bergmann's rule'

In a remarkable study, the longstanding scientific principle known as Bergmann’s rule, which posits that animals in colder, high-latitude climates are typically larger than those in warmer regions, is being challenged.

Originating in the 1800s, this rule has been a cornerstone of ecological and evolutionary theory. Yet, researchers from the University of Alaska Fairbanks and the University of Reading have uncovered evidence from the fossil record. This evidence, particularly involving dinosaurs, tells a different story.

This new research suggests that the traditional understanding of Bergmann’s rule may not apply universally across different species and climates. Consequently, this challenges decades of scientific consensus.

Bergmann’s rule

Bergmann’s Rule states that within a broadly distributed taxonomic group, the size of an animal increases with latitude and correlates with the temperature of their environment.

It is a key concept in ecology and evolution. Scientists have applied and tested it across different animals like birds, mammals, and insects. It falls under biogeography which studies how species and ecosystems spread across places and time.

The rule is particularly relevant for endothermic (warm-blooded) animals because they must regulate their internal body temperature.

According to this rule, larger-bodied animals in colder regions have an advantage in conserving heat due to their reduced surface area-to-volume ratio, which minimizes heat loss.

Conversely, smaller-bodied animals in warmer regions can dissipate body heat more efficiently because of their higher surface area-to-volume ratio.

Challenging Bergmann’s rule

Lauren Wilson, a graduate student at the University of Alaska Fairbanks and a lead author of the study published in Nature Communications, shares that their findings reveal the complexity of evolutionary traits.

“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,” Wilson explains.

She also emphasizes the specificity of Bergmann’s rule. The rule seems to apply only to homeothermic animals, those that maintain stable body temperatures, and even then, only under certain conditions. This revelation hints at the rule being more of an exception rather than a universal principle.

Dinosaurs in the snow

The study, inspired by a conversation between Wilson and her advisor, explored if Bergmann’s rule applied to dinosaurs.

After a comprehensive review of data from the fossil record, including dinosaurs from Alaska’s Prince Creek Formation which endured freezing conditions, the researchers found no significant correlation. The animals’ body size did not seem to relate to their arctic environment.

Modern birds and mammals

Extending their research to modern birds and mammals, the descendants of ancient mammals and dinosaurs, the team discovered similar patterns.

Subsequently, latitude proved to be an unreliable predictor of body size among these species. This finding further complicates the supposed straightforward relationship Bergmann’s rule suggests.

Fossil records challenge scientific norms

Jacob Gardner, a postdoctoral researcher at the University of Reading and another lead author of the paper, highlights the fossil record’s value. He points out how it challenges present-day scientific beliefs.

“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,” Gardner states.

Consequently, this approach opens the door to reevaluating other established scientific principles through the lens of paleontological evidence.

Pat Druckenmiller, director of the University of Alaska Museum of the North and co-author of the study, underscores the importance of historical context in understanding contemporary ecosystems.

“You can’t understand modern ecosystems if you ignore their evolutionary roots,” he remarks. He advocates for a comprehensive view that includes the ancient past to fully grasp the current state of our natural world.

Study implications

The study’s implications extend far beyond challenging Bergmann’s rule. It reshapes our understanding of evolutionary adaptation and species diversity.

By demonstrating that body size evolution cannot be solely attributed to latitude or temperature, it prompts a reevaluation of ecological and evolutionary theories. This insight encourages scientists to explore additional factors influencing species adaptation.

The study also underscores the importance of integrating paleontological data into current biological research, offering a more comprehensive view of life’s history on Earth.

Furthermore, it highlights the need for a nuanced approach to studying biological principles, recognizing that exceptions to long-standing rules can lead to new scientific discoveries and understandings.

The full study was published in the journal Nature Communications.

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