Dinosaurs break 200-year-old zoology rule

A new analysis of the fossil record shows that dinosaurs bucked an ecological trend known as Bergmann’s rule.

The rule was put forward by German biologist Carl Bergmann in 1847. It suggests that larger animals are found in colder environments. It is most often applied to birds and mammals.

For example, the largest penguins are found in Antarctica. A bit further north, the average penguin size – such as the Magellanic penguin – are a bit smaller. Galapagos penguins – the furthest north, virtually right on the equator – are among the smallest in the world.

Similar trends can even be seen in humans. Taller people tend to be found in higher latitudes such as Scandinavia and northern Europe.

A new paper published in Nature Communications, shows the rule doesn’t always apply.

“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,” says lead author Lauren Wilson, a graduate student at the University of Alaska Fairbanks.

“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.”

The findings emerged when Wilson set out to answer the question: does Bergmann’s rule apply to dinosaurs.

Hundreds of data points were included. Among them were the northernmost dinosaurs to have been found – those in Alaska’s Prince Creek Formation. The analysis showed no notable change in size correlated to latitude.

The same analysis was then done on modern mammals and birds. The results were largely the same.

Biological rules should apply to ancient creatures in the same way they do living animals, says co-author 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 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,” adds co-author Jacob Gardner, a postdoctoral researcher at the University of Reading, UK.

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