In the mid-nineteenth century, German biologist Carl Bergmann decided there was enough evidence to state that within a given species, larger-sized specimens are found in colder environments, while smaller-sized are found in warmer regions – an observation that eventually became known as “Bergmann's rule” as other researchers found examples, such as the giant penguins of frigid Antarctica versus the smaller one of warmer climes in South America. “Bergmann's rule” popped up again this week in a species quite a bit little larger than penguins – megalodons.
"Scientists constantly search for rules of life that help us predict natural patterns, and it seems that Bergmann's rule applied to Otodus megalodon."
Victor Perez, a paleontologist at Maryland’s Calvert Marine Museum, has been studying the only evidence we have of the existence of Otodus megalodon – giant teeth that put the prehistoric shark’s size at up to 65 feet in length and 50 tons in weight. Perez is co-author of a new study in Historical Biology which upends conventional thinking that all megalodons were monsters, no matter where on Earth they swam. The key to invoking “Bergmann's rule” for the megalodon was the assumption that smaller megalodon teeth founds near the equator meant that these warmer waters were used as shark nurseries for baby megalodons. Coauthor Harry Maisch, a faculty member at Bergen Community College and Fairleigh Dickinson University in New Jersey, thinks “Bergmann's rule” better explains the smaller teeth in warmer waters.
“But our study shows that fossil localities consisting of smaller Megalodon teeth may instead be a product of individual sharks attaining smaller overall body sizes simply as a result of warmer water.”
According to Bergmann, colder environments influenced the evolution of larger animals because their size helps them retain heat more efficiently. To determine the size of megalodons with just teeth and a few fossilized vertebrae and feces, the researchers used upper anterior teeth, which provide reliable ratios to megalodon length. Interestingly, co-author Martin Becker, a professor of environmental science at William Paterson University in New Jersey , says the idea to see if megalodons grew bigger in colder waters came from a recent fishing trip to the Florida Keys. The results show that a trip to find large fish should move out of tropical waters and into arctic ones. Unfortunately, climate change is making those waters harder to find – which bodes poorly for larger sharks and fish.
At least now we know where to look for the biggest megalodon teeth.