Warm-blooded megalodon may have gone extinct due to climate change

Scientists from UCLA, UC Merced, and William Paterson University has shed new light on the largest marine predator that ever lived, the megalodon. Contrary to its image as a cold-blooded killer, the analysis of isotopes in the megalodon's tooth enamel suggests that it was a warm-blooded animal capable of regulating its body temperature. This finding may also provide insights into why the megalodon eventually went extinct.

The researchers discovered that the megalodon was able to maintain a body temperature approximately 13°F (7°C) warmer than the surrounding water. This temperature difference is greater than that observed in other contemporary sharks, indicating that megalodons can be categorized as warm-blooded creatures.

Published in the Proceedings of the National Academy of Sciences, the study proposes that the energy expended by the megalodon to maintain its warm body temperature might have contributed to its extinction. Moreover, these findings have broader implications for understanding the impact of ongoing climate change on large marine predators in modern ocean ecosystems.

Lead researcher Robert Eagle, an assistant professor of atmospheric and oceanic sciences at UCLA, emphasized the significance of studying the factors that led to the extinction of such a successful predatory shark species like the megalodon. By doing so, researchers can gain valuable insights into the vulnerability of large marine predators in the face of environmental changes.

Megalodons, which were believed to grow up to 50 feet in length, belonged to the mackerel shark group, which also includes the great white and thresher sharks. Unlike most fish that are cold-blooded, mackerel sharks possess the ability to keep parts or all of their bodies warmer than the surrounding water. This unique characteristic is referred to as mesothermy and regional endothermy.

While sharks are not fully warm-blooded like mammals, they store heat generated by their muscles. Mammals, on the other hand, have a region in their brain called the hypothalamus, which regulates body temperature.

Previous evidence had hinted that the megalodon might have been mesothermic, but without data from the soft tissues responsible for maintaining body temperature in modern sharks, it was challenging to determine the extent of its endothermic capabilities.

An upper tooth from a megalodon (right) dwarfs that of a white shark. Credit: Harry Maisch/Florida Gulf Coast University

The recent study focused on analyzing the teeth of the megalodon, as they are the most abundant fossil remains of the species. Teeth contain a mineral called apatite, which consists of carbon and oxygen atoms. These atoms exist in different forms known as isotopes, with “light” and “heavy” variants. The isotopic composition of apatite in teeth can provide information about an animal's habitat, diet, and even its body temperature, as these factors influence the isotopes incorporated during tooth formation.

Randy Flores, a UCLA doctoral student involved in the study, explained that isotopes in teeth act as a “thermometer” that can retain its reading for millions of years. By measuring the isotopic composition of fossil teeth, researchers can estimate the temperature at which the teeth formed and infer the approximate body temperature of the animal when it was alive.

Most sharks, both ancient and modern, are unable to significantly raise their body temperatures above that of the surrounding seawater. As a result, the isotopes in their teeth reflect temperatures that closely align with the ocean temperature. In contrast, teeth from warm-blooded animals capture the influence of the animal's body heat, leading to higher temperatures recorded in the isotopes compared to the surrounding seawater.

Based on this understanding, the scientists hypothesized that any divergence in isotope values between the megalodon and other contemporary sharks would indicate the extent to which the megalodon could warm its own body.

To test their hypothesis, the researchers collected teeth from megalodons and other sharks that lived during the same period from various global locations. These teeth were then analyzed using mass spectrometers at UCLA and UC Merced. Through statistical modeling, the scientists estimated the seawater temperatures at the respective collection sites and found that the average temperatures derived from megalodon teeth consistently indicated the species' impressive ability to regulate body temperature.

The megalodon's warm body temperature provided several advantages, such as increased speed, tolerance to colder waters, and wider distribution across the globe. However, the study suggests that this evolutionary advantage may have contributed to the species' extinction. During the Pliocene Epoch, which lasted from approximately 5.33 million to 2.58 million years ago, global cooling caused significant changes in sea levels and ecosystems that the megalodon could not survive.

According to Aradhna Tripati, a UCLA professor and project co-leader, the team plans to extend this approach to studying other species. Understanding the prevalence of endothermy (warm-bloodedness) among apex marine predators throughout geological history is a future goal of their research.

Source: University of California, Los Angeles

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