Megalodon sharks could reach up to three times the size of the largest great white ever recorded.
Herschel Hoffmeyer/Shutterstock
Unplanned, mindless evolution can, and often does, push a species up to and over the edge of a cliff, resulting in extinction, because it has no way to tell the future.
This makes no sense as the product of an intelligent process, of course, especially a process controlled and directed by an omniscient god, for whom the future is knowable and predictable, and it is simply not the work of such an intelligent, omniscient designer to deliberately design species such as the megalodon to go extinct.
Now scientists from the University of California - Los Angeles, USA (UCLA) together with colleagues from the William Paterson University of New Jersey, USA, the University of California–Merced, USA, Florida Gulf Coast University, Fort Myers, USA, Goethe University Frankfurt, Frankfurt am Main, Germany, Princeton University, Princeton, USA and DePaul University, Chicago, USA believe they have worked out why the megalodon went extinct.
Determining the body temperature in life from isotopes in fossil teeth.A paper in 2019 suggested that the main cause was competition from the newer and smaller, great white sharks, but this team's findings point to the difficulty in maintaining a body temperature several degrees warmer than the sea water it lived in. Of course, the two are not mutually exclusive and a dynamic which demanded a high-energy food intake could be pushed out of balance by competition for food.
Scientists can estimate the body temperature of live animals by analyzing the isotopes of oxygen and carbon found in their fossil teeth using a method known as stable isotope analysis. Here's an overview of how this process works:It is important to note that these methods provide approximations and are subject to various uncertainties and limitations. However, they offer valuable insights into the paleobiology and ecology of ancient organisms, including their body temperature ranges.
- Oxygen Isotopes: The ratio of oxygen isotopes (oxygen-18 to oxygen-16) in the body is influenced by various factors, including the temperature and the isotopic composition of the water an animal consumes. As animals drink water or consume food, the oxygen isotopes from those sources become incorporated into their tissues, including teeth.
Animals that maintain a relatively constant body temperature, such as mammals, have a consistent relationship between their body temperature and the oxygen isotope composition of their tissues. This relationship is often referred to as the "oxygen isotope thermometer."
By analyzing the oxygen isotopes preserved in fossil teeth, scientists can compare them to the isotopic composition of modern animals with known body temperatures. This comparison allows them to estimate the body temperature of the ancient animals.- Carbon Isotopes: The carbon isotopes (carbon-13 to carbon-12) found in fossil teeth can provide additional information about an animal's diet and metabolism, which can be indirectly related to body temperature.
Different types of food sources have distinct carbon isotope signatures. For instance, plants using the C3 photosynthetic pathway have a different carbon isotope composition compared to plants that use the C4 pathway. Animals feeding on different types of plants will exhibit different carbon isotope ratios in their tissues, including teeth.
By analyzing the carbon isotopes in fossil teeth, scientists can infer the type of plants consumed by an animal and gain insights into its dietary habits. This information, in combination with oxygen isotope analysis, helps refine temperature estimates.
The team arrived at the conclusion that the megalodon was warm-blooded by examining the fossilized remains of megalodon teeth which contain isotopes of oxygen and carbon deposited when the shark was alive, so making a permanent record of the relative abundance of these isotopes, which vary according to the temperature of the water they lived in.
The research and its significance are explained in a press release from the UCLA Newsroom:
Key takeaways
- How the megalodon, a shark that went extinct 3.6 million years ago, stayed warm was a matter of speculation among scientists.
- Using an analysis of tooth fossils from the megalodon and other sharks of the same period, a UCLA-led study suggests the animal was able to maintain a body temperature well above the temperature of the water in which it lived.
- The finding could help explain why the megalodon went extinct during the Pliocene Epoch.
The largest marine predator that ever lived was no cold-blooded killer.
Well, a killer, yes. But a new analysis by environmental scientists from UCLA, UC Merced and William Paterson University sheds light on the warm-blooded animal’s ability to regulate its body temperature — and might help explain why it went extinct.
After analyzing isotopes in the tooth enamel of the ancient shark, which went extinct about 3.6 million years ago, the scientists concluded the megalodon could maintain a body temperature that was about 13 degrees Fahrenheit (about 7 degrees Celsius) warmer than the surrounding water.
That temperature difference is greater than those that have been determined for other sharks that lived alongside the megalodon and is large enough to categorize megalodons as warm-blooded.
The paper, published in Proceedings of the National Academy of Sciences, suggests that the amount of energy the megalodon used to stay warm contributed to its extinction. And it has implications for understanding current and future environmental changes.
Megalodons, which are believed to have reached lengths up to 50 feet, belonged to a group of sharks called mackerel sharks — members of that group today include the great white and thresher shark. While most fish are cold-blooded, with body temperatures that are the same as the surrounding water, mackerel sharks keep the temperature of all or parts of their bodies somewhat warmer than the water around them, qualities called mesothermy and regional endothermy, respectively.Studying the driving factors behind the extinction of a highly successful predatory shark like megalodon can provide insight into the vulnerability of large marine predators in modern ocean ecosystems experiencing the effects of ongoing climate change.
Assistant Professor Robert A. Eagle
Department of Atmospheric and Oceanic Sciences,
Center for Diverse Leadership in Science,
Institute of the Environment and Sustainability,
University of California–Los Angeles, Los Angeles, CA, USA.
Sharks store heat generated by their muscles, making them different from fully warm-blooded or endothermic animals like mammals. In mammals, a region of the brain called the hypothalamus regulates body temperature.
Various lines of evidence have hinted that megalodon might have been mesothermic. But without data from the soft tissues that drive body temperature in modern sharks, it has been difficult to determine if or to what extent megalodon was endothermic.
In the new study, the scientists looked for answers in the megalodon’s most abundant fossil remains: its teeth. A main component of teeth is a mineral called apatite, which contains atoms of carbon and oxygen. Like all atoms, carbon and oxygen can come in “light” or “heavy” forms known as isotopes, and the amount of light or heavy isotopes that make up apatite as it forms can depend on a range of environmental factors. So the isotopic composition of fossil teeth can reveal insights about where an animal lived and the types of foods it ate, and — for marine vertebrates — information like the chemistry of the seawater where the animal lived and the animal’s body temperature.An upper tooth from a megalodon (right) dwarfs that of a white shark.
Harry Maisch/Florida Gulf Coast University
Because most ancient and modern sharks are unable to maintain body temperatures significantly higher than the temperature of surrounding seawater, the isotopes in their teeth reflect temperatures that deviate little from the temperature of the ocean. In warm-blooded animals, however, the isotopes in their teeth record the effect of body heat produced by the animal, which is why the teeth indicate temperatures that are warmer than the surrounding seawater.You can think of the isotopes preserved in the minerals that make up teeth as a kind of thermometer, but one whose reading can be preserved for millions of years. Because teeth form in the tissue of an animal when it’s alive, we can measure the isotopic composition of fossil teeth in order to estimate the temperature at which they formed and that tells us the approximate body temperature of the animal in life.
Maintaining an energy level that would allow for megalodon’s elevated body temperature would require a voracious appetite that may not have been sustainable in a time of changing marine ecosystem balances when it may have even had to compete against newcomers such as the great white shark.
Randon J. Flores, co-author
Department of Atmospheric and Oceanic Sciences
Center for Diverse Leadership in Science
Institute of the Environment and Sustainability
University of California–Los Angeles, Los Angeles, CA, USA.
The researchers hypothesized that any difference between the isotope values of the megalodon and those of other sharks that lived at the same time would indicate the degree to which the megalodon could warm its own body.
The researchers collected teeth from the megalodon and other shark contemporaries from five locations around the world, and analyzed them using mass spectrometers at UCLA and UC Merced. Using statistical modeling to estimate sea water temperatures at each site where teeth were collected, the scientists found that megalodons’ teeth consistently yielded average temperatures that indicated it had an impressive ability to regulate body temperature.
Its warmer body allowed megalodon to move faster, tolerate colder water and spread out around the world. But it was that evolutionary advantage that might have contributed to its downfall, the researchers wrote.Having established endothermy in megalodon, the question arises of how frequently it is found in apex marine predators throughout geologic history.
Professor Aradhna Tripati, co-author Department of Atmospheric and Oceanic Sciences
Center for Diverse Leadership in Science
Institute of the Environment and Sustainability
University of California–Los Angeles, Los Angeles, CA, USA.
The megalodon lived during the Pliocene Epoch, which began 5.33 million years ago and ended 2.58 million years ago, and global cooling during that period caused sea level and ecological changes that the megalodon did not survive.
Project co-leader Aradhna Tripati, a UCLA professor of Earth, planetary and space sciences and a member of the Institute of Environment and Sustainability, said the scientists now plan to apply the same approach to studying other species.
The team have published their findings in the open access journal, PNAS:
SignificanceSo, having headed down an evolutionary cul-de-sac, megalodons were unable to reverse out when they found themselves in an environment in which they were unable to get sufficient food to maintain their body temperatures - something that is entirely understandable, even predictable as the result of mindless, unplanned evolution, but incomprehensible as the work of a designer, unless that designer is no better than a mindless natural process, and a far cry from the supremely intelligent, omniscient magic supernatural god of the creationist cult.
Otodus megalodon was a gigantic shark that went extinct around 3.6 Mya. It could grow to the enormous size of at least 15 m long, making it one of the largest apex marine predators since the Mesozoic. Here, we test hypotheses relating to its extinction by providing quantitative estimates of its body temperature, thereby constraining its thermal physiology. We found that O. megalodon had body temperatures significantly elevated compared to other sharks, consistent with it having a degree of internal heat production as modern warm-blooded (endothermic) animals do. High metabolic costs associated with having at least partial endothermy may have contributed to its vulnerability to extinction compared to other shark species that persist until this day.
Abstract
The evolution of the extinct megatooth shark, Otodus megalodon, and its close phylogenetic relatives remains enigmatic. A central question persists regarding the thermophysiological origins of these large predatory sharks through geologic time, including whether O. megalodon was ectothermic or endothermic (including regional endothermy), and whether its thermophysiology could help to explain the iconic shark’s gigantism and eventual demise during the Pliocene. To address these uncertainties, we present unique geochemical evidence for thermoregulation in O. megalodon from both clumped isotope paleothermometry and phosphate oxygen isotopes. Our results show that O. megalodon had an overall warmer body temperature compared with its ambient environment and other coexisting shark species, providing quantitative and experimental support for recent biophysical modeling studies that suggest endothermy was one of the key drivers for gigantism in O. megalodon and other lamniform sharks. The gigantic body size with high metabolic costs of having high body temperatures may have contributed to the vulnerability of Otodus species to extinction when compared to other sympatric sharks that survived the Pliocene epoch.
Griffiths, Michael L.; Eagle, Robert A.; Kim, Sora L.; Flores, Randon J.; Becker, Martin A.; Maisch, Harry M.; Trayler, Robin B.; Chan, Rachel L.; McCormack, Jeremy; Akhtar, Alliya A.; Tripati, Aradhna K.; Shimada, Kenshu
Proceedings of the National Academy of Sciences. 120(27), e2218153120. DOI: 10.1073/pnas.2218153120
Copyright: © 2023 The authors.
Published by PNAS Open access.
Reprinted under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0).
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