MSGID: 1:317/3 649a65ef   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Megalodon was no cold-blooded killer    
    A killer, yes, but analysis of tooth minerals reveals how the warm-   
   blooded predator maintained its body temperature    
      
     Date:   
         June 26, 2023   
     Source:   
         University of California - Los Angeles   
     Summary:   
         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 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.   
      
      
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   FULL STORY   
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   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.   
      
   "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," said lead researcher Robert Eagle,   
   a UCLA assistant professor of atmospheric and oceanic sciences and member   
   of the UCLA Institute of the Environment and Sustainability.   
      
   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.   
      
   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.   
      
   "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," said Randy Flores, a UCLA doctoral student and   
   fellow of the Center for Diverse Leadership in Science, who worked on the   
   study. "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."  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.   
      
   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.   
      
   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.   
      
   "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," Flores said.   
      
   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.   
      
   "Having established endothermy in megalodon, the question arises of   
   how frequently it is found in apex marine predators throughout geologic   
   history," she said.   
      
       * RELATED_TOPICS   
             o Plants_&_Animals   
                   # Fish # Marine_Biology # Nature # Sea_Life   
             o Fossils_&_Ruins   
                   # Early_Mammals # Dinosaurs # Fossils # Origin_of_Life   
       * RELATED_TERMS   
             o Homo_(genus) o Mammoth o Ichthyosaur o Extinction   
             o Endangered_species o Cretaceous o Shark o   
             Temperature_record_of_the_past_1000_years   
      
   ==========================================================================   
   Story Source: Materials provided by   
   University_of_California_-_Los_Angeles. Original written by Holly   
   Ober. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Michael L. Griffiths, Robert A. Eagle, Sora L. Kim, Randon   
      J. Flores,   
         Martin A. Becker, Harry M. Maisch, Robin B. Trayler, Rachel   
         L. Chan, Jeremy McCormack, Alliya A. Akhtar, Aradhna K. Tripati,   
         Kenshu Shimada.   
      
         Endothermic physiology of extinct megatooth sharks. Proceedings   
         of the National Academy of Sciences, 2023; 120 (27) DOI:   
         10.1073/pnas.2218153120   
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   Link to news story:   
   https://www.sciencedaily.com/releases/2023/06/230626164144.htm   
      
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