![]() The team used this technique on teeth from the different sharks, as well as fossil samples from other ancient ocean contemporaries including whales and mollusks. The abundance of these bonds is “only affected by temperature,” offering a more unambiguous thermometer than using a single element’s isotopic abundance, Eagle says. Eagle and his colleagues used a technique that examines the abundance of “clumped isotopes” - bonded-together heavy forms of carbon (carbon-13) and oxygen (oxygen-18) - as a kind of ancient geochemical thermometer. The tooth enamel contains both heavier and lighter forms, or isotopes, of carbon, oxygen and other elements, and the relative abundances of these isotopes is linked to body temperature. To get more direct evidence of the body temperatures of these shark species, and therefore better understand their respective metabolisms, the team turned to the only fossils the sharks have left behind: their teeth.įossilized teeth offer a wealth of encapsulated environmental data. “ Carcharodon probably had a lower requirement for food to maintain its metabolic rate.” “The Carcharodon were much smaller … and persisted, whereas the Otodus went extinct,” Eagle says. Climate change during the Pliocene Epoch, which spanned 5.3 million to 2.6 million years ago, led to a collapse in the population of marine mammals, the primary food source for both sharks. One hypothesis has been that this competition helped drive O. Great white sharks emerged around 3.5 million years ago, and they competed for food with their massive cousins. megalodon appeared around 23 million years ago and went extinct sometime between 3.5 million and 2.6 million years ago. In particular, the team wondered how its body temperatures compared to one of its primary ocean competitors, which appeared on the scene late in the shark’s reign: Carcharodon carcharias, better known as the great white shark ( SN: 6/29/22). megalodon was endothermic - it’s how endothermic it was. The question, Eagle adds, isn’t really whether O. megalodon was a transoceanic superpredator, able to swim faster than any living shark species and fully consume prey the size of today’s largest predators. ![]() A recent study by Cooper and colleagues that modeled the shark’s body in 3-D estimated that adult O. The shark was also known to have a very large geographic range around the globe, actively hunting in colder as well as warmer waters, which argues for some warm-bloodedness. Scientists have long thought that megalodon was regionally endothermic, Eagle says, based on a variety of evidence such as estimates of the megashark’s body shape, as well as its likely swimming speeds and energy requirements. (The other, Cooper says, is filter feeding, employed by gentler giants such as whale sharks.) “Indeed, regional endothermy is one of just two known evolutionary pathways toward giant sizes in sharks,” says Jack Cooper, a paleobiologist at Swansea University in Wales who was not involved in the new study. For example, many modern lamniform sharks - the group that includes species like mako and great white sharks - have this ability ( SN: 8/2/18). But some fish lineages, both living and extinct, are capable of regional endothermy, maintaining some body parts at higher temperatures than the surrounding water ( SN: 6/10/10). ![]() Mammals are well known for being able to metabolically elevate and maintain their body heat, even in colder environments, a trait called endothermy. Gigantism has a high metabolic cost, says UCLA marine biogeochemist Robert Eagle: Bigger bodies require more food, and the massive sharks may have been particularly vulnerable to extinction when the climate changed and food became scarcer. But the shark’s voracious appetite may have also spelled the species’ ultimate doom. megalodon become a swift, fearsome apex predator and grow up to 20 meters long, making it among the largest carnivores to ever live on Earth. That warm-bloodedness may have been a double-edged sword. ![]()
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