Mammals are known for their ability to increase their metabolic rate and maintain their body temperature even in colder environments, and this trait is called warm-bloodedness. But some lineages of living and extinct fish have the characteristic of “regional warmth”; in such a way that they keep the temperature of some parts of their body higher than the temperature of the surrounding environment. Many sharks (a group that includes species such as mako sharks and great white sharks) have this ability.
Jack Cooper“Regional warming is one of two known evolutionary pathways to large size in sharks,” says paleontologist at the University of Swansea, Wales, who was not involved in the new study. “The other way of feeding is by scavenging, which is used by sharks like whale sharks.”
Scientists have long thought that Megalodon was regionally warm, based on evidence such as estimates of body shape as well as possible swimming speeds and energy requirements. Also, this shark had a wide geographic range around the world and hunted in cold waters as well as in warm waters, which indicates that it is warm-blooded.
A recent study by Cooper and his colleagues, which modeled the shark’s body in 3D, estimated that the adult Megalodon was an ocean-going super predator that could swim faster than any living shark species and devour prey as whole as today’s largest predators.
The question, Eagle says, is not whether Megalodon was really warm-hearted, but how warm-hearted it was! The researchers were curious about the body temperature of this shark with the body temperature of the great white shark.Carcharodon carcharias) that appeared at the end of Megalodon’s reign, what was the difference.
Megalodon appeared about 23 million years ago and became extinct about 3.5 million to 2.6 million years ago. Great white sharks appeared about 3.5 million years ago, competing for food with their larger cousins. One hypothesis of scientists is that this competition played a role in the extinction of Megalodon. Climate changes during the Pliocene (5.3 million to 2.6 million years ago) led to the decline of marine mammal populations, which were the main food source for both sharks. “Carcharodons (great white sharks) were much smaller and survived, while Otadus became extinct,” Eagle says. “Carcharodon probably needed less food to maintain its metabolic rate.”
To obtain more direct evidence of these sharks’ body temperatures and better understand their metabolism, researchers turned to the only fossils left of these sharks, their teeth.
Fossilized teeth provide a wealth of environmental information. Tooth enamel contains heavy and light forms or isotopes of carbon, oxygen and other elements, and the relative abundance of these isotopes is related to body temperature.