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Scientists have discovered that ancient sea reptiles may have been as warm-blooded as modern-day whales and dolphins.
Most reptiles and fish are cold-blooded, meaning that their body temperature is often the same as the water they swim in. Few reptiles and fish can self-regulate their own temperature, though some - such as the tuna and swordfish - can, to some extent.
Three types of large ancient reptiles, Icthyosaurs, mosasaurs, and plesiosaurs, lived during the Mesozoic period about 251 million to 65 million years ago. By studying fossils, scientists were able to determine the oxygen isotopes in the teeth of the ancient predators. The levels of oxygen isotopes within the teeth accurately reflect the level of oxygen that would have been in the blood of the reptiles. These levels can be used to determine the sea monster's relative body temperature. When compared to other sea creatures that lived in the same waters, scientists found that the body temperatures were higher in the reptiles.
Scientists expected to find self-regulation in plesiosaurs and icthyosaurs, as they were active predators. However, mososaurs are ambush predators, and though the data is ambiguous, scientists believe that the species likely had the ability to self-regulate its temperature to some degree. The predator's higher body temperatures also suggest the possibility that they had heat-conservation systems such as blubber layers and specialized blood circulation.
"From here we can really begin to investigate how this might have evolved," said Ryosuke Motani, a vertebrate paleontologist at the University of California, Davis. "These [sea reptiles] all came from land reptiles, who we're pretty sure were so-called cold-blooded, and it was probably the same when they started swimming. But over time it looks like homeothermy evolved, and so we need to figure out when that happened and why," he said.
"Maybe it evolved as they became better at cruising, or [because] there were changes in average temperature or in sea level."
Source: National Geographic