Scientists have wondered whether ancient reptiles like pleisiosaurs were warm-blooded or cold-blooded. Scientists from the University of Plymouth studied many animals of different sizes from insects to whales that dive and hold their breath. They found that larger animals can hold their breath longer than smaller animals because they can store more oxygen. They also found this difference was much bigger for warm-blooded animals than for cold-blooded animals. They said this could be why whales became so large. They think since plesiosaurs were also large, like whales, they were more likely to be warm-blooded than cold-blooded.