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